N. ILINA, V. GAVRILOV (ITEP, Moscow) Study of jet transverse structure using the second moment of ET radial distribution N. ILINA, V. GAVRILOV (ITEP, Moscow) O. KODOLOVA (SINP MSU) RDMS Physics and DPG workshop 12/03/2009

Outline Introduction Samples Variables Study of systematic shifts and uncertainties Predictions of different generators (PYTHIA vs. HERWIG++) Possibility to measure quark jets fraction Summary RDMS Physics and DPG workshop 12/03/2009

Introduction The study is important for CMS commissioning Validation of CMSSW: detector modelling Validation of generators The jet shape study could provide the tool for quark-gluon jets separation The internal structure of a jet is expected to depend on the type of parton creating the jet (light-quark or gluon) and ET of the jet the study of jet shapes can help to test the models of underlying events and parton cascades S.D.Ellis, Z.Kunszt and D.E. Soper, Phys.Rev.Lett. 69, 3615 (1992); J.Pumplin, Phys.Rev. D 44, 7(1991) RDMS Physics and DPG workshop 12/03/2009

pp collisions at TeV , 10 pb-1 Samples. pp collisions at TeV , 10 pb-1 IC5 Algorithm L2L3 jet energy corrections JetPlusTrack method HERWIG++ Summer08 samples: (CMSSW2.2.1 for analysis): PYTHIA generator level (CSA08): (CMSSW2.0.10 for analysis) All distributions in AN at calorimeter level to measure detector based systematics to compare predictions on generator level from PYTHIA and HERWIG to compare predictions from PYTHIA and HERWIG on generator level RDMS Physics and DPG workshop 12/03/2009

Variables at CMS: dR2, dj2, dh2 The integrated jet shapes (CDF definition) – the average fraction of the jet transverse momentum that lies inside a cone of radius r concentric to the jet cone (was used in CMS Note 2008/024). We suggest CMS to use variables - second moment of ET radial distribution - which doesn’t depend on any inner radius: Variables sensitive to internal jets structure and detector effects RDMS Physics and DPG workshop 12/03/2009

dR2 vs PT for matched jets at |h| < 1 Particle level Calorimetric level gen corr All jets become narrower when their transverse momentum increases Particle level jets and calorimetric jets have a similar behavior RDMS Physics and DPG workshop 12/03/2009

dR2 vs PT for different h-regions Quark jets Gluon jets RDMS Physics and DPG workshop 12/03/2009

Detector related systematic shifts and uncertainties RDMS Physics and DPG workshop 12/03/2009

The sources of detector based systematic shifts for dR2 Sources of systematics: strong magnetic field non linear calorimeter response to hadrons hadron shower and calorimeter tower transversal sizes jet angular resolution jet energy scale and jet energy resolution RDMS Physics and DPG workshop 12/03/2009

Systematic shift due to magnetic field Particle level Calorimetric level Jets do not have large difference in size in η and j directions on particle level On calorimetric level jets become oblong in j direction due to influence of magnetic field RDMS Physics and DPG workshop 12/03/2009

Jet shapes with tracks Particle level Calorimetric level Magnetic field doesn’t affect dR2tracks Tracker jet shapes: RDMS Physics and DPG workshop 12/03/2009

Systematic shift due to jet energy scale (MC L2L3 jet energy corrections) The systematic shift due to jet energy scale can be calculated from the difference of tracker jet shapes δR2tracks(PTcal) and δR2tracks(PTgen) RDMS Physics and DPG workshop 12/03/2009

Systematic shift due to jet energy scale (JetPlusTrack jet energy scale) JetPlusTrack Algorithm There is no dependence on jet type (quark ar gluon) for JetPlusTrack algorithm RDMS Physics and DPG workshop 12/03/2009

Predictions from different generators PYTHIA vs. HERWIG++ RDMS Physics and DPG workshop 12/03/2009

dR2(PT) : HERWIG++ vs. PYTHIA6 Particle level All matched jets Quark jets Gluon jets The main difference between PYTHIA and HERWIG++ samples is in gluon jet shape RDMS Physics and DPG workshop 12/03/2009

dR2(PT) : Theoretical and detector systematics gen Very preliminary! RDMS Physics and DPG workshop 12/03/2009

dR2(PT) for different h-regions. Herwig++ predictions gen Jet shapes for all jets(black lines) depend on h while jet shapes for gluon/quark jets are invariant. There are different quark/gluon jets fraction in the rapidity regions RDMS Physics and DPG workshop 12/03/2009

Measurement of quark-jets fraction from jet shapes RDMS Physics and DPG workshop 12/03/2009

Measurement of quark-jets fraction Fraction of quark jets was calculated in 2 ways: I. From ET spectrum: II. From jet shapes: The calculation of quark jets fraction from jet shapes can be applied for data RDMS Physics and DPG workshop 12/03/2009

q-jets fraction from PT spectrum and from jet shapes Particle level gen Fraction of quark jets determined from jets spectrum is in good agreement with q-jets fraction determined from δR2 distributions Fraction of quark jets rises with increasing transverse momentum RDMS Physics and DPG workshop 12/03/2009

q-jets fraction for different h-regions PYTHIA vs. HERWIG++ gen HERWIG++ and PYTHIA predict the similar quark jets fraction RDMS Physics and DPG workshop 12/03/2009

Summary The details of the jet shapes study is in https://twiki.cern.ch/twiki/bin/view/CMS/StudyOfJetShapes RDMS Physics and DPG workshop 12/03/2009

Summary Pre-approval of the study is scheduled on April, 14 12/03/2009 RDMS Physics and DPG workshop 12/03/2009

Back-up RDMS Physics and DPG workshop 12/03/2009

PT spectra for matched jets at |h| < 1 Calorimetric level Particle level For 1 sample: JetEt150/s156 RDMS Physics and DPG workshop 12/03/2009

Fraction of q-jets for different h-regions Particle level Calorimetric level In central rapidity region the fraction of quark jets is smaller It rises in endcap and forward regions (in endcap jets becomes narrower) RDMS Physics and DPG workshop 12/03/2009

Statistical advantage of new CMS variable Integrated jet shape 1-y(0.2) (CDF variable) dR2 (CMS variable) Sensibility = D/sstat, where D = ; sstat = For 500 GeV < Pt < 550 GeV: D/sstat(1-y(0.2) = D/sstat (dR2) = So dR2 gives ~2 times better accuracy than y(0.2) with the same number of events RDMS Physics and DPG workshop 12/03/2009