Search for New Physics Beyond the SM

S. Su DOE Review, 2010(Photo courtesy of Maruša Bradač.)

Copyright CERN

Search for New Physics Beyond the SM

Shufang Su • U. of Arizona

DOE Review 2010

(Photo courtesy of Maruša Bradač.)

Copyright CERN

Monday, November 15, 2010

S. Su DOE Review, 2010 2

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My work focuses on My work focuses on searching for new physics beyond the SMsearching for new physics beyond the SM



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Involve experiments inInvolve experiments in

−− Nuclear physics Nuclear physics

−− Particle physics Particle physics

−− Astrophysics/Cosmology Astrophysics/Cosmology



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Direct Searches



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Indirect Searches

Direct Searches



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−− Astrophysics/Cosmology Astrophysics/CosmologyDark Matter

Indirect Searches

Direct Searches



Students and Postdoc - Postdocs

− Brooks Thomas (group postdoc, 2007 - 2010) ⇒ Univ. of Hawaii− Vikram Rentala (group postdoc, 2010 - now)

Graduate Students− Ethan Dolle (graduated Jan, 2010)− Xinyu Miao (passed thesis defense, Oct, 2010)− Jonathan Eckel (3rd year)

Undergraduate Students− Jessica Goodman ⇒ Univ. of California, Irvine, particle theory− Will Parker ⇒ Univ. of Wisconsin, Madison, CMS group− Kara Farnsworth ⇒ Univ. of California, Davis, particle theory

− James Kieler



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Dark Matter



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Inert Higgs Doublet Model

➡ Introduce another Higgs field that only couples to gauge sector

impose Z2 parity: SM particles + , extra Higgs: -

H1 = HSM

relic density could be obtained for the dark matter mass around 40 GeV − 80 GeV or largerthan 600 GeV. Ref. [14, 15] studied the neutrino signatures from dark matter annihilationin the IHDM. Continuous gamma ray spectrum from fragmentation and monochromaticgamma ray lines are studied in Ref. [13] and [16] respectively. Positron and antiprotonsignatures are studied in Ref. [17]. There are also collider analysis on the LEP II limit forthe IHDM [18] as well as collider signatures of SA associated production with A → Sl+l−

at the LHC [19]. Direct detection of the IHDM dark matter has been studied in [7, 13, 20].In this work, we performed a complete analyzed the dark matter relic in the IHDM

over the whole parameter space, taken into account various theoretical and experimentalconstraints on the IHDM. The latest results of the collider constraints based on χ0

1χ02 search

at the LEP are imposed. Unlike in Ref. [13], in which only a low SM Higgs mass mh = 100GeV and 200 GeV are considered, we also considered a high Higgs mass mh = 500 GeV.In Ref. [13], the mass splitting between A, H± and the dark matter candidate S is fixed tobe 10 (5) GeV and 50 (10) GeV respectively for low (high) mass region. We studied thecases when the mass splittings between A, H± and the dark matter candidate S are small,in which the coannihilation plays an important role, as well as the cases when the masssplittings are large. In regions that overlap with those analyzed in Ref. [13], our resultsagree with the literature. We identified additional regions of parameter space, in whichthe dark matter relic density is also consistent with the WMAP result but was overlookedbefore. We also present our results in the parameter spaces of physical Higgs masses andHiggs couplings, which can easily be used for the purpose of collider study and dark matterdetections.

The rest of the paper is organized as follows: Sec. II briefly present the IHDM. Wediscussed the theoretical and experimental constraints on the model parameter space inSec. III. Sec. IV presented our results on the relic density analysis. We concluded in Sec. V.

II. THE INERT HIGGS DOUBLET MODEL

The IHDM is an extension of the Higgs sector of the SM. Besides the usual Higgs doubletH1, additional Higgs doublet H2 is introduced:

H2 =

(

H+

(S + iA)/√

2

)

, (2)

which is charged under SU(2)L × U(1)Y as (2, 1/2). Unlike the SM Higgs boson, whichcouples to both the gauge bosons and matter fermions, the extra Higgs doublet couplesto the gauge sector only. Such couplings can be guaranteed by imposing a Z2 symmetry(sometimes also called as matter parity) where all the particles except H2 are even under theZ2. While H1 obtains a vacuum expectation value (VEV) v/

√2 = 174 GeV as in the SM,

H2 does not obtain a VEV: 〈H2〉 = 0. The Z2 symmetry is, therefore, not spontaneouslybroken. The lightest particle in H2 is stable and could be a good dark matter candidate.

3

lightest one: DM candicate

Dark Matter in the Inert Higgs Doublet Model E. Dolle (U. of Arizona)

−The Inert Dark Matter E. Dolle and S. Su, Phys. Rev. D 80 (2009) 055012.



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Dark Matter Studies

120_50_8

The dashed and dot-dashed curves in the left plot of Fig. 2 shows the relic densitydependence for δ2=8 GeV and 5 GeV respectively. Coannihilation effects get stronger forsmaller mass splittings. Therefore, for most of the mS region between 40 − 60 GeV, thecoannihilation cross section is too large and the relic density is too small.

Curves in the right plot of Fig. 2 correspond to λL=0.01, 0.1, 0.2, 0.3 and 0.5,respectively, while (δ1, δ2) is fixed to be (50, 10) GeV. Similar Z-pole and h-pole featuresappear. The relic density is smaller for larger λL, since SS annihilation via h-exchange isincreased due to the increased SSh coupling.

mS [GeV]

!L

10 20 30 40 50 60 70 80 90 100!0.5

!0.4

!0.3

!0.2

!0.1

0

0.1

0.2

0.3

0.4

0.5

mS [GeV]

!L

10 20 30 40 50 60 70 80 90 100!0.5

!0.4

!0.3

!0.2

!0.1

0

0.1

0.2

0.3

0.4

0.5

FIG. 3: WMAP 3σ allowed region (enclosed by blue curves) in mS − λL plane for mh=120 GeV.The mass splittings are chosen to be (δ1, δ2) = (50, 10) GeV (left plot) and (50,8) GeV (right

plot). Shaded regions are excluded either by LEP I+II searches (yellow, light shade), electroweakprecision constraints (orange, medium shade), dark matter direct detection (purple, medium-dark

shade), vacuum stability (red, dark shade along bottom), and perturbativity (hatched region).

Fig. 3 shows the WMAP 3σ relic density allowed region (enclosed by two blue curves)in the mS − λL plane for mS < 100 GeV with mh = 120 GeV for (δ1, δ2) =(50, 10) GeV(left plot) and (50, 8) GeV (right plot). Shaded regions are excluded by various theoreticaland experimental constraints, as described in Sec. III.

For (δ1, δ2) =(50, 10) GeV (left plot), the gap around mS ∼ 40 GeV corresponds to theZ-pole. The gap around mS ∼ 60 GeV corresponds to the h-pole. The LEP constraint(yellow, light shade region) is very strong due to the strong constraints on mA and mS

when δ2 > 8 GeV. The precision electroweak constraints (orange, medium shade region)is weak since δ1 > δ2 is slightly preferred by the fit to the S − T contour. Given all theconstraints, only a small region around mS ∼ 80 GeV survives. The value for λL for theallowed region, however, could be as large as −0.2. Such a large value of λL would beimportant for generating a large signal in the indirect detection of dark matter.

The LEP constraints on mS and mA, however, are weakened for small mass splittingδ2

<∼ 8 GeV. For such a small mass splitting, mS as low as around 40 GeV is still allowed.In the right plot of Fig. 3, the allowed parameter space is given for (δ1, δ2) =(50, 8) GeV. In

10

mS [GeV]

!L

400 500 600 700 800 900 1000 1100 1200!0.5

!0.4

!0.3

!0.2

!0.1

0

0.1

0.2

0.3

0.4

0.5

mS [GeV]

!L

400 500 600 700 800 900 1000 1100 1200!0.5

!0.4

!0.3

!0.2

!0.1

0

0.1

0.2

0.3

0.4

0.5

FIG. 7: WMAP 3σ allowed region (enclosed by blue curves) in mS − λL plane for mh=120 GeV.

The mass splittings are chosen to be (δ1, δ2) = (1, 1) GeV (left plot), (1, 10) GeV (right plot). Redregion are excluded by vacuum stability while he hatched region are excluded by perturbativityconstraints.

(hatched region), however, shifts to the left for larger δ1,2. Therefore, no allowed regionleft if at least one of δ1,2

>∼ xxx GeV. increase one of the delta to see at which deltathere is no allowed region.

For a large SM Higgs mass mh = 500 GeV, large mass splitting δ1>∼ 150 GeV is needed

to satisfy the precision electroweak constraints. There is no region in mS −λL survive afterall the experimental and theoretical constraints are taken into account. does the relicdensity region change for mh? cross section gets smaller, could not compensatefor large δ1.

V. CONCLUSION

We studied the simple extension of the SM Higgs sector when an extra inert Higgsdoublet is introduced that couples to the gauge sector only. The lighter of the neutralcomponents could be a good dark matter candidate. We explored the parameter regionsof the IHDM, taken into account the relic density constraints from WMAP and varioustheoretical and experimental constraints. We showed that there are five distinctive regionsthat could provide the right amount of cold dark matter in the Universe while satisfy allthe constraints.

• (I) Low mh, mS ∼ 20 GeV, λL ∼ −0.2 for large δ1 and δ2.

• (II) Low mh, 60 GeV < mS < 80 GeV, −0.2 < λL < 0.2 when at least one of δ1, δ2

is large.

14

120_1_1



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Direct Searches



Inert Doublet Model - Collider Signatures in the Inert Doublet Model

E. Dolle, X. Miao, B. Thomas (U. of Arizona)− Dilepton Signals of Dark Matter in the IHDM E. Dolle, S. Su, B. Thomas, X. Miao, arXiV: 0909.3094, PRD 81 (035003), 2010

+W (*)

+ Z (*)

+W(*)H±

A

Spp→ SA→ SSZ(∗), SSW (∗)W (∗)

Signatures: jets + leptons + missing ET



Dilepton Signals-

•LH2: mS = 40 GeV, (δ1, δ2)=(70,70) GeV

Signal: pp→SA→SSZ→SSl+l-, l=e,µ

Mll < 70 GeV

! "! #!! #"!#!

!$

#!!%

#!!#

#!!

Mll(GeV)

1 σdσ

dM

ll/1G

eV

&

&

W WZZ/γ∗

tt̄W Z/γ∗

SA

WW

ZZ/γ∗

tt̄

WZ/γ∗

SA



Direct Searches -


Level III CutsBenchmark σSA σH+H− σhZ σWW σZZ/γ∗ σtt̄ σWZ/γ∗ σWt σcomb

BG S/B S/√

B

(fb) (fb) (fb) (fb) (fb) (fb) (fb) (fb) (fb)LH1 3.42 0.04 1.28 11.59 36.99 4.55 19.52 3.82 77.79 0.04 3.87LH2 0.89 ∼ 0 0.01 0.07 0.24 0.11 0.08 0.07 0.58 1.53 11.66LH3 0.18 ∼ 0 ∼ 0 0.03 0.15 0.05 0.04 0.06 0.34 0.52 3.04LH4 0.19 ∼ 0 0 0.03 0.15 0.05 0.04 0.06 0.34 0.57 3.29LH5 0.004 ∼ 0 ∼ 0 0.13 0.04 ∼ 0 0.04 0.01 0.23 0.02 0.02HH1 0.65 ∼ 0 0 0.45 13.41 0.55 5.85 0.45 20.71 0.03 1.42HH2 0.37 0.01 0 0.08 0.26 0.12 0.09 0.12 0.67 0.56 4.55HH3 1.01 ∼ 0 0 17.49 1.06 1.60 0.76 1.65 22.56 0.04 2.12

TABLE V: Cross-sections for the processes pp → SA → "+"− $ET , pp → H+H− → "+"− $ET , andpp → h(∗)Z → "+"− $ET at the LHC for each of the benchmark points presented in Table I afterthe application of our Level III cuts. Cross-sections for the dominant SM backgrounds (WW ,ZZ/γ∗,etc.) after the application of the Level III cuts are also shown, as is the total backgroundcross-section including all of these individual contributions. An entry of “∼ 0” indicates a cross-section less than 1 ab. The last two columns display the signal-to-background ratio S/B andstatistical significance (as given by S/

√B) corresponding to an integrated luminosity of L =

100 fb−1 after the application of these same cuts.

V. RESULTS

Now that we have discussed in detail the event-selection procedure to be used in ournumerical analysis of dilepton signals in the IDM, we turn to present the results of thatnumerical analysis. In Table V, we list the cross-sections for the signal process and the mostrelevant backgrounds after the application of our Level I+II+III cuts. The last two columnsin the Table display the signal-to-background ratio S/B and the statistical significance (asgiven by S/

√B at an integrated luminosity of L = 100 fb−1) for each benchmark point4 in

our analysis, after the implementation of these same cuts. Note that the numbers quotedhere for benchmark LH4 with small δ1 include, in addition to the usual pp → SA →"+"− + $ET contribution, contributions from the processes pp→ H±A→ "+"−jj + $ET andpp → H±A → "+"−"± + $ET in which the additional jets or leptons from H± decay aresufficiently soft as to escape detection. It should be noted that taking these contributionsinto account results in an increase in the statistical significance of discovery in this channelfrom 2.07σ to 3.29σ. For the other benchmark points listed in Table I, δ1 ≥ 50 GeV, and

4 One modification is made in the case of LH5. For this point, both signal and background event rates arequite low, and consequently the significance value quoted in the last column of Table V was obtainedusing Poisson statistics rather than S/

√B.

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Direct Searches -



BG S/B S/√

B





V. RESULTS





√B.

15

•LH2: mS = 40 GeV, (δ1, δ2)=(70,70) GeV



Direct Searches -



BG S/B S/√

B





V. RESULTS





√B.

15



Trilepton Signals-

Signal: pp→H±A→SSWZ→SSlllν, l=e,µ

including those from W + jets and heavy-flavor processes, are effectively eliminated bythis choice of cuts.

After the imposition of the Level I and Level II cuts, we impose one further battery ofevent-selection criteria (hereafter referred to as our Level III cuts). Unlike these first twosets of cuts, which are applied universally to all benchmark points used in this analysis, ourLevel III cuts are individually tailored to optimize the statistical significance of discoveryfor each benchmark point. A wide variety of possible criteria could in principle be usedin this optimization process; however, we find that one particularly useful criterion thatcan be used to differentiate between signal and background events is the invariant massM!Z!Z of the requisite pair of SFOS charged leptons (which we dub !+

Z and !−Z) that anyevent must include in order to pass the Level I cuts. If only one SFOS pairing can beconstructed for a given event, M!Z!Z is unambiguously defined. In cases in which morethan one SFOS combination exists and δ2 ≥ 70 GeV, the pair whose invariant mass isclosest to min(δ2,MZ) will be identified as !+

Z and !−Z , and that invariant mass will beidentified as M!Z!Z . In cases in which δ2 < 70 GeV, the pair whose invariant mass isclosest to 70 GeV will be so identified.3

50 100 150 20010

!2

10!1

100

Mlzlz (GeV)

1 σdσ

dM

lz

lz/5G

eV

tt̄(j)W Z/γ∗

AH±

tt̄(j)

AH±

WZ/γ∗

50 100 150 20010

!2

10!1

100

Mlzlz (GeV)

1 σdσ

dM

lz

lz/5G

eV

tt̄(j)W Z/γ∗

AH±

tt̄(j)

AH± WZ/γ∗

FIG. 2: Distributions of the invariant mass of the SFOS lepton pair after the application of theLevel I+II cuts described in the text, in our benchmark scenarios LH1 (left panel) and LH3 (rightpanel), both for the signal process and for the dominant SM backgrounds. Note that the areaunder each distribution curve has been normalized to one.

The distribution for M!Z!Z peaks around MZ for the Standard-Model WZ/γ∗ back-ground. For the signal process, the peak is around min(δ2,MZ), as shown clearly in Fig. 2

3 We choose this criterion for identifying the SFOS pair, rather that simply selecting whichever pair has aninvariant mass closer to δ2. This is because for δ2 ! 70 GeV, the latter procedure would result in morefrequent misidentification of which leptons were produced via Z/γ∗ decay in the WZ/γ∗ backgroundsample, and consequently lower statistical significance values.

9

50 100 150 20010

!2

10!1

100

MTW(GeV)

1 σdσ

dM

TW

/5G

eV

tt̄(j)W Z/γ∗

AH±

tt̄(j)

AH±

WZ/γ∗

50 100 150 20010

!2

10!1

100

MTW(GeV)

1 σdσ

dM

TW

/5G

eV

tt̄(j)W Z/γ∗

AH±

tt̄(j)AH±

WZ/γ∗

FIG. 3: Distributions of the transverse mass variable MTW defined in Eq. (6), after the applicationof the Level I+II cuts described in the text, in our benchmark scenarios LH1 (left panel) andLH3 (right panel), both for the signal process and for the dominant SM backgrounds.

depending on the benchmark point in question. As we shall see, such cuts on M!Z!Z andMTW will turn out to be particularly useful in distinguishing a trilepton signal from thedominant WZ/γ∗ background.

It can also be useful to impose a more stringent lower limit pminT!

on the transversemomentum pT!

of the charged leptons than that imposed at Level I:

• pT!≥ pmin

T!> 15 GeV.

Likewise, a cut on the total-transverse-momentum variable HT :

• HT ≥ HminT ,

with HT defined in terms of the sum

HT = "ET +3∑

i=1

|pT !i|, (7)

can also be useful in differentiating signal from background. A roster of the particular cutsimplemented for each benchmark used in our analysis is compiled in Table IV.

IV. RESULTS

In Table V, we show the discovery potential for the trilepton signal at the LHC (assuminga center-of-mass energy of 14 TeV) for each of the IDM benchmark points defined above,assuming an integrated luminosity of 300 fb−1 in each of the two detectors. The bestprospects for discovery are obtained for the benchmarks LH2 and LH6, each of which

11

S. Su, B. Thomas, X. Miao, arXiV: 0909.3094, PRD 82 (082009), 2010

•LH3: mS = 82 GeV, (δ1, δ2)=(50,50) GeV



Trilepton Signals-


Benchmark Mmax!Z!Z

MminTW

MmaxTW

∆Rmax!! Hmin

T pminT !

LH1 100 GeV 90 GeV − 1.6 240 GeV −LH2 65 GeV − 60 GeV 1.3 150 GeV −LH3 50 GeV − 60 GeV 1.2 140 GeV −LH6 65 GeV − − 1.1 200 GeV 20 GeVLH7 100 GeV − 65 GeV − 200 GeV −LH8 40 GeV − − − − −

TABLE IV: A list of the optimized Level III cuts used in the analysis of each of the benchmarkpoints presented in Table I. An entry of “−” indicates that the corresponding cut is not imposed.For more details on the definition of the thresholds used, see text.

Level III CutsBenchmark σH±A σWZ/γ∗ σtt̄(j) σWt(j) σcomb

BG S/B S/√

B

(fb) (fb) (fb) (fb) (fb) (300 fb−1)LH1 0.038 0.159 0.020 0.011 0.191 0.20 2.15LH2 0.078 0.073 0.019 0.021 0.114 0.68 5.64LH3 0.035 0.093 0.023 0.014 0.131 0.27 2.36LH6 0.101 0.185 0.030 0.007 0.221 0.46 5.27LH7 0.270 7.137 0.084 0.038 7.259 0.04 2.45LH8 0.031 0.385 0.144 0.061 0.591 0.05 1.00

TABLE V: Cross-sections for the signal process pp→ AH± → "+"−"±+ $ET and for the dominantSM backgrounds from WZ/γ∗, tt̄(j) and Wt(j) production for each of the benchmark pointspresented in Table I, after the application of our Level III cuts. The total background cross-section is also shown. The last two columns display the signal-to-background ratio S/B, andthe statistical significance (as given by S/

√B) corresponding to an integrated luminosity of

L = 300 fb−1 in each detector at the LHC (operating at a center-of-mass energy√

s = 14 TeV),after the application of these same cuts.

yields a statistical significance of more than 5σ. The reason why these benchmarks arecomparatively auspicious is twofold. First, both involve a light LIP, with a mass mS ∼40 GeV. Second, both also feature a mass splitting δ2 ∼ 70 GeV, which, on the one hand, issmall enough that A→ SZ → S#+#− decays will occur through an off-shell Z boson, but,on the other hand, is large enough so that the resulting charged leptons will not generallybe too soft to escape detection.

For LH7, which features a similarly light LIP, with mS ∼ 40 GeV, but for which (δ1, δ2) =(70, 100) GeV, the primary difficulty in resolving the signal is that the (dominant) WZ/γ∗

background cannot be suppressed by applying a Z veto on M!Z!Z , since A→ SZ → S#+#−

decays occur via an on-shell Z. Indeed, this two-body decay mode of the A is analogous

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Trilepton Signals-


Benchmark Mmax!Z!Z

MminTW

MmaxTW

∆Rmax!! Hmin

T pminT !




BG S/B S/√

B










12

•LH2: mS = 40 GeV, (δ1, δ2)=(70,70) GeV



Trilepton Signals-


Benchmark Mmax!Z!Z

MminTW

MmaxTW

∆Rmax!! Hmin

T pminT !




BG S/B S/√

B










12



Exotic 4th Generation Mirror Quark-

Exotic 4th generation mirror quarks J. Alwall (National Taiwan Univ.), J. Feng (UCIrvine), J. Kumar (Univ. of Hawaii)

− DM-Motivated Searches for Exotic 4th Generation Mirror Quarks at the Tevatron and Early LHC Data

J. Alwall, J. L. Feng, J. Kumar, S. Su, PRD81 (114027), 2010







chiral under SM gauge group








same chargeopposite chirality








charge under hidden symmetry

same chargeopposite chirality



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Dark Matter: long-lived on cosmological time scale Charge under a new unbroken symmetry ⇒ absolutely stable

๏ have only gravitational interaction with the SMcan not be discovered at colliders

๏ couple to SM through connector Y YY production with y → f X

DM

X Y f

connector SM

4th Generation Mirror Quark



-




DM

X Y f

connector SM

SM charge & dark charge




-




DM

X Y f

connector SM

SUSY neutralino squark quark R-parity

ExD KK gauge boson KK quark quark KK-parity

Our study DM(no SM charge) exotic quark quark dark charge

SM charge & dark charge




-

Y particle appears as exotic 4th generation mirror quarks Q’

p

p

Qʼ

Qʼ

DM

qDM

q

Collider Signal T’T’→ttXX, B’B’ →bbXX

Signal: T ′T̄ ′ → t(∗)Xt̄(∗)X → bW+Xb̄W−X




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(GeV)T’m

300 320 340 360 380 400 420 440 460 480 500

(G

eV

)X

m

0

20

40

60

80

100

120

140

160

180

200

-12 fb

-15 fb

-110 fb

-120 fb

t + mX = mT’m

Semileptonic channel

X at the Tevatront t X ! T’Exclusion for T’

(GeV)T’m

300 320 340 360 380 400 420 440 460 480 500

(G

eV

)X

m

0

20

40

60

80

100

120

140

160

180

200

-12 fb

-15 fb

-110 fb

-120 fb

t + mX = mT’m

Hadronic channel


FIG. 3: 95% CL Tevatron exclusion contours for the semi-leptonic channel (left) and the hadronicchannel (right) for integrated luminosities 2, 5, 10, and 20 fb−1. For each point in parameter space,the cut with the best significance has been chosen.

luminosity of 20 fb−1 at the end of Tevatron running, a reach of up to 455 GeV for thehadronic channel can be achieved.

The reach in mT ′ is almost independent of mX for small to medium mX . However, whenmX approaches the on-shell decay threshold of mT ′ − mt, the reach is limited since the topand X are produced nearly at rest in the T ′ rest frame, and the T ′T̄ ′ system therefore needsa transverse boost for the X particles to produce large missing transverse momentum. Thisleads to the dip in the exclusion curves at mX close to mT ′ − mt, and indeed there is noexclusion reach at the Tevatron for mT ′ − mt − mX

<∼ 15 GeV. For 20 fb−1 integratedluminosity and mT ′ between 370 and 390 GeV, mX could be excluded up to 160 GeV at95% CL using the hadronic mode. For smaller mT ′ , the reach in mX is decreased due to thesoftness of the X particle distributions, while for larger mT ′ , it is decreased because of thesmall T ′T̄ ′ production cross section.

Figure 4 shows the 3σ (Gaussian equivalent2) Tevatron discovery contours for both thesemi-leptonic and hadronic channels for integrated luminosities of 2, 5, 10, and 20 fb−1. A3σ signal could be observed for mT ′ < 360 GeV and mX

<∼ 110 GeV in the semi-leptonicchannel with 20 fb−1 integrated luminosity. The hadronic channel is more promising. With5 fb−1 integrated luminosity, a reach in mT ′ up to 360 GeV could be achieved when mX isnot too large. With 20 fb−1 integrated luminosity, the reach is extended to 400 GeV for mX

up to about 80 GeV. For larger mX , the reach in mT ′ decreases.Figure 5 shows the 95% CL exclusion contours for a 10 TeV early LHC run, in the semi-

leptonic and hadronic channels for integrated luminosities 100, 200, and 300 pb−1. With just100 pb−1, the LHC exclusion reach for mT ′ exceeds the Tevatron exclusion reach with 20 fb−1

luminosity. Exclusions of mT ′ up to 490, 520, and 535 GeV could be achieved with 100,

2 By Gaussian equivalent, we mean that we have converted the one-sided Poisson probability into the

equivalent σ deviation in a two-sided Gaussian distribution, which is more commonly used in the literature.

12

(GeV)T’m300 320 340 360 380 400 420 440 460 480 500

(G

eV

)X

m

0

20

40

60

80

100

120

140

160

180

200

-1100 pb

-1200 pb

-1300 pb

t + mX = mT’m


X at 10 TeV LHCt t X ! T’Discovery for T’

(GeV)T’m300 320 340 360 380 400 420 440 460 480 500

(G

eV

)X

m

0

20

40

60

80

100

120

140

160

180

200

-1100 pb

-1200 pb

-1300 pb

t + mX = mT’m

Hadronic channel


FIG. 6: 3σ (Gaussian equivalent) discovery contours for a 10 TeV LHC run, in the semi-leptonicchannel (left) and the hadronic channel (right), for integrated luminosities 100, 200, and 300 pb−1.For each point in parameter space, the cut with the best significance has been chosen.

channel could provide a 3σ signal for mT ′<∼ 490 GeV and mX

<∼ 170 GeV with 300 pb−1

luminosity. We might also observe a positive signal for mX up to about 170 GeV in theoff-shell decay region (mT ′ − mX < mt) for mT ′

<∼ 330 GeV.It is clear from the discovery and exclusion contours, both for the Tevatron and the

LHC, that the fully hadronic channel has considerably larger reach than the semi-leptonicchannel, for reasons enumerated in Sec. IV. In this channel, the full, currently viable, regionin parameter space can be excluded at a 10 TeV LHC run.3 In case both channels are visible,they can be used to distinguish between different model and mass hypotheses.

VI. CONCLUSIONS

We have considered the prospects for hadron colliders to pair produce new exotic quarksthat decay directly to a pair of dark matter particles and SM particles. Although we have aparticular interest in the WIMPless dark matter scenario [7] (including a specific example [8]that can potentially explain the DAMA annual modulation result), this scenario is motivatedon quite general grounds, and, with minor modifications, our analysis applies to many otherdark matter scenarios and other new physics models.

We have focused on the up-type exotic quark T ′. T ′ pair production leads to T ′T̄ ′ →tt̄XX, and we have then analyzed the semi-leptonic and fully hadronic channels. The fullyhadronic channel (vetoing events with leptons) seems to be the most efficient, because of

3 The results obtained here can be readily translated to an LHC run at 7 TeV, by multiplying the integrated

luminosities needed by roughly a factor of 3. This approximation accounts for the difference in cross

sections at different center of mass energies, assuming that the cut efficiencies for both the signal and

backgrounds do not change significantly.

14



-


(GeV)T’m

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FIG. 3: 95% CL Tevatron exclusion contours for the semi-leptonic channel (left) and the hadronicchannel (right) for integrated luminosities 2, 5, 10, and 20 fb−1. For each point in parameter space,the cut with the best significance has been chosen.

luminosity of 20 fb−1 at the end of Tevatron running, a reach of up to 455 GeV for thehadronic channel can be achieved.

The reach in mT ′ is almost independent of mX for small to medium mX . However, whenmX approaches the on-shell decay threshold of mT ′ − mt, the reach is limited since the topand X are produced nearly at rest in the T ′ rest frame, and the T ′T̄ ′ system therefore needsa transverse boost for the X particles to produce large missing transverse momentum. Thisleads to the dip in the exclusion curves at mX close to mT ′ − mt, and indeed there is noexclusion reach at the Tevatron for mT ′ − mt − mX

<∼ 15 GeV. For 20 fb−1 integratedluminosity and mT ′ between 370 and 390 GeV, mX could be excluded up to 160 GeV at95% CL using the hadronic mode. For smaller mT ′ , the reach in mX is decreased due to thesoftness of the X particle distributions, while for larger mT ′ , it is decreased because of thesmall T ′T̄ ′ production cross section.

Figure 4 shows the 3σ (Gaussian equivalent2) Tevatron discovery contours for both thesemi-leptonic and hadronic channels for integrated luminosities of 2, 5, 10, and 20 fb−1. A3σ signal could be observed for mT ′ < 360 GeV and mX

<∼ 110 GeV in the semi-leptonicchannel with 20 fb−1 integrated luminosity. The hadronic channel is more promising. With5 fb−1 integrated luminosity, a reach in mT ′ up to 360 GeV could be achieved when mX isnot too large. With 20 fb−1 integrated luminosity, the reach is extended to 400 GeV for mX

up to about 80 GeV. For larger mX , the reach in mT ′ decreases.Figure 5 shows the 95% CL exclusion contours for a 10 TeV early LHC run, in the semi-

leptonic and hadronic channels for integrated luminosities 100, 200, and 300 pb−1. With just100 pb−1, the LHC exclusion reach for mT ′ exceeds the Tevatron exclusion reach with 20 fb−1

luminosity. Exclusions of mT ′ up to 490, 520, and 535 GeV could be achieved with 100,

2 By Gaussian equivalent, we mean that we have converted the one-sided Poisson probability into the

equivalent σ deviation in a two-sided Gaussian distribution, which is more commonly used in the literature.

12

(GeV)T’m300 320 340 360 380 400 420 440 460 480 500

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eV

)X

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FIG. 6: 3σ (Gaussian equivalent) discovery contours for a 10 TeV LHC run, in the semi-leptonicchannel (left) and the hadronic channel (right), for integrated luminosities 100, 200, and 300 pb−1.For each point in parameter space, the cut with the best significance has been chosen.

channel could provide a 3σ signal for mT ′<∼ 490 GeV and mX

<∼ 170 GeV with 300 pb−1

luminosity. We might also observe a positive signal for mX up to about 170 GeV in theoff-shell decay region (mT ′ − mX < mt) for mT ′

<∼ 330 GeV.It is clear from the discovery and exclusion contours, both for the Tevatron and the

LHC, that the fully hadronic channel has considerably larger reach than the semi-leptonicchannel, for reasons enumerated in Sec. IV. In this channel, the full, currently viable, regionin parameter space can be excluded at a 10 TeV LHC run.3 In case both channels are visible,they can be used to distinguish between different model and mass hypotheses.

VI. CONCLUSIONS

We have considered the prospects for hadron colliders to pair produce new exotic quarksthat decay directly to a pair of dark matter particles and SM particles. Although we have aparticular interest in the WIMPless dark matter scenario [7] (including a specific example [8]that can potentially explain the DAMA annual modulation result), this scenario is motivatedon quite general grounds, and, with minor modifications, our analysis applies to many otherdark matter scenarios and other new physics models.

We have focused on the up-type exotic quark T ′. T ′ pair production leads to T ′T̄ ′ →tt̄XX, and we have then analyzed the semi-leptonic and fully hadronic channels. The fullyhadronic channel (vetoing events with leptons) seems to be the most efficient, because of

3 The results obtained here can be readily translated to an LHC run at 7 TeV, by multiplying the integrated

luminosities needed by roughly a factor of 3. This approximation accounts for the difference in cross

sections at different center of mass energies, assuming that the cut efficiencies for both the signal and

backgrounds do not change significantly.

14

− B’B’ at Tevatron and LHC J. Alwall, J. L. Feng, J. Kumar, S. Su, in preparation



SUSY Golden Region- Sbottom searches

H. Li (Shandong Univ.), W. Parker (U. of Wisconsin, Madison), Z. Si (Shandong Univ.)

− Sbottom Signatures of Supersymmetric Golden Region H. Li, W. Parker, Z. Si, S. Su, arXiv: 1009.6042, submitted to PLB.

LEP Higgs search limit: mHSM > 114.4 GeV @ 95% C.L. MSSM: mh < mZ @ tree level, receive large loop corrections from stop large mstop is needed, fine tuning in EWSB.

⇒ SUSY golden region: small μ, small mQ3, mU3, large At

mQ3mu3

md3At µ mA tanβ M1 M2 M3 mq̃ ml̃

548.7 547.3 1000 1019 250 200 10 1000 1000 1000 1000 1000

TABLE I: MSSM input parameters defined at the weak scale for the benchmark point of theMSSM golden region, taken from Ref.[6]. All dimensionful parameters are in unit of GeV.

mt̃1 mt̃2 mb̃1mχ0

1mχ0

2mχ±

1

mh0 mH0 mA mH±

398 688 550 243 253 247 118 201 200 216

TABLE II: Physical spectrum of light sparticles for the benchmark point in the MSSM golden

region, in unit of GeV.

which can also be applied to the light CP-even Higgs boson in the decoupling region of theMSSM parameter space. Although MSSM could accommodate a lighter Higgs (around 90GeV) [9] while still being consistent with the LEP Higgs search results, it only happensin a restricted region of the MSSM parameter space, which can be viewed as additionalsource of fine-tuning. In Ref. [6], authors used the LEP limit of 114.4 GeV as a lowerbound on the light MSSM CP-even Higgs mass. The dominate loop contribution to themass of the light CP-even Higgs boson comes from the stop sector. Accommodating theLEP Higgs search bound requires heavier stop masses and/or large left-right stop mixing.Taking into account the collider search limit on sparticle masses, constraints from the ρparameter, rare decays b → sγ, as well as minimizing the fine tuning, we are limited to theMSSM golden region with small µ and mA, relatively small value for m2

Q3, m2

u3and large

value for At.In our analyses, we used the benchmark point chosen in Ref. [6]. The MSSM input

parameters at the weak scale are given in Table I. We assume there is no flavor off-diagonal terms and all the tri-linear A terms are zero except At. All the gaugino massesM1,2,3 as well the masses for the slepton and first two generation squarks are chosen to be1 TeV. The mass parameter for the b̃R, md3

, is also chosen to be heavy. Varying thoseparameters does not have significant effects on the Higgs potential, as well as the lightsbottom (mostly b̃L in our case) pair production channel that we consider below.

The physical mass spectrum of light particles for the benchmark point is given inTable II, which is obtained using SOFTSUSY 2.0.11[10]. With the small value of µ, thetwo lightest neutralinos and charginos are almost degenerate, which are mostly Higgsinos.The mass for the light CP-even Higgs is about 118 GeV, above the LEP Higgs searchlimit. The heavy CP-even Higgs, as well as the CP-odd Higgs and the charged Higgses arearound 200 GeV. Due to the large left-right mixing in the stop sector, there is a large masssplitting in the two stop mass eigenstates: mt̃2 − mt̃1 > mZ , which is a generic feature ofthe MSSM golden region. Utilizing this feature, Ref. [6] studied the process of t̃2t̃∗2 pairproduction at the LHC with at least one t̃2 decays via t̃2 → t̃1Z. Inclusive signature ofZ + 2 b-jets + #ET + X is analyzed, where Z decays leptonically into pair of electrons ormuons. It is found that by requiring the reconstruction of the lepton pair around the Zpeak, a large pT cut on the first two leading jets with at least one b-tagging, a large boost

4



SUSY Golden Region-

process σi(fb) Ntotal cut-I(%) cut-II(%) cut-III(%) σIIIf (fb) cut-IV(%) σIV

f (fb)

b̃1b̃∗1 2.14 × 102 40000 11 49 49 5.6 33 1.8

tt̄ 5.38 × 105 1827154 5.1 3.4 3.5 33 27 8.8

tt̄W 5.22 × 102 120161 13 8.1 12 0.6 38 0.2

tt̄Z 6.85 × 102 166420 15 11 14 1.6 33 0.5

WZjj 3.90 × 104 1259561 1.5 4.5 15 4.0 7.8 0.3

WWjj 6.88 × 104 1260060 1.4 3.1 11 3.4 4.8 0.2

Wjjjj 2.55 × 107 2512703 0.5 1.3 4.4 71 0 0

S/√

B 5.3 S/√

B 5.8

S/B 0.05 S/B 0.18

TABLE III: Summary of the cross sections and cut efficiencies (with respect to the previous level

of cut) for the signal and background processes at the 14 TeV LHC before and after each cut. TheWZjj, WWjj and Wjjjj cross section before the cuts are calculated with a precut of pTj > 10GeV, |ηj | < 5 and ∆Rjj > 0.2. The third column shows the total number of events that is

simulated for each process.

to further suppress the SM backgrounds.Table III summarize the signal and background cross sections, as well as the cut

efficiencies. After three levels of cuts, the remaining dominant background is Wjjjj,followed by tt̄. For an integrated luminosity of 100 fb−1, about 560 b̃1b̃∗1 events can be foundat LHC after Cuts-I, II and III. The significance is about S/

√B = 5.3 for L = 100 fb−1

with S/B = 0.05.To further reduce the Wjjjj background with non-b-jets, we can demand b-tagging on

at least one jet:

• Cut IV, at least one b-tagging in the two leading jets.

The resulting cross sections after this cut are shown in the last two columns of Table III.Backgrounds Wjjjj, WZjj and WWjj are reduced greatly with b-tagging. tt̄ background,however, now becomes dominant, which leads to a final significance level1 of S/

√B = 5.8

with S/B = 0.18 for 100 fb−1 integrated luminosity. Imposing such b-tagging could beused to suppress other SUSY processes with non-b-jets that have similar signatures.

Note that we have chosen the cuts to demonstrate the feasibility of a 5 σ discovery ofpp → b̃1b̃∗1 → 2jb +2 jets+1 lepton+ $ET +X channel at the LHC with 100 fb−1 luminosity.

1 For Wjjjj process, zero event (out of 2,512,703 total number of events) left after all the cuts. Using

Poisson statistics, we would expect an upper limit of 3 events at 95% C.L., which leads to a Wjjjj

cross section of 30 fb. Similarly, 3 out of 1,260,060 events are left for WWjj channel after all the cuts.

Poisson statistics gives an upper limit of 7.75 events at 95% C.L., corresponding to a cross section of

0.4 fb. Using these 95% C.L. upper limits, the resulting final significance level S/√

B is 2.9 for 100 fb−1

integrated luminosity with S/B = 0.04.

7

Signature:

factor of Z boson and a large !ET cut, a 3 σ observation of this inclusive signal is possiblewith 75 fb−1 luminosity, while a 5 σ discovery is possible with 210 fb−1 data.

Ignoring the left-right mixing in the sbottom sector, the mass of b̃L is also determinedby mQ3

. Therefore, in the MSSM golden region, one of the sbottom is also relativelylight, which can be copiously produced at the LHC. For the benchmark point presentedin Table I, the mass of the light sbottom is 550 GeV. The leading order pair productioncross section at the 14 TeV LHC is about 214 fb. The light sbottom dominantly decaysinto tχ−

1 and W−t̃1, with branching ratio of 51.4% and 46.5%, respectively. χ±1 decays

into χ01 with soft jets and leptons, due to the small mass splittings between charged and

neutral Higgsinos. t̃1 dominantly decays into bχ+1 , with χ+

1 further decays. Therefore, thedecay products of b̃1 include at least one b-jet plus W plus χ0

1. In our analyses below, weconsider the pair production of b̃1b̃∗1 at the LHC with

√s = 14 TeV. Demanding one W

decay leptonically and one W decay hadronically, we study the collider signature of

pp → b̃1b̃∗1 → 2jb+ ≥ 2 jets+ ≥ 1 lepton + !ET . (4)

Note that for the parameter choices of the benchmark point in Table I, M1,2,3 are takento be very heavy and the light neutralinos χ0

1,2 and charginos χ±1 are mostly Higgsinos. For

smaller value of M1, the decay branching ratios of b̃1 do not change much since b̃1 → bχ0i is

suppressed by either the small U(1) gauge coupling or the small bottom Yukawa coupling.For smaller value of M2, channels of b̃1 → tχ±

1,2 both open up, which do not change the

collider signature of Eq. (4) given the further decay of χ±1,2. b̃1 could also decay into bχ0

i

with sizable branching ratio, where χ0i is mostly wino. Our results below could be rescaled

by the branching ratio for such case of small M2.

III. COLLIDER ANALYSES

We generate the event samples for the signal process at parton-level using the MadGraph4.4.26 [11] package. These events were subsequently passed through PYTHIA 6.420 [12] forparton showering and hadronization, and then through PGS4 [13] to simulate the effectsof a realistic detector. The corresponding total leading order cross section for sbottompair production at the 14 TeV LHC is estimated to be about 214 fb. The dominating SMbackground comes from tt̄, with one W decay leptonically and the other decay hadronically.Another irreducible background is tt̄Z, with Z → νν̄, mimicking the missing energysignature from the lightest neutralino. Other possible backgrounds are tt̄W , WZjj, WWjjand Wjjjj, with j being light quarks. All the background events are generated similar tothe signal process, except Wjjjj, which is generated using ALPGEN 2.13[14].

The first set of cuts (referred to Cut I) is designed to mimic a realistic detectoracceptance:

• At least four jets with |ηj| < 3 and pTj > 40 GeV.

• At least one charged lepton (electron or muon) with p!T > 15 GeV and |η!| < 2.4.

5

Benchmark

mQ3mu3

md3At µ mA tanβ M1 M2 M3 mq̃ ml̃

548.7 547.3 1000 1019 250 200 10 1000 1000 1000 1000 1000

TABLE I: MSSM input parameters defined at the weak scale for the benchmark point of theMSSM golden region, taken from Ref.[6]. All dimensionful parameters are in unit of GeV.

mt̃1 mt̃2 mb̃1mχ0

1mχ0

2mχ±

1

mh0 mH0 mA mH±

398 688 550 243 253 247 118 201 200 216

TABLE II: Physical spectrum of light sparticles for the benchmark point in the MSSM golden

region, in unit of GeV.

which can also be applied to the light CP-even Higgs boson in the decoupling region of theMSSM parameter space. Although MSSM could accommodate a lighter Higgs (around 90GeV) [9] while still being consistent with the LEP Higgs search results, it only happensin a restricted region of the MSSM parameter space, which can be viewed as additionalsource of fine-tuning. In Ref. [6], authors used the LEP limit of 114.4 GeV as a lowerbound on the light MSSM CP-even Higgs mass. The dominate loop contribution to themass of the light CP-even Higgs boson comes from the stop sector. Accommodating theLEP Higgs search bound requires heavier stop masses and/or large left-right stop mixing.Taking into account the collider search limit on sparticle masses, constraints from the ρparameter, rare decays b → sγ, as well as minimizing the fine tuning, we are limited to theMSSM golden region with small µ and mA, relatively small value for m2

Q3, m2

u3and large

value for At.In our analyses, we used the benchmark point chosen in Ref. [6]. The MSSM input

parameters at the weak scale are given in Table I. We assume there is no flavor off-diagonal terms and all the tri-linear A terms are zero except At. All the gaugino massesM1,2,3 as well the masses for the slepton and first two generation squarks are chosen to be1 TeV. The mass parameter for the b̃R, md3

, is also chosen to be heavy. Varying thoseparameters does not have significant effects on the Higgs potential, as well as the lightsbottom (mostly b̃L in our case) pair production channel that we consider below.

The physical mass spectrum of light particles for the benchmark point is given inTable II, which is obtained using SOFTSUSY 2.0.11[10]. With the small value of µ, thetwo lightest neutralinos and charginos are almost degenerate, which are mostly Higgsinos.The mass for the light CP-even Higgs is about 118 GeV, above the LEP Higgs searchlimit. The heavy CP-even Higgs, as well as the CP-odd Higgs and the charged Higgses arearound 200 GeV. Due to the large left-right mixing in the stop sector, there is a large masssplitting in the two stop mass eigenstates: mt̃2 − mt̃1 > mZ , which is a generic feature ofthe MSSM golden region. Utilizing this feature, Ref. [6] studied the process of t̃2t̃∗2 pairproduction at the LHC with at least one t̃2 decays via t̃2 → t̃1Z. Inclusive signature ofZ + 2 b-jets + #ET + X is analyzed, where Z decays leptonically into pair of electrons ormuons. It is found that by requiring the reconstruction of the lepton pair around the Zpeak, a large pT cut on the first two leading jets with at least one b-tagging, a large boost

4



- Leptophilic Higgs B. Thomas (U. of Arizona)

− H→µµ in ttH at the LHC B. Thomas, S. Su, Phys. Lett. B 677 (2009) 296.

− The LHC discovery potential of a leptophilic Higgs B. Thomas, S. Su, Phys. Rev. D79 (2009) 095014.

110 120 130 140 15010−1

100

101

102

mh (GeV)

Stat

istic

al S

igni

fican

ce

L2HDM L=30 fb−1

5 !

WBF(h" ##)tth(h" ##)gg" h " ##WBF(h" µµ)tth(h" µµ)gg" h " µµ

110 120 130 140 150 16010−1

100

101

102

mh (GeV)

Stat

istic

al S

igni

fican

ce

L2HDM L=30 fb−1

5 !

tth(h" bb)gg" h " ##WBF(h" WW)h" ZZh" WW

Leptophillic Higgs



Simplified Model Approach-

LHC topology: simplified model approach A. Freitas (U. of Pittsburgh), V. Rentala (Univ. of Arizona)

Most of current study

Model dependent, parameter dependent

Losses in sensitivity for more general scenarios

Existing results difficult to translate into results for more general models

Simplified model approach

Relevant topologies are more transparent

Kinematic boundaries are easy to make manifest

Results are easier to translate into other models

Limits of a more complete new physics scenarios



τ+τ--

LHC topology: simplified model approach A. Freitas (U. of Pittsburgh), V. Rentala (Univ. of Arizona)

− τ+τ- resonance A. Freitas, S. Su, submitted to working group contribution

τ+τ

−

Authors: A. Freitas, S. Su

I. INTRODUCTION

The relevant SU(3)JQ quantum numbers of a τ+τ− resonance are 1

0,1,20 . For a simplified

model we only consider a spin-0 CP-odd pseudoscalar, since CP-even scalar would typically

also have tree-level couplings to WW or ZZ and the decay branching ratio to the τ+τ− final

state is usually suppressed. The spin of the τ+τ− resonance can have some impact on the

acceptance of the signal selection (because of the production angle dependence), but this

effect does not justify a separate simplified model for each spin.

II. SIMPLIFIED MODEL DEFINITION

The model only contains the pseudoscalar A0 besides SM particles. After EWSB it takes

on the form

L =1

2∂µA0 ∂µA0

−1

2m2

A(A0)2 + icτ τ̄A0γ5τ + icbb̄A0γ5b +

cG

ΛA

A0GµνG̃µν , (1)

where Gµν is the gluon field strength tensor, G̃µν = εµναβGαβ, and ΛA is an a priori arbitrary

scale, which we fix to be ΛA ≡ 246 GeV, inspired by the two-Higgs-doublet model (2HDM).

Besides the mass mA, the model contains the free dimensionless coupling parameters cτ , cb,

and cG. At least one of the coupling coefficients cb and cG needs to be non-zero so that

production at the LHC can occur through bb̄ annihilation or A0b(b) associated production

(cb) and/or gluon fusion (cG). The couplings of A0 to light quarks are highly constrained

from flavor physics and, absent fine-tuning, must be very small and thus are not included

in this simplified model.

We could also consider a CP-even scalar S0, with the Lagrangian being

L =1

2∂µS

0 ∂µS0−

1

2m2

S(S0)2 + icτ τ̄S0τ + icbb̄S0b +

cG

ΛS

S0GµνGµν , (2)

The collider analysis is almost identical to the CP-odd case. The decay branching ratio to

the τ+τ− final state, however, is usually suppressed for a heavy S0 if it couples to WW and

τ+τ

−

Authors: A. Freitas, S. Su

I. INTRODUCTION

The relevant SU(3)JQ quantum numbers of a τ+τ− resonance are 1

0,1,20 . For a simplified

model we only consider a spin-0 CP-odd pseudoscalar, since CP-even scalar would typically

also have tree-level couplings to WW or ZZ and the decay branching ratio to the τ+τ− final

state is usually suppressed. The spin of the τ+τ− resonance can have some impact on the

acceptance of the signal selection (because of the production angle dependence), but this

effect does not justify a separate simplified model for each spin.


The model only contains the pseudoscalar A0 besides SM particles. After EWSB it takes

on the form

L =1

2∂µA0 ∂µA0

−1

2m2

A(A0)2 + icτ τ̄A0γ5τ + icbb̄A0γ5b +

cG

ΛA

A0GµνG̃µν , (1)

where Gµν is the gluon field strength tensor, G̃µν = εµναβGαβ, and ΛA is an a priori arbitrary

scale, which we fix to be ΛA ≡ 246 GeV, inspired by the two-Higgs-doublet model (2HDM).

Besides the mass mA, the model contains the free dimensionless coupling parameters cτ , cb,

and cG. At least one of the coupling coefficients cb and cG needs to be non-zero so that

production at the LHC can occur through bb̄ annihilation or A0b(b) associated production

(cb) and/or gluon fusion (cG). The couplings of A0 to light quarks are highly constrained

from flavor physics and, absent fine-tuning, must be very small and thus are not included

in this simplified model.

We could also consider a CP-even scalar S0, with the Lagrangian being

L =1

2∂µS

0 ∂µS0−

1

2m2

S(S0)2 + icτ τ̄S0τ + icbb̄S0b +

cG

ΛS

S0GµνGµν , (2)

The collider analysis is almost identical to the CP-odd case. The decay branching ratio to

the τ+τ− final state, however, is usually suppressed for a heavy S0 if it couples to WW and

3

120 140 160 180 200!!!!!!!!!!!!!!!mΦ

GeV

100

50

30

70

Σ !pp $ Φ"%BR&!&Φ $ ΤΤ&" #pb$

FIG. 1: Estimated current limits on σ[pp → φ] × BR[φ → τ+τ−], for φ being either A0 or S0, at

the 7 TeV LHC, derived from Tevatron searches with the assumption that either only the cG (red)

or only the cb (blue) operator contributes.

IV. EXISTING LIMITS

Strong limits on MSSM Higgs bosons can be derived from precision flavor observables.

However, these limits depend on details of the complete MSSM theory and thus cannot be

applied to the simplified model considered here.

LEP has searched for pseudoscalars in the type-II 2HDM only in modes where it is

produced together with a CP-even scalar (see e.g. [2]).

More model-independent constraints are obtained from Tevatron searches. The latest

combined CDF analysis using 2.3 fb−1 of data [6] gives a bound on σ[pp̄ → φ] × BR[φ →

τ+τ−] for mH between 100 GeV to 150 GeV. An earlier combined CDF and DØ analysis

[7] extends the reach up to mH = 200 GeV. There is also a DØ analysis using 4.3 fb−1 of

data [8] for the channel of φb associated production with φ → τ+τ−, which does not lead

to stronger limits. Assuming that either only the cG or only the cb operator contributes

in the production, these bounds can be translated straightforwardly into limits for σ[pp →

φ] × BR[φ → τ+τ−] at the LHC by taking into account the relevant PDFs, see Fig. 1.

V. POSSIBLE REACH

A preliminary reach estimate for MSSM Higgs bosons (mh-max scenario) in the bbφ

associated production with φ → τ+τ− channel for 1 fb−1 at 7 TeV has been released by the

CG

Cb

mA, σ(pp→A), Br(A→ττ)

LHC 7



l+l+-

− l+l+ resonance V. Rentala, S. Su, in preparation

!+!+/W +W +

Authors: V. Rentala, S. Su

I. INTRODUCTION

We discuss a simplified model for a same sign !±!± resonance. The relevant SU(3)JQ

quantum number is 10,1,22 . For simplicity, we only consider a spin 0 scalar in the simplified

model. The !±!± resonance is typically referred to as doubly charged Higgs in the literature,

which is denoted as H±±. In the case that H±± resides in a SU(2)L representation with

a neutral component which obtains a non-zero vacuum expectation value (vev) 〈H0〉, a

H±± − W∓∓ − W∓∓ coupling arises, whose coupling is proportional to 〈H0〉. Such doubly

charged Higgs could also be considered as a same sign W±W± resonance that we will briefly

comment on at the end.


The same sign dilepton resonance can be simply modeled (in addition to the Standard

Model Lagrangian) by the addition of a pair of doubly charged scalars H±±. Such scalars can

arise from various SU(2)L multiplets. We consider three simplest cases where H±± resides

in a singlet, doublet or triplet SU(2)L representation. This specification fixes the couplings

of the doubly charged Higgs to SM gauge bosons.

A. Representations

We classify H±± models by the SU(2)L multiplet in which they appear. We consider only

the cases where the H++ is the maximally electrically charged particle in the multiplet [1].

• H++ in a singlet Φ = H++: (T = 0, T3 = 0, Y = 2) .

• H++ in a doublet Φ =

H++

H+

: (T = 1/2, T3 = 1/2, Y = 3/2) .

!+!+/W +W +

Authors: V. Rentala, S. Su

I. INTRODUCTION

We discuss a simplified model for a same sign !±!± resonance. The relevant SU(3)JQ

quantum number is 10,1,22 . For simplicity, we only consider a spin 0 scalar in the simplified

model. The !±!± resonance is typically referred to as doubly charged Higgs in the literature,

which is denoted as H±±. In the case that H±± resides in a SU(2)L representation with

a neutral component which obtains a non-zero vacuum expectation value (vev) 〈H0〉, a

H±± − W∓∓ − W∓∓ coupling arises, whose coupling is proportional to 〈H0〉. Such doubly

charged Higgs could also be considered as a same sign W±W± resonance that we will briefly

comment on at the end.


The same sign dilepton resonance can be simply modeled (in addition to the Standard

Model Lagrangian) by the addition of a pair of doubly charged scalars H±±. Such scalars can

arise from various SU(2)L multiplets. We consider three simplest cases where H±± resides

in a singlet, doublet or triplet SU(2)L representation. This specification fixes the couplings

of the doubly charged Higgs to SM gauge bosons.

A. Representations

We classify H±± models by the SU(2)L multiplet in which they appear. We consider only

the cases where the H++ is the maximally electrically charged particle in the multiplet [1].

• H++ in a singlet Φ = H++: (T = 0, T3 = 0, Y = 2) .

• H++ in a doublet Φ =

H++

H+

: (T = 1/2, T3 = 1/2, Y = 3/2) . 2

• H++ in a triplet Φ =

H+/√

2 H0

H++ −H+/√

2

: (T = 1, T3 = 1, Y = 1) .

Here we have picked the normalization for the hypercharge Y being: Q = T3 +Y . Note that

in the cases of a triplet, there is also a neutrally component H0 in the multiplet. In our

discussion below for the simplified model, we assume that the H++ is the lightest member

of the multiplet and all other components are heavy and therefore decouple from the low

energy phenomenology of the doubly charged Higgs.

B. Interactions

1. Gauge interactions

The gauge interactions of the SU(2)L multiplet Φ that containing the double charged

Higgs are:

LGaugeint = (DµΦ)†(DµΦ) (1)

Here Dµ is given as usual by

Dµ = ∂µ + igT aW aµ + ig′Y Bµ (2)

and the matrices T a are the hermitian generators of SU(2)L transformations, in the repre-

sentation of the Φ multiplet. g and g′ are the usual SU(2)L and U(1)Y gauge couplings.

The electromagnetic and neutral current interactions of the H++ then follow after re-

defining W 3µ and Bµ in terms of Zµ and Aµ,

LGauge,3ptint = QeJµAµ +

e

sin θW cos θW

(T3 − Q sin2 θW )JµZµ, (3)

where Jµ = i(H−−(∂µH++) − (∂µH−−)H++). These vertices can lead to Drell-Yan pair

production of H++. We skip the charge current interactions of H±± since it will involve

other components (H+) in the multiplet that we assumed to be heavy.

The four point interactions Φ−Φ−V −V also arises from gauge interactions. In particular,

interactions of H++H−− with a pair of photons/Zs are of the form

LGauge,4ptint =

[

(Qe)2AµAµ +

(

e

sin θW cos θW

(T3 − Q sin2 θW )

)2

ZµZµ

]

H++H−−, (4)

Production: Drell-yan pair production two photon fusion

mH++, σ, Br(H++→l+l+)



-

l+l+5

80 100 120 140 160 180 200

101

102

mH

++ (GeV)

!(H

++H!!)"

Br2

(H±±#

l±±l$±±)

(f

b)

% Triplet

% Doublet

Singlet #Tevatron

D0 µµ

CDF ee

CDF eµ

CDF e&

CDF µ&

50 60 70 80 90 100

101

102

103

mH

++ (GeV)

!(H

++H!!)"

Br2

(H±±#

l±±l$±±)

(f

b)

LEPL3 ee

OPAL µµ

OPAL eµ

OPAL e&

OPAL µ&

DELPHI &&

Triplet

Doublet

Singlet

FIG. 2: The current experimental direct search limit from Tevatron Run II (left panel) and LEP

at√

s = 206 GeV (right panel). Also shown are the Drell-Yan pair production cross sections for

doubly charged Higgses in triplet, doublet and singlet multiplet. Curves for experimental results

are taken from Refs. [9–14] and combined.

are two Higgs triplet, HL charged under SU(2)L and HR charged under SU(2)R. The HL

triplet is the same as the triplet Φ in the simplified model. In the Higgs triplet model [6, 7],

the Higgs triplet is introduced to give a majorana mass to νL once its neutral component

obtains a vev.

III. RELEVANT VARIABLES/PLOTS

The free parameters in the model are the mass of double charged Higgs mH±± , and

relevant couplings to lepton pairs h!!′ and W pairs. The dominant Drell-Yan pair production

cross section and the subdominant two photon fusion cross section only depends on mH±±

since the coupling is fixed for a given SU(2)L multiplet. Single production cross section of

H±± at LEP and HERA depends on h!!′ in addition. As far as experimental studies are

concerned, it is convenient to use mH±±, σpair or σsingle, and decay branching ratios into

particular final states Br(H±± → #±#′±), Br(H±± → W±W±) as a useful parametrization.

Experimental results are best presented in plots of σ × Br as a function of mH±±.

7

102

103

10!2

10!1

100

mH

++ (GeV)

he

l

L3 BhabhaOPAL h

ee (ee)

OPAL hee

(µµ)

OPAL hee

(!!)

H1 heµ

H1 he!

FIG. 3: The current experimental limits on he! from both direct and indirect measurements at

OPAL, L3 and H1. Curves are taken from Refs. [13, 15, 16] and combined.

100 150 200 250 300 350 400 450 50010

!1

100

101

102

mH

++ (GeV)"

(H+

+H!!)#

Br2

(H±±$

l±±l%±±)

(f

b)

LHC 7 TeV

Triplet

Doublet

Singlet

FIG. 4: Drell-Yan pair production cross sections at the 7 TeV LHC for doubly charged Higgses in

singlet, doublet and triplet representation.

An upper limit on hee of 0.042, 0.049 and 0.071 was set at OPAL through ee, µµ and ττ

channel for mH++ < 160 GeV, assuming 100% decay branching ratio [15]. The null search

results at H1 can be used to set limit on he!. For hee, the limit is weaker than the OPAL

result. For heµ and heτ , the coupling is exclude up to 0.4 and 0.7 for mH++ = 150 GeV [16].

Indirect searches

Doubly charged Higgs contributes to Bhabha scattering e+e− → e+e− via t- channel,

therefore modifies the cross section and angular distribution of outgoing electrons. Results

from OPAL and L3 can be used to derive an indirect limit on hee, which is shown in Fig. 3



-

Slepton Discovery via neutralino/chargino pair production M. Ramsey-Musolf (U. of Wisconsin, Madison), W. Shepherd (Northwestern and UC Irvine)

Other direct searches



-

Indirect Searches for New Physics



Indirect Searches-Energy frontier: LHC

Precision (intensity) frontier: low energy precision measurements

Standard Model PredictionErler, Kurylov & Ramsey-Musolf,Phys. Rev. D 72, 073003 (2005)

NuTeV SLAC E158

Jlab MollerQWe

PVDIS

Qweak

Cs APV

Jlab MollerQWe

Qweak



Indirect Searches-

Low Energy Precision Supersymmetry M. Ramsey-Musolf (UW Madison)

- Kion Leptonic Decay and Supersymmetry

M. Ramsey-Musolf, S. Su, in preparation.



Indirect Searches-

Like-sign Dilepton Asymmetry in $B$ Meson System B. Thomas (Univ. Hawaii)

- New Physics Contributions to Like-sign Dilepton Asymmetry in $B$ System

B. Thomas, S. Su, in preparation.



-

Other Activities



Organization of conferences/workshops-

๏ Organizer for KITPC 2011 program: Dark matter and new physics, Sep 21st - Nov 6, 2011.

๏ Organizer for Aspen 2009 Summer Program: Beyond the Standard Model Physics at the Threshold

๏ Convener for LCWS 2010, session on SUSY and New Physics at the Terascale.

๏ Organizer for Frontier Physics Working Month, INPAC, May 24 - June 18, 2010.



Organization of conferences/workshops-

๏ Convener for ALCPG09, physics working group: Charged Particle Momentum Mesurement, V0 Reconstruction, and Identification of Stable Charged Particles

๏ Convener for muon collider workshop (09), physics working group: Higgs Physics

๏ Serve as coordinator for the group: Connection to Astro and Cosmo of LHC wiki page (http://wiki.pheno.wisc.edu/lhc)


http://wiki.pheno.wisc.edu/lhc

http://wiki.pheno.wisc.edu/lhc


-

Future Plans

๏ Collider related physics: understand what data really means

− Communicate (more) with our exp neighbour (LHC/ ALTAS, D0)

− Train students to work on collider (LHC) physics simulation tools for new physics and SM background experimental physics observables/ capabilities …

− New physics phenomenology / distinguish various new physics

๏ Connection to cosmology

− New candidate for dark matter

− Collider studies of dark matter properties



-

!ank y" !


Search for New Physics Beyond the SM

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