study of the higgs boson particle in associate production with … · francesco micheli sapienza...
TRANSCRIPT
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&
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
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&
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
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
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
[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
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
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
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
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
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
Compact Muon Solenoid
8
• General purpose detector to fully reconstruct product decays• Detectable particles:
• Electrons, photons, muons, hadrons
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
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
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
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
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
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
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
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
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
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
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
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
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
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)
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
Energy flow monitoring method
16
Paolo Meridiani
EB MONITORING AT XTAL LEVEL
7
Uncorrected energy
Corrected energy
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
Energy flow monitoring method
17
Paolo Meridiani
EB MONITORING AT XTAL LEVEL
7
Uncorrected energy
Corrected energy
Radiation → lower energy response
Recovery during inter-fills period
If narrow distribution→ OK for the narrow Higgs peak!
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
Paolo Meridiani
EB MONITORING AT XTAL LEVEL
7
Energy flow monitoring method
18
BAD
Paolo Meridiani
EB MONITORING AT XTAL LEVEL
7
GOOD
Larger distribution
Corrections not working properly
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
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.
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
Expected results and prospects
20
T
g
qNew theories → new particles:
top heavy partners, composite Higgs...
• 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.
q
t
t
H
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
t
t
HT
q
q
Expected results and prospects
21
Final state: top, Higgs, jets
Very similar to this analysis!
New theories → new particles:
top heavy partners, composite Higgs...
• 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.
g
Francesco Micheli Sapienza Università di Roma-INFN Roma 1
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