Kinematics of Top Decays in the Dilepton and the Lepton + Jets channels: Probing the Top Mass
Same sign dilepton events with jets and large missing transverse energy at the LHC with CMS
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Transcript of Same sign dilepton events with jets and large missing transverse energy at the LHC with CMS
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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
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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
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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
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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!
Marc Weinberg, University of Wisconsin 4
Red = baryonic matter (from X-rays)Blue = total mass (from grav lensing)
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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
Marc Weinberg, University of Wisconsin 5
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
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1
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B
W
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q
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21
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~,,~ 21
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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
Marc Weinberg, University of Wisconsin 6
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)1(U
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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
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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)
Marc Weinberg, University of Wisconsin 8
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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
Marc Weinberg, University of Wisconsin 9
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LHC collisions
Marc Weinberg, University of Wisconsin 10
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
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Experiments at the LHC
Marc Weinberg, University of Wisconsin 11
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Compact Muon Solenoid
Marc Weinberg, University of Wisconsin 12
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Size of CMS
Marc Weinberg, University of Wisconsin 13
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CMS magnet
Marc Weinberg, University of Wisconsin 14
• 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
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CMS tracker
Marc Weinberg, University of Wisconsin 15
• 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
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Electromagnetic calorimeter
Marc Weinberg, University of Wisconsin 16
• 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
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Hadronic calorimeter
Marc Weinberg, University of Wisconsin 17
• 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
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Muon system
Marc Weinberg, University of Wisconsin 18
• 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
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Particle identification at CMS
Marc Weinberg, University of Wisconsin 19
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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
Marc Weinberg, University of Wisconsin 20
Trigger rejection ~ 4 x 105
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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
Marc Weinberg, University of Wisconsin 21
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
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e/γ identification in L1 trigger
Marc Weinberg, University of Wisconsin 22
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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
Marc Weinberg, University of Wisconsin 23
Drift tubes Cathode strip chambers
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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:
Marc Weinberg, University of Wisconsin 24
mSUGRA cross section)pb 100at events 000,16(
pb 1601
LM1
Starting where the Tevatron leaves off
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SUSY study work flow
Marc Weinberg, University of Wisconsin 25
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
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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
Marc Weinberg, University of Wisconsin 26
, , , eeee
~~ mme
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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
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Generator lepton pT
Marc Weinberg, University of Wisconsin 28
Require both ss leptons pT > 10 GeV
Events shown require both ss leptons pT > 5 GeV
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Generator lepton isolation
Marc Weinberg, University of Wisconsin 29
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
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Generator jet multiplicity
Marc Weinberg, University of Wisconsin 30
Require ≥ 3 jets
All jets shown: ET > 50 GeV
Reduce EW boson backgrounds
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Generator jet ET
Marc Weinberg, University of Wisconsin 31
Require next-to-next-to-leading jet ET > 55 GeV
Require next-to-leading jet ET > 130 GeV
Require leading jet ET > 175 GeV
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Generator missing ET
Marc Weinberg, University of Wisconsin 32
Require missing ET > 200 GeV
e.g. prev. study
QCD
ss 2μ
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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%)
Marc Weinberg, University of Wisconsin 33
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Previous study of ss dimuons only
Marc Weinberg, University of Wisconsin 34
• 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
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Results from previousss dimuon study
Marc Weinberg, University of Wisconsin 35
CMS reach for same sign dimuons at different luminosities
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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
Marc Weinberg, University of Wisconsin 36
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Extra slides
Marc Weinberg, University of Wisconsin 37
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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
Marc Weinberg, University of Wisconsin 38
max 4 x 4 region