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."


One of four major experiments at the LHC:"•  ATLAS"•  CMS"•  LHCb"•  ALICE"

CMS Detector at the LHC in Geneva, Switzerland

Introduction - CMS Detector

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."


•  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�

t¯tH Production

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"


Terminology:"•  Background: Uninteresting SM events that have

the same signature in the detector."•  Signal: Interesting events that"have the topology we’re looking"for."


Backgrounds:"•  W + jets"•  Z + jets"•  Single top"•  tt + jets"•  ttV + jets"•  VV"


Model used:"Sum of two Crystal Ball functions"each with tail to the right.""


P (x) = c1f1(x) + (1� c1)f2(x)

""""""•  Preliminary (more cuts are to be applied)"•  Include opposite flavor as well as same flavor"


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"



[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)"


•  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

BACKUP"

t¯tH Production

[GeV]HM100 150 200 250

BR

[pb]

× m

-410

-310

-210

-110

1

10

LHC

HIG

GS

XS W

G 2

012

= 8TeVs

µl = e, oi,µi,ei = i

q = udscb

bbi± lAWH

bb-l+ lAZH

b ttbAttH

-o+o AVBF H

-o+o

aa

qqi± lAWW

i-li+ lAWW

qq-l+ lAZZ

ii-l+ lAZZ -l+l-l+ lAZZ

h to ww razor analysis

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