higgs searches at tevatron
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Kazu HanagakiKazu Hanagaki 11
Higgs Searches at TevatronHiggs Searches at Tevatron
MotivationMotivationExperimental strategy (and Experimental strategy (and
detector)detector)Higgs search statusHiggs search statusProspectsProspectsConclusionsConclusions
花垣和則 (Kazunori Hanagaki) / Fermilab for the CDF & DØ collaborations
MotivationMotivation
Kazu HanagakiKazu Hanagaki 33
Electroweak Symmetry BreakingElectroweak Symmetry Breaking Gauge invariant Gauge invariant no mass term no mass term Higgs mechanism [with U(1) vector field]Higgs mechanism [with U(1) vector field]
L = (DL = (DDD – V( – V(- ¼ F- ¼ FFF D D ∂∂+ieA+ieA, F, F ∂ ∂AA - ∂ - ∂AA
V(V() = ) = 22 + | + ||(|())22
is complex scalar doublet: Higgs fieldis complex scalar doublet: Higgs field ee22AAAAin (Din (DDD
(e(e22vv22)/2·A)/2·AAA mass term!! mass term!! One Higgs doublet in SMOne Higgs doublet in SM
4 degree of freedom – 3 x (gauge boson) 4 degree of freedom – 3 x (gauge boson) one Higgs boson one Higgs boson
Spontaneous symmetry breakingSpontaneous symmetry breaking22>0 (hot) potential minimum at >0 (hot) potential minimum at =0=022<0 (cold=present world) at <0 (cold=present world) at 00
<<> = > = v/sqrt(2)v/sqrt(2)
Kazu HanagakiKazu Hanagaki 44
Why is Higgs Preferred?Why is Higgs Preferred?
Unitarity: individual diagraUnitarity: individual diagram diverges with sqrt(s)m diverges with sqrt(s) gauge cancellationgauge cancellation
spin 1 intermediate statespin 1 intermediate state spin 0 componentspin 0 component due to w due to w
rong helicity state of erong helicity state of e++ee-- must be canceled by spi must be canceled by spin 0 particlen 0 particle
proportional to mass proportional to mass Higgs coupling!Higgs coupling!
WW-- WW++
ee-- ee++
WW-- WW++
ee-- ee++
ZZ
WW-- WW++
ee-- ee++
WW-- WW++
ee-- ee++
HH
Kazu HanagakiKazu Hanagaki 55
Needs to be light (160-180 GeV) for a theory valid up to Needs to be light (160-180 GeV) for a theory valid up to Plank scalePlank scale
Finding a Higgs at MFinding a Higgs at MHH ~ 120 GeV would be an evidence o ~ 120 GeV would be an evidence of new physicsf new physics
115-200 GeV is our target mass range115-200 GeV is our target mass range
Higgs MassHiggs Mass
unstable unstable vacuumvacuum
Higgs self-Higgs self-coupling coupling divergesdiverges
energy scale (GeV)energy scale (GeV)
MMHH > 114.4 GeV @95% CL sear > 114.4 GeV @95% CL search by LEP2ch by LEP2
MMH H < 175 (207) GeV @95% CL < 175 (207) GeV @95% CL global EW fittingglobal EW fitting
Kazu HanagakiKazu Hanagaki 66
Fermion remains masslessFermion remains massless Nucleon mass almost unchanged, but proton woNucleon mass almost unchanged, but proton wo
uld be heavier than neutronuld be heavier than neutron Spontaneous symmetry breaking by QCD Spontaneous symmetry breaking by QCD W/Z W/Z
mass ~1/2500 (W,Z vs mass ~1/2500 (W,Z vs ) ) very rapid inversed very rapid inversed beta decay (pbeta decay (pn+en+e++++))
Unstable proton Unstable proton no hydrogen atom no hydrogen atom
Completely different world !!Completely different world !!
If the symmetry is not broken…?If the symmetry is not broken…?
Mechanism of electroweak symmetry breaking isMechanism of electroweak symmetry breaking is
the mystery relevant for existence of ourselves the mystery relevant for existence of ourselves
Experimental Strategy and Experimental Strategy and DetectorDetector
Kazu HanagakiKazu Hanagaki 88
Search StrategySearch Strategy
MMHH < 135 GeV < 135 GeV H H b b-bar dominant b b-bar dominant too much BG in too much BG in
gg gg H H b b-bar b b-bar qqqqW/Z+H(W/Z+H(bb)bb)
For high MFor high MHH range range H H WW dominant WW dominant gg gg H H WW WW
For medium MFor medium MHH range range W/Z+H(W/Z+H(WW) helpsWW) helps
Kazu HanagakiKazu Hanagaki 99
The DetectorThe Detector
= -ln[tan(= -ln[tan(/2)]/2)]
Kazu HanagakiKazu Hanagaki 1010
Silicon Tracker for b-jets IdentificationSilicon Tracker for b-jets Identification
Silicon micro-strip detector for preciseSilicon micro-strip detector for precisemeasurement of charged particle trajectorymeasurement of charged particle trajectory
New silicon detector in DØ for New silicon detector in DØ for improvement of b-jet IDimprovement of b-jet ID installed and tested in this shuinstalled and tested in this shu
tdown periodtdown period
Kazu HanagakiKazu Hanagaki 1111
Identification of b-jetsIdentification of b-jets
ccb-hadronb-hadron ~ 400-500 ~ 400-500 m m tra travel by a few mm from primarvel by a few mm from primary vertexy vertex S(Lxy) = Lxy/(Lxy) or S(IP) S(IP)
= d= d00//dd00 with V0 (Ks etc.)
removal
prim
ary
verte
x seco
ndar
y
verte
xL xyd 0
DØDØ
CDFCDF
sec.vertex basesec.vertex base
Higgs Search StatusHiggs Search Status
Standard ModelStandard Model MSSMMSSM
Kazu HanagakiKazu Hanagaki 1313
Standard Model – Low Mass HiggsStandard Model – Low Mass Higgs
W/Z identificationW/Z identification WWll: high p: high pTT isolated lepton + isolated lepton +
missing Emissing ETT W mass W mass ZZ: large missing E: large missing ETT
ZZll: high pll: high pTT isolated dilepton isolated dilepton Z massZ mass
High pHigh pTT dijets with b-ID dijets with b-ID dij dijet masset mass
q(’)q(’) W*/Z*W*/Z*
HH
W/ZW/Z
xBr(W/ZxBr(W/Zff) = 0.015-0.003 ff) = 0.015-0.003 pbpb
BackgroundsBackgrounds W/Z+bb/cc/jj, top, W/Z+Z(W/Z+bb/cc/jj, top, W/Z+Z(bb), bb),
QCD…QCD… b-jet ID, jet energy resolution arb-jet ID, jet energy resolution ar
e importante important
bb
bb
ff
ff
Z(Z()H()H(bb) Lbb) Lintint = 261 pb = 261 pb-1-1
Kazu HanagakiKazu Hanagaki 1414
W(W(ll)H()H(bb)bb) ppTT(e or (e or ) > 20 GeV) > 20 GeV Missing EMissing ETT > 20 GeV (CDF) > 20 GeV (CDF)
> 25 GeV (DØ) > 25 GeV (DØ) CDF: jet ECDF: jet ETT>15 GeV, |>15 GeV, ||<2|<2 DØ: jet EDØ: jet ETT>20 GeV, |>20 GeV, ||<2.5|<2.5 b-jet taggingb-jet tagging
Consistent Consistent with SM with SM background background expectationsexpectations backgroundbackground
s well s well understoodunderstood
Kazu HanagakiKazu Hanagaki 1515
Standard Model – High MassStandard Model – High Mass
Two isolated high pTwo isolated high pTT leptons leptons + missing E+ missing ETT
Dominant background is qqDominant background is qqWWWW different decay angular correlatiodifferent decay angular correlatio
n with Higgs signaln with Higgs signal
DØ Run II Preliminary Lint = 950 pb-1
W+ e+
W- e-
Kazu HanagakiKazu Hanagaki 1616
The Other AnalysesThe Other Analyses WH(WH(WW) WW) l l±±ll±±XX
high phigh pTT isolated isolated like signlike sign dil dilepton (ee,epton (ee,,e,e))
large missing Elarge missing ETT diboson production is the mdiboson production is the m
ain background due to charain background due to charge mis-identificationge mis-identification
t(t(bW)t(bW)t(bW)H(bW)H(bb)bb) exactly one e or exactly one e or missing Emissing ETT 5 or more jets5 or more jets 3 or more b-jets3 or more b-jets
Kazu HanagakiKazu Hanagaki 1717
Standard Model Higgs SummaryStandard Model Higgs Summary
~1~155
First DØ combined result First DØ combined result Z(Z(ll)H not yet includedll)H not yet included
Kazu HanagakiKazu Hanagaki 1818
MSSM HiggsMSSM Higgs
t
0
b
0
Amplitude 1/tan Amplitude tan
+
b
b
0
Amplitude tan
Two Higgs doublet in MSSM to avoid anomalyTwo Higgs doublet in MSSM to avoid anomaly 8 degrees of freedom – 3 x (longitudinal polarization of 8 degrees of freedom – 3 x (longitudinal polarization of
WW± ± and Z) and Z) 5 scalars ( 5 scalars (h, H, Ah, H, A, H, H±±)) tantan = <H = <Huu>/<H>/<Hdd>>
At high tanAt high tan, , (h or H, A) is enhanced(h or H, A) is enhanced Br(ABr(Abb)~90%, Br(Abb)~90%, Br(A)~10%)~10%
00
Kazu HanagakiKazu Hanagaki 1919
MSSM Higgs Search StatusMSSM Higgs Search Status
CDF: CDF: ; DØ: b(b); DØ: b(b)b(b)bb, b(b)bb,
ProspectsProspects
Kazu HanagakiKazu Hanagaki 2121
LuminosityLuminosity
4-8 fb4-8 fb-1-1 by 2009by 2009
100E3100E300
200E30200E30 Improvement by the recycler Improvement by the recycler as a storage ring of p-baras a storage ring of p-bar
Electron cooling at the recyclerElectron cooling at the recycler
Kazu HanagakiKazu Hanagaki 2222
Improvement of b-tag at DØImprovement of b-tag at DØQCD data (fake rate)
SVT JLIP CSIPSVT JLIP CSIP
SV
T JLI
P
C
SIP
SV
T JLI
P
C
SIP + jet data
(efficiency)
SVT JLIP CSIPSVT JLIP CSIP
SV
T JL
IP
CSIP
SV
T JL
IP
CSIP
correlation coefficientcorrelation coefficient
Three b-tag algorithms in Three b-tag algorithms in DØ; SVT, JLIP, and CSIPDØ; SVT, JLIP, and CSIP correlated in efficiencycorrelated in efficiency small correlation for fakesmall correlation for fake significant improvement by significant improvement by
combination by Neural combination by Neural Network (~30% per jet)Network (~30% per jet)
Kazu HanagakiKazu Hanagaki 2323
The Future of SM Higgs SearchThe Future of SM Higgs Search
Comparison w.r.t. Comparison w.r.t. old old sensitivity studysensitivity study For MFor MHH=115GeV: =115GeV:
Limit/Limit/ =15 @~330pb =15 @~330pb-1-1 by by DØ aloneDØ alone vs vs 95% CL exclusion 95% CL exclusion @2fb@2fb-1-1
We can reach very close to the sensitivity studyWe can reach very close to the sensitivity study
itemitem gaingain cross efficiencycross efficiency 1.11.1lum(2/0.33)lum(2/0.33) 2.42.4 L0/L1calL0/L1cal 1.11.1
NN b-tagNN b-tag 1.41.4 multivariate multivariate selectionselection 1.51.5
jet resolutionjet resolution 1.21.2 reduced syst.reduced syst. 1.11.1new channelsnew channels 1.11.1 combine with CDFcombine with CDF 1.41.4increased increased acceptanceacceptance 1.11.1 grand totalgrand total 1414
ConclusionsConclusions
Kazu HanagakiKazu Hanagaki 2525
ConclusionsConclusions Mechanism of electroweak Mechanism of electroweak
symmetry breaking is a symmetry breaking is a profound mysteryprofound mystery
Searches have been carried Searches have been carried out with 194-950 pbout with 194-950 pb-1-1 of data of data Remaining events consistent Remaining events consistent
with SM backgroundswith SM backgrounds If the (SM) Higgs exists and If the (SM) Higgs exists and
is light, there is a great is light, there is a great potential to find the Higgspotential to find the Higgs
Now is the Time to Search for Now is the Time to Search for Higgs at TevatronHiggs at Tevatron
BackupBackup
Kazu HanagakiKazu Hanagaki 2727
Projection of MSSM Higgs SearchProjection of MSSM Higgs Search Tevatron will prob
e below
b
t
m
mtan
Kazu HanagakiKazu Hanagaki 2828
MSSM ParametersMSSM Parameters
22
2
19
9
1
tan2
bb
SMSUSYBR
radiative correction depending oradiative correction depending on many parametersn many parameters
GeVGeVmGeVGeVGeVGeVM
TeVXTeVTeVMmixingnom
g
t
SUSY
h
160080020020020020002
21max
2
HhA
Kazu HanagakiKazu Hanagaki 2929
New Technique of Jet ReconstructionNew Technique of Jet Reconstruction Charged track information in jet reconstructionCharged track information in jet reconstruction
EEcalcal = E(e/ = E(e/) + E(neutral hadron) + E(chrgd had)) + E(neutral hadron) + E(chrgd had) EEtrkcaltrkcal = E = Ecal cal – E– Eexpectexpect(chrgd had) + E(chrgd had) + Etrktrk(chrgd had)(chrgd had)
resolution measured in resolution measured in +jet data+jet dataDØ Run II PreliminaryDØ Run II Preliminary
similar similar improvemenimprovement at CDF as t at CDF as wellwell
Kazu HanagakiKazu Hanagaki 3030
b-tag efficiency measurement at b-tag efficiency measurement at DØDØ
Solve 8 equations for 8 unknownsSolve 8 equations for 8 unknowns
unknownunknownss
+jet+jet+jet && opposite tag+jet && opposite tag
number of number of eventsevents
before b-tagbefore b-tag
b-tag by muonb-tag by muon
b-tag by tagger under b-tag by tagger under testingtesting
b-tag by both taggerb-tag by both tagger
example to measure JLIP effiexample to measure JLIP efficiency with the combinatiociency with the combination of muon tagn of muon tag
Kazu HanagakiKazu Hanagaki 3131
Low Mass Higgs Search at DØLow Mass Higgs Search at DØ
W(W(e/e/++)H()H(bb): bb): xBR = 0.015 pbxBR = 0.015 pb Z(Z(ee/ee/)H()H(bb): bb): xBR = 0.003 pbxBR = 0.003 pb Z(Z()H()H(bb): bb): xBR = 0.015 pbxBR = 0.015 pb
for 261-389 pbfor 261-389 pb-1-1 effeff SS BB S/sqrt(B)S/sqrt(B)
W(W(ee)H)H 3.4%3.4% 0.180.18 4.74.7 0.080.08
W(W()H)H 1.7%1.7% 0.100.10 4.04.0 0.050.05
Z(Z(ee)Hee)H 4.5%4.5% 0.050.05 1.41.4 0.040.04
Z(Z()H)H 5.9%5.9% 0.050.05 3.13.1 0.030.03
Z(Z()H)H 5.2%5.2% 0.210.21 9.09.0 0.070.07
W(W()H miss lep.)H miss lep. 4.2%4.2% 0.150.15 9.09.0 0.050.05
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