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TTeruki KamonFor the CMS Collaboration

Mitchell Institute for Fundamental Physics and AstronomyTexas A&M University

&Department of Physics

Kyungpook National University

Ninth Particle Physics Phenomenology Workshop (PPP9)National Central University (NCU), Taiwan, June 3 ~ June 6, 2011

SUSY Searches at CMSJJune 2011 11

Searches at CMS

SummaryOUTLINE3

1) Why? … Dark Matter and SUSY2) Where? … LHC & CMS Detector3) How? … SUSY Searches

PrologueIt has been 13.8 B years, sincethe LHC machine was set up. Themachine finally started providingproton-proton collisions at acenter-of-mass energy of 7 TeVon March 30, 2010 and becamethe energy frontier machine tolead discoveries of new particles.The Standard Model (SM) iscurrently well tested up to ~100GeV, but is expected to breakdown in the TeV domain wherenew physics should occur. This isprecisely the domain that we willstudy at the LHC.

SSUSY Searches at CMSTTeruki Kamon 22

~0.0000001 seconds

Now

CMB

Teruki KKamon

annihilation

combination

LHC

http://www.damtp.cam.ac.uk/user/gr/public/bb_history.html

Dark Matter and SUSY

Probing 10-7 sec. after Big Bang

SUSY Searches at CMS 33

LHC at CERN

27 km ring

Teruki Kamon 44SUSY Searches at CMS

The CMS (21 m x 15 m x 15 m, 12,500 tonnes) is one of two super-fast & super-sensitive detectors,consisting of 15 heavy elements, collecting debris from the collision and converting a visualimage for us. “Particle” Telescope at CERN vs. Hubble Space Telescope in outer space

Compact Muon Solenoid & PF

TTeruki Kamon 55SSUSY Searches at CMS

(see Appendix A)

As of May 31

�Fully hadronic searches:– SUS-10-003 (arXiv:1101.1628, PLB698 (2011) 196) & SUS-11-001: ��T

– SUS-10-011: MET + b-jets + �T

– SUS-10-005: inclusive MET + 3jets– SUS-10-009: Inclusive search with “Razor” variables

�Searches with leptons: – SUS-10-006: MET + jets + single lepton– SUS-10-004 (arXiv:1104.3169): MET + jets + LS dilepton– SUS-10-007 (arXiv:1103.1348, JHEP): MET + jets + OS dilepton.– SUS-10-008: Multileptons– SUS-10-010 & SUS-11-012(~200 pb-1): MET + jets + Z

�Searches with photons: – SUS-10-002 (arXiv:1103.0953, PRL): MET + jets + photons– SUS-11-002 (arXiv:1105.3152): MET + photon + lepton


CMS SUSY Searches in 2010UURL: https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResultsSUS

EExxaammppllee:: SSUUSSYYg~g~ , q~g~ , or q~q~ production will be dominant, followed

by their decays (e.g., 02��~qq~� ). �� JJeettss

R parity conservation � Stable lightest supersymmetric particle (LSP)

� If LSP is the lightest neutralino ( 01��~ ),

� it will escape the detector �� MMEETT (( TE�� ))� 0

1~�� = Cold Dark Matter candidate �� CCoossmmoollooggyy

� Thus, the evidence of SUSY-like new physics will appearin the Jets+MET final states.

CCoossmmoollooggyy �� LLHHCC= [Exciting Motivation]��[Right Place&Timing]

Missing ET(& Jets) at the LHC

MET - inferring new physics (e.g., Dark Matter)Teruki Kamon 77SUSY Searches at CMS


http://cdsweb.cern.ch/record/1343076/files/SUS-10-005-pas.pdf

�“All hadronic inclusive” analysis with key variables:– HT = scalar sum of Jet pT (selecting large s-hat production)– MHT = negative vector sum of Jet pT

�Baseline Event selection: – HT Trigger– 3 jet with pT > 50 GeV & |�| < 2.5 (central production)

– Veto events with isolated electrons & muons (suppress EWK background)

– �(MHT, Jet1,2,3) > (0.5, 0.5, 0.3) (reduce QCD background)– HT > 300 GeV & MHT > 150 GeV � baseline selection

�Final Event Selection: – High HT (HT > 500 GeV): High eff. for signals with long cascade

decay chains– High MHT (MHT > 250 GeV): High background rejection


Analysis Strategy

Baseline selectionw/o MHT cut

Baseline selection

HHT > 300 GeV & MMHT > 150 GeV An out-of-box comparison of Data vs MC for HT and MHT

Baseline Selection

High HTHigh MHT

>150 GeV

>300 GeVMajor BGs:� Invisible Z(�) +

Jets .. Irreduciblebackground

� Top / W + Jets� QCD Jets

Data-driven BG Estimate


0,0,10tan,250,60]1[

0

2/10

��

GeV GeV LM

Amm

Invisible Z

� Three different methods using boson+jets were employed to obtainthe data-driven estimates of this background (substitute boson withMHT)

� Cross check of different channels: “photon + jets” provides anaccurate prediction (Appendix B) � Solely used for limit calculation

remove�� -��

�+

remove�

removeW-

��WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW ��

�-_

– Similar to Z+jets at largepT (MHT)

– High stat (no branchingratio)

– Similar event topology– Higher stat than Z�

(W+jets rate is about x 2.5of Z+jets)

– Lower statistics than �and W

– Suffer fromBr(Z��) / Br(Z�)=1/6


�� MMET /

MHT


Invisible Z

– FRAG : Correct for fragmentation photons based on JETPHOX– PUR : Correct for photons from light mesons using shower shape

2 1

1 2

jetsdatadatadata/MCMC

Reco MC

jets)Z(data NPURIDFRAG

jetsjets)Z(

N ��

��

��

��

Leptons failing the lepton veto contribute tobackground. There can be 3 reasons to loseleptons:

� the lepton is not reconstructed

� not isolated

� out of acceptance


W �l W/Top

MMET /MMHT

[Step 1] Start with a control sample of eventswith exactly one muon and measure theidentification and isolation (in)efficienciesfrom data

[Step 2] Scale the control sample accordingto the measured (in)efficiencies from data

[Step 1] Start with a muon+jets sample

[Step 2] Replace the muon by tau response template derived from MC

[Step 3] Recalculate HT and MHT including this expected energy from tau

[Step 4] Correct for

– muon acceptance

– Trigger efficiency, Reco efficiency

– BR(W�� )/BR(W��)* BR(��hadrons)


W/Top

Jet

MET /MHTIdeal Reality

QCDT /

Significant pT imbalance due to� Physics effects: semi-leptonic decay of heavy

flavor quarks� Detector effects:� Intrinsic jet energy resolution� Dead channels (a significant contribution from ECAL)

Balanced multijet Response functions Smearing

[Step 0] Jet response and resolution functions using � + jets and dijetevents


[Step 1] Rebalance the data events (jets with pT > 10 GeV) using jet pTresolutions by maximizing a likelihood (LJets), being subject toconstraint MHT = 0 � create the pseudo-particle-level QCD events

[Step 2] Smear rebalanced jets (pT > 10 GeV) with resolution functions

� R+S predicts full event kinematics (jet pT and angular distributions)� Consistent with “Factorization Method” (extrapolate two-variable

correlation to signal region)Teruki Kamon 116SUSY Searches at CMS

QCD: Rebalance + Smearing

Baseline selection w/o MHT cut Baseline selection

MHT HT HT

MHT >150 GeV

No excess of observed events over expected StandardModel prediction. Setting limits.


Results


� MMHT = 693 GeV & HT = 1132 GeV� MMeff = MHT + HT = 1.83 TeV� NNo b-tagged jet & No isolated lepton � IIncompatible with W or top mass� IInvisible Z???

For Future Excitement

HT

MHT

00,10tan

25060]1[

0

2/1

0

��

�

GeV

GeV LM

Amm

� Gluino masses up to ~700 GeV are excluded. Less sensitive to tan��(see Appendix C)� Sensitivity greater than ATLAS at high m0. High HT search region was effective.� Sensitivity lower than ATLAS at high m1/2. Need to look at 2 jet events� See Appendix D for Simplified Model (currently only �3 jets)


Within the mSUGRA/cMSSM

10tan �

� 44 parameters and a sign: m0, m1/2, tan�, A0, sign(�)– mm0: common mass for “spin 0” particles at the GUT scale

– mm1/2: common mass for “spin 1/2” particles at the GUT scale

10tan �

� CHALLENGE: All hadronicinclusive search iscomplete at the samepace as other searches.

� ROBUST data-driventechniques for all SUSYsearches in 36 pb-1 in2010

� GOOD agreement withthe SM predictions

� HOT: ~1 fb-1/month. Bigexcitement in 2011 &2012


Summary

• Cross-section limits 0.5 – 30 pb,excluding m(gluino) < 700 GeV inthe mSUGRA/cMSSM plane.

0,0,10tan,250,60]1[

0

2/10

��

GeV GeV LM

Amm


Personal Remarks

Excluded by1) Rare B decay b�� s�2) No CDM candidate3) Muon magnetic moment

abc

CDMS II

Rouzbeh Allahverdi, Bhaskar Dutta, Yudi SantosoarXiv:0912.4329

Teruki Kamon

Remark 1: MET + Jets + Taus

Stau - neutralino co-annihilation scenario (e.g., Arnowitt, Dutta, Gurrola, Kamon, Krislock, Toback, PRL100 (2008) 231802)

SSUSY Searches at CMS 222

Remark 2: Bs ��

Teruki Kamon SSUSY Searches at CMS 223

jbWbWjttpp )()( ��

jj �ljjjjWpp ��

�l

Remark 3: MET + Jets + W’sBi-Event Subtraction Technique (hep-ph/1104.2508)

B. Dutta, T. Kamon, N. Kolev, A. Krislock

Teruki Kamon SUSY Searches at CMS

�

24

BEST: “jet” mixingfrom two different events

(TTbar, TTbar), (TTbar,W), (W,W)

BEST in TTbar & SUSY

mjj mbW

mjW

mjjTeruki Kamon SSUSY Searches at CMS 225

SummaryInterconnection between Particle Physics and Cosmology

PPC 2011 at CERN, June 14-18PPC 2012 at ???


Remark 4: PPC

CSI: Supersymmetry

at the LHCCollider Scene Investigation

“Simplified” Grand Summary

LHC – keep going!TTeruki Kamon 227SSUSY Searches at CMS

Appendix A: CMS Detector & PF

228SSUSY Searches at CMS

� In this search, all physics objects (jets, leptons, HT, MHT etc) are reconstructed with the PF algorithm.

� Basic idea:– Reconstruct and identify all different types of particles– Apply corresponding calibrations– The list of “particles” is given to the jet clustering and missing ET

(MET) reconstruction algorithm


Particle Flow (PF) Algorithm

CCharged hadrons~65% of jet energy

Use the high resolution tracker~1% at 100 GeV

Teruki Kamon SSUSY Searches at CMS

PPhotons~25% of jet energy

Use high resolution / good granularity ECALGranularity: 0.02 (��)Energy resolution: ~2%/�E


NNeutral hadrons~10% of jet energy

Use HCALGranularity: 0.1 (��)Energy resolution: ~100%/�E


Jet:Charged hadron (solid)Photon (dashed line)Neutral hadron (dotted line)

Particles clustered in jets

TTeruki Kamon SSUSY Searches at CMS

� PPF algorithm improves the performance of jet and missingET reconstruction significantly.

Calorimeter jet

PF jetJet energyresponse

Calorimeter jet

PF jet


PF Jet and MET Performance

Jet energyresolution

� Baseline selection:

� Consistent with photons and with simulation.� Z � from photon results best precision: therefore solely used

for limit calculation

� Method using leptonic W samples

� Method using leptonic Z samples

HLTRECOIsoW ��

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where

,


Appendix B: Invisible Z

4.121(17

)12(32)(1310

168

2918

!�

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��

��

:Sim) Z

:Combined

: eeZ

� Less sensitive to tan��


Appendix C: Large tan� Case

50tan �10tan �

Low tan� vs. High tan�

� Focus on topology instead of underlying physics model (physics is not understood anyway)

� Provide ability to characterize data in model-independent and more comprehensive ways

– Provide intuitive guidance for investigation– Allow one to factorize the key elements potentially present in a

new signal in order to answer specific questions.

� Set limit on cross section (�.Br)� Any model with same topology (parent particle mass,

decay chain, duaghters mass) can be “easily” compared with experimental results.


Appendix D: Simplified Model

m(gluino) – m(LSP) m(squark) – m(LSP)


Within Simplified Model

Appendix E:Old Limits on mSUGRA/cMSSM

4 parameters and a sign: m0, m1/2, tan�, A0, sign(�)m0: common mass for “spin 0” particles at the GUT scale

m1/2: common mass for “spin 1/2” particles at the GUT scale

339

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