Higgs%CP%measurements%in%di0boson% decays%ias.ust.hk/program/shared_doc/201501fhep/Kirill...
Transcript of Higgs%CP%measurements%in%di0boson% decays%ias.ust.hk/program/shared_doc/201501fhep/Kirill...
Outline
• Present spin-‐parity measurements
• CP mixing and anomalous couplings
• Measurements for the LHC run-‐II and HL-‐LHC
• Beyond the HL-‐LHC.
page 2
Introduc@on
• The run-‐I of the LHC: about 5 D-‐1 at √s = 7 TeV and about 20 D-‐1 at √s = 8 TeV per experiment. – Observa@on of the new resonance: WW, ZZ*, γγ (10 D-‐1) – Confirma@on: full run-‐I dataset.
• Spin and parity measurement: considering spin-‐0,1,2.
– Integer spin: decay to two vector bosons. – Spin-‐1 hypothesis is strongly disfavored due to the observa@on of
decay to two on-‐shell photons.
• Direct spin and parity analyses performed in both ATLAS and CMS.
page 3
Spin and parity analyses • Observed decays (full LHC run-‐I dataset) and corresponding spin-‐CP analyses:
• Combined spin and parity measurements:
– ATLAS: WW+ZZ*+γγ (Phys. Le). B 726 (2013), pp. 120-‐144)
– CMS: WW+ZZ*+γγ (arXiv:1411.3441v1) page 4
ATLAS CMS
Significance observed
Spin-‐CP analysis
Significance observed
Spin-‐CP analysis
Hàγγ 7.4 σ ✔ 3.9 σ ✔
HàZZ(*)à4l 6.6 σ ✔ 6.7 σ ✔
HàWW(*)àlνlν 3.8 σ ✔ 4.0 σ ✔
Hàττ 4.2 σ ? >3 σ ? VH (Hàbb) 1.4 σ ? 2.1 σ ? VBF (any) ? ?
The spin-‐0 par@cle • The absolute majority of these studies were based on direct exclusion of
alterna@ve JP hypotheses in favor of the JP=0+ suggested by the Standard Model.
• DØ constraint on 0-‐ scenario at 97.9% CL from W/Z+bb (DØ Note 6406-‐CONF);
constraint on 2+ scenario at 99.9% CL from W/Z+bb (DØ Note 6387-‐CONF). – Assuming Standard Model produc@on CS X BR.
page 5
JP hypotheses ATLAS CMS exclusion
Exclusion (%CL) channel Exclusion (%CL) channel
0-‐ 97.8 ZZ* >99.9 ZZ*+WW
1+ >99.9 ZZ*+WW >99.9 ZZ*+WW 1-‐ 99.7 ZZ*+WW >99.9 ZZ*+WW 2+m >99.9 ZZ*+WW+γγ >99.9 ZZ*+WW+γγ
Phys. Le). B 726 (2013), pp. 120-‐144 CMS-‐PAS-‐HIG-‐13-‐005 CMS-‐PAS-‐HIG-‐13-‐002 arXiv:1411.3441v1
The spin-‐0 par@cle • LHC Run-‐I data: Large campaign on excluding alterna@ve hypotheses in favor of
the Standard Model JP=0+ hypothesis. – CMS has published pre-‐final run-‐I results, ATLAS analyses are also
converging.
page 6 Phys. Le). B 726 (2013), pp. 120-‐144
CMS: a large number of spin-‐2 models of both pari@es including scenarios with higher dimension operators. Both ggF and qq produc@on mechanisms. Combined ZZ*+WW* exclusion > 3.5σ for each model.
1411.3441v1
) + 0 /
LP J
ln(L
×-2
-60-40-20
020406080
100120 CMS (7 TeV)-1 (8 TeV) + 5.1 fb-119.7 fb ZZ + WW→X
Observed Expectedσ 1± +0 σ 1± PJσ 2± +0 σ 2± PJσ 3± +0 σ 3± PJ
- 1 + 1 m+ 2 h2+ 2 h3+ 2 h+ 2 b+ 2 h6+ 2 h7+ 2 h- 2 h9- 2 h10
- 2 m+ 2 h2+ 2 h3+ 2 h+ 2 b+ 2 h6+ 2 h7+ 2 h- 2 h9- 2 h10
- 2
qq gg production productionqq
Spin-‐0 par@cle? • HàZZ*à4l: vector-‐
pseudo-‐vector admixture. – Ignoring possible Zγ*
and γγ* contribu@ons.
• HàZZ*à4l: Non-‐interfering states: narrow resonances with different spin and parity AND nearly degenerate mass. Both spin-‐1 and spin-‐2 cases.
page 7
1411.3441v1
b2f0 0.2 0.4 0.6 0.8 1
)+ 0 /
LP J
ln(L
×-2
-20
-10
0
10
20
30
40
50
60
CMS (7 TeV)-1 (8 TeV) + 5.1 fb-119.7 fb
ZZ→ X → qq
+0Expected at 95% CLExpected at 68% CL
ObservedPJ
Expected at 95% CLExpected at 68% CL
b2f0 0.2 0.4 0.6 0.8 1
)+ 0 /
LP J
ln(L
×-2
-20
-10
0
10
20
30
40
50
60
CMS (7 TeV)-1 (8 TeV) + 5.1 fb-119.7 fb
ZZ→X
+0Expected at 95% CLExpected at 68% CL
ObservedPJ
Expected at 95% CLExpected at 68% CL
)Pf(J
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
m+ 2
gg production
h2+ 2
productionqq
h3+ 2
(gg acceptance)decay-only discriminants
h+ 2 b+ 2 h6+ 2 h7+ 2 h- 2 h9- 2 h10
- 2 m+ 2 h2+ 2 h3+ 2 h+ 2 b+ 2 h6+ 2 h7+ 2 h- 2 h9- 2 h10
- 2 m+ 2 h2+ 2 h3+ 2 h+ 2 b+ 2 h6+ 2 h7+ 2 h- 2 h9- 2 h10
- 2σ 1±Best fit Excluded at 95% CLExpected at 95% CLExpected at 68% CL
CMS (7 TeV)-1 (8 TeV) + 5.1 fb-119.7 fb ZZ→H
Spin-‐0 par@cle?
• Hàγγ, HàZZ*: Direct measurement of compa@bility with spin-‐0 hypothesis. – Differen@al cross sec@on as the func@on of produc@on angle |cos θ*|. – Spin-‐sensi@ve: isotropic for spin-‐0, polynomial up to cos2JΘ* for other spin
values.
page 8 JHEP09(2014)112 Phys. Le). B 726 (2013), pp. 120-‐144. Physics Le)ers B 738 (2014) 234-‐253
Why tensor structure?
• Spin and parity analyses to-‐date suggest that the observed Higgs boson has spin-‐0. Is it the Standard Model Higgs boson? – Exclusion of pure JP=0-‐ at 97.9% CL (WW+ZZ: ATLAS hypotheses tests) and
>99.9CL (ZZ hypotheses tests, ZZ+WW indirect from tensor couplings measurement).
• Almost all Beyond the Standard Model theories with extended Higgs sector predict possible anomalous contribu@on and/or CP-‐viola@on in the Higgs sector.
• Example: scalar h0 and pseudo-‐scalar A0 in 2HDM. – If Higgs poten@al is not CP-‐symmetric, the lightest mass eigenstate is their
superposi@on.
• Model-‐independent approach: measure the couplings structure and compare it to the Standard Model.
page 9
Opportuni@es at 125.5 GeV for the LHC
page 10
HVV Hff HàZZ* in decay
HàWW in decay
ggàH+gg in produc@on
VBF HàX in produc@on
VHàX in produc@on
Hàττ in decay
uHàX in produc@on
…certainly there are more ways…
Loop-‐induced CP-‐odd coupling Tree-‐level CP-‐odd coupling
Anomalous couplings framework • Proposed in YR3 (CERN-‐2013-‐004) and Snowmass Higgs report (1310.8361).
• Applied in recent CMS analyses HàZZ*à4l + HàWWàlνlν (1411.3441v1).
So far the only direct measurement of the tensor structure. – ATLAS results are not yet finalized.
page 11
CP-‐Even CP-‐Odd Expected couplings size in the SM: a1=2, a2, a2Zγ,a2γγ~10-‐3. Standard Model: a1 = 1, a2,3=0; Completely CP-‐odd state: a1,2 = 0, a3 ≠ 0. CP-‐mixing scenario: a1 ≠ 0 and a3 ≠ 0.
ZZ,WW Zγ* γ*γ*
Anomalous couplings framework • Proposed in YR3 (CERN-‐2013-‐004) and Snowmass Higgs report (1310.8361).
• Applied in recent CMS analyses HàZZ*à4l + HàWWàlνlν (1411.3441v1).
So far the only direct measurement of the tensor structure. – ATLAS results are not yet finalized.
page 12
Complex couplings: parameters ai can have both real and imaginary parts. They acquire complex part if the corresponding par@cles in loops are lighter than Higgs mass/2.
CP-‐Even CP-‐Odd
ZZ,WW Zγ* γ*γ*
Λ1: an expansion of a1, reflec@ng possible BSM contribu@on to the tree-‐level SM coupling.
Anomalous couplings framework • Measurement parameteriza@on model: effec@ve frac@onal cross sec@ons
and phases.
• Here σi is the effec@ve cross sec@on corresponding to ai=1, aj≠i=0. – fai are bound between 0 and 1 and are independent of defini@ons used
for a’s.
• Transla@on to the |ai|/|a1| basis exists.
page 13
Final state observables
page 14
• Four-‐vectors of the final state par@cles give access to boson decay planes and to the tensor structure.
• Easier in ZZ*à4l case, harder in WWàlνlν case.
• Reasonable target: 10% CP-‐odd admixture corresponds to fCP< 10-‐5 in VV decays. (Snowmass)
0+; 0-‐
Φ
Cos θ1
mZ2
HàZZ*à4l
cosθ1,2,Φ,mZ1, mZ2,m4l
General measurement methodology • Suppose we have Monte Carlo model(s) for various range(s) of anomalous
coupling(s).
• Direct fit of all observables is challenging. – 5 observables to iden@fy the mixed states + at least 3 observables to
separate signal and background: (cosθ1,2,Φ,mZ1,mZ2) + (m4l,pT4l,η4l ,…). – 8+ dimensions to be covered by Monte Carlo simula@on. – ZZ*: low background but also low signal observa@on: order of 1 signal
candidate per D-‐1 in the Higgs signal region at 8 TeV.
• Possible measurement strategies. – Compressing observables into MC-‐trained mul@variate discriminants at
separa@on of various mixed states and signal to backgrounds. Fit. – Analy@cal descrip@on of decay as func@on of the FS 4-‐vectors. Es@ma@ng
the detector acceptance from MC. Fit. – At large sta@s@cs: unfolding detector acceptance/resolu@on up to level of
diff. distribu@on of observables. Fit. page 15
CMS current measurements • ZZà4l: 5.1 D-‐1 at 7 TeV + 19.6 D-‐1 at 8 TeV.
• Discriminant constructed using the Matrix element likelihood approach:
where probabili@es P are constructed using LO Matrix Elements.
• 2 or 3D templates
composed of the above observables for various sets of couplings + Likelihood fit.
page 16
arXiv:1411.3441v1
Dbckg =Psig
Psig +PbckgD
JP=
PSM
PSM +PJP
VS Observables:
bkgD0 0.2 0.4 0.6 0.8 1
Even
ts /
0.05
0
5
10
15
20ObservedSM
=1a3f*γZZ/Z
Z+X
CMS (7 TeV)-1 (8 TeV) + 5.1 fb-119.7 fb
0-D0 0.2 0.4 0.6 0.8 1
Even
ts /
0.05
0
2
4
6
8ObservedSM
=1a3f*γZZ/Z
Z+X
CMS (7 TeV)-1 (8 TeV) + 5.1 fb-119.7 fb
> 0.5bkgD
etc..
CMS current measurements • Possible observables in WWàlνlν case: Δφll, mll, mT.
– ME calcula@on is difficult due to unobserved neutrinos. – 2D template fit based on mll, mT. – 0 and 1 jet (5%VBF) categories. Low sensi@vity.
page 17 arXiv:1411.3441v1
(GeV)llm0 50 100 150 200
Even
ts /
8.0
GeV
0
200
400
600
ObservedSM
=-0.4a2WWf
VVTopW/Z+jets
CMS (7 TeV)-1 (8 TeV) + 4.9 fb-119.4 fb
0-jetµe
(GeV)Tm100 150 200 250
Even
ts /
7.3
GeV
0
200
400
600
800ObservedSM
=-0.4a2WWf
VVTopW/Z+jets
CMS (7 TeV)-1 (8 TeV) + 4.9 fb-119.4 fb
0-jetµe
CMS current measurements
page 18 arXiv:1411.3441v1 Allowed 95% CL intervals for the ZZ* analysis
0
2
4
6
8
10
12
14
)a3φ cos(a3f-1 -0.5 0 0.5 1
)a2φ
cos
(a2f
-1
-0.5
0
0.5
195% CL68% CLBest fitSM
CMS (7 TeV)-1 (8 TeV) + 5.1 fb-119.7 fb
ln L
∆-2
π = 0 or a3φ,
a2φ
0
2
4
6
8
10
12
14
a3f0 0.2 0.4 0.6 0.8 1
a2f
0
0.2
0.4
0.6
0.8
195% CL68% CLBest fitSM
CMS (7 TeV)-1 (8 TeV) + 5.1 fb-119.7 fb
ln L
∆-2
Measurements of anomalous couplings with fixed and profiled phases in ZZ* channel. In WW the couplings are considered to be real.
CMS current measurements • Combined exclusion in WW and ZZ channels with assump@ons of custodial
symmetry and assump@ons of equality of ra@os of couplings.
)a2φ cos(a2f-1 -0.5 0 0.5 1
lnL
∆-2
0
2
4
6
8
10
12
14
16
18
20
22 ZZ→H
=0.5a2WW, R→H
=0.5a2ZZ+WW, R→H
ZZ1=aWW
1=0.5, a
a2ZZ+WW, R→H
ZZ→H
=0.5a2WW, R→H
=0.5a2ZZ+WW, R→H
ZZ1=aWW
1=0.5, a
a2ZZ+WW, R→H
ZZ→H
=0.5a2WW, R→H
=0.5a2ZZ+WW, R→H
ZZ1=aWW
1=0.5, a
a2ZZ+WW, R→H
ZZ→H
=0.5a2WW, R→H
=0.5a2ZZ+WW, R→H
ZZ1=aWW
1=0.5, a
a2ZZ+WW, R→H
CMS (7 TeV)-1 (8 TeV) + 5.1 fb-119.7 fb
68% CL
95% CL
)a3φ cos(a3f-1 -0.5 0 0.5 1
lnL
∆-2
0
5
10
15
20
25ZZ→H
=0.5a3WW, R→H
=0.5a3ZZ+WW, R→H
ZZ1=aWW
1=0.5, a
a3ZZ+WW, R→H
ZZ→H
=0.5a3WW, R→H
=0.5a3ZZ+WW, R→H
ZZ1=aWW
1=0.5, a
a3ZZ+WW, R→H
ZZ→H
=0.5a3WW, R→H
=0.5a3ZZ+WW, R→H
ZZ1=aWW
1=0.5, a
a3ZZ+WW, R→H
ZZ→H
=0.5a3WW, R→H
=0.5a3ZZ+WW, R→H
ZZ1=aWW
1=0.5, a
a3ZZ+WW, R→H
CMS (7 TeV)-1 (8 TeV) + 5.1 fb-119.7 fb
68% CL
95% CL
arXiv:1411.3441v1 page 19
Prospec@ve studies -‐ I page 21
• CMS: Snowmass 2013 projec@on by scaling the 7 TeV + 8 TeV results in HàZZ*à4l channel alone to 300 D-‐1 and 3000 D-‐1 at 14 TeV.
• Scaling the signal and background yields assuming the present detector performance.
• Expected: fa3<0.13 at 95%CL for 300 D-‐1 and fa3<0.04 at 95%CL at 3000 D-‐1.
1307.7135v2
Prospec@ve studies -‐ II
page 22
• ATLAS: Dedicated Monte Carlo CP-‐mixing study in HàZZ*à4l decay channel for 14 TeV, 300 D-‐1 and 3000 D-‐1. – Monte Carlo generator level with smearing func@on and weights
modeling future detector resolu@on and efficiency.
• Scaling the event yields according to the cross sec@on change, assuming the reducible background as 50% of ZZ* yeild. – S/B~1.87 in 115 <M4l< 130 GeV.
• Measurement of (g1, g4) and (g1, g2) pairs in ra@os.
– In this nota@on fa3= fg4.
Re(g4 )g1
Im(g4 )g1
ATL-‐PHYS-‐PUB-‐2013-‐013 Arxiv:1208.4018
page 23
ME-‐observable fit
Re(g4 )g1
Im(g4 )g1
• Using LO Matrix Element re-‐weigh@ng to simulate effect of different combina@ons of couplings on the final state observables. – Producing an MC sample for each point on examined plane.
• Making a likelihood fit to data for each combina@on of couplings.
• Finding a global minimum in 2D distribu@on of nega@ve log likelihood (or
other test sta@s@c).
− lnL Re(g4 )g1
; Im(g4 )g1
;µ̂"
#$
%
&'
Parity-‐sensi@ve observable
BDT(J=0 vs Z
Z) ZZ
Signal
For a given (g1,g4)
The signal strength is fiued individually for every point of the plane.
ATLAS-‐PHYS-‐PUB-‐2013-‐013
8D fit • Construc@ng an 8-‐dimensional per event likelihood by using the full
analy@cal expression of the ME of the H→ ZZ*→4l process calculated at LO.
• The calculated ME depends on the coupling constants gi and on the parity-‐sensi@ve observables.
• Detector acceptance and resolu@on effects are described by parametriza@ons based on simulated events.
• Simula@on-‐based templates to describe background pdf’s.
• Scan the nega@ve log likelihood, find the global minimum.
page 24 ATLAS-‐PHYS-‐PUB-‐2013-‐013
ATLAS prospec@ve studies
page 25
• Both approaches give a consistent result at high sta@s@cs.
• Assuming the Standard Model input, the limits for 300 D-‐1 (3000 D-‐1) are es@mated fg2<0.29 (0.12) at 95%CL; fg4 (fa3)< 0.15 (0.037) at 95%CL.
• Consistent with the CMS Snowmass extrapola@on.
ATLAS-‐PHYS-‐PUB-‐2013-‐013
page 27
• Effec@ve field theory descrip@on valid up to some new physics scale Λ.
• Spin-‐0 par@cle interac@on Lagrangians with vector bosons.
CERN-‐2013-‐004
Higgs Characterisa@on model
ki are dimensioneless coupling parameters. All couplings “k” are real. Mixing between 0+ and 0-‐ is introduced through cos α
The CP-‐viola@ng coupling ra@o a3/a1 corresponds to
kAVV/kSM tgα ~
Independent sensi@vity es@mates
• Quick access to the anomalous couplings in the HZZ interac@on: study of asymmetries of the angular func@ons sensi@ve to the CP viola@on. – Proposed in arXiv:0708.0458v2.
• Observables sensi@ve to the presence of the BSM contribu@on in the HZZ
interac@on: angular func@ons of the final state O1 .. O6.
page 28 To be published Based on arXiv:0708.0458v2
CP-‐odd angular func@ons genera@ng asymmetries in presence of CP-‐viola@ng couplings.
Momenta of the FS leptons l1Ī1l2Ī2 taken in Z or H rest frames.
[Im(a3)]
[Re(a3)]
14 TeV collisions
• MG5 simula@on of the HàZZ*à4l process and dominant backgrounds. Pythia 6 parton shower and PGS detector simula@on.
• Generic LHC-‐like detector.
• Combinatorial 4l final state selec@on.
page 29 5O
0.5− 0.4− 0.3− 0.2− 0.1− 0 0.1 0.2 0.3 0.4 0.5ex
pN
0
10
20
30
40
50
ZZ-Continuum) = 1.0αcos() = 0.5αcos(
-1 L = 300 fb∫
4O0.5− 0.4− 0.3− 0.2− 0.1− 0 0.1 0.2 0.3 0.4 0.5
exp
N
0
10
20
30
40
50
60
70
80 ZZ-Continuum) = 1.0αcos() = 0.5αcos(
-1 L = 300 fb∫
1O1− 0.8− 0.6− 0.4− 0.2− 0 0.2 0.4 0.6 0.8 1
exp
N
0
5
10
15
20
25
30
ZZ-Continuum) = 1.0αcos() = 0.5αcos(
-1 L = 300 fb∫
To be published
Asymmetries • Propor@onal to the probed anomalous couplings. Becomes non-‐zero only if
the corresponding BSM contribu@on is present. • The asymmetries are defined through the simple coun@ng experiment:
page 30
αcos 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00
| i|A
0
0.02
0.04
0.06
0.08
0.1
0.12
0.141O2O3O4O5O6O
To be published
Asymmetries amplitudes for HàZZ*à4l process at 14 TeV including background es@mates.
HL-‐LHC exclusions • 95% CL exclusions based on
asymmetry significances are consistent with ATLAS and CMS es@mate.
• Full likelihood fit of all observables may improve this result.
page 31
300 D-‐1 excluded at 95%CL
3000 D-‐1 excluded at 95%CL
To be published
Back to Snowmass 2013 • Precision on the fCP(fa3) measurements for the HVV vertex at different
machines.
page 32
14 TeV pp collider in HàZZ*à4l decay.
14 TeV pp collider VBF, VH topologies.
Lepton collider results for the VH topologies.
1310.8361
Back to Snowmass 2013
• Available es@mates show that the HL-‐LHC will achieve an order of 10-‐2 precision on the fa3 measurements in decays. Can we do beuer?
page 33 1310.8361
Summary
• Fixed hypotheses spin and parity results suggest we deal with a spin-‐0 par@cle.
• Current CP-‐mixing and anomalous couplings results from CMS are consistent with the Standard Model expecta@ons. – Beuer limits than expected. – The corresponding ATLAS measurements are in progress.
• The exis@ng projec@ons all agree that for the most sensi@ve channel
HàZZ*à4l, the upper limit on fa3 of the order of 10-‐2 will be set at 3000 D-‐1. – The WW decay will provide weaker exclusion. – The VBF/VH topologies provide stronger fa3 limit due to the different CS
ra@os.
• Hff vertex measurements need to be seriously explored. Most importantly, the Hττ.
page 34
The spin-‐0 par@cle • The absolute majority of these studies were based on direct exclusion of
alterna@ve JP hypotheses in favor of the JP=0+ suggested by the Standard Model.
• DØ constraint on 0-‐ scenario at 97.9% CL from W/Z+bb (DØ Note 6406-‐CONF);
constraint on 2+ scenario at 99.9% CL from W/Z+bb (DØ Note 6387-‐CONF). – Assuming Standard Model produc@on CS X BR.
• The only data-‐based CP-‐mixing study to-‐date is published by CMS in ZZ*à4l decay
page 36
JP hypotheses ATLAS CMS exclusion
Exclusion (%CL) channel Exclusion (%CL) channel
0-‐ 97.8 ZZ* >99.9 ZZ*
1+ >99.9 ZZ*+WW >99.9 ZZ*+WW 1-‐ 99.7 ZZ*+WW >99.9 ZZ*+WW 2+m >99.9 ZZ*+WW+γγ >99.9 ZZ*+WW+γγ
Phys. Le). B 726 (2013), pp. 120-‐144 CMS-‐PAS-‐HIG-‐13-‐005 CMS-‐PAS-‐HIG-‐13-‐002
CMS-‐PAS-‐HIG-‐13-‐002
arXiv:1411.3441v1
Experimental CP-‐mixing studies • Spin and parity analyses to-‐date suggest that the observed Higgs boson
has spin 0. Dominant CP-‐even parity (JP=0+) established in ZZ* decay.
• Almost all Beyond the Standard Model theories with extended Higgs sector predict possible anomalous contribu@on and/or CP-‐viola@on in the Higgs sector.
• Di-‐boson decays and VBF produc@on probing the VVH vertex. – Already accessible with the run-‐I LHC dataset (25 D-‐1). Some work is
done in ZZ* decays. – Growing interest to individual and combined VBF studies: VBF Hàττ,
Hàγγ, HàWW and ZZ.
• Fermion decays probing Hff vertex. – Signal observed in Hàττ. Most probably, run-‐I data will not allow for
meaningful measurement, however, run-‐II sta@s@cs should greatly help.
– uH?
page 37
Recent CMS results (ICHEP 2014) • Mixing in the spin-‐0 sector: results in ZZ*, WW* and combina@on.
page 38
Amplitude used for the ZZ* analysis now includes the Zγ* and γγ* terms.
In both ZZ* and WW* analyses, an expansion of a1, reflec@ng possible BSM contribu@on to the tree-‐level SM coupling.
Expected couplings size in the SM: a1=2, a2, a2Zγ,a2γγ~10-‐3. CMS limit at 20xSM. The Zγ* and γγ* terms in principle modify the m34 distribu@on. But they are very sensi@ve to the m12 cut (40 GeV in CMS). Are we sensi@ve? Is γ*γ* interes@ng provided we measure Hàγγ?
Prospec@ve studies -‐ II
page 41
• ATLAS: Dedicated Monte Carlo CP-‐mixing study in HàZZ*à4l decay channel for 14 TeV, 300 D-‐1 and 3000 D-‐1. – Generator level with smearing func@on and weights modeling
detector resolu@on and efficiency.
• Measurement of (g1, g4) and (g1, g2) pairs in ra@os.
The results of the measurement is expressed in (fg2, fg4, Φg2, Φg4) parametriza@on. In this nota@on, fa3= fg4.
Re(g4 )g1
Im(g4 )g1
ATL-‐PHYS-‐PUB-‐2013-‐013 Arxiv:1208.4018
page 42
ME-‐observable fit
• Considering several observables sensi@ve to the rela@ve magnitude and sign of the real and complex parts of coupling. – Log(|ME(0+)|2/|ME(0-‐)|2): |g4|/g1 sensi@ve. – Log(|ME(0+)|2/|ME(0+h)|2): |g2|/g1 sensi@ve.
• Pdfs are extended to 2D by a ZZ-‐sensi@ve
discriminant. – BDT trained per final state on parity
insensi@ve observables: pT, η, m4l, cosθ*, Δφ.
• Test sta@s@c: -‐2ln(L) where Nsig (fixed to expecta@on) and Nbckg are signal and background expecta@ons respec@vely and μ is the signal strength.
Parity-‐sensi@ve observable
BDT(J=0 vs Z
Z)
ZZ
Signal
For a given (g1,g4)
L(µ,N, syst) = (µ ⋅Nsig ⋅ pdfsig + Nbckg ⋅ pdfbkg )∏
ATLAS prospec@ve studies
page 43
• Both approaches give a consistent result at high sta@s@cs.
• Assuming the Standard Model input, the limits for 300 D-‐1 (3000 D-‐1) are es@mated fg2<0.29 (0.12) at 95%CL; fg4< 0.15 (0.037) at 95%CL.
ATLAS-‐PHYS-‐PUB-‐2013-‐013
ATLAS prospec@ve studies
page 44
• Exclusion limits for |g4|/g1 and |g2|/g1 at 300 D-‐1 and 3000 D-‐1.