Searches for Physics Beyond the Standard Model CMS - TTUslee/HCP2010/HCP2010_LEE.pdf · Sungwon Lee...

Sungwon Lee Physics at LHC 2006, Cracow 1

Sung-Won Lee Texas Tech University

for the CMS Collaboration

Searches for Physics Beyond the Standard Model @ CMS

Hadron Collider Physics Symposium, HCP-2010, Toronto, Canada Aug. 23~27, 2010

The Standard Model has been enormously successful, but it

Many theories/models attempt to address these issues.

What can be (non-SUSY) BSM? Many possibilities !

Extended Gauge Symmetries, Dynamical EWSB, Extra Dimensions, Compositeness, etc… (see next slide)

The Standard Model of particle physics is a description of the known particles and their interactions

leaves many important questions unanswered:

What is the origin of mass ? Why are there three generations ?

Why the large difference between Plank and EWK scale ? How can we incorporate gravity ?

Are fermions point-like or do they have substructure ? What is the source of dark matter ?

SUSY is most commonly invoked to address these, but there are many other models that seek to answer some or all of these questions

Sung-Won Lee HCP 2010, Toronto 2

Roadmap: Beyond the S.M.

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Low Scale Gravity Non Commutative Geometry

SUSY mSUGRA GMSB AMSB RPV(?)

Heavy, Excited, Composite States q* l* ν*

LQ H

{ }

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SUSY

Technicolor, Black Holes

Extra Dimensions

W′

Presented by Rob McPherson (Univ. of Victoria) @ ICHEP 2002, Amsterdam

Roadmap: Beyond the S.M.

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Large Extra Dimension (ADD)

Warped Extra Dimension (RSG)

SUSY mSUGRA GMSB RPV Split SUSY

Heavy, Excited, Composite States q* l* ν*

LQ H

{ }

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W1 W2 W3

νe

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SUSY

Technicolor, Black Holes

Extra Dimensions

Unparticles, Hidden Valleys, Little Higgs, HSCP, etc…

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Universal Extra Dimension

Sungwon Lee Physics at LHC 2006, Cracow 5

  This talk (Searches for New Physics @ CMS) describes

  Some of early new physics searches we’ve performed   via signature-based & compare how well the early LHC data

agrees with the S.M.

  Some of the important theories we’ve tested so far   Excited Quarks, Axigluon/Colorons, Contact Int.   String Resonances   SUSY: stau, gloinos, stop, etc…

  Some of new strategy & method we’ve developed

  High-Mass Dilepton & Diphoton Resonances   Z′ , e*, µ*, boosted Z, RS G → ZZ, γγ, LV → ff

  High-Mass Non-Resonant Signals   W′ , C.I. → µν(µµ), LED (γγ,µµ,ee,γ+MET), UED, Unparticles

  LQ

  Multijets Final States   Dijet: Mass, Centrality Ratio, Angular distribution   BH, Multi-jet Resonance, Mono-jet, High mass resonance (ZZ/WW)

  Long-lived Particles   HSCP, Stopped gluinos, GMSB γ, …

  Top Pair BSM: Z′ → ttbar

  Fourth Generation   b′b′→ tWtW (bZbZ, cWcW, bZcW), t′t′→ tZtZ (bWbW), W′→ tb, etc…

  SUSY

HCP 2010, Toronto Sung-Won Lee 6

Sung-Won Lee 7 HCP 2010, Toronto

New Physics Searches with Dijet


New Physics Search with Dijet events   We study the inclusive dijet final state using dijet mass spectrum and the dijet centrality ratio observables.   These provide a test of QCD and sensitivity to new physics BSM.

Mass Spectrum Centrality Ratio simple test of cross section vs dijet mass from QCD and PDFs

detailed measure of QCD dynamics from angular distribution

provide most sensitive “bump” hunt for new particles decaying to dijets

less sensitive to dijet resonances, but important confirmation that “bump” is not QCD fluctuation

because of experimental uncertainties, less sensitive to quark compositeness

sensitive search for quark compositeness


Specific Dijet Resonance Models

Parton resonances decaying to dijet are predicted by various theory models   Axigluons / Colorons   Excited Quarks, E6 Diquarks   RS Gravitons   New vector bosons (Zʼ,Wʼ)

Recent theoretical development: String Resonances   Regge excitations of quarks and gluons   cross section higher than q* models by factor of 25 (due to color, spin, chirality effects)

String resonances would produce a spectacular bump in the dijet mass spectrum.


Dijet Mass Spectrum Events accepted by single jet trigger   one jet with ET > 50 GeV uncorrected   trigger fully efficient at 220 GeV/c2

Two Anti-Kt calo-jets (ΔR=0.7) with |Δη| < 1.3, |η| < 2.5   jet energy corrected for detector effects (from MC) + 10% systematic   spectrum extends to 1.9 TeV with 836 nb-1

The data is in good agreement with the full CMS simulation of QCD from PYTHIA


Highest Mass Dijet Events


Cross Section Stability

Stability vs. run is excellent   RMS of cross section vs. run is 3%, constraining JEC stability to 0.5% of better


Smooth Fit of Mass Spectrum

Data well fit with four parameters   χ2/ndf = 25.9/25   No indication of new physics

String resonances have largest cross section and provide the highest search sensitivity


Model-Independent Cross Section Limits We obtain generic cross section limits on qq, qg, gg resonances. The upper limits are compared to the predicted cross sections for 7 models.

Model

95% C.L. Mass Limit (TeV) using CTEQ6L

CMS 836 nb-1

CDF 1.13 fb-1

ATLAS** 315 nb-1

String 2.10 1.4 --- q* 1.14 0.87 1.20

Axigluon 1.06 1.25 --- E6 Diquark 0.58 0.63 ---

  CMS now well beyond the Tevatron for both string resonances and q*

  CMS competitive with ATLAS q* limits** (arXiv:1008.2461)


Model-Independent Cross Section Limits Observed/expected cross section limits on qg, and qq resonances are close !!

Type of Limit

95% CL Mass Limit on qg & gg (TeV) String

qg q* qg

Axigluon qq

E6 Diquark qq

Observed 2.10 1.14 1.06 0.58

Expected 2.10 1.10 0.98 0.54


Dijet Centrality Ratio   Quantifies the centrality of the dijet angular distribution at a given dijet mass   Complimentary to the mass spectrum analysis   Many experimental uncertainties cancel in the ratio (e.g. absolute jet energy scale, luminosity)

  roughly flat for t-channel QCD   rises for quark C.I.   bumps in dijet mass for resonances

The data agree well with NLO + non-perturbative corrections


New Physics with Dijet Centrality Ratio

Comparison of data, QCD, C.I., q* models show no sign of new physics


Long-Lived Heavy Particles


LLH Particle Signatures @ CMS Long-Lived Heavy particles appear in many BSM Scenarios   Some SUSY flavors predict LL gluino, stop, stau…   Hidden valley models, certain GUTs   Life-times 102~103s are of particular interested in cosmology

Two main classes of LLH particles   Lepton-like: no strong interactions   Hadron-ike: hadronize to form R-Hadrons

If charged,   slow moving particle will loss E more quickly than mip (higher dE/dX)   some of them will stop in the detector and eventually decay out-of-time w.r.t. beam crossing

Two complementary analyses in CMS 1. Search for charged tracks with anomalously high dE/dx 2. Search for stopped particles

Both methods offer high sensitivity with early LHC data

STOP MC

Simulated R-hadron stopping locations


Search for Heavy Stable Charged Particles

Signature based search – look for high pT tracks with high dE/dX   track+muon (muon-like signature: e.g. mGMSB stau mass ~ 100-300 GeV)   track-only (others: e.g. stop & gluino R-hadron, mass ~ 130-900 GeV)

Event selection   preselect track with pT > 7.5 GeV, relative uncertainty on pT > 0.15, I.P. < 2.5 mm, > 3 Si strip hits   apply cluster cleaning   split into subsample by η and Nhits   cut on track pT and dE/dx discriminator

Selection optimization   tight selection for signal box   loose selection to cross-check background estimate


Results from HSCP Search in 198 nb-1

  After loose selection, mass distribution: good agreement b/w data and MC,   After tight selection, no events observed in signal region   Set 95% C.L. limit on production cross-section for gluinos, stop, stau

track + muon


Search for Stopped Gluinos Gluinos, bound into R-Hadron, can decay either monojet or dijet Use dedicated calorimeter trigger for non-collision   gap between filled bunches during LHC fills   observation of signal during these periods will be a sign of BSM physics

Q: where will they sop? A: ~20% gluinos can be stopped somewhere in CMS

Performed detailed study of backgrounds   cosmics & instrumental noise measured with 08/09 cosmic runs   beam background observed in 900 GeV & 7 TeV data   signal efficiency ~17% (of all R-hadrons)

Counting Experiment Results   perform counting experiment in lifetime (τ) bins   no excess above expected background observed   proceed to set 95% C.L. limits


Stopping Model-Independent Results Limit on cross section x stopping probability   independent of the model of interaction with matter   14 orders of magnitude covered in τg

Time-Profile analysis   As well as counting experiment, we analyze the distribution of observed event times   assuming a life-time < 100 µs, calculate a PDF for signal event time, using luminosity profile   background PDF is flat in time, signal peaks at bunch crossing   fit the data → set 95% C.L. on the signal

decays during BX veto: τ < ~100 ns decays within the orbit: τ < ~10-4 s decay over the full fill (~104s)

R-hadron

slow decays after fill

(loose sensitivity)


Stopping Model-Dependent Limits Result translated into a gluino cross-section limit   use R-Hadron stopping probability for specific models “cloud model,” “EM only”, “Neutral R-Baryon”   e.g. m(g) = 200 GeV & m(χ0) = 100 GeV

  Included time-profile analysis (dot lines) to improve the sensitivity for τ(g) < 100 ns   excluded lifetime range 120 ns < τ(g) < 6 μs for m(g) = 200 GeV   also extend D0 result below 30 µs

Result translated into a gluino mass limit   limit for fixed lifetimes, as function of m(g), m(χ0)   fixed m(g)-m(χ0) = 100 GeV   no sensitivity below m(g) =150 GeV (efficiency drop)   time profile analysis (τ = 200 ns): m(g) < 229 GeV   counting exp. (τ = 2.6 μs): m(g) < 225 GeV

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Commissioning of SUSY Searches

Early LHC data preparation for

SUSY searches at CMS


Discovery Potential & Search Strategy

7 TeV data ~100 pb-1 should provide sensitivity to SUSY parameter space beyond current TEVATRON limits

Fully Hadronic Signature

Achieving this, sensitivity strongly depends on   how well we measure SM backgrounds e.g. Z(νν)+ Jets, W(lν) + X, QCD ...   how well we understand physics object (lepton,jets,MET)

Currently, SUSY commissioning focused on specific tools for searches   background discriminating variables (e.g. αT, Δφ*, ΔΦ(MHT, MPT))   data-driven strategies for QCD background estimate   huge effort going on to understand the SM backgrounds with data (see next few slides)

SS dilepton


Hadronic Analyses

αT is a powerful variable for suppress QCD Multijets to hadronic SUSY   combines jet pT and angles; complementary to MET MC shows strong QCD suppression with αT > 0.55 in dijet/multijets, and improving with increasing HT. Validated αT behavior in data

Suppressing QCD with Δφ*

Suppressing QCD with αT

A complementary observable, Δφ*, to diagnose background events where one jet mis-measured

confirm expected behavior in both di- and multi-jet: small Δφ* for QCD, more uniform for real MET

Relative isolation0 0.5 1 1.5 2 2.5

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CMS preliminary-1 = 7 TeV, 53 nbs

control = 248)T

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(17.9)±Prompt: 251.2 control = 72)

T (M

stat. (11.3)±Background: 66.2


Lepton+Jets+MET

e+jet+MET: select control sample by inverting selection cuts & perform template fit using relative isolation distributions.

MET background to lepton+jets+MET signatures from real MET (e.g. W/Z) & MET due to mis-measurements

e+jet+MET predicted observed RI < 0.3 224 ± 13 263

RI < 0.3 && MET > 20 215 ± 13 215

µ+jet+MET predicted observed Prompt µ MET < 20 251 ± 18 248

Background MET < 20 66 ± 11 72

µ+jet+MET: based on an extrapolation from a sideband fit to a functional form


Same-Sign Dilepton

No discrepancy observed Method in place, more statistics to come

Data driven method for estimating SM background for SS ee , μμ and eμ channels

Use a control sample (loose lepton-ID & isolation) to measure efficiency of passing all analysis cuts as a function of lepton kinematics

Monitor measured Tight-to-Loose-Ratios using different jet-triggered sample.

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CMS Preliminary = 7 TeVs, -136 nb

Predictions obtained using HLT_Jet15U

Electrons Muons


Conclusions   CMS is searching for evidence of different models of new physics

in several channels using the early LHC data & already exploring new territory beyond the Tevatron.

  Only recent results shown here. Many new physics searches are underway.

  No signals of the new physics observed in the early LHC data yet.

  More LHC data on the way; Analyses of 1pb-1 data samples just beginning.

New exciting results are in the pipe-line. Stay tuned!


Extra Slides


Future Prospects

CMS is exploring new territory beyond the Tevatron string, q*, Axigluon, E6 Diquark resonance mass limits.

We expect to surpass Tevatron limit of Λ > 2.8 TeV at 95% C.L. with 4 pb-1.

Conservative expectations for limits as function of integrated luminosity


Dijet Resonance Mass Limits

Model

95% C.L. Mass Limit (TeV) using CTEQ6L

CMS observed 836 nb-1

CMS expected 836 nb-1

CDF

1.13 fb-1

ATLAS observed 315 nb-1

ATLAS** expected 315 nb-1

String 2.10 2.10 1.4*** --- --- q* 1.14 1.10** 0.87 1.20 0.98

Axigluon 1.06 0.98 1.25 --- --- E6 Diquark 0.58 0.54 0.63 --- ---

  ** CMS expected limit with 315 nb-1 is 0.93 TeV

  *** CMS evaluation of string resonance cross section

Searches for Physics Beyond the Standard Model CMS - TTUslee/HCP2010/HCP2010_LEE.pdf · Sungwon Lee...

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