same sign dilepton events with jets and large missing transverse energy at the lhc with cms

Same sign dilepton events with jets and large missing transverse energy

at the LHC with CMS

Marc Weinberg

University of Wisconsin

Preliminary Examination

Apr 20, 2023 1Marc Weinberg, University of Wisconsin

Outline of talkn Introductionn The LHC and CMSn Kinematics and reconstructionn Searching for supersymmetry (SUSY)n SUSY signals in CMSn Summary and plans

2Marc Weinberg, University of Wisconsin

The Standard Model (SM)n Constituents of matter

u Quarks and leptonsu All fermions

n Force-mediating particlesu Photon, W and Z, gluonsu All bosons

n Higgs bosonu Gives mass to SM

particlesu Not yet discovered

n Tests and predictionsu Predicted: W and Z,

gluons, top and charm quarks

u EW sector of SM tested precisely

Marc Weinberg, University of Wisconsin 3

Problems with the SMn Dark matter

u All SM particles excluded as dark matter candidates!

n Hierarchy problemu From mW, mZ:

u From loop-order:

u Quadratically divergent correction!


Red = baryonic matter (from X-rays)Blue = total mass (from grav lensing)

2UV2

2

0

2

int

8

UV

f

ffH

f

dppFm

ffHL

scaleEW ~2Hm

Supersymmetryn Central idea: each boson paired with a fermion, each fermion paired with a boson

u Every SM particle has “superpartner” yet to be discoveredu SUSY must be broken symmetry

n R-parity: multiplicative quantum numberu u Devised to explain stability of proton

n Also:u Neutralinos: ; mixtures of neutral gauginosu Charginos: ; mixtures of charged gauginos


Particle Symbol Spin R-parity Super partner

Symbol Spin R-parity

Fermions quarks squarks

leptons sleptons

Bosons gluons gluino

photon photino

W Wino

B Bino

Higgs Higgsino

sLBRP

231

H

B

W

g

l

q

0

1

1

1

1

21

21

1

1

1

1

1

1

1

H

B

W

g

l

q

~

~

~

~

~

~

~

21

21

21

21

21

0

0

1

1

1

1

1

1

1

04

01

~,,~ 21

~,~

How SUSY helps the SMn Predicts TeV scale

superpartnersu Solves hierarchy problem:

makes EW scale Higgs reasonable

u Fermion loop gives negative sign

u All quadratically divergent terms cancel!

n R-parityu Conserved in many models:

forces stable lightest supersymmetric particle (LSP)

u Neutral LSP is dark matter candidate!

n Precise gauge coupling unification

u Unification approximate in SM


2UV2

2

2

int

8

q

H

qq

m

qqHL

2UV2

~2

22~

~

int

16

~

qH

qq

m

qHL

q q~

)1(U

)2(SU

)3(SU

Searching for SUSYn Missing ET

u R-parity conserving models: LSPs pair produced

u Stable LSPs carry energy out

n Jetsu Decays of colored

superpartnersu production expected

to be dominant

n Leptonsu Can be same signu Decays ofu Produced in later stages

of decay chainMarc Weinberg, University of Wisconsin 7

gq ~ ,~

l~ ,~ ,~ 0

Why same sign dileptons?n SM ss dilepton backgrounds are small

u QCD; heavy flavor production, neutral B mixingu Top production; semi-leptonic t and b decaysu Electroweak single boson + jets

l Hadron in jet fakes electron or decays into muonu Electroweak diboson + jets

n SUSY sources of same sign dileptonsu Gluino-gluino: Majorana particle—equal probability of

positive/negative charged lepton in decayu Squark-squark: charge correlated with proton valence quarksu Other superpartner pairs: gluino-squark, chargino-squark, etc.

n Other non-SM sources of same sign dileptonsu Little Higgs models u Universal extra dimensions (UED)


How do we look for new physics?

n The Large Hadron Collideru 27 kilometer

ring near Geneva, Switzerland

u Proton-proton collisions

u 7 TeV / beam


LHC collisions


TeV 14s• 7x higher than Tevatron •Search for new massive particles up to m ~ 5 TeV

1234design scm 10 L

• 102x higher than Tevatron• Search for rare processes with small σ (N = Lσ)

ns 25spacingBunch

Experiments at the LHC


Compact Muon Solenoid


Size of CMS


CMS magnet


• High magnetic field in tracker: axial magnetic field of 4T• Field bends charged particles• Tracking resolution depends on

• Put EM calorimeter and hadronic calorimeter inside solenoid• Largest solenoid on Earth: 6 m diameter, stores 2.5 GJ energy

lB d

CMS tracker


• Precise measurement of trajectories of charged particles• Coverage extends out to |η| < 2.5• Resolution:• Silicon pixel detectors used closest to interaction region•Silicon strip detectors used in barrel and endcaps

% 5.0TeV15 TTT ppp

Electromagnetic calorimeter


• Measures e/γ energy and position out to |η| < 3• ~ 76,000 lead tungstate (PbWO4)

crystals• Resolution: 2

222

%26.0MeV 124%83.2

EEE

Hadronic calorimeter


• Samples showers to measure their energy and position• Barrel / endcap region Resolution:

• Brass / scintillator layers• |η| < 3

• Forward region Resolution:• Steel plates / quartz fibers• 3 < |η| < 5

2

22

5.5%115

EE

2

22

11%280

EE

Muon system


• Identify muons, provide position information for track matching• Drift tube chambers in barrel out to |η| < 1.3• Cathode strip chambers in endcaps

• Wires / strips measure r / φ respectively• Coverage: 0.9 < |η| < 2.4

• Resistive plate chambers• Capture avalanche charge on metal strips• Coverage: |η| < 2.1

Particle identification at CMS


CMS trigger systemn Reduces 40 MHz beam

crossing with 1 GHz QCD events

n Level 1 (L1) triggeru Analyzes calorimeter and

muon information within 3 μsl Finds leptons, photons,

jets, and missing ET

l Reduces rate to 100 kHz

n High level trigger (HLT)u Offline-like algorithms of

progressive complexityl Better identify / measure

leptons, photons and jetsl Reduces rate to 100 Hz


Trigger rejection ~ 4 x 105

Level 1 triggern Information from

calorimeters and muon detectorsu Electron / photon

identificationu Muon identificationu Jet identificationu ET, global sums

n Highly complexu Trigger primitives: ~ 5,000

electronics boards of 7 typesu Regional / global: 45 crates,

630 boards, 32 board types

n Flexibleu Most algorithms implemented

in reprogrammable FPGAs


HFHF HCALHCAL ECALECAL RPCRPC CSCCSC DTDT

PatternPatternComparatorComparator

TriggerTrigger

RegionalRegionalCalorimeterCalorimeter

TriggerTrigger

4 4 4 4 4+4 4+4

4 4 (with MIP/ISO bits)(with MIP/ISO bits)

MIP+MIP+ISO bitsISO bits

e, J, Ee, J, ETT, H, HTT, E, ETTmissmiss

Calorimeter TriggerCalorimeter Trigger Muon TriggerMuon Trigger

max. 100 kHz L1 Accept

Global TriggerGlobal Trigger

Global Muon TriggerGlobal Muon Trigger

GlobalGlobalCalorimeterCalorimeter

TriggerTrigger

Local Local DT TriggerDT Trigger

Local Local CSC TriggerCSC Trigger

DT TrackDT TrackFinderFinder

CSC TrackCSC TrackFinderFinder

40 M

Hz

pip

elin

e, l

aten

cy <

3.2

s

HFHF HCALHCAL ECALECAL RPCRPC CSCCSC DTDT

PatternPatternComparatorComparator

TriggerTrigger

RegionalRegionalCalorimeterCalorimeter

TriggerTrigger

4 4 4 4 4+4 4+4

4 4 (with MIP/ISO bits)(with MIP/ISO bits)

MIP+MIP+ISO bitsISO bits

e, J, Ee, J, ETT, H, HTT, E, ETTmissmiss

Calorimeter TriggerCalorimeter Trigger Muon TriggerMuon Trigger

max. 100 kHz L1 Accept

Global TriggerGlobal Trigger

Global Muon TriggerGlobal Muon Trigger

GlobalGlobalCalorimeterCalorimeter

TriggerTrigger

Local Local DT TriggerDT Trigger

Local Local CSC TriggerCSC Trigger

DT TrackDT TrackFinderFinder

CSC TrackCSC TrackFinderFinder

40 M

Hz

pip

elin

e, l

aten

cy <

3.2

s

e/γ identification in L1 trigger


Muon identification in L1 triggern Link local track segments into distinct 3D muon tracks

u Reconstruction in η suppresses accelerator muons

n Measure pT, η and φ of muon candidates from reconstructed tracksu Provides independent measurement of muon momentum


Drift tubes Cathode strip chambers

Simulation of SUSYn Specific SUSY model studied

in analysis: minimal supergravity (mSUGRA)

n Five free parameters in mSUGRA

n Too many points in parameter space; need to pick one. For LM1:u m0 = 60 GeV

u m1/2 = 250 GeV

u tan β = 10u A0 = 0

u sign(μ): +

n High cross section:


mSUGRA cross section)pb 100at events 000,16(

pb 1601

LM1

Starting where the Tevatron leaves off

SUSY study work flow


SUSY spectrum (ISASUGRA 7.75)

Decay simulation (SDECAY

1.2)

Hadronization (PYTHIA 6.409)

Detector simulation (CMSSW GEANT)

Reconstruction (CMSSW RECO)

Analysis (CMSSW

ANALYSIS)

= steps performed for this analysis

= next steps

Selecting same sign dileptonsn mSUGRA assumptions:

u Same mass:u Same couplings to other particles

n Four different cases to consider:u Ordered by pT for:

u Previous studies only looked atl CMS Internal Note 2006/087

n Methodology:u Leptons ordered by decreasing pT

u If exists, choose same-sign pair with largest pT

u If two same-sign pairs found with opposite signs, choose lepton pair with largest scalar sum of pT


, , , eeee

~~ mme

Signal identification strategyStart with LM1 same sign dileptons; pT

l1, pTl2 > 5 GeV, |η| < 2.4 (17% of total σ)

Nevt = 2.9K events at Lint = 100 pb-1

Requirement Justification

Leptons

all leptons pT ≥ 10 GeVQCD background lepton pT spectrum

falls more steeply than signal

Isol1 ≤ 10 GeV, Isol2 ≤ 6 GeV QCD background leptons produced in jets; not isolated

Jets

njets ≥ 3 with |η| ≤ 5, ET ≥ 50 GeV EW diboson background events have low jet multiplicity

ETj1 ≥ 175 GeV, ET

j2 ≥ 130 GeV, ET

j3 ≥ 55 GeVSUSY events have more

energetic jets than background

Missing ET

ETmiss ≥ 200 GeV SUSY characterized by large

MET due to neutral LSPsMarc Weinberg, University of Wisconsin 27

Generator lepton pT


Require both ss leptons pT > 10 GeV

Events shown require both ss leptons pT > 5 GeV

Generator lepton isolation


Require next-to-leading ss lepton Iso < 6 GeV

Require leading ss lepton Iso < 10 GeV

Isolation parameter: pT sum of particles within ΔR < 0.3 of lepton

Generator jet multiplicity


Require ≥ 3 jets

All jets shown: ET > 50 GeV

Reduce EW boson backgrounds

Generator jet ET


Require next-to-next-to-leading jet ET > 55 GeV

Require next-to-leading jet ET > 130 GeV

Require leading jet ET > 175 GeV

Generator missing ET


Require missing ET > 200 GeV

e.g. prev. study

QCD

ss 2μ

Signal identificationStart with LM1 same sign dileptons; pT

l1, pTl2 > 5 GeV, |η| < 2.4 (17% of total σ)

Nevt = 2.9K events at Lint = 100 pb-1

Requirement Justification Events surviving

Leptons

all leptons pT ≥ 10 GeVQCD lepton pT spectrum falls

more steeply than signal1.6K (55%)

Isol1 ≤ 10 GeV, Isol2 ≤ 6 GeV QCD background leptons produced in jets; not isolated

190 (6.7%)

Jets

njets ≥ 3 with |η| ≤ 5, pT ≥ 50 GeV

EW diboson background events have low jet multiplicity

22 (0.77%)

ETj1 ≥ 175 GeV, ET

j2 ≥ 130 GeV, ET

j3 ≥ 55 GeVSUSY events have more

energetic jets than background21 (0.73%)

Missing ET

ETmiss ≥ 200 GeV SUSY characterized by large

MET due to neutral LSPs12 (0.41%)


Previous study of ss dimuons only


• Study: CMS Internal Note 2006/087• Same sign dimuons only

• Plot: missing ET

• SM events (shaded area) and LM1 (solid line)• Done for integrated luminosity 10 fb-1

• Table: number of events passing requirements• SM backgrounds and LM1• Note: missing ET powerful discriminator

Results from previousss dimuon study


CMS reach for same sign dimuons at different luminosities

Summary / future plansn Same sign dilepton signal

u Likely discovery channel for new physicsu Significant reduction of SM backgroundsu Wide range of mSUGRA parameter points can be detected with

100 pb-1 luminosity

n Future Monte Carlo studiesu Produce fully reconstructed signal datau Compare with MC backgroundsu Refine selection criteria for dilepton pairsu Optimize requirements for low luminosities

n Work on regional calorimeter trigger: lepton/jet identification vital to analysis

n Prepare to take real data at CMS


Extra slides


Jet identification in L1 trigger

n Jet ET

u 12 x 12 trigger tower ET sums in 4 x 4 region steps with central region > others

u Larger trigger towers in HF but ~ same jet region size, 1.5 η x 1.0 φn Output

u Top 4 jets in central rapidity and top 4 jets in forward rapidity


max 4 x 4 region

same sign dilepton events with jets and large missing transverse energy at the lhc with cms

Documents

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grav lensingmarc weinberg

sm particlesnot

bosonevery sm particle

nonsm sources

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