CDF実験のヒッグス粒子探索の結果
清矢 良浩(大阪市立大学高エネルギー物理学研究室)

物理学会，岡山大学津島キャンパス
２０１０年３月２０日

Outline
Standard Model and Higgs Boson
Tevatron and CDF Detector
SM Higgs Searches at CDF
Future Prospects
Conclusions

2

Standard Model and Higgs Boson

3

Standard Model Higgs Boson
Standard Model
Gauge theory: SU C (3) ⊗ SU L(2) ⊗U Y (1)Left (right) handed fermion =SUL(2) doublet (singlet)
Higgs boson
Elementary complex scalar
No color, SUL(2) doublet, Y = +1/2
Responsible for the spontaneous
breaking of the electroweak (EW)
gauge symmetry

V (φ )µ2 > 0Gauge boson masses

Physical state

T3 = −1/2, Y = +1/2, Q = 0Also assumed to generate fermion
massesNo experimental confirmationµ <02φ =v
φV (φ ) =1 2 2 1µ φ + λφ 4244

Status of SM Higgs
Indirect limit from global EW fit
mt = 173.1 ± 1.3 GeV/c2
mW = 80.399 ± 0.023 GeV/c2and precision EW measurements
at LEP and SLD

mH = 87+35−26 GeV/c2

Direct search at LEP

mH > 114.4 GeV/c2 (95% C.L.)
mH < 186 GeV/c2 (95% C.L.)

CDF and DØ are probing Higgs in
the most probable region :100 < MHH < 200 GeV/c225

Tevatron and CDF Detector

6Tevatron Accelerator
Proton-antiproton collider at √ s = 1.96 TeV
36×36 bunch, bunch space 396 ns
Np~10000e9, Npbar~3000e9, typical peak luminosity ~ 0.3 nb−1/s
Store duration ~ 12 hrs
Two major detectors at collision points : CDF and DØCDFD∅

Tevatron
Main Injector

Fermilab

7

Tevatron Luminosity Progress
Peak luminosity

Total and weekly delivered

3.5 × 1032 cm-2s-1

60 pb−1/week

2.5 × 1032 cm-2s-1

04/01/01~now

Weekly integrated : 50~60 pb-1
Integrated luminosity
Delivered : 8.2 fb-1
Acquired : 6.8 fb-1
Analyzed : 5.4 fb-1
8

Proton-Antiproton Collisions

9

CDF ExperimentIntegrated luminosity
1981.01
1984−85
1985.10
1987.01−87.05
1988.06−89.05
1990−92
1992.04−93.05
1993.12−95.08
1995.10−96.02−2000.Fall
2000.Fall−01.Spring
2001.03−

TDR
Beam tests
First collisions
Test run
Run 0
Beam tests
Run IaRun IbRun IcUpgradesComissionning
Run II

Collaboration size
87

~20 events
25 nb−1
4.4 pb−1

190√s = 1.8 TeV
19 pb−1
80 pb−1
7 pb−1358

106 pb−1~750 √s = 1.96 TeV
10CDF Detector

Calorimeters: projective tower geometry

11

CDF Detectory(Buffalo)xz(Village)(Hirise)Pseudo-rapidityθ⎞⎛η = − log⎜ tan ⎟⎝Calorimeters: projective tower geometry

2⎠

12

CDF Detector(m)3-level trigger system
Particle identification

Central region
η=0Photons
EM cluster w/o track

Plug region

Electrons
EM cluster w/o track

Muons

η=2
η=3

Muon detectors at theoutermost position

Neutrinosz(m)Proton beamTransverse

pT = p sin θ
ET = E sin θ

Heavy flavor quarks (b, c)

Impact parameter (d0)Momentum imbalance in thetransverse plane

QuarksJets (calorimeter clusters)

Taus
Narrow jets w/ 1 or 3 tracks

Identification = “tagging”
Displaced secondary decay vertex
Large impact parameter
Semileptonic decay
13

SM Higgs Searches at CDF

14

SM Higgs Production at the Tevatron(0.2~1.0 pb)(0.02~0.3 pb)(0.02~0.1 pb)~60% of Wh

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SM Higgs Production at the Tevatron(0.2~1.0 pb)~0.19 pb @ m=115(0.02~0.3 pb)~0.44 pb @ m=160~0.11 pb @ m=115(0.02~0.1 pb)~60% of Wh

16

Higgs Decays
Low mass ( < 140GeV/c2)
bb is dominant.
73% @ m=115

High mass ( > 140GeV/c2)
WW is dominant.
~92% @ m=160

17Search Channels

A = e, µHiggs production
and W/Z decays

Higgs decays
h→bbh→WW→(ℓν)(ℓν)

hToo large QCD BG

2ℓ (opposite-sign=OS) + missing ET

Wh→(ℓν)hℓ + missing ET + 2b

2ℓ (OS)/2ℓ (like-sign=LS)/3ℓ + missing ET

Zh → (νν)hMissing ET + 2b2ℓ (OS) + missing ET

2ℓ (OS) + 2b

Multilepton + missing ET

Too large QCD BG

2ℓ (OS) + missing ET→ (ℓℓ)hqqH

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CDF Papers of SM Higgs Searches

Run IRun II

Wh → (ℓν)(bb)

PRL 79, 3819

1997

109 pb−1

Vh → (jj)(bb)

PRL 81, 5748

1998

91 pb−1

Zh → (ℓℓ)(bb), (νν)(bb) PRL 95, 051801

2005

106 pb−1

Wh → (ℓν)(bb)

PRL 96, 081803

2006

320 pb−1

h→ WW

PRL 97, 081802

2006

360 pb−1

Wh → (ℓν)(bb)

PRL 100, 041801
PRD 78, 032008

2008
2008

1000 pb−11000 pb−1

Zh → (νν)(bb)

PRL 100, 211801

2008

1000 pb−1

Zh → (ℓℓ)(bb)

PRL 101, 251803

2008

1000 pb−1

h→ WW

PRL 102, 021802

2009

3000 pb−1

Wh → (ℓν)(bb)

PRD 80, 012002

2009

1900 pb−1

Wh → (ℓν)(bb)

PRL 103, 101802

2009

2700 pb−1

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Analysis Overview
Event selection
Trigger selection
Kinematical and geometrical acceptanceParticle identification
Topological selection

Efficiency and background estimation
ε = 0.2 ~ 2% from σ(h)⋅B(h→XX)∆ε/ε = 10~20%∆B/B = 10~20%

ResultLimit on the production cross section
Use distributions of some variables
Binned maximum likelihood method
Bayesian interpretation in most cases
20Analysis Overview
Bayesiane −µ µn,p (n | S , B ) =n!

µ = S + B = L (σ B F )ε + B

p (n obs | S , B ) → p (S , B | n obs )π (S , B )dSdB
Posterior probability density

p (S | n obs )dS =Marginalization

Prior probability density∫ dB p (S , B | nobs∫∫ dBdS p (S , B | n)π (S , B )obs)π (S , B )Nuisance parameter

21Analysis Overview
Bayesian 95% credibility limit

For illustration
Flat prior for S
Exact B (prior = δ function)
Poisson~Gaussian,S << B, nobs=B
Posterior function− (S + B )ne(S+B)(Normalization = 1/0.5)n!

~12π (S + B )Gaussian 2.5%~

12π Bee1 ⎛ n −S − B ⎞− ⎜⎟2 ⎝ S +B ⎠1⎛ S ⎞− ⎜⎟2⎝ B ⎠

22Gaussian 2.5% =1.96σ~2σ→ S95 ~ 2√B
S95/S ~ 2√B/S22

Analysis Overview
For distributions∏ p (n | S , B )i = biniii

Combining different channels⎛⎞⎜ ∏ p (n i | Si , Bi ) ⎟ π (B )⎝ i =channel⎠
Common (correlated) nuisanceparameters23(1) Wh→(ℓν)(bb), 2006
L = 320 pb−1
High pT inclusive lepton trigger
Lepton + 2j + missing ET signature≥1b tagging
Secondary vertex
Semileptonic decay w/ large d0S(m=115) ~ 2 fb, B ~ 550 fb
W+bb dominant
S/√B/√L~0.09

Mbb distribution for limits
b jet specific energy correction
1b ⊕ 2b (independent likelihood)
Expected limit ~ 6 pb (m=115)
ε ~ 1.5%, B ~ 175
S95 ~ 6×320×0.015 ~ 29 ev
29/√175 ~ 2.2

Expected limit• Frequentist view
• BG-only pseudo-experiments → limits (median)24

(1) h→WW, 2006
360 pb−1Triggers
High pT inclusive lepton trigger
Plug electrons + missing ET trigger

Plug electrons
Topological cut

Drell-Yan veto
Mℓℓ>16 GeV (cc/bb resonance veto)Mℓℓ<mh-5 GeV
Large missing ET
Fake missing ET veto (Z→ττ veto)

Jet veto (tt veto)S(m=160) ~ 1.6 fb, B ~ 39 fb
WW dominantS/√B/√L~0.26−ν∆φℓℓ distribution for limits
ℓ−W−H

ν

W+ℓ+25

(2) Wh→(ℓν)(bb), 2008

L = 1 fb−1
Neural net (NN) b tagging+5% improve1b ⊕ 2b+20% improve

S(m=115) ~ 2.1 fb, B ~ 440 fb
S/√B/√L~0.10 (cf. 0.09)

26

(1) Zh→(νν)(bb), 2008
L = 1 fb−1
Missing ET trigger
Include missing lepton + bb from Wh
2 or 3 jets
≥1b tag
Mbb distribution for limits
Introduction of control regions (CR)Check of ε and BG estimation
Calibration of ε and BG
CR in this analysis

1b2bCR1 = Multijet signatureCR2 = One lepton

S(m=115) ~ 1.6 fb, B ~ 260 fb
QCD (fake missing ET) dominant
S/√B/√L~0.10
Sensitivity (νν)(bb) ~ (ℓν)(bb)27

(1) Zh→(ℓℓ)(bb), 2008
L = 1 fb−1
Higi pT inclusive lepton trigger
Added plug electrons as the 2ndlepton
NN jet energy correction
Mass resolution 18% → 11%

1b ⊕ 2b
2D NN outputs for limits
Zh vs. Zbb
Zh vs. tt

S(m=115) ~ 0.81 fb, B ~ 110 fb
S/√B/√L~0.08 ( Run I ~ 0.10)
Worse than Run I
But expected limit is ~ 4 timesbetter than L scaling28

(2) h→WW, 20093 fb−1More lepton categories
MIP tracks
Isolated tracks passing detector cracks

Matrix-element-based probability (ME)G G G
G
1 dσ LO Gp (x obs ) =εyGx()(Gobs , y )dy∫dyσ
ME Efficiency Detector
responseHigh S/B ⊕ Low S/B
NN for limits
S(m=160) ~ 3.9 fb, B ~ 260 fb
S/√B/√L~0.24 (cf. 0.26)
Expected limit ~50% improvement otherthan L scaling29

(2) h→WW, 2009
Central e
Plug eIsolated tracks

Central mu
Extension mu

Central MIP
Plug MIP
Isolated tracks

30

(3) Wh→(ℓν)(bb), 2009

L = 1.9 fb−1
Added missing ET + plug electron trigger
Added plug electrons
Add d0-based b-tagging
NN for limits
S(m=115) ~ 2.3 fb, B ~ 660 fb
S/√B/√L~0.09 (cf. 0.10)
Expected limit ~ 40% improvement31

(4) Wh→(ℓν)(bb), 2009
L = 2.7 fb−1
Added missing ET + 2j trigger
Isolated tracks as leptons
30% acceptance gain

ME→BDT
15% sensitivity gain

NN + MEBDT → NN (Superdiscriminant)
15% sensitivity gain

S(m=115) ~ 3.2 fb, B ~ 820 fb
S/√B/√L~0.11 (cf. 0.09)
Expected limit ~ 50% improvement

10 times SM higgs (m=115)32

(2) Zh→(νν)(bb), now

L = 3.6 fb−1
Missing pT to reduce QCD
Added d0-based b tagging
Two staged NN
QCD rejection
Other BG

33

(2) Zh→(νν)(bb), now

For MHH = 115 GeV/c22 w/ 3.6 fb-1-1
Expected limit : 4.2 × σSM
SM
Observed limit : 6.1 × σSM
SM

S(m=115) ~ 3.4 fb, B = 810 fB
S/√B/√L~0.12 (cf. 0.10)~70% improvement34(5) Wh→(ℓν)(bb), now
Two analyses to be combined
NNMENNL = 4.3 fb−1
Not much new things
Bayesian NN
S(m=115) ~ 3.2 fb, B ~ 930 fb
S/√B/√L~0.11

ME
L = 4.8 fb−1
Not much new things
Added 3 jets
2j ⊕ 3j
S(m=115) ~ 3.9 fb, B ~ 1200 fb
S/√B/√L~0.1135

(5) Wh→(ℓν)(bb), now
Neural Nets
(2 jets, double tag)

Matrix Element(2 jets, double tags)

MH = 115 GeV/c2

Expected limit

Observed limit

Luminosity

CDF (NN)

4.0 × σSM

5.3 × σSM

4.3 fb-1CDF (ME)

3.8 × σSM

3.3 × σSM

4.8 fb-1
36

(2) Zh→(ℓℓ)(bb), now
4.1 fb−1
Added the trackless trigger≥2jHigh S/B ⊕ low S/B
Isolated tracks

b-taggingNN-based filter
d0-based tagger

ME → 2D NN

Dijet mass37

(2) Zh→(ℓℓ)(bb), now
For MHH = 115 GeV/c22 w/ 4.1 fb-1-1
Expected limit : 6.8 × σSM
SM
Observed limit : 5.9 × σSM
SM
S(m=115) ~ 0.88 fb, B ~ 140 fb
S/√B/√L~0.07 (cf. 0.08)+16% improvement38(3) h→WW, now
4.8 fb−10j ⊕ 1j ⊕ ≥2j
ME-NN for 0j
Added Vh, qqh
Lowered Mℓℓ cut
Likelihood electron ID
NN for each sub-sample

39

(3) h→WW, now
For MHH = 165 GeV/c22 w/ 4.8 fb-1-1
Expected limit : 1.21 × σSM
SM
Observed limit : 1.23 × σSM
SM
S(m=160) ~ 6.6 fb, B ~ 360 fb
S/√B/√L~0.35 (cf. 0.24)+44% improvement40

CDF SM Higgs Combination
CDF combined results with L = 2.0 - 4.8 fb-1
Included channels
WH → ℓνbb (4.3 fb-1)
VH → E/ T + bb (3.6 fb-1)ZH → ℓℓbb (4.1 fb-1)
VH, VBF, ggH→ 2 jets + ττ (2.0 fb-1)
VH → 2 jets + bb (2.0 fb-1)
ggH → WW* → ℓνℓν (4.8 fb-1)
VH → VWW* (4.8 fb-1)
ForFor M
MHH == 115
115 GeV/cGeV/c22
Expected
Expected limit
limit :: 2.38
2.38 ×× σσSMSM
Observed
Observed limit
limit :: 3.12
3.12 ×× σσSMSMFor
For M
MHH == 165
165 GeV/cGeV/c22
Expected
Expected limit
limit :: 1.19
1.19 ×× σσSMSM
Observed
limit:1.18×σObserved limit : 1.18 × σSM
SM41

Tevatron SM Higgs Combination
Combined results of CDF and DØ with L = 2.0 – 5.4 fb-1
¾ Systematics correlation b/w experiments are taken into account.

Observed
Observed (expected)(expected) limit
limit at
at M
MHH == 115
115 GeV/c
GeV/c22 :: 2.70
2.70 (1.78)(1.78) ×× σσSMSM
22
Excluded
Excluded mass
mass range
range at
at 95%
95% C.L.
C.L. :: 163
163 -- 166
166 GeV/c
GeV/c(Expected(Expected exclusion
exclusion rangerangearXiv:0911.3930[hep-ex]:: 159159 –– 168
168 GeV/cGeV/c22 ))as of November 200942

Future Prospects

43

Luminosity Prospects
Tevatron performance and projection
We expect ~ 9 fb-1 by the end of FY10.
If FY11 budget is approved, we can go up to ~12 fb-1.
1212 fb
fb-1-1 delivereddelivered luminosity
luminosity doubles
doublesthethe current
current data
data set
set andand results
results inin-1
analysisanalysis withwith 10
10 fb
fb-1..
We are here~ 12 fb-1

9.3 fb-1
7.8 fb-1

44

SM Higgs Sensitivity Prospects
For MH = 115 GeV/c2

For MH = 160 GeV/c2

Analysis improvements help the sensitivity increase better than 1/sqrt(L).
Expect to reach 115GeV Higgs with 6~10 fb-1

45

SM Higgs Sensitivity Prospects

If CDF and D∅ analyze 7 fb−1 each,mh < 180 GeV/c2 would all be excluded if not there
46

Conclusions
Tevatron and the CDF detector are performing very well.
Delivered 8.2 fb-1, Acquired 6.8 fb-1, Analyzed 5.4 fb-1
Expect ~ 9 fb-1 by the end of FY10¾ We all thank accelerator people for excellent beam !

SM Higgs searches are in progress in various production and decaychannels.
Increasing luminosity, analysis improvements, …
We can go further !

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Backup Slides

48

Spring 2009 Result49

Multivariate Techniques
Both experiments use advanced multivariate techniques, which combine
information from kinematical, topological and particle identification variables,
to enhance the signal/background discrimination.
Artificial
Artificial Neural
NeuralNetworks
Networks (NN)
(NN)

Single variable discriminant

Boosted
Boosted Decision
Decision
Trees
Trees (BDT)(BDT)

MatrixMatrix Element
Element (ME)(ME)
Calculating event probability
integrating the LO matrix elements

Neural network output

50

Higgs Bosons Beyond the SM51

MSSM Higgs at the Tevatron
Two-Higgs-doublet fields provide
5 physical Higgs bosons.
3 neutral : φ = h, H, A
2 charged : H±
¾ Phenomenology described attree level by tanβ and MA.

Neutral Higgs
Coupling to d-type quarks
enhanced by tanβ ⇒ σ φ ∝ tan2βBr(φ → ττ) ~10%, Br(φ → bb)~90% for low and intermediatemasses

Charged Higgs
For (MH+ < Mt – Mb), a top quark
can decay into H±b.

TotalAHhMSSM: tanβ = 30

Tevatron
Tevatron has
has sensitivity
sensitivity forforsomesome MSSM
MSSM scenarios.
scenarios.

52

MSSM Neutral Higgs : φ → τ+τ−gg, bb → φ → ττgluon fusion

bb fusion

Tau pairs are identified in τeτµ,τeτhad, and τµτhad.
Background :
••

Model
independentlimit

Z → ττ, Z → ee/µµ
Diboson, tt, W + jets

Combined CDF and DØ results
Interpretation to typical
MSSM scenario :Maximal stop mixingµ = −200GeV53

MSSM Neutral Higgs : φb → bbb
gb → φb → bbb

Required 3 b-tagged jets.
Large multijet backgroundSearch for peak in dijet mass
CDF : 1.9 fb-1, DØ : 2.6 fb-1

54

MSSM Charged Higgs
Search for H± in top decayst → H ±b
• H± → cs (for small tanβ)• H± → τν (for large tanβ)τ + lepton

dileptonℓ + jets, 2tagℓ + jets, 1 tag

If H± exists, there would be deviationfrom the SM prediction for the final
states of tt decay.

Dijet mass

Consistent with SM55Fermiophobic Higgs
In some BSM models, Higgs couplings
to fermions are suppressed.
⇒ Higgs decays to vector bosons are
significantly increased.
Low mass region : H → γγHigh mass region : H → WW/ZZ

Benchmark scenario
No fermion couplings and SM couplings tovector boson

56