Download - H to WW Razor Analysis
Razor Variable Search for a High-MassH ! WW in the Leptonic Final State
Georges Obied
August 22, 2013
Mentor: Prof. Maria SpiropuluCo-Mentor: Yi Chen
• Context and Introduction"– History"– CMS Detector"– Observation of a new
boson"– Current Questions"
• My Summer Project"– Production"– Analysis"
• Outlook"– Where are we going?"
H ! WW Razor Analysis
tt̄HH ! WW
• 1960: Jeffrey Goldstone shows that there would be massless particles when breaking a continuous symmetry"
• 1962: P. W. Anderson proposes nonrelativistic precursor to Higgs mechanism"
• 1964: Peter Higgs publishes a complete model of the ‘Higgs Mechanism’ predicting the existence of the Higgs boson."
Introduction - History
• 1967: Electroweak Unification based on "Higgs boson (Weinberg, Salam, Glashow)"• 1973 and 1983: Confirmations of electroweak
theory from CERN"• 1995: top quark discovered at Fermilab"... the Higgs boson is the only missing piece from the Standard Model"• July 4th, 2012: Higgs-like boson announced."
Introduction - History
One of four major experiments at the LHC:"• ATLAS"• CMS"• LHCb"• ALICE"
CMS Detector at the LHC in Geneva, Switzerland
Introduction - CMS Detector
Standard Model"• Describes 3 of 4 fundamental "forces:"– Strong, Weak, electromagnetic"
• Agrees with experiment to "high precision"• But it is incomplete…"
Introduction - Observation
• Announced July 4th, 2012"• Significance Level over 5σ"• Combined significance from two channels:"– γγ"– ZZ"
• Same observation made independently by ATLAS."
Introduction - Observation
• Properties of the discovered boson:"– Production cross-sections"– Branching ratios"– Spin parity"– Couplings to known particles"
• Verification whether the discovered boson is a SM Higgs"
Introduction - Current Questions
• Higgs production mechanisms:"– Gluon-gluon fusion (ggF)"– Vector Boson fusion (VBF)"– Associated W/Z Production (VH Production)"– Associated with top quark pair (ttH Production)"
t¯tH Production
Time
Motivation:"• Confirms Higgs coupling to top quark"• Allows direct, model independent measurement
of the Higgs boson coupling to the top quark"• Essential to confirm consistency with the SM
Higgs"
t¯tH Production
Some terminology:"• Cross-section (σ): measure of how often a
process happens in a collision"• Luminosity (L): measure of the intensity of the
colliding beam"
• Integrated luminosity (Lint): measure of the amount of data we have"
t¯tH Production
dNdt = L� ) N =
RL�dt = Lint�
Produc'on cross-‐sec'ons for mH=125 GeV
ggF
VBF
VH
>H
t¯tH Production
Higgs Branching ra'os for mH=125 GeV
bb
gg
γγ
Zγ
WW
ZZ
4f
t¯tH Production
�tt̄H = 0.129pb�ggfusion = 19.3pb
N = �tt̄HLint ⇡ 2500
N ⇥BR(H ! ZZ)⇥ P (ZZ ! 4l) ⇡ 0.3
To get 50 events before selection we need:
Lint = 3⇥ 10
3fb�1
Motivation:"• Possibility of existence of higher mass Higgs-
like state"• Possibility that 125 GeV Higgs not related to
electroweak symmetry breaking"• Other scenarios feasible:"– Higgs multiplet models"– Higgs mixing with heavy "electroweak singlet"
H ! WW ! 2l2⌫ Razor Analysis
Razor Variables:"• Invented by researchers at Caltech, CERN,
Fermilab."• Invisible neutrinos give rise to missing energy"• Razor variables give sensitivity to mass scale of
original decaying particle"
H ! WW ! 2l2⌫ Razor Analysis
Terminology:"• Background: Uninteresting SM events that have
the same signature in the detector."• Signal: Interesting events that"have the topology we’re looking"for."
H ! WW ! 2l2⌫ Razor Analysis
Backgrounds:"• W + jets"• Z + jets"• Single top"• tt + jets"• ttV + jets"• VV"
H ! WW ! 2l2⌫ Razor Analysis
Model used:"Sum of two Crystal Ball functions"each with tail to the right.""
H ! WW ! 2l2⌫ Razor Analysis
P (x) = c1f1(x) + (1� c1)f2(x)
""""""• Preliminary (more cuts are to be applied)"• Include opposite flavor as well as same flavor"
H ! WW ! 2l2⌫ Razor Analysis
Similar analyses carried out previously:"• Evidence for a particle decaying to W+W- in the
fully leptonic final state in a SM Higgs boson search in pp collisions at the LHC. (CMS-PAS-HIG-13-003)"– Excludes Higgs in the range 128-600 GeV"
• Search for a standard-model-like Higgs boson with a mass in the range 145 to 1000 GeV at the LHC. (CMS-HIG-12-034)"– Excluded Higgs in the range 127-710 GeV"
H ! WW ! 2l2⌫ Razor Analysis
H ! WW ! 2l2⌫ Razor Analysis
[GeV]Hm
SMm/
m95
% C
.L. L
imit
on
-110
1
10
210
100 200 300 400 500 600
Observed
Median Expected
m 1±Expected
m 2±Expected
m 1±=125 GeV H
Injection m
CMS Preliminary-1=7 TeV, L = 4.9 fbs
-1=8 TeV, L = 19.5 fbs 0/1-jeti2l2AWWAH
Similar Razor Analyses:"• Search for the Higgs Boson in W+W- to 2l2ν in
pp collisions at 7 TeV with razor variables. (CMS internal note CMS AN AN-12-071)"– Excludes Higgs in the range 128-220 GeV"
• Higgs Boson Decaying to WW in the Leptonic Final State Measurement Using Razor Variables. (CMS internal note CMS AN AN-13-002)"
H ! WW ! 2l2⌫ Razor Analysis
• Analysis is to be continued…"• Hopefully discover a higher-mass Higgs-like
particle or extend the 95% CL exclusion range for a high mass Higgs."
Outlook
• Prof. Maria Spiropulu"• Yi Chen"• Emanuele Di Marco"• Cristian Pena"• Javier Duarte"• Alex Mott"
• Caltech SFP"
Acknowledgements