Andrey Korytov, UF 12 October 2006, Boston University 1 Higgs Physics at LHC (gearing up for...
-
Upload
annabella-jefferson -
Category
Documents
-
view
216 -
download
1
Transcript of Andrey Korytov, UF 12 October 2006, Boston University 1 Higgs Physics at LHC (gearing up for...
Andrey Korytov, UF 12 October 2006, Boston University 1
Higgs Physics at LHC(gearing up for discovery)
Andrey Korytov
Andrey Korytov, UF 12 October 2006, Boston University 2
Outline
• Introductory remarks (what we know)
• LHC, ATLAS, and CMS
• Gold-plated channel HZZ4 at CMS (in full scrutiny)
• Other SM Higgs discovery channels
• MSSM Higgs discovery channels
Andrey Korytov, UF 12 October 2006, Boston University 3
SM Higgs Trivia
• Start from scalar fieldo doublet pseudo-scalar in SM
• Require local gauge invarianceo need massless gauge fields Ao lagrangian acquires terms
• Mexican hat potentialo min V() is not at =0 o non-zero vacuum expectation value v0—ether of 21 centuryo expand around minimumo effective mass terms for gauge bosonso effective mass for h-field itself
• Free lunch: o force interact with fermions with ad hoc couplings f o effective fermion masses (within the P-violation framework!)
Two important points to remember: • Higgs boson mass is the only free parameter• (Higgs-particle coupling) ~ (mass of particle)
o Production mechanisms: first one needs to produce heavy particleso Decay channels: higgs likes to decay to heaviest particles it can
decay to
( )x
( ) ( ) ( )x U x x
g AA2 42( )
2V
2 20~ vhm
2 20~ vAm g
2 20~ vf fm
f f
0v h
Andrey Korytov, UF 12 October 2006, Boston University 4
What we know: theory
After renormalization• (Q)• If mH were small at 1 TeV,
runs down, flips sign at some scale Q, and vacuum breaks loose
• If mH were large at 1 TeV, runs up, coupling explodes at some scale, theory becomes non-perturbative, and theorists can retire
SM Higgs has a very narrow window of opportunity to be self-sufficient due to a fine-tuned (apparently accidental) cancellation of large correction factors
non-p
ert
urb
ati
ve
un
sta
ble
vacu
um
N
ew
Ph
ysic
s E
ner
gy
Sca
le
(G
eV
)
103
1
06
1
09
10
12
1
01
5
10
18
0 200 400 600
Higgs mass MH (GeV)
Andrey Korytov, UF 12 October 2006, Boston University 5
What we know: direct search at LEP
}MJJ=MH =?
}MJJ=MZ=91 GeVZ0
H bb
jet (b-tagged)
jet (b-tagged)
q
q jet
jet
e+
e-
Z0
LEP Energy209 GeV
Andrey Korytov, UF 12 October 2006, Boston University 6
What we know: direct search at LEP
MH (GeV/c2)
Points—dataDashed line—expected background (no-Higgs processes)
ALEPH Collaboration data - 2000
small excess?Formally, it looked like 4 effect!If it was Higgs, they saw too many...
LEP was let run longer to get more data
Tight Cuts
After taking more data and combining results of all 4 experiments,
the final word from LEP:
No discovery...
Consistency with background: ~1.7
Limit on Higgs mass:
MH > 114.4 GeV @95% CL
Phys. Lett. B565 (2003) 61
Andrey Korytov, UF 12 October 2006, Boston University 7
What we know: direct search at Tevatron
Some lessons (example on MH=110 GeV):• SM Higgs exclusion at 95% CL was expected at L=1.2
fb-1
• Now at L~300 pb-1, the excluded x-section should’ve been a factor of two above the SM x-section
• The actual difference is a factor of ten
Andrey Korytov, UF 12 October 2006, Boston University 8
What we know: circumstantial evidence
Presence of too light or two heavy Higgs in loops would make various SM precision measurements less self-consistent
• mH<166 GeV at 95% CL
• mH<199 GeV at 95% CL, if the direct search limit mH>114 GeV is included
LEP EW Working Group July 2006 WW
H
Andrey Korytov, UF 12 October 2006, Boston University 9
Large Hadron Collider
2007 (Dec)• hardware commissioning run• sqrt(s)=900 GeV• Lint ~ 100 nb-1 (0.0001 fb-1)
2008• first physics run• sqrt(s)=14 TeV• Lint ~ 0.1-1 fb-1
2009• sqrt(s)=14 TeV• Lint ~ 10 fb-1
2010• sqrt(s)=14 TeV• Lint ~ 20-100 fb-1
Switzerland
France
Geneva airport
6 miles
Andrey Korytov, UF 12 October 2006, Boston University 10
ATLAS
Andrey Korytov, UF 12 October 2006, Boston University 11
Compact Muon Solenoid
Andrey Korytov, UF 12 October 2006, Boston University 12
CMS Endcap Muon Chambers
3.3 m
1.5 m
muon is detected with ~100 m precision ~ 4 ns time resolution
We need 500 of them to cover ~1000 m2
President of France J. Chirac is observing live muons detected by the Endcap Muon Chambers.
Andrey Korytov, UF 12 October 2006, Boston University 13
CMS Physics Technical Design Report
Physics TDR
• Comprehensive/up-to-date overview of CMS physics reach
• First part of TDR is devoted to 11 in-depth (showcase) analyses; HZZ4 is one of them
• TDR is out for print last month
650 pages308 figures 207 tables1.50 kg
Andrey Korytov, UF 12 October 2006, Boston University 14
SM Higgs: discovery signatures at L=30 fb-1
Colored cells = { detailed studies available }YES = { sure discovery in the appropriate range of masses at L=30 fb-1 }
Hbb H H HWW HZZ
inclusive YES YES YES
qqH YES YES YES
W/Z+H
ttH
Andrey Korytov, UF 12 October 2006, Boston University 15
HZZ4dominant 4 backgrounds
tt Wb + Wb BX + BX X + X 4X
Zbb + BB + X + 2(X) + X 4X
ZZ
tt 4 + X
Zbb 4 + X
Higgs signal H 4
Z/+Z/ 4 with spectacular peak at m4=mZ
(this s-channel contribution was overlooked in all previous studies)
t-channel s-channel
Andrey Korytov, UF 12 October 2006, Boston University 16
HZZ4analysis strategy
Peak in mdistribution Cut variables: • muon isolation: 2 muons in tt and Zbb appear in B-decays, i.e. within
jets• displaced vertex: 2 muons in tt and Zbb appear in B-decays• missing energy: tt will have hard neutrinos• Kinematics: muons in Zbb and tt tend to be softer• NOT USED:
o pT() for Higgs is larger than for ZZ, but the non-zero pT appears only at NLO, which is not accounted for in the current MC simulation
o Number of jets for Higgs (ggHZZ) is larger than for ZZ (qqZZ), but this effect of hard jets is again NLO…
Cut optimization• mH-dependent (read m4-dependent)• identify most important and not-correlated cuts
o isolation cut on the least isolated muon (i.e., the same cut for all muons)o pT cut for the 3rd softest muon
• and produce smooth cut(m4) functionsThis strategy makes the search automatically optimized for any mass at which Higgs boson may chose to show up
Peak search:• Include statistics and systematics into significance evaluation
Final probabilistic interpretation
Andrey Korytov, UF 12 October 2006, Boston University 17
HZZ4understanding ZZ bkgd
Knlo(m4)
Box-diagram
Control samples
QCD scale uncertainties
PDF scale uncertainties
Isolation cut uncertainties
Muon efficiency uncertainty
2+ + x + …
2
Andrey Korytov, UF 12 October 2006, Boston University 18
~20% over LO
Zecher, Matsuura, van der Bijhep-ph/9404295
HZZ4understanding ZZ bkgd
Formally (by counting vertices), NNLOHowever, - it is the LO for ggZZ and - contribution is large due to large gg “luminosity”
Knlo(m4)
Box-diagram
Control samples
QCD scale uncertainties
PDF scale uncertainties
Isolation cut uncertainties
Muon efficiency uncertainty
Andrey Korytov, UF 12 October 2006, Boston University 19
HZZ4ZZ bkgd
Knlo(m4)
Box-diagram
Control samples:• qq Z 2
o very similar origin to ZZ bkgdo huge statistics
• ZZ 4 sidebandso would be perfect, if not for rather complicated shape o and very limited statistics
QCD scale uncertainties
PDF scale uncertainties
Isolation cut uncertainties
Muon efficiency uncertainty
L=10 fb-1
Total 8 eventsExp bkgd 0.8 evtsScL = 4.7
Andrey Korytov, UF 12 October 2006, Boston University 20
HZZ4ZZ bkgd
Knlo(m4)
Box-diagram
Control samples
QCD scale uncertainties• estimate of higher-order
contributions
PDF scale uncertainties
Isolation cut uncertainties
Muon efficiency uncertainty
Normalization to Z2
Andrey Korytov, UF 12 October 2006, Boston University 21
HZZ4ZZ bkgd
Knlo(m4)
Box-diagram
Control samples
QCD scale uncertainties
PDF scale uncertainties
Isolation cut uncertainties • Underlying Event is the main source for energy flow in vicinity of
muons in the irreducible ZZ-bkgd; but UE activity is poorly predicted…• Use data to calibrate UE activity:
o UE activity in Z must be very similar to that in ZZ (qq …)o MC studies confirm this statement
Muon efficiency uncertainty: use data
three colors: different UE models— ZZ events- - Z events (random cones)
Andrey Korytov, UF 12 October 2006, Boston University 22
HZZ4ZZ background
Knlo(m4)
Box-diagram
Control samples
QCD scale uncertainties
PDF scale uncertainties
Isolation cut uncertainties: use data
Muon efficiency uncertainty: use data
• single muon trigger; well reconstructed muon 0
• take advantage of muon being measured twice: in Tracker and Stand Alone Muon system
• find Z-peak three times…• (efficiency) ~ 1%
0
1 0
( )in
t k Z
v
r
M trk
N N
0
3 0
( )
GR
GRM SAM TRK
inv
M
GRM
ZN N
M
0
2 0
( )in AM
Z
v S
SAM
M
N N
Andrey Korytov, UF 12 October 2006, Boston University 23
HZZ4Higgs signal over ZZ bkgd
Peak search results: • Significance:
o Counting Experimento LLR for m spectrum
• Luminosity needed• Including systematics
Andrey Korytov, UF 12 October 2006, Boston University 24
HZZ4Higgs signal over ZZ bkgd
Peak search results: • Significance• Luminosity needed• Including systematics
Andrey Korytov, UF 12 October 2006, Boston University 25
HZZ4Higgs signal over ZZ bkgd
Peak search results: • Significance• Luminosity needed• Including systematics
o significance must be derated
o effect depends on how we define the control sample: Z2 peak vs ZZ4 sidebands
Andrey Korytov, UF 12 October 2006, Boston University 26
HZZ4lcombining four channels
new
Andrey Korytov, UF 12 October 2006, Boston University 27
HZZ4word of caution
Search in a broad range of parameter phase space
mH=115-600 GeV
Probability of finding a local excess somewhere is much higher than naïve statistical significance might imply: e.g. S=3 is almost meaningless
A priori assumptions must be clearly defined
Background-onlypseudo experiment
Search for Higgs peak
— actual probability
- - probability implied by local statistical significance
Andrey Korytov, UF 12 October 2006, Boston University 28
SM Higgs: discovery signatures at L=30 fb-1
Colored cells = { detailed studies available }YES = { sure discovery in the appropriate range of masses at L=30 fb-1 }
Hbb H H HWW HZZ
inclusive YES YES YES
qqH YES YES YES
W/Z+H
ttH
Andrey Korytov, UF 12 October 2006, Boston University 29
Standard Model Higgs: H
Backgrounds:• prompt • prompt + jet(brem , )• dijet
Analysis:• Cut-based
o PT, isolation, M
o events sorted by “em shower profile quality”
• Optimizedo loose cuts and sortingo event-by-event kinematical Likelihood Ratioo bkgd pdf from sidebands, signal pdf from MC
• Systematic errors folded in
CMSM < 1%
new
CMS
Andrey Korytov, UF 12 October 2006, Boston University 30
Standard Model Higgs: HWW2l2
Backgrounds:• WW, tt, Wt(b), WZ, ZZ • ggWW (box)
Analysis:• KNLO(pT
WW)
• cuts: o e/ kinematics, isolation, jet veto,
MET
• counting experiment, no peak• background from a control sample:
o signal: 12<mll<40 GeV
o control sample: me>60 GeV
• reduce syst. errors; pay stat. penalty
• systematic errors are folded in
Signal Region Control Sample
new
CMS
Andrey Korytov, UF 12 October 2006, Boston University 31
Standard Model Higgs: qqH, HWW2l2
Backgrounds:• tt, WWjj, Wt
Analysis:• 2 high pT leptons + MET• 2 forward jets (b-jet veto)• central jet veto• counting experiment, no peak:• background from data:
o Signal: all cutso Control sample: no lepton cuts
Result• better than inclusive WW (!!!)
jet
jet
ATLAS
ATLASMH=160 GeVHWWe
Signal Region Control Sample
Andrey Korytov, UF 12 October 2006, Boston University 32
Standard Model Higgs: qqH, H
Backgrounds:• Zjj, tt
Analysis:• two forward jets, central jet
veto• two leptons (e, , -jet)+MET
l+ l l+ -jet
• mass(l; l or -jet; pTmis)
o despite 3 or 4 ’s present, works quite well in collinear approximation
He
ATLAS 30 fb-1
ATLAS
H
pT
mis
Andrey Korytov, UF 12 October 2006, Boston University 33
Difficult (impossible) channel: ttH, Hbb
30 fb-1
ATLAS
SM Higgs: ttH, Hbb
CMS: • careful study of systematic errors in the Physics TDR• syst error control at sub-percent level is needed: not
feasible...
Andrey Korytov, UF 12 October 2006, Boston University 34
Standard Model Higgs: Summary
Benchmark luminosities:• 0.2 fb-1: exclusion limits will start carving into SM Higgs x-
section• 1 fb-1: discoveries become possible if MH~170 GeV• 10 fb-1: SM Higgs is discovered (or excluded) in full range
NLO cross sectionsSystematic errors included
new
Andrey Korytov, UF 12 October 2006, Boston University 35
mtop=174.3 GeV
MSSM Higgs bosons: h, H, A, H±
• SUSY stabilizes Higgs mass• 2 Higgs field doublets needed• Physical scalar particles: h, H, A, H±
• Properties at tree levelo fully defined by 2 free parameters: MA, tano CP-even h and H are almost SM-like in vicinity
of their mass limits vs MA: hmax and Hmin
o large tan ~ enhances coupling to “down”
fermions: b and are very important!~ suppresses coupling to Z and W
o CP-odd A never couples to Z and W:~ decays: bb, (and tt for small tan)
o H± strongly couples to tb and o all Higgs bosons are narrow (<10 GeV)
• Loop corrections o gives sensitivity to other SUSY parameterso mh
max scenario = { most conservative LEP limits }
Andrey Korytov, UF 12 October 2006, Boston University 36
MSSM Higgs boson: h, H, A production
• x-sections are large, often much larger than SM (dotted line)
• bb(h/H/A) production is very important
h H A
h H A
tan=3
tan=30
Andrey Korytov, UF 12 October 2006, Boston University 37
MSSM Higgs: SM-like signatures
CMS:• better detector
simulation• systematics included• contours recessed…
ATLAS:• no systematics
included
CMS 2003 CMS 2006
ATLASnew
Andrey Korytov, UF 12 October 2006, Boston University 38
MSSM Higgs: heavy neutral H, A• production in association with bb (especially good at large
tan)• bb-decay mode (~80%) is overwhelmed with QCD background• -decay mode (~20%) is the next best• -decays (~0.1%) allow for direct measurement of • better detector simulation (i.e. more realistic) • systematics included
• contours recessed (low MA band, qqH, moved to SM-like Higgs plot)
ATLAS
CMS 2003 CMS 2006
new
Andrey Korytov, UF 12 October 2006, Boston University 39
MSSM Higgs: H±
Heavy H± (M>mt):• production via gg tbH± bjj+b and gb tH±
bjj+o H± (H± tb overwhelmed by
bkgd)o tWbjjb
• backgrounds: tt, Wt, W+jets
Light H± (M<mt):• production via gg/qq tt
b+blo t H±b, H± o tWblb
• backgrounds: tt, Wt, Wjjj
new
Andrey Korytov, UF 12 October 2006, Boston University 40
Difficult (impossible) channels…
MSSM Higgs: bb(H/A), (H/A)bb MSSM Higgs: H±tb
Andrey Korytov, UF 12 October 2006, Boston University 41
MSSM Higgs bosons: h, H, A, H±
Loop corrections give sensitivity to the rest of SUSY sector, more specifically to:• stop quark mixing Xt
• squark masses MSUSY
• gluino mass Mg
• SU(2) gaugino mass M2
• higgsino mass parameter
*Suggested by Carena et al. , Eur.Phys.J.C26,601(2003)
Special benchmark points*:• max stop mixing (mhmax):
o mh < 133 GeVo MSUSY~1 TeVo most conservative LEP limits
• no mixing: o mh < 119 GeVo MSUSY~1 TeV
• gluophobic h o ggh is suppressed
(top+stop loop cancellation)o mh < 119 GeVo MSUSY~350 GeV
• small eff (mix h/H):o and bb-decays
suppressed even for large tan
o mh < 123 GeVo MSUSY~800 GeV
Andrey Korytov, UF 12 October 2006, Boston University 42
MSSM Higgs: other benchmark points?
ATLAS studies:• preliminary (no
syst)
• vector boson fusion:o qq(h/H)o h/H, WW,
• caveat for small eff: decoupling from is compensated by WW enhancement
• all four special points are well covered at L=30 fb-1
Andrey Korytov, UF 12 October 2006, Boston University 43
ATLASL=300 fb-1
MSSM Higgs or SM Higgs?
SM-like h only:• considerable area…• even at L=300 fb-1
Any handles?• decays to SUSY
particles?• SUSY particle decays?• measure branching
ratios?
Andrey Korytov, UF 12 October 2006, Boston University 44
MSSM Higgs or SM Higgs?
Decays to SUSY:
• h22
(2l1)+(2l1
)
• Signature:o Four leptonso Large MET
Msleptons=250 GeV ATLAS300 fb-1
BR for different channels: • R = BR(hWW) /
BR(h)• =|RMSSM-RSM|/expimental
Andrey Korytov, UF 12 October 2006, Boston University 45
MSSM Higgs: yet another twist
CP-violation in Higgs sector
• complex couplings:o mass eigenstates H1, H2, H3
are mixtures of h, H, Ao production/decay modes
change
• new benchmark point CPX (maximum effect) suggested by Carena et al., Phys.Lett B495 (2000) 155
• new parameterization: MH± ; tan
• uncovered holes remain• more studies needed
ATLAS preliminary
o qqH, HWW, o bbH, Ho tbH± and tH±, H±o …
ATLASL=30 fb-1
not excludedat LEP
Andrey Korytov, UF 12 October 2006, Boston University 46
Summary
Standard Model Higgs:• expect to start excluding SM Higgs at L~0.1 fb-1
• discoveries may be expected already at L~1 fb-1
• SM Higgs, if that’s all we have, is expected to be discovered by the time we reach L~10 fb-1
MSSM Higgs:• nearly full (M, tan) plane is expected to be covered at
L~30 fb-1
• there is a serious chance to see only a SM-like Higgs…
Andrey Korytov, UF 12 October 2006, Boston University 47
Summary Plots
Andrey Korytov, UF 12 October 2006, Boston University 48
SM Higgs
newCMS 2003 CMS 2006
Andrey Korytov, UF 12 October 2006, Boston University 49
MSSM SM-like Higgs
ATLAS
CMS 2003 CMS 2006 new
Andrey Korytov, UF 12 October 2006, Boston University 50
MSSM H and A
new
ATLAS
CMS 2003 CMS 2006
Andrey Korytov, UF 12 October 2006, Boston University 51
ATLAS
MSSM H+- (old/new plots)
newCMS 2003 CMS 2006