INSTITUT FUR EXPERIMENTELLE KERNPHYSIK

Search for H to bb in association with single top quarks as a test of Higgs

boson couplingsHiggs Hunting 2015, OrsaySimon Fink for the CMS Collaboration | 30.07.2015

KIT – University of the State of Baden-Wurttemberg and

National Laboratory of the Helmholtz Association

www.kit.edu

Introduction

search for associatedproduction of Single Top Quarkswith Higgs Bosons decaying toBottom Quarks

public result: HIG-14-015

very small production crosssection

[GeV]HM120 122 124 126 128 130 132

H +

X)

[pb]

→(p

p σ

-210

-110

1

10

H (NNLO + NNLL QCD + NLO EBW)→pp

qqH (NNLO QCD + NLO EW)→pp

WH (NNLO QCD + NLO EW)→pp

ZH (NNLO QCD + NLO EW)→pp

ttH (NLO QCD)→pp

= 8 TeVs

tHq (NLO QCD)→pp

M. Farina et al., JHEP 1305 (2013) 022

Why even bother searching?

Simon Fink tHq, H → bb 30.07.2015 2/10

Introduction

two feynman diagram for the tHq production

qq′

bt

H

t

W

qq′

bt

H

W

W

destructive interference in SM

A ∝ (κV − κt)

with anomalous coupling (κt = −1)cross section increases to 234 fb

interference can increase production cross section by ∼ 13

Simon Fink tHq, H → bb 30.07.2015 3/10

Signal enriched phase

tHq reconstruction ttbar reconstruction

tHq variables ttbar variables global variables

final MVA discriminatortHq vs. backgrounds

fit on MVA output

Simon Fink tHq, H → bb 30.07.2015 4/10

Event Selection

event topology:4 b quarks1 isolated lepton1 light forward jet

q

g

q′

b

b

b

b

`+

ν

W

b

tH

W

3 tag signal region3 b-tags CSVT

# jets ≥ 4exactly onemuon/electron

4 tag signal region4 b-tags CSVT

# jets ≥ 5exactly onemuon/electron

tt control region2 b-tags CSVT

# jets = 4

Simon Fink tHq, H → bb 30.07.2015 5/10

Event Selection

event topology:4 b quarks1 isolated lepton1 light forward jet

3 tag signal region3 b-tags CSVT

# jets ≥ 4exactly onemuon/electron

4 tag signal region4 b-tags CSVT

# jets ≥ 5exactly onemuon/electron

S/B3 tag region ∼ 0.7% (13/1900 events)4 tag region ∼ 2.1% (1.4/66 events)

Simon Fink tHq, H → bb 30.07.2015 5/10

Reconstruction using MVAsjet assignment ambiguous⇒ MVA criteria to reconstruct events!

training on signal MCcorrect interpretation: all fourquarks matched to a jet

wrong interpretations: all otherpossible jet assignmentstrain MVA to discriminate betweencorrect and wrong interpretations

kinematic variablesb-tagging informationangular correlations

MVA response-0.5 0.0 0.5 1.0

Arb

itrar

y un

its

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14Event interpretation

correct exam wrong examcorrect train wrong train

Simulation Preliminary CMS 8 TeV

application to unknown eventsreconstruct all interpretations

take the one with largest MVA response

Simon Fink tHq, H → bb 30.07.2015 6/10

Event Interpretation

provide each event with two interpretations

under tHq hypothesis

e.g. |η(light jet)|

(light jet)|η|0 1 2 3 4 5

Eve

nts

/ Bin

wid

th

0

500

1000Data

=-1t

tHq, y+btt

b+btt+1,2ctt+LFtttt/

ttHEWK50x tHq

PreliminaryCMS

(8 TeV)-120 fb

Muon channel3T region

=125 GeVHm

(light jet)|η|0 1 2 3 4 5

MC

Dat

a-M

C

-0.50

0.5

under tt hypothesis

e.g. m(thad)

hadtlog m

4.5 5 5.5 6

Eve

nts

0

100

200

300

Data=-1

ttHq, y

+bttb+btt

+1,2ctt+LFtttt/

ttHEWK50x tHq

PreliminaryCMS

(8 TeV)-120 fb

Muon channel3T region

=125 GeVHm

hadtlog m

4.5 5 5.5 6

MC

Dat

a-M

C

-0.50

0.5

Simon Fink tHq, H → bb 30.07.2015 7/10

Classification MVA

use eight different variables in MVA obtained under different hypotheses4 tHq variables 3 tt variables 1 global variable

simultaneous fit in all four signal channelsconsider all relevant systematics

tt + heavy flavor templates are determined in situ assuming large uncertaintieslargest impact from Q2 scale and jet energy scale

0 0.5 1

Eve

nts

0

100

200

300

Data=-1

ttHq, y+btt

b+btt+1,2ctt+LFtt

tSingle t/ttHDibosonW+Jetsstat.+sys.50x tHq

PreliminaryCMS

(8 TeV)-120 fb

Muon channel3T region

=125 GeVHm

MVA output0 0.5 1

MC

Dat

a-M

C

-0.50

0.5stat.+sys. 0 0.5 1

Eve

nts

0

5

10

Data=-1

ttHq, y+btt

b+btt+1,2ctt+LFtt

tSingle t/ttHDibosonW+Jetsstat.+sys.20x tHq

PreliminaryCMS

(8 TeV)-120 fb

Muon channel4T region

=125 GeVHm

MVA output0 0.5 1

MC

Dat

a-M

C

-101

stat.+sys.

Simon Fink tHq, H → bb 30.07.2015 8/10

Limits

set limits on tHq withH→ bb and κt = −1

exclude production crosssection larger than 1.77 pbat 95% C.L.

observation agrees well withb-only and s+b hypotheses (S/B)

10log

-7 -6 -5 -4 -3 -2 -1

Eve

nts

-110

1

10

210

310

410

(8 TeV)-120 fb

=125 GeVH

)q, mbtH(b

Preliminary)µ3T+4T regions (e+CMS

Data=-1ttHq, y

All bkgs.Stat.+sys.

Expected Observed

Limit 5.14+2.14−1.44 7.57

Simon Fink tHq, H → bb 30.07.2015 9/10

Conclusions

presented search for tHq with H→ bb and κt = −1

excluded production cross section larger than 1.77 pb at 95% C.L.

results public under HIG-14-015

Outlookcombination paper with othertHq channels in the pipeline

looking forward to 13 TeVanalysis

Simon Fink tHq, H → bb 30.07.2015 10/10

Simon Fink tHq, H → bb 30.07.2015 11/10

Cross sections

cross section is challengingly smallthe main background is t t ; its cross section is provided for comparison

Cross-section 8 TeV 14 TeV

tHq, yt = +1 (SM) 18.3± 0.4 fb 88.2+1.7−0.0 fb

tHq, yt = −1 233.8+4.6−0.0 fb 980+30

−0 fb

t t 245+9−10 pb 950+40

−30 pb

tHq cross sections are cited according to M. Farina et al., JHEP 1305 (2013) 022

[arXiv:1211.3736]. Cross-sections for t t are calculated in M. Czakon, P. Fiedler, Phys. Rev.

Lett. 110 (2013) 252004 [arXiv:1303.6254]. Uncertainties are combined following R. Barlow,

arXiv:physics/0306138

Simon Fink tHq, H → bb 30.07.2015 12/10

Impact of uncertainty sources

Source Typeimpact as exclusive

source on final limit [%]improvement of final limit

after removal [%]JES shape 17 3JER shape < 1 < 1BTag light flavor shape 13 < 1BTag heavy flavor shape 17 < 1Pile up normalization < 1 < 1Unclustered energy shape 3 1Lepton efficiency normalization 5 < 1Luminosity normalization 10 < 1Cross section (PDF) normalization 8 < 1Cross section (Scale) normalization 9 < 1MC Bin-by-Bin unc. shape < 1 < 1Q2 scale (tHq + t t) shape 20 4Matching shape 2 2Top pT reweighting shape 19 2t t HF rates (b) normalization 13 < 1t t HF rates (bb) normalization 15 < 1t t HF rates (c / cc) normalization 13 1

Simon Fink tHq, H → bb 30.07.2015 13/10

tHq input variables

Simon Fink tHq, H → bb 30.07.2015 14/10

tt input variables

Simon Fink tHq, H → bb 30.07.2015 15/10

MVA input variables

Simon Fink tHq, H → bb 30.07.2015 16/10

post-fit electron channel

0 0.5 1

Eve

nts

0

100

200

Data=-1

ttHq, y+btt

b+btt+1,2ctt+LFtt

tSingle t/ttHDibosonW+Jetsstat.+sys.50x tHq

PreliminaryCMS

(8 TeV)-120 fb

Electron channel3T region

=125 GeVHm

MVA output0 0.5 1

MC

Dat

a-M

C

-0.50

0.5stat.+sys. 0 0.5 1

Eve

nts

0

5

10

Data=-1

ttHq, y+btt

b+btt+1,2ctt+LFtt

tSingle t/ttHDibosonW+Jetsstat.+sys.20x tHq

PreliminaryCMS

(8 TeV)-120 fb

Electron channel4T region

=125 GeVHm

MVA output0 0.5 1

MC

Dat

a-M

C

-101

stat.+sys.

Simon Fink tHq, H → bb 30.07.2015 17/10