QCD Physics at CMS University of Illinois at Chicago CTEQ Collaboration Meeting Northwestern November 0, 009 1
QCD Physics at CMS University of Illinois at Chicago CTEQ Collaboration Meeting Northwestern November 0, 009
QCD Physics at CMS University of Illinois at Chicago CTEQ Collaboration Meeting Northwestern November 0, 009 3
Introduction Jet Algorithms and Calibration @ CMS QCD @ CMS Low-Q : Tracking Analyses Underlying Event Particle Spectra High-Q Processes Jet Structure Event Shapes Dijet Azimuthal Decorrelation Dijet Angular Distributions & Dijet Mass Ratio Inclusive Jet Cross Section Dijet Mass Cross Section Summary 4
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Round-the-clock operations started on Oct 6 Current(?) Plan: Startup in Nov 09 (it s happening!) Data: 900 GeV Collisions in Dec ~40 pb -1 @ 7 TeV (early 010) ~70 pb -1 @ 8-10 TeV 7
Posted on twiki page: https://twiki.cern.ch/twiki/bin/view/cms/physicsresults 8
Calorimeter Jets Clustering of energy depositions EM+HAD towers Track Jets Clustering of tracks Sampling only charged particles JetPlusTrack Primarily used in QCD analyses Calorimeter jets with energy corrections based on tracks Particle Flow (PFlow) Clustering of identified particles 9
CMS-JME-07-003 dij = min( p d = ii p T,i T, i, pt, j ) R D ij 10
Fast kt Algorithm improves speed from O(N 3 ) to O(N lnn) G.Salam, M.Cacciari, Phys. Lett. B641, 41 (006) Add ghost particles to determine the area of jets Could be used to subtract pile-up contributions Already adopted as the default k T algorithm at LHC Other recombination algorithms: p d ii = p T, i p=1 regular k T jet algorithm p=0 Cambridge/Aachen jet algorithm d = min(p Dokshitzer, Leder, Moretti, Webber 97 (Cambridge) Wobisch, Wengler 99 (Aachen) p=-1 Anti-k T jet algorithm Cacciari, Salam, Soyez 08 Soft particles will first cluster with hard particles before among themselves Almost a cone jet near hard partons No merge/split Recently adopted by CMS (and ATLAS) as the default cone algorithm ij p T, i,p p T, j ) ΔR D ij 11
CMS-JME-07-00 1
CMS-JME-07-003, CMS-JME-09-007 M jj or 13
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Study track multiplicity and p T density in transverse jet region CDF approach Use track jets Statistics as for 100/pb Tracks: p T > 900 MeV η < Decrease systematic effects with ratio: 0.9/1.5 Different Pythia tunes HERWIG, no MPI CMS-QCD-07-003 15
Unidentified charged hadron analysis Count clusters in the layers of the Pixel Barrel (4, 7, and 10 cm radii) Strategy developed by Phobos @ RHIC No need for tracking, sensitivity down to 30 MeV Correction of loopers, secondaries; systematic uncertainty expected below 10% CMS-QCD-08-004 16
Unidentified charged hadron analysis CMS-QCD-09-00 Reconstruct tracklets line segments of hits in the inner two layers of Pixel Barrel projected to the vertex Strategy developed by Phobos @ RHIC Complementary to hit-counting and track-reconstruction method Systematic uncertainty expected ~10% 17
CMS-QCD-07-001 Charged hadrons Pions Protons Empirical fits pp @ 14 TeV Limit in pt for de/dx differentiation Tracks from pixel triplet seeding (tracking down to 75 MeV) M events with one month of running at 1 Hz bandwidth 18
Photon Analyses Photon production Photon+jet productions Photon+jet angular distributions Di-photons Jet Analyses: Jet Shapes Event Shapes Multi-jet Studies Topological Distributions Ratio of cross sections (3-jet/-jet, etc) Dijet Azimuthal Decorrelation Dijet Angular Distribution Dijet Mass Ratio Inclusive Jet Production Di-jet Mass Distribution 19
Motivation: Jet shapes probe the transition between a parton produced in the hard process and the observed spray of hadrons Sensitive to the quark/gluon jet mixture Test of parton shower event generators at non-/perturbative levels Useful for jet algorithm development and tuning pp @ 14 TeV Quark Jets Gluon Jets 0
Definition: Integrated Jet Shape is defined as the average fraction of jet transverse momentum that lies inside a cone of radius r concentric to the jet axis Ψ( r) = 1 N jets jets p p T T (0, r) (0, R) Ψ( R) = 1 pqcd Contributions ( r) 1-Ψ(r) radiation inside the jet Quark jets are narrower than gluon jets Soft radiation from outside the jet 1
Gluon enriched jets (low-x/low-p T jets at Tevatron) are broader (i.e. less collimated, higher multiplicity of soft energy particles) than Quark-enriched jets (high-x/high-p T jets) Consistent with results from LEP and HERA (a Jet is a Jet no matter where you measure it!) UVA Seminar Aug 6, 009
Gluon enriched jets (low-x/low-p T jets at Tevatron) are broader (i.e. less collimated, higher multiplicity of soft energy particles) than Quark-enriched jets (high-x/high-p T jets) Consistent with results from LEP and HERA (a Jet is a Jet no matter where you measure it!) UVA Seminar Aug 6, 009 3
pp @ 14 TeV Quark jets are narrower than Gluon jets 4
CMS-QCD-08-005 pp @ 14 TeV Gluon Quark jets 5
CMS-QCD-08-00 δr jet ( p To avoid the Magnetic Field effects Study the charged particles (tracks) within jets with p T >1 GeV Use the JetPlusTrack (JPT) algorithm Use the nd central moments of η and φ δϕ c c c = δϕ (δϕ) δη = δη (δη) δ R = δϕ + δη c c T ) R constituent, constituent _ in _ jet _ cone = constituent pt ( jet)* p constituent T 6
10 pb -1 pp @ 10 TeV Differences between Pythia and Herwig++ Quark Gluon Jets 7
Central Transverse Thrust: T,C =1 for process T,C =1 for homogeneously distributed event pp @ 14 TeV τ T, C, C CMS-QCD-08-003 1 T max η T, C p i ηt p, i i, i 10 pb -1 sys+stat errors Systematic Errors from JES and Resolutions ~ -10% 8
DØ: N jets for 700 pb -1 y <0.8 CMS: N jets / pb -1 y <1.3 Sqrt(s) pt>0.5 TeV pt>1 TeV (DØ) 34 (700 pb -1 ) - 6 50 / pb -1 0.3 / pb -1 10 30 / pb -1 5 / pb -1 14 860 / pb -1 0 / pb -1 DØ: # evts for M jj >1TeV, 700 pb -1 y 1, y <.4 For CMS: # evts/m jj /pb -1 y 1, y < 1.3 Sqrt(s) M jj >1 TeV M jj >1.4 TeV M jj > TeV (DØ) ~00 (700 pb -1 ) 6 8.4 / pb -1 0.6 / pb -1 10 50 / pb -1 7.4 / pb -1 14 140 / pb -1 0 / pb -1 9
PRL 94, 1801 (005) -jet event Jet Jet 1 φ=π 3-jet event Jet 3 Jet φ<π Jet 1 φ distribution of leading jets is sensitive to higher order radiation w/o explicitly measuring the radiated jets UVA Seminar Aug 6, 009 30
PRL 94, 1801 (005) -jet event 3-jet event Jet 1 Jet 1 Jet 3 φ<π φ=π Jet Jet φ distribution of leading jets is sensitive to higher order radiation w/o explicitly measuring the radiated jets UVA Seminar Aug 6, 009 Sensitivity to ISR 31
CMS-QCD-09/003 10 pb -1 -jet event Jet Jet 1 φ=π 3-jet event Jet 3 Jet φ<π Jet 1 Sim. Data corrected distributions Corrections are dominated by jet energy and position resolution effects <5% for π/3 < φ < π (consistent among MC generators) pp @ 14 TeV 3
CMS-QCD-09/003 10 pb -1 -jet event Jet Jet 1 φ=π 3-jet event Jet 3 Jet φ<π Jet 1 Sim. Data corrected distributions Corrections are dominated by jet energy and position resolution effects <5% for π/3 < φ < π (consistent among MC generators) pp @ 14 TeV 33
dσ [ QCD + Interference + Compositeness ] 1 1 ˆ α s ( µ ) α ( ) u s µ tˆ tˆ Λ uˆ Λ q q q q dσ ~ 1/(1-cosθ * ) angular distribution dσ ~ (1+cosθ * ) angular distribution ŝ << Λ From cosθ * variable to χ χ = y* e y * = 1 ( y 1 y ) y = 1 boost ( y 1 + y ) Rutherford LO QCD cosθ * with contact term M jj ~ Λ dν/dχ sensitive to contact interactions χ 34
dσ [ QCD + Interference + Compositeness ] 1 1 ˆ α s ( µ ) α ( ) u s µ tˆ tˆ Λ uˆ Λ q q q q dσ ~ 1/(1-cosθ * ) angular distribution dσ ~ (1+cosθ * ) angular distribution ŝ << Λ From cosθ * variable to χ χ = y* e y * = 1 ( y 1 y ) y = 1 boost ( y 1 + y ) Rutherford LO QCD cosθ * with contact term M jj ~ Λ dν/dχ sensitive to contact interactions χ 35
Limits Compositeness (Λ): ~.8 3 TeV ADD LED (GRW, M s ): ~1.6 1.7 TeV TeV 1 Extra Dim (M C ): ~1.6 1.7 TeV UVA Seminar Aug 6, 009 36
Angular distributions are insensitive to PDFs Reduced sensitivity to detector effects Particle level information Errors dominate by JEC 37
s =14 TeV Tevatron Tevatron Limit With 10 pb -1 @ 14 TeV (~30 pb -1 @ 10 TeV): Can probe contact interactions up to 5 TeV CMS-SBM-07/001 38
CMS-QCD-08/001 Can probe contact interactions beyond the Tevatron reach with early data at 10 TeV Main uncertainty: Jet energy scale assume 10% on day 1 39
Jet Algo k T 0.6 @ 10 TeV Jet Algo SISCone, R=0.7 @ 10 TeV CMS-QCD-08/001 Hadronization Corrections for inclusive jet cross section Can probe contact interactions beyond the Tevatron reach with early data at 10 TeV Main uncertainty: Jet energy scale assume 10% on day 1 40
LHC will start producing collisions this year! After 0 years of R&D, construction, and installation the CMS Detector is ready for data First steps: understand detector performance with beam and re-establish the SM First CMS measurements will be on QCD analyses Small amount of data will be enough to exceed the Tevatron reach Rich QCD program at startup and beyond New physics might be around the corner! 41