Higgs and new particle
searches at Tevatron
Yukihiro Kato
Kinki University
(behalf of CDF collaboration)
Mar.1
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Contents
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•
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Higgs
SUSY
Technicolor
High mass particles (b’)
This talk includes the new results since summer 2006
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Tevatron
D0
pp collisions at s  1.96 TeV
CDF
Tevatron
Integrated luminosity is 2.4fb-1
Peak luminosity record
2.89 ×1032 cm-2s (Feb 25, 2007)
Main injector
Mar.1
Tevatron delivered 165pb-1 in Jan. 2007
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CDF


CDF has collected over 2 fb-1
data at Feb. 2007
653pb-1 delivered in FY06,
82% to tape (~5% trigger,
~5% beam conditions )
General purpose detectors
Precision tracking with silicon
vertex detector
Good particle identification (K, p)
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On going analyses of the exotic
physics at CDF
• Higgs:
SM Higgs, non-SM Higgs
• SUSY
• High mass particles:
Z’, W’, RS gravitons, b’
• Leptoquarks: 1st, 2nd, 3rd generation
• Technicolor: Techni-rho
• Others:
Diphoton+x, large extra dimension, lepton+photon+x
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Search for Higgs
・ SM channels:
WH → bb, jjbb
Low mass Higgs
ZH → ννbb, bb, jjbb
H → WW
High mass Higgs
WH → WWW
・ Extended Models
H → tt
bbH → bbbb
H → gg
H+hf → W+hfhf → W+gggg
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WH →  bb
Event selection
・ Identified e/μ, pT > 20GeV
・ Two jets: ET > 15 GeV, |η| < 2.0
・ At least one b-tagged jet
(>2 tag, 1 tag w/ NN tag)
・ Missing ET > 20 GeV
Data sample: 955 pb-1
Dominant backgrounds
・ W backgrounds: Wbb, Wcc, Wqq (false b-tag)
・ Top backgrounds: single top, tt
・ Multi-jet (non W-QCD)
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WH →  bb
Result
Upper limit on Higgs mass from 110 GeV/c2 to 150 GeV/c2
 ( pp  WH)  BR ( H  bb )  3.9  1.3( pb)
New result with 955 pb-1
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ZH→ννbb
Event selection
・ Two jets, ET>60, 20 GeV
・ Lepton veto
・ Missing ET > 70 GeV,
cut on direction with two jets
・ 1 or 2 b-tags
(single/double tag sample)
Data sample: 973 pb-1
Dominant backgrounds
・ Multi-jet (QCD)
・ W/Z + heavy flavor
・ Top
・ Diboson
・ Mistag
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Number of expected event after the cuts
1 b-tag
2 b-tags
Total B.G
310±40
19.6±3.1
Observed
333
24
ZH (115 GeV)
0.77±0.09
0.25±0.05
WH (115 GeV)
0.64±0.07
0.22±0.04
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ZH→ννbb
Sliding dijet mass cut for
limit setting
95% C.L. upper limit with
respect to the SM
cross-sections
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Higgs
mass
ZH
Exp.
WH
Exp.
Combined
Exp.
Obs.
110
25.5
34.8
14.9
17.8
115
28.4
34.0
15.4
16.0
120
31.7
35.1
16.8
15.6
125
40.5
39.2
20.0
21.4
130
50.0
41.5
22.6
22.8
H→
+
WW→
νν
Good sensitivity of the “high-mass” region (mH > 150GeV)
gg → H
It’s large!
σ(gg →H0) = 431fb @ Mh=160 GeV
Br(H0→WW) = 90% @ Mh=160 GeV
Detector signature:
Two opposite-sign leptons
 Missing transverse energy

Same final state
Vector Boson fusion
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H → W+W- → νν
Summary of event selection vs. mH
Dominant backgrounds:
Diboson
(WW, WZ, ZZ)
Drell-Yan
Wγ
 tt
Data sample: 1fb-1
Event selection:
 Isolated leptons with opposite charge:
pT(1) > 20 GeV, pT(2) > 10 GeV
 16 GeV < M < MH/2 – 5 GeV
 # of jet cuts
 Missing ET > MH/4
 Higgs mass dependent event cuts:
 Relations between pT(1), pT(2), missing ET
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H → W+W- → νν
Look in Δφ(1, 2) distributions
A statistically significant
contribution of the Higgs
signal is not observed
( Histograms include the signal and B.G.)
Set a 95% C.L limit
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MSSM Higgs →ττ
MSSM ⇒SUSY with minimal Higgs content
Requires two higgs field doublets
H±; A (CP-odd); h, H (CP-even)
In the following f is used to
denote any of A, h, H
At tree level defined by mA and tanb  vu/vd
 A couplings to b, t enhanced by ～tanb
 For large tanb, one of the h/H is SM-like and low mass (m<135 GeV), the
other almost mass-degenerate with A, similar couplings

gg  H
bb  H
Dominant A decays: bb (～85－95%), tt (～5－15%)
bb: larger BR, but need associated b-jets
search for Higgs →tt
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MSSM Higgs →ττ
Signatures are determined by the decay modes of t
Mode
Used in
this search
Fraction (%)
t et e
3
Large Z/g*→ee B.G.
t mt m
3
Large Z/g*→mm B.G.
t et m
6
Low jet backgrounds
tethad
23
golden
tmthad
23
golden
thadthad
41
Challenging (jet B.G)
Z/g*→ee
 Z/g*→mm
 Misidentified jet as thad (w+jets, multi-jets)
 Diboson
 Top pair production

Dominant backgrounds
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MSSM Higgs →ττ
Data sample (992pb-1) :
 tethad, tmthad from lepton plus track trigger
(one e/m and isolated track pT>5GeV/c)
 tetm from di-lepton trigger
Event selection
hadronic t decay
3-prong = (3p)
Good isolation lepton with pT > 10GeV/c
1-prong = (1p)
 thad-ID: ETcl>9 GeV, pT(thad) > 15(1p), 20(3p) GeV/c,
Mhad <1.8(1p), 2.2(3p) GeV, isolation(track, p)
 Df(t1,t2)>0.5 rad
 Diboson, tt, W+jets suppression
Transverse momentum balance between t1, t2, missing ET
 Soft QCD suppression
・ te/mthad: |pThad|+|ETe(pTm)|+|mis.ET| > 55 GeV:
(3p)
|pThad|+|ETe(pTm)|+|mis.ET| > 45(50)GeV: (1p) tmthad(tethad)
・tetm:
|ETe|+|pTm| > 30 GeV

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MSSM Higgs →ττ
Backgrounds
and
observed events
mvis distribution
mvis = invariant mass of
the visible t decay products
and missing ET
No signal evidence for
mA = 90 – 250 GeV/c2
mA = 160 GeV/c2
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MSSM Higgs →ττ
Observed and expected limits at 95% CL
Results
Excluded region in tan b vs mA
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Search for SUSY
• Squarks and Gluinos
• Charginos + Neutralinos:
like-sign dilepton, trilepton
• R-parity violation:
multi-lepton, stop, sneutrino
• GMSB: long-lived neutralinos (decays to photon
and gravitino)
• Rare decays and stable particles:
Bs and Bd →mm, long-lived particles
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Chargino – Neutralino production
~
χ1 ~
χ 20 production at hadron colliders
leptonic decay of ~
χ1 and ~
χ 20
(~
χ10 is LSP and undetected )
Multi-lepton (trilepton, like-sign dilepton) is a strong tool!
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Chargino – Neutralino production
Event selection and backgrounds
Trilepton
 isolated three e/m, isolated two e/m and one track
pT1, pT2, pT3,trk (GeV/c) = (20,8,5), (20,5,5), (15,5,4), (5,5,5)
low-p
high-pT
T
 missing ET > 15 GeV
 reject Mass window: M < 20 GeV/c2, 76< M < 106 GeV/c2
 Dominant backgrounds – dibosons, Drell-Yan+conversion
Like-sign dilepton
 Pair of same charge e/m
 isolated two e/m with ET(pT) > 20 GeV, 10 GeV
 Missing ET > 15 GeV
 Z veto ( 66 < M < 116 GeV/c2)
 Dominant backgrounds – Drell-Yan, diboson, W/Z+1jet
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Chargino – Neutralino production
Results of event selections
trilepton
# of observed events
are consistent with SM
expectations
Like-sign dilepton
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Chargino – Neutralino production
SUSY scenarios for this analyses
(1) mSUGRA:
five free parameters (M0, M1/2, A0, tanb, sign(m)),
~
χ10 is the LSP and CDM candidate.
parameters: M0 = 60 GeV/c2, A0 = 0, tanb = 3, m>0, 162 < M1/2 < 230 GeV/c2
(2) MSSM with no slepton mixing:
keep mSUGRA relations with slepton mixing off (diagonal terms of the mixing matrix
χ1 , ~
χ 20 to e/m
to zero in Softsusy). → enhances the BR of ~
χ 2 ) ~ M(~
χ1 ) ~ 2M(~
χ1 )
parameters: tan β  3, μ  0, M(~
0

0
(3) MSSM with W/Z decay: keep the relation in below in the MSSM framework.
parameters: M(~
χ1 )  M(~
χ 20 )  2M(~
χ10 )
Br( ~
χ 20    ~
χ10 )  Br(Z 0    ) Br( ~
χ1  ν~
χ10 )  Br(W   )
Acceptance of high-pT sample
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Chargino – Neutralino production
The excluded cross section limit vs. chargino mass
mSUGRA
MSSM
no slepton mixing
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with W/Z decay
~
0
~
χ1  g G
GMSB (Gauge Mediated Supersymmetry Breaking models)
Neutralino can be have a long life(free parameter). The lightest neutralino is
NLSP. LSP is gravitino. NLSP decays to photons and missing ET(gravitino).
Feynman diagram for GMSB processes
The arrival time is different from
prompt g and decay g
Compare arrival time of photons
in the g+missing ET+jets events
Monte Carlo simulation
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~
0
~
χ1  g G
Dominant backgrounds

Data sample: 570pb-1
Collision photon:
W→e, g+jet+fake missing ET,
2jets+fake missing ET, jets fake g

Non-collision photon:
cosmic rays, beam effect
Selection criteria
 gID: ET > 30 GeV, |h|<1.1
 Missing ET > 40 GeV
 Jet ET > 35 GeV
 Df(missing ET, jet) > 1.0
 2.0 < tarrival < 10ns
 Cosmic rejection
 Collision fiducial
Mar.1
Observed : 2 events
# of backgrounds: 1.3±0.7
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~
0
~
χ1  g G
The expected and observed 95% C.L. cross section limit
The exclude region in
the neutralino lifetime
and mass space
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Technicolor
Technicolor model:
・ New interaction to induce spontaneous
symmetry breaking of the gauge theory.
・ At Tevatron energy, new particle (ρT) could
be produced.
pp  T  W p T0  bb
Search for W+2jet (b-tag) signature
Data sample: 955 pb-1
Mar.1
・ isolated e/μ with ET(pT) > 20 GeV
・ missing ET > 25 GeV
・ two jets with ET > 20GeV, |η| < 2.0
・ b-tag: one tag with NN, double tag w/o NN
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Technicolor
Dataset agree with B.G.
1 tag w/ NN
2 tag w/o NN
Backgrounds:
・ W/Z + heavy flavors
・ tt production
・ diboson production
・ Non-W QCD
・ mistag
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b’b’ → bZbZ → bbqq
Event selection
・ At least one pair of e/μ with pT>20 GeV
・ Z mass window 81 < M < 101 GeV
・ # of jets (with ET>30 GeV, |η| <2) ≧ 3
Search for new particle
decaying to Z0
Target range of b’
150 < mb’ < 350 GeV
→ b’ quark may have
a large branching ratio
to bZ0
Data sample: 1055 pb-1
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Backgrounds:
・ Z0 + jets
・ Diboson (WZ, ZZ) + jets
・ tt + jets
・ QCD multi-jet
b’b’ → bZbZ → bbqq
Data compared to the Z0+jets B.G
(J30T = scalar sum of ET’s of all jets)
No significant excess
Set cross section limit
mb’ > 270 GeV
( BR(b’→ bZ0) = 100 % )
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summary
• Tevatron and CDF are working well.
• CDF has collected the over 2fb-1 data
• CDF has been exploring the new
phenomena using ~ 1fb-1 data.
• Please expect the interesting results of
the new particles searches at summer
conference.
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Backup slides
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By A. Anastassov
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Expected 95% C.L limits
Run same likelihood procedure using
“pseudoexperiments”
i.
Replace Nobs in each channel with a Poisson fluctuated value with mean
equal to the total expected background.
ii. Replace the kinematic distribution with one randomly constructed from the
above Poisson number, and the total background distribution.
iii. Replace the Gaussian constrained background values in the likelihood
function with a Gaussian fluctuated value with mean equal to that
background value. The error are left the same.
iv. Repeat many times.
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