higgs boson studies at the tevatron in run iitrj/trj_aps_higgs.pdf · higgs br + total uncert 10-3...

Higgs Boson Studies at the Tevatron in Run II

Thomas R. Junk Fermilab

On Behalf of the CDF and D0 Collabora;ons

APS April Mee;ng, Denver, CO April 14, 2013

T. Junk Tevatron Higgs Results

•  The Tevatron, CDF, and D0 •  Higgs Boson Produc;on and Decay •  Highlights of Search Techniques – What we Learned •  Results: Limits, Cross Sec;ons, Significance •  Results: Couplings, BSM models

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T. Junk Tevatron Higgs Results 2

Fermilab from the Air

CDF D0

Chicago→

Main Injector – new for Run II pbar recycler – not used to recycle pbars but used as a second storage ring to accumulate pbars

Tevatron

!

pp Collisions at s =1.96 TeV

pbar accumulator

1 km

4/14/13

4/14/13 T. Junk Tevatron Higgs Results T. Junk Tevatron Measmnts and Disc. 3

The Tevatron, Like All Accelerators, Improved in Performance Over Time

Total delivered luminosity: ~12 W-‐1 each to CDF and D0. Acquired and analyzed: ~10 W-‐1 each.

Many thanks to the Fermilab Beams Division!


First CDF pp event: 1985 End of opera;ons: 2011

Lepton coverage: |η| < 1.5 (muons) |η| < 2.0 (electrons) b-‐tagging with |η| < ~1.4 Jets to |η| < 2.8 Higgs analyses restrict to |η| < 2.0 Dijet mass resoluMon: ~16%

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The Detector

New Innermost Silicon Layer added between Run IIa and Run IIb

Lepton coverage: |η| < 2 (muons) |η| < 2.6 (electrons) b-‐tagging with |η| < ~2 Jets to |η| < 3

Similar dijet mass resolu;on to CDF

Scin;lla;ng fiber tracker Trigger similar to CDF’s

Good Feature: Regular Switching of Solenoid Field – Cancels Some Systema;c Uncertain;es

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1

10

10 2

10 3

100 125 150 175 200 225 250 275 300mH [GeV]

(pp

H+X

) [fb]

Tevatrons=1.96 TeV

pp–H (NNLO+NNLL QCD + NLO EW)

pp–

WH (NNLO QCD + NLO EW)

pp–ZH (NNLO QCD + NLO EW)

pp– qqH (NNLO QCD + NLO EW)pp–tt–H (NLO QCD)

[GeV]HM100 200 300 400 500 1000

Higg

s BR

+ T

otal

Unc

ert

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LHC

HIG

GS

XS W

G 2

011

bb

cc

ttgg

Z

WW

ZZ

SM Higgs Boson Production and Decay Rates

Primary analysis modes: mH<130 GeV: VHàVbb mH>130 GeV: ggàHàWW

Addi;onal modes: Hàττ, Hàγγ, HàZZà4l

Gluon Fusion

Associated Produc;on

Vector Boson Fusion

t

t iH

T. Junk Tevatron Higgs Results 4/14/13


Tevatron Hàbb Publications, Summer 2012

CDF, D0, and Tevatron Publica;ons: CDF lvbb: Phys. Rev. Lei. 109, 111804 (2012) Includes new HOBIT b-‐tagger CDF llbb: Phys. Rev. Lei. 109, 111803 (2012) Includes new HOBIT b-‐tagger CDF METbb: Phys. Rev. Lei. 109, 111805 (2012) Uses old SECVTX+JetProb b-‐taggers CDF Combined Hàbb: Phys. Rev. Lei. 109, 111802 (2012) D0 lvbb: Phys. Rev. Lei. 109, 121804 (2012) D0 llbb: Phys. Rev. Lei. 109, 121803 (2012) D0 METbb: Phys. Lei. B 716, 285 (2012) D0 Combined Hàbb: Phys. Rev. Lei. 109, 121802 (2012) Tevatron Combined Hàbb: Phys. Rev. Lei. 109, 071804 (2012)

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Associated production VH

H

b

b!

l-

l

Jet

Jet

ν

l

ν

ν!

1)

2)

3)

V

Friday, November 9, 12

“lvbb”

“METbb” or “vvbb”

“llbb”

Drawing Credit: CMS Higgs TWiki. CDF also seeks qqHàqqbb and iHàibb

The Main Associated Production Search Channels

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Tevatron Hàbb Results, Summer 2012

Maximum local significance: 3.3σ at mH=135 GeV/c2 Global significance: 3.1σ – Evidence for VHàVbb. Local significance at mH=125 GeV/c2 is 2.8σ

Cross sec;on fit at mH=125 GeV/c2

(!WH +! ZH )!B(H" bb ) = 0.23#0.080+0.090 (stat+syst) pb

SM Predic;on: 0.12 ± 0.01 pb

Phys. Rev. Lei. 109, 071804 (2012)

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Status from the LHC

A Higgs-‐like parMcle is firmly established, its mass looks to be between 125 and 126 GeV, and its properMes are consistent with the SM Higgs boson

Many more superb results are available at hips://twiki.cern.ch/twiki/bin/view/AtlasPublic/HiggsPublicResults hips://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsHIG


(as of HCP 2012)

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Recent Publications Contributing to the Final Higgs Combination

CDF: METbb: Phys. Rev. D 87, 052008 (2013). HWWàlvlv: PRD in prepara;on. FERMILAB-‐PUB-‐13-‐029-‐E All Hadronic final state: JHEP 1302, 004 (2013) iHàibb: Phys. Rev. Lei 109, 181802 (2012). SM/SM4/FP/Coupling Combina;on: arXiv:1301.6668 (2013). Submiied to Phys. Rev. D

D0: H/WH/ZHàleptons+tau+jets: arXiv:1211.6993. Accepted by Phys. Rev. D WH/ZH Trileptons and same-‐sign dileptons: arXiv:1302.5723 Submiied to Phys. Rev. D H/WH/ZHàlvbb+lvjj + lvjjjj: arXiv:1301.6122 Accepted by Phys. Rev. D HàDiphotons: arXiv:1301.5358 Accepted by Phys. Rev. D HàWWàlvlv: arXiv:1301.1243 Accepted by PRD SM/SM4/FP Combina;on: arXiv:1303.0823 Submiied to Phys. Rev. D

Tevatron Combina;on Manuscript: arXiv:1303.6346 Submiied to Phys. Rev. D

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All CDF SM Search Channels



All D0 SM Search Channels

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T. Junk Tevatron Higgs Results 14

B-‐Tagging

Mistag rates typically ~1% for light-flavor jets

Example candidate event (lvbb)

Impact parameter resolution for high-pT tracks ~18µm

L00 single-sided silicon + 5-layer double-sided silicon+ 2-layer ISL

B-‐tagging relies on displaced vertex reconstruc;on: high mass, long life;me

D0: Boosted Decision Treetagging algorithm. Per-jetefficiency = 50-70% (of taggablejets) for 1-5% Mistag rate

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CDF’s HOBIT b-tagger – Improved Sensitivity With Respect to the SECVTX, Roma, and BNess taggers

HOBIT Tight and Loose opera;ng points chosen to have similar mistag rates as older SECVTX opera;ng points. More signal More b background Similar LF background

A neural-‐network b-‐tagger using inputs from other b-‐taggers, as well as lepton ID to include semileptonically decaying B hadrons.

J. Freeman et al., Nucl. Instrum. Methods A 697, 64 (2012). see also M. Stancari, Fermilab Joint Experimental/Theore;cal Seminar, Mar. 7 2012

OperaMng Point

Mistag rate

SECVTX efficiency

HOBIT efficiency

Tight 1.4% 39% 54%

Loose 2.9% 47% 59%

per-‐jet efficiencies shown

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q

q’

W* W

l

ν

H0 b

b

D0 Collab., PRL 109, 121804 (2012); D0 Collab., arXiv:1301.6122 [hep-‐ex]; CDF Collab., PRL 109, 111804 (2012)

Associated Production of a Higgs Boson with a W Boson

Double Tight Tag yields (D0) Expected signal: 17.3±1.7 events of WH (mH=125 GeV) 1.9±0.1 events of ZH (mH=125 GeV) Expected Background: 10404±1059 events Data 10071 events Expected limit @125: 4.7*SM (2.8*SM for CDF)

Dijet mass resolu;on: 13% to 23% depending on the number of jets and tags. 3-‐jet events or 1-‐tag events: more likely to misassign an ISR/FSR jet to the Higgs decay

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q

q

Z0* Z0

ν

ν

H0 b

b

Double Tight Tag yields (CDF) Signal (ZH) 1.9±0.3 events (mH=125 GeV) Background: 131±26 events Data: 117 Events Expected limit @125: 3.9*SM CDF, (5.1*SM for D0)

CDF Collab., PRL 109, 11803 (2012) D0 Collab., PRL 109, 121803 (2012)

ZHàllbb: A Fully Reconstructed Channel

125 GeV Final Discriminat 0 0.5 1

Even

ts/B

in

-210

-110

1

10

210 data Z+lf Z+bb Z+cc WW WZ ZZ tt fake ZZH(125)x10

+ Two Jets, Two Tight b-Tags -µ+µ

-1CDF Run II Prelimary 9.45 fbVery innova;ve channel! •  Loose lepton ID. Tag and probe lepton ID efficiency calibra;on in data •  Split into 2 jet, 3 jet, single, double, ;ght, and loose b-‐tags •  NN dijet mass using MET projec;ons •  Cascade of neural networks: Train networks to separate ibar, Diboson, Wbb backgrounds from signal.

Excellent reconstruc;on countered by low Zàll branching ra;o

“Raw” dijet mass

Dijet mass a}er NN Correc;on 12% resol. in some channels

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CDF Collab., PRL 109, 111805 (2012) Updated with HOBIT: PRD 87, 052008 (2013) D0 Collab., Phys. Lei. B 716, 285 (2012)

VHàMETbb Analysis

Cascade of neural networks: First an;-‐QCD, second Higgs vs. remaining backgrounds

Double-‐;ght tags, CDF yields: Signal (WH125): 5.3±0.5 Signal (ZH125): 5.4±0.5 Background: 759±86 Data: 692 Expected limit: 3.3*SM (3.9*SM for D0)

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HàWW Searches

D0 Collab., PRD 86, 032010 (2012) CDF Collab., FERMILAB-‐PUB-‐13-‐029-‐E (in prepara;on)

W-

W+ e+

e-

ν

ν

Largest signal is from gluon fusion, but WH, ZH, and VBF contribute as well.

Dominant background at the Tevatron is nonresonant WW produc;on

ΔRll tends to be smaller in signal events than for background events

But we split the samples into lvlv + 0j lvlv + 1j lvlv + 2 or more jets and the backgrounds vary by subsample.

H0

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0-jet DY-BDT-1 -0.6 -0.2 0.2 0.6 1

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310

410

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610

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Bkg. syst.

TE, ee + -1DØ, 9.7 fb

Signature: Two oppositely-‐signed leptons, large missing ET. Low ΔΦll, low ΔRll Large DY background in ee and μμ channels, not so much in eμ. DY has low missing ET, mll near mZ, and other characteris;cs. Recent improvements: •  Looser lepton ID •  low-‐mll channel, •  modify isola;on requirement so leptons don’t spoil each other’s isola;on. •  Split channels into more categories: Data calibra;on of lepton ID efficiency for new loose lepton categories. Control regions to validate backgrounds: DY, WW, Wγ, W+jets, ibar

HàWW Searches

DY BDT removes most of DY(+jets)

0-jet WW-depleted Final BDT0 0.2 0.4 0.6 0.8 1

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Bkg. syst.

TE, ee + -1DØ, 9.7 fb

WW-‐enriched WW-‐depleted

D0 Collab., arXiv:1301.1243 [hep-‐ex]

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Validation of HàWW Analysis by Measuring the WW Cross Section

Cross Section (pb)

TE, ll + -1DØ, 9.7 fb

5 10 15 20 25 30

eeWW 1.1 (syst)± 1.1 (stat) ±13.3

µµWW 0.7 (syst)± 0.9 (stat) ±11.5

µeWW 0.6 (syst)± 0.6 (stat) ±11.1

combinedWW 0.6 (syst)± 0.4 (stat) ±11.6

NLOWW 0.7±11.3

Campbell and Ellis, PRD 60, 113006 (1999)

(s/b)10

log-3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5

Even

ts

0

100

200

300

400 Data - BkgdSignal (WW)1 s.d. on Bkgd±

TE, ll + -1DØ, 9.7 fb

Same Selec;on, Similar MVA’s Measure WW cross sec;on of (1.02±0.06)*SM(MCFM v6.0)

D0 Collab., arXiv:1301.1243 [hep-‐ex]

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1

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Expe

cted

Lim

it/SM Summer 2005

Summer 2006Summer 2007Winter 2008Fall 2008

Fall 2009Summer 2010Summer 2011Winter 2012

mH=115 GeV/c2

SM=1

1

10

0 2 4 6 8 10 12 14Integrated Luminosity (fb-1)

Expe

cted

Lim

it/SM Summer 2004

Summer 2005Summer 2007Winter 2008Fall 2008

Spring 2009Fall 2009Summer 2010Summer 2011Winter 2012

mH=160 GeV/c2

SM=1

Sensitivity Evolution over Time

We collected data, and we also learned how to get more out of the data. •  Beier MVA’s •  Beier Event Selec;on •  Beier lepton ID •  Beier jet energy resolu;on •  More triggers •  More analysis categories •  Sharing improvements between analyses

CDF sensi;vi;es shown. D0’s sensi;vi;es are similar

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Tevatron Diboson Search in the Higgs Analyses

! (WZ + ZZ ) = 4.4± 0.3 pb

SM Predic;on:

Measurement:

! (WZ + ZZ ) = 3.0± 0.6 pb

A look at the summed mjj distribu;on


)2Dijet Mass (GeV/c0 50 100 150 200 250 300 350 400

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2=125 GeV/cHm

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Check of the VHàVbb channels using the WZ+ZZ signal as a standard candle

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SM Combined Data Summary at mH=125 GeV/c2

Background Hypothesis fit to data Bins of similar s/b added together Data error bars are sqrt(nobs)


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mH=125 GeV/c2

Tevatron Run II, Lint 10 fb-1

SM Higgs combination

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SM Combined Data Summary at mH=125 GeV/c2

Same as before, but fiied background subtracted from the data. Data error bars are sqrt(s+bfit)


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±1 s.d. on background


SM Higgs combination

mH=125 GeV/c2log10(s/b)

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H 1.5 (m× H

-1 10 fb intTevatron Run II, LSM Higgs Combination

Tevatron Combined SM LLR Distributions

LLR is a ra;o of the compa;bility of the data with the signal+background hypothesis and the background-‐only hypothesis. Data show a clear preference for a Higgs boson with mH between 115 and 140 GeV 4/14/13


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H 1.5 (m× H


August 2006

March 2013: Final

Tevatron Combined LLR Over the Years

Dec. 2007 Apr. 2008

4/14/13

Tevatron Final SM Higgs Rate and Mass Limits

Excluded regions: 90 < mH < 109 GeV/c2 and 149 < mH < 182 GeV/c2 Expect to exclude if no Higgs: 90 < mH < 120 GeV/c2 and 140 < mH < 184 GeV/c2


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SM Higgs combinationObservedExpected w/o HiggsExpected ±1 s.d.Expected ±2 s.d.Expected if mH=125 GeV/c2

SM=1

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Tevatron Combined SM Higgs Boson Search p-value

Observed local significance at mH=125 GeV/c2 is 3.1σ Expected significance assuming mH=125 GeV/c2 is shown with a doied line (not quite 2σ)

Look-‐Elsewhere Effect: •  mH~125 GeV has been firmly established by the LHC •  CDF+D0’s mass resolu;on is not very sharp -‐-‐ ~2 independent search results in Hàbb, ~2 in HàWW •  Technical challenge – MVA’s trained at each mH separately. Histograms of predic;ons exchanged. Would need to exchange correlated pseudoexperiments to compute LEE exactly.


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)2=125 GeV/cH

1.5 (m× H


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Best-Fit Tevatron Combined Cross Sections at mH=125 GeV/c2

H! !! : 5.97"3.12+3.39 #SMH!W +W " : 0.94"0.83

+0.85 #SM

H! ! +! " : 1.68"1.68+2.28 #SMVH!Vbb : 1.59"0.72

+0.69 #SM

Combined : 1.44!0.56+0.59 "SM


Br)/SM× Best Fit (0 1 2 3 4 5 6 7 8 9 10

b VbVH

-+ H

-W+ WH

H

2 = 125 GeV/cHm

Combined (68% C.L.)

Single channel

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±1 s.d.±2 s.d.

ObservedH x 1.5 (mH=125 GeV/c2)H x 1.0 (mH=125 GeV/c2)

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Final Tevatron Combined VHàVbb Cross Section Measurements

The SM predic;on is

! (WH + ZH )!Br(H" bb ) = 0.120± 0.008 fb

At mH=125 GeV/c2, the measured rate is

! (WH + ZH )!Br(H" bb ) = 0.19#0.09+0.08 pb

arXiv:1303.6346


! (WH + ZH )!Br(H" bb ) = 0.23#0.08+0.09 pb

at mH=125 GeV/c2

Phys. Rev. Lei. 109, 071804 (2012)

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H x 1.5 (mH=125 GeV/c2)

H x 1.0 (mH=125 GeV/c2)

The change is due to CDF’s updated METbb channel

4/14/13


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Tevatron Combined HàWW Searches

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Observed

H x 1.5(mH=125 GeV/c2)

H x 1.0(mH=125 GeV/c2)

4/14/13

Zoom-‐in at lower masses:


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SM H + - combination

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Expected w/o Higgs

Observed

Expected ±1 s.d.

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Tevatron Combined Hàτ+τ- and Hàγγ Searches

A bit of an excess (2σ at mH=125 GeV) seen in Hàγγ

4/14/13

Extensions to the SM: Fourth-Generation Models (SM4)

A heavy fourth genera;on of quarks would scale the gg→H produc;on rate at colliders by a factor of ~9. But watch out for H→ν4ν4 decays. E. Arik et al., Acta Phys. Polon. B 37, 2839 (hep-‐ph/0502050)

Kribs, Spannowsky, Plehn, Tait, Phys. Rev. D 76, 075016 (2007) T. Junk Tevatron Higgs Results 4/14/13

Searches for ggàHàWW – Model Independent and SM4 interpretation

SM4 Cross Sec;ons computed at NNLO in QCD by Anastasiou, Boughezal, and Furlan, JHEP 1006, 101 (2010)

Searches op;mized specifically for ggàH (NN’s not trained with WH, ZH, or VBF). Limit on cross sec;on ;mes b.r. shown along with SM4 model predic;ons.

Low-‐Mass scenario: ml4=100 GeV, mv4=80 GeV High-‐Mass scenario: ml4=mv4=1 TeV Both Scenarios: md4=400 GeV, mu4=450 GeV Note: mv4 lower bound is from L3’s unstable 4th genera;on neutrino search. P. Achard et al., PLB 517, 75 (2001). A stable v4 could be lighter. K. Belotsky et al., PRD 68, 054027 (2003).

Low-‐mass scenario exclusions: Expected exclusion: 118 < mH < 270 GeV/c2 Observed exclusion: 121 < mH < 225 GeV/c2


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Exp. 95% C.L. LimitObs. 95% C.L. Limit±1 s.d. Exp. Limit±2 s.d. Exp. LimitSM4 (low mass)SM4 (high mass)

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SM4(low mass)=1

Expected w/o HiggsObserved±1 s.d. Expected±2 s.d. ExpectedSM4 (high mass)

4/14/13

A Test of the Fermiophobic Higgs Model Model tested: Assume SM-‐like behavior for the Higgs boson, except switch off all couplings to fermions. Decays for Hàbb, Hàττ, and Hàgg are highly suppressed. ggàH produc;on is neglibly small. WH, ZH, VBF produc;on cross sec;ons are as predicted by the SM HàWW, ZZ par;al widths are as predicted by the SM. Hàγγ is modified – loss of the fermion loop increases the decay rate. Hàγγ search is re-‐op;mized for this search because the pT spectrum of the H is harder in WH and ZH than for ggàH Branching ra;os recomputed using the modified decay widths.

Included channels: Hàγγ, HàWW, HàZZà4l

Observed exclusion: 100 < mH< 116 GeV/c2 Expected exclsuion: 100 < mH< 135 GeV/c2


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Constraining the Couplings of the Higgs Boson to Fermions and Gauge Bosons

We follow the procedures and nota;on of the LHC Higgs Cross Sec;on WG A. David et al., arXiv:1209.0040

The model: SM-‐like, but Hff couplings are scaled together by κf HWW coupling is scaled by κW HZZ coupling is scaled by κZ For some studies, we scale the HWW and HZZ couplings by κW=κZ=κV Standard Model: κf = κW = κZ = 1


Step 1: Scale cross secMons for each process according to couplings

LO rela;ons, but mostly true at higher order (most QCD affects the colored ini;al-‐state par;cles. There is ggàWH at higher order, however.)

Constraining Couplings

! (gg!H ) =! SM (gg!H )(0.95" f2 + 0.05" f"V )

! (WH ) =! SM (WH )"V2

! (ZH ) =! SM (ZH )"V2

! (VBF) =! SM (VBF)"V2

A. David et al., LHCHXSWG-‐2012-‐001. arXiv:1209.0040


Step 2: Recompute all Higgs boson decay branching raMos from scaled parMal widths α and β come from Spira et al., arXiv:hep-‐ph/9504378 α=1.28 β = -‐0.28

Constraining Couplings

!(H" gg) = !SM (H" gg)(0.95! f2 + 0.05! f!V )

!(H"W +W # ) = !SM (H"W +W # )!V2

!(H" bb ) = !SM (H" bb )! f2

!(H" " +" # ) = !SM (H" " +" # )! f2

!(H" cc ) = !SM (H" cc )! f2

!(H" ZZ ) = !SM (H" ZZ )!V2

!(H" ## ) = !SM (H" ## )$!V +%! f2

Br(H! XX) = "(H! XX)"i

i#

Other modes, like Hàμ+μ-‐ and HàZγ have very small widths


Posterior Constraints on Coupling Scalings

•  Uniform priors assumed. •  Coupling scalings not shown are fixed to their SM values

Excess in the Hàγγ searches drives the asymmetry from posi;ve and nega;ve coupling scale factors


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Two-Dimensional Coupling Parameter Constraints


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The Tevatron sees an excess of events consistent in all decay channels with the SM-‐Higgs-‐like par;cle observed at the LHC near mH=125 GeV/c2. Significance: 3.1σ at mH=125 GeV/c2. The Higgs boson does not look like that of the Fermophobic model or the SM with a fourth genera;on. Higgs boson couplings to W, Z, and fermions are consistent with SM predic;ons Extrac;ng coupling informa;on from the data requires full predic;ons of signal rates and shapes in all discriminants of all channels. Channels that contribute liile to the total SM sensi;vity can have outsized impacts on exo;c coupling scenario tests.

Summary

4/14/13

higgs boson studies at the tevatron in run iitrj/trj_aps_higgs.pdf · higgs br + total uncert 10-3...

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