Rochester Physics Analysis Activities on CMS

Rochester Physics Analysis Activities on CMS

Henning Flächer

for the Rochester CMS GroupOutline: • Physics Analysis Activities• Jet and MET Commissioning• Dijet Resonances• Dijet Centrality Ratio• SUSY Multi-jet + MET Searches• Conclusions

DOE Site Visit - 2nd Sep. 2010

Overview of Group ActivitiesGroup Members

Analysis Preparation Jet and Missing Energy (MET) Commissioning

Profit from groups hardware and detector commissioning experience Hadron Calorimeter & Silicon Tracker

Calorimeter Noise Studies Jet Reconstruction Performance and comparison of Jet

algorithms Jet Quality (Jet ID) Jet based missing energy Studies (MHT)

Physics Analyses (early discovery) Dijet Resonances Dijet Centrality Ratio Susy Multi-Jet and Missing Energy Search

02 Sep. 2010 Henning Flaecher DOE Site Visit

CMS Physics Analysis Group

Teaching Faculty: Demina (PI) Bodek (PI) Slattery (PI) Melissinos (PI) Garcia-Bellido

Postdocs: Cammin ???(until Feb 09) Chung Flaecher Gotra Harel Han Goldenzweig

Senior Scientists: Zielinski de Barbaro Sakumoto Budd

Graduate students: Miner Orbaker??? Betchart Vishnevsky Eshaq

Undergraduates: Qi Pedro Moolekamp02 Sep. 2010 Henning Flaecher DOE Site Visit

Jet Commissioning: Algorithms CMS Jet Algorithms group -- Zielinski a co-convener since 2007

Jet algorithms define the procedure to cluster input objects: partons, particles, calo towers, tracks

We led algorithmic studies of jet performance and validation Based on this work, in 2009 CMS adopted Anti-KT algorithm

as the default jet reconstruction for LHC data Harel developed jet quality criteria for calorimeter jets

Reconstructing jets in calorimeter: Cells contribute to tower energy if they

pass energy thresholds Current thresholds (Scheme 6) for CMS

software developed with strong Rochester

contributions (Zielinski, Qi) based on

measurements of HCAL performance in

Global Runs (Miner, de Barbaro, Vishnevsky) New thresholds significantly improve performance

of calorimeter jets with respect to old Scheme B Implemented in RECO in fall of 2009, and in High Level Trigger in spring 2010

Jet reconstruction using tracks under development (Garcia-Bellido, Eshaq)02 Sep. 2010 Henning Flaecher DOE Site Visit

CMS AN-2010/024

CMS AN-2010/067, AN-2009/087, PAS JME-08-008

Jet Performance at 7 TeV

JME-10-003: “Jet Performance in pp Collisions at √s= 7 TeV” Public CMS document for ICHEP Based on Lint~75 nb-1 of 7 TeV data Co-edited by Zielinski

Very broad range of jet performance studies Jet energy corrections

MC-truth JEC In-situ calibration:

Offset correction Relative response Absolute response

Jet resolutions MC-truth Jet pT resolutions Data-driven jet pT resolutions Jet position resolutions Relative jet responses and resolutions

(Zielinski, Pedro, Garcia-Bellido)02 Sep. 2010 Henning Flaecher DOE Site Visit

CMS AN-2010/121

PAS JME-10-003

CMS AN-2010/134 PAS JME-10-003

Jet Quality Criteria:Jet ID

Brought JetID studies to publication as CMS Physics Analysis Papers: Jet ID studies for early physics – PAS JME-09-008 Jet commissioning note – PAS JME-10-001

New study: Developed detailed Jet ID for the forward region Only calorimetry information available Noise samples collected with LHC operating, in empty bunch crossings Adopted by analysers of forward jet production, e.g., CMS DP-2010/026

Fully integrated with CMS reconstruction and analysis frameworks

Recommended by JetMET as CMS standard


LSLS

Data from empty bunch crossings

effective noise sample

Simulated physical jets

Analogue of EM fraction

Optimized at each energy:

entries normalized in each “x” slice

LooseTight

Selection

Harel

Missing Energy Commissioning

Missing energy performance in MinBias and dijet events

Co-edited by Flaecher

Rochester contribution Commission missing energy

inferred from jet measurements

Redundancy by comparing different approaches to jet reconstruction

HT and MHT distribution well behaved – no long tails

CMS approved documents: JME-10-002 (0.9 & 2.36 TeV)

JME-10-004 (7 TeV)


Demina,Flaecher,Betchart

Phenomenology Connections: LPC and CTEQ

We are involved in CTEQ and LPC LPC is a major USCMS center for analysis We have trained many students at LPC

(Demina, Zielinski) CTEQ aims to provide guidance to LHC

collaborations concerning Standard Model issues and backgrounds to searches for New Physics

Zielinski is CTEQ member since 2006 and active at LPC since 2004 On Organizing Committee for the first CTEQ

Workshop on LHC Physics 2007 Lecturing on jet issues at CTEQ Summer

School 2007 CTEQ-LPC liaison for the joint Workshop on

Higgs Physics at LHC and Tevatron, 2009 Co-organizer of the visit of several CTEQ

members at LPC as part of the “Experimentalist/Theorist of the Week” program in March 2010

On Organizing Committee for the workshop on “Standard Model Benchmarks at the Tevatron and LHC” – joint venue between the three CMS LPC’s, Argonne, and Fermilab in Nov 2010 02 Sep. 2010 Henning Flaecher DOE Site Visit

New Physics Searches at LHC

Rochester is involved in early discovery analyses Dijet Resonances Dijet Centrality Ratio Susy Multi-Jet and Missing

Energy Search

Jet Pairs and SUSY particles are expected to be produced via strong interaction in LHC Production rates are large Quickly surpass Tevatron

sensitivity


gg

gq

qq

Ratio of LHC/TeV Parton-Parton Lumi in pb

Search for Dijet Resonances in Mjj

Heavy particles decaying to dijets could be observed as resonant peaks in the dijet mass spectrum Such resonances are predicted by various

theory models of physics beyond Standard Model

This approach complements the searches using the Dijet Centrality Ratio

Using the luminosity of 836 nb-1 CMS has established upper limits on the production of several resonance types at 7 TeV In particular, we exclude a string resonance

with mass M < 2.1 TeV at 95% CL – currently the best limit

We expect to exceed the Tevatron limits for other resonances with several pb-1 of data

(Zielinski)02 Sep. 2010 Henning Flaecher DOE Site VisitCMS AN-2010/108

PAS EXO-10-010

Dijet centrality ratio

Observable:

Measure as a function of dijet invariant mass

Simple measure of angular distribution Robust with respect to systematic

uncertainties


Dijet angular distributions distinguish between: s-channel productiont-channel

Discovery observable for hadronic contact interactions

Sensitive to resonant dijet production

Harel,Miner

Dijet centrality ratio measurementDeveloped tools for the statistical analysis.

Test of QCD modelsp-value of our consistency test statistic is 0.8 for

corrected NLO and 0.7 for PythiaNLO/LO

Set CLS limits with an LLR observable


We exclude Λ<1.86TeV at 95% CLExpected exclusion

~1.3TeVTevatron exclusion

2.8TeVWill reach Tevatron limit

with ~4pb-1

Exclusion for a 500GeV q* resonance still only at ~90% CL

PAS EXO-10-002

Harel,Miner

Commissioning for SUperSYmmetry

SUSY signatures are challenging and involve multiple objects (jets, leptons, photons) accompanied by missing energy SUSY events come from a variety of triggers Good understanding of the detector and

data flow is crucial for SUSY searches

SUSY Commissioning group was organized with this goal in mind Demina was asked to co-lead this effort Flaecher leading SUSY Prompt Validation

Team.

Responsibilities involve: Verification of the key variables (e.g. missing

energy) using cosmic and early collision data

Defining triggers and data sets, ensuring efficient access to data

Prompt monitoring of variables relevant for SUSY searches

Established close coordination with detector performance and physics objects groups


Demina, Flaecher, Betchart

TRENDPLOT

MET 95% Quantile

SUSY: Jets + Missing Energy Search

• CMS SUSY group is organised based on signatures

Reference Analyses based on jets, leptons, photons

• Rochester group’s focus is on: Search for a missing energy

signature in multi-jet events Large sensitivity due to high cross

section Signal is evidence for a Dark

Matter candidate (WIMP) Production of WIMP in cascade

decays of heavy new particles WIMP escapes the detector and

remains undetected => missing energy signature

• WIMP candidate in many models: SuperSymmetry, Extra Dimensions,

Little Higgs, Technicolor

New approach to Jets + MET searches using kinematic variable αT

For dijets:

For Multijets: recombine jets to form dijet system

Main background: QCD events For ideal QCD dijets: αT = 0.5 For mismeasured QCD: αT < 0.5

Approved CMS studies: PAS-SUS-08/005, SUS-09-001, SUS-10-

001 Extension of PTRD-II studies to dijet

topology


DeminaFlaecherBetchart

€

T=ET j2MT j1 j 2

=ET j2 /ET j1

2(1− cosΔϕ )

Analysis does not rely on calorimetric MET MHT inferred from measured jets

well suited for early data

CMS SUSY Reference Analysis Require and αT > 0.55 Still clear separation of QCD from signal after jet

recombination αT cut value motivated by underlying physics Expected event yields for selected benchmark signal

points for 10 pb-1 @ 7 TeV LM0/LM1: mSugra points beyond Tevatron reach

Signal/Background ~ 4 - 7 Negligible contribution from QCD αT edge stable under systematic variations

(e.g. severe jet mismeasurements) Improve on Tevatron with ~10pb-1, publication in 2010

αT analysis with multi-jets

Jet Mult.

Selection

QCD EWK

LM1 LM0

n = 2 αT > 0.55 0.0 0.4 1 2

n >= 3 αT > 0.55 0.0 2 14 5


dijet

>=3 jets

€

HT = pTjet i

i=1n∑ > 350GeV

DeminaFlaecherBetchart

Outlook on SensitivityαT Analysis: exceed

Tevatron limits with 10pb-

1


1fb-1

100pb-1

Constraining Parameter Space of New Physics Models, e.g. SUSY Simultaneous fit of CMSSM

parameters m0, m1/2, A0, tanβ (μ>0) to more than 30 collider and cosmology data

Low energy data → Flavour physics, g-2

High energy data → Precision EW Obs., MW, Mtop

Cosmology and Astroparticle data → relic density

Probe squark masses of ~600 GeV and gluino masses of > 500 GeV with 100 pb-1

Probe squark masses of ~850-1000 GeV and gluino masses of ~600-900 GeV with 1 fb-1

1fb-1 by end of 2011 run

Complementary to direct Dark Matter Searches

L=10pb-1

0% systematic25% systematic50% systematic

MasterCode Collaboration – Flaecher et al.

5σ discovery

Current CMS data as of July 21,2010: 78 nb-1

[Aug. 31, 2010 we have ~ 3 pb-1]

More u quarks than d quarks in

the proton. W asymmetry measures the d/u

ratio at small x

W/Z physics – W asymmetry

With 25 pb-1 our expected W asymmetry errors match PDF errors

(4000 W’s per pb-1 )

Pt>20 GeV

Pt>10 GeV Expected error with 25 pb-1

So with 100 pb-1 (expected mid 2011), we can constrain d/u at small x and reduce PDF uncertainties at the LHC

Z/DY physics : 340 Z dimuon events as of Aug.15, 2010.

We now have 340 Zs in 1 pb-1 of data (mu-mu channel)

Note: Z cross section is factor of 10 smaller than W cross section. So need a factor of 10 more luminosity.

For 1 fb-1 (end of 2011) we expect ~0.4 Million Z’s and ~4 Million W’s.

18

W Transverse Mass distribution. Z Mass distribution.

Z/Drell-Yann Physics

( 0.4 Million DY/Z’s and 4 Million W’s).

1. Compare Afb and dN/dM to SM expectation (y>1). LHC not yet competitive with Tevatron

2. Measure Z angular coefficients. We will have similar statistics as the Tevatron, so compare to theory and to CDF measurements at the Tevatron, and determine fraction of Compton vs q-qbar processes. Dilution for A4=3/8(Afb) different for different QCD Monte Carlos.

Z/DY Physics with 1fb-1(end of 2011)

Conclusions Coherent physics programme building on hardware and algorithm expertise

Covering different aspects of early LHC physics: Dijet Mass Distribution

Improved limit on String resonances with 120nb-1, excited quarks to follow soon

Dijet ratio Sensitivity to Contact Interactions and Excited Quarks Limit with 120nb-1, expect to surpass Tevatron limit with 4pb-1

Electroweak Physics test and constrain Parton Distribution Functions Start to improve PDFs with >25pb-1

Leading SUSY Commissioning Activities developed good understanding of detector and Jet/MET quantities

Prompt monitoring of quantities relevant for SUSY searches

Leading role in multi-jet SUSY analysis New approach using αT variable

“SUSY Reference Analysis” – targeted as first CMS SUSY publication with ~10pb-1

Surpass Tevatron limits for many searches with O(10) pb-1

Group is fully involved in 7 TeV data analysis!



BACKUP

Jet Studies for SUSY One of the major backgrounds to SUSY

searches in hadronic channels comes from mismeasured jets in QCD multi-jet events Jet response distributions exhibit non-

Gaussian tails due to detector effects and heavy flavor decays

This can lead to a large fake Missing ET

We are involved in Determination of jet response

distributions from CMS simulation Development of data-driven method to

measure response shapes from photon+jet events

Studies of various contributions to jet resolutions and their tails

Studies of the impact of jet resolution tails on Missing ET

(Zielinski, Pedro, Garcia-Bellido)02 Sep. 2010 Henning Flaecher DOE Site Visit

CMS AN-2010/151

PAS JME-10-003

Search for Dijet Resonances in Mjj

Heavy particles decaying to dijets could be observed as resonant peaks in the dijet mass spectrum Such resonances are predicted by various

theory models of physics beyond Standard Model

This approach complements the searches using the Dijet Centrality Ratio

Using the luminosity of 120 nb-1 CMS has established upper limits on the production of several resonance types at 7 TeV In particular, we exclude a string resonance

with mass M < 1.67 TeV at 95% CL – currently the best limit

We expect to exceed the Tevatron limits for other resonances with several pb-1 of data

(Zielinski)02 Sep. 2010 Henning Flaecher DOE Site VisitCMS AN-2010/108

PAS EXO-10-001

Henning Flaecher DOE Site Visit

A first look at systematicsTo get a rough idea:

Jet energy scale variation by +- 10% for QCD MC

Data-MC agree within these uncertainties More detailed studies to follow

>=3 jets

02 Sep. 2010

Outlook on SensitivityExceed Tevatron limits

with 10pb-1

0% systematic

25% systematic

50% systematic


Probe squark masses of ~600 GeV and gluino masses of > 500 GeV with 100 pb-1

Probe squark masses of ~850-1000 GeV and gluino masses of ~600-900 GeV with 1 fb-1

1fb-1 by end of 2011 run

L=10pb-1

Phenomenology:Constraining parameter

space of MSSM

Combine as much experimental information as possible to constrain New Physics models!

Famous example: SM fit to electroweak precision data

Extend it to include New Physics modelsMinimal SuperSymmetric Standard Model (MSSM)

What observables are used to constrain the model?

Low energy (precision) data → Flavour physics, g-2

High energy (precision) data → Precision EW Obs.

Cosmology and Astroparticle data → relic density

Simultaneous fit of CMSSM parameters m0, m1/2, A0, tanβ (μ>0) to more than 30 collider and cosmology data

e.g. MW, Mtop, g-2, BR(B→Xγ), relic density

JHEP 0809:117(2008), Eur.Phys.J.C64:391-415(2009), Phys.Rev.D 81,035009(2010)O.Buchmueller, R.Cavanaugh, A.De Roeck, J.R.Ellis, H.F., S.Heinemeyer, G.Isidori, K.A.Olive, P.Paradisi, F.J.Ronga, G.Weiglein

“CMSSM fit clearly favors low-mass SUSY” σpS

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WIMP Mass [GeV]

68% CL95% CL


Rochester Physics Analysis Activities on CMS

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