Study of the Higgs boson particle in associate production with … · Francesco Micheli Sapienza Università di Roma-INFN Roma 1 The Higgs Boson 2 • Fundamental ingredient of Standard

Study of the Higgs boson particle in associate production with

vector bosons and top quarks at the CMS Experiment

Francesco Micheli

Supervisor: Dr. Paolo Meridiani

Francesco Micheli Sapienza Università di Roma-INFN Roma 1

The Higgs Boson

2

• Fundamental ingredient of Standard Model theory

• Evidence of a new boson with 125 GeV/c2 mass compatible with SM

• Result reported by both ATLAS and CMS experiments

• Observation only a starting point to establish the Higgs properties

• Is it really the Standard Model Higgs?• How many Higgs bosons?

• Spin?

• Couplings to fermions and bosons?

Higgs&discovery&

[1]&ATLAS&Collabora@on,&Observa@on&of&a&new&par@cle&in&the&search&for&the&Standard&Model&Higgs&boson&with&the&ATLAS&detector&at&the&LHC,&Phys.&Lea.&B&716&(2012)&1–29,&arXiv:1207.7214&[hepKex].&&[2]&CMS&Collabora@on,&Observa@on&of&a&new&boson&at&a&mass&of&125&GeV&with&the&CMS&experiment&at&the&LHC,&Phys.&Lea.&B&716&(2012)&30–61,&arXiv:1207.7235&[hepKex].&

4th&July&2012,&ATLAS&[1]&and&CMS&[2]&collabora@ons&announced&the&observa@on&of&a&new&par@cle.&

ATLAS'channels'7&+&8&TeV&&(4.8&mK1&7&TeV&and&5.8&mK1&8&TeV)&:&

•  H&→&γγ;&•  H&→&ZZ&→&4l;&•  H&→&WW&→&lν&lν.&

24/01/2013& A.&Gabrielli&K&INFN&K&Università&di&Roma&"Sapienza"& 7&


The Higgs Boson

3

• Fundamental ingredient of Standard Model theory

• Evidence of a new boson with 125 GeV/c2 mass compatible with SM

• Result reported by both ATLAS and CMS experiments

• Observation only a starting point to establish the Higgs properties

• Is it really the Standard Model Higgs?• How many Higgs bosons?

• Spin?

• Couplings to fermions and bosons?

Higgs&discovery&

[1]&ATLAS&Collabora@on,&Observa@on&of&a&new&par@cle&in&the&search&for&the&Standard&Model&Higgs&boson&with&the&ATLAS&detector&at&the&LHC,&Phys.&Lea.&B&716&(2012)&1–29,&arXiv:1207.7214&[hepKex].&&[2]&CMS&Collabora@on,&Observa@on&of&a&new&boson&at&a&mass&of&125&GeV&with&the&CMS&experiment&at&the&LHC,&Phys.&Lea.&B&716&(2012)&30–61,&arXiv:1207.7235&[hepKex].&

4th&July&2012,&ATLAS&[1]&and&CMS&[2]&collabora@ons&announced&the&observa@on&of&a&new&par@cle.&

ATLAS'channels'7&+&8&TeV&&(4.8&mK1&7&TeV&and&5.8&mK1&8&TeV)&:&

•  H&→&γγ;&•  H&→&ZZ&→&4l;&•  H&→&WW&→&lν&lν.&

24/01/2013& A.&Gabrielli&K&INFN&K&Università&di&Roma&"Sapienza"& 7&


Higgs production mechanisms

4

[GeV] HM80 100 200 300 400 1000

H+X

) [pb

]

→(p

p σ

-210

-110

1

10

210= 8 TeVs

LHC

HIG

GS

XS W

G 2

012

H (NNLO+NNLL QCD + NLO EW)

→pp

qqH (NNLO QCD + NLO EW)

→pp

WH (NNLO QCD + NLO EW)

→pp

ZH (NNLO QCD +NLO EW)

→pp

ttH (NLO QCD)

→pp

ggH

Associate production

VBF

σ : cross section → production probability

Different production mechanisms for Higgs @ LHC


[GeV] HM80 100 200 300 400 1000

H+X

) [pb

]

→(p

p σ

-210

-110

1

10

210= 8 TeVs

LHC

HIG

GS

XS W

G 2

012

H (NNLO+NNLL QCD + NLO EW)

→pp

qqH (NNLO QCD + NLO EW)

→pp

WH (NNLO QCD + NLO EW)

→pp

ZH (NNLO QCD +NLO EW)

→pp

ttH (NLO QCD)

→pp

Higgs production mechanisms

5

Higgs discovery driven by ggH (+VBF)

g

g

H

q

q

W/Z

H

q

q

ggH

Associate production

VBF

Now enough data collected! →associate production modes

Different production mechanisms for Higgs @ LHC

σ : cross section → production probability


Associate production modes

6

H

W

W

bq

q

l𝜈

b

Associated production (VH)Final state: Higgs + 2 jets

Top associated production (ttH)Final state: Higgs + jets and lepton(s)

t

t

q

q

W/Z

H

q

q

g

g

• Jets or leptons in the final state!• Very characteristic feature despite the low xsec

• Exclusive analysis in 𝜸𝜸 decay channel identifying these production modes

whereH➝γγ


Associate production modes

7

H

W

W

bq

q

l𝜈

b

tq

q

W/Zq

q

g

g

coupling Higgs-bosonscoupling Higgs-fermions

predicted by Standard Model

• N ~ couplings

• Considering these production modes:

• increase sensitivity to couplings measurement →data in agreement with SM?

tH

whereH➝γγ


Compact Muon Solenoid

8

• General purpose detector to fully reconstruct product decays• Detectable particles:

• Electrons, photons, muons, hadrons


VH events in CMS

9

ECALHCAL

q

q𝜸

𝜸

VH

What is peculiar?• Two jets coming from the W/Z

q

q

W/Z

q

q

H


VH events in CMS

10

VH

→Use of jet kinematic analysis

Dijet Mass

Dijet Mass is resonant

ECALHCAL

q

q𝜸

𝜸

What is peculiar?• Two jets coming from the W/Z

W/Z

q

q

H

q

q


ttH events in CMS

11

ECALHCAL

q

𝜸

𝜸

q

e

b

b

ttH

What is peculiar?

• Many energetic jets in the final state

H

W

b

q

q

l𝜈b

t

t

g

g


ttH events in CMS

12

ECALHCAL

q

𝜸

𝜸

q

e

b

b

ttH

→Look at number of jets

# jets

What is peculiar?• Many energetic jets in the final state

H

W

b

q

q

l𝜈b

t

t

g

g


ttH events in CMS

13

ECALHCAL

q

𝜸

𝜸

q

e

b

b

ttH

→Look at jet transverse momentum

pt 1st jet

What is peculiar?• Many energetic jets in the final state

H

W

b

q

q

l𝜈b

t

t

g

g


Why H→𝜸𝜸?

14

• Low branching ratio (decay probability)

• Very clean final state:

• Two high energy photons

• Well known Background:

• Events with 𝜸𝜸 not coming from H


H→𝜸𝜸

15

July

4th 2

012

The

Sta

tus

of th

e H

iggs

Sea

rch

J.

Inca

ndel

a fo

r the

CM

S C

OLL

AB

OR

ATIO

N

Search%for%a%narrow%mass%peak%with%two%isolated%high%Et%photons%%

!  Blind%analysis%in%2012%!  ReVreco%2011%data%into%

unchanged%2011%analysis%

!  Background%MC%only%used%for%analysis%optimization,%ZV>ee%also%to%measure%%photon%efficiencies%and%resolution%with%data%

2012 8 TeV

34

• Two high energy clusters in ECAL

• ECAL: Homogeneous calorimeter PWO xtals

• Narrow peak over falling background distribution → ECAL energy resolution crucial!

• Energy seen by xtals NOT constant because of radiation (transparency loss)

• We should be sure to measure always the right energy to catch the Higgs peak!

• Laser System to monitor xtal behaviour

• First part of my PhD work: data driven calibration method (Energy Flow method)


Energy flow monitoring method

16

Paolo Meridiani

EB MONITORING AT XTAL LEVEL

7

Uncorrected energy

Corrected energy



17

Paolo Meridiani


7

Uncorrected energy

Corrected energy

Radiation → lower energy response

Recovery during inter-fills period

If narrow distribution→ OK for the narrow Higgs peak!


Paolo Meridiani


7


18

BAD

Paolo Meridiani


7

GOOD

Larger distribution

Corrections not working properly


Expected results and prospects

19

• Current amount of data: ~20fb-1 @ 8TeV, ~6 fb -1 @7 TeV

• Adding VH (had+lep), ttH production mechanism to ggH and VBF:

• 10% improvement on Higgs couplings measurement • We will understand if Higgs is really the Standard Model one. If not ...• Many theories beyond SM to verify.



20

T

g

qNew theories → new particles:

top heavy partners, composite Higgs...




q

t

t

H


t

t

HT

q

q


21

Final state: top, Higgs, jets

Very similar to this analysis!

New theories → new particles:

top heavy partners, composite Higgs...




g


Conclusions and road map

22

• 2012:• Efforts on ECAL calibration to fully exploit the detector

knowledge in H (➝𝛾𝛾) data analysis

• End 2012- Fall 2013:

• Full optimised analysis on VH/ttH (➝𝛾𝛾) production modes on the complete CMS dataset in the SM framework

• End 2013-2014:• Search for exotic scenarios with VB, top pairs and Higgs in the

final state

Documents

Study of the Higgs boson particle in associate production with … · Francesco Micheli Sapienza Università di Roma-INFN Roma 1 The Higgs Boson 2 • Fundamental ingredient of Standard