Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen Soft QCD Phenomena in High-E T Jet Events at CDF Abstracts covered in this talk A356 Fragmentation Differences of Quark and Gluon Jets at CDF A362 Measurement of Jet Shapes and Energy Flows in Dijet Production at the Tevatron A353 Jet Evolution and the Underlying Event in Run 2 at CDF Official Title Studies of Jet Shapes and Fragmentation Differences of Quark and Gluon Jets with the CDF Detector (note: Underlying Event fell out from the title) Better Title Studies of Soft QCD Phenomena in High-E T Jet Events with the CDF Detector Andrey Korytov (for the CDF Collaboration)

Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen Soft QCD Phenomena in High-E T Jet Events Anatomy of events with high E T jets:  hard scattered partons  final state radiation  initial state radiation  multi-parton interactions  proton/antiproton remnants  Note: separation between sub-processes is not clean due to entangled color connections… Soft QCD Phenomena:  Jet fragmentation is largely driven by soft QCD  So is the UE physics Tools available:  re-summed pQCD approximations (analytic, but only for limited number of observables)  Monte Carlo generators (generic, but have many tunable ad-hoc knobs) JETS UNDERLYING EVENT

Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen Why bother? Jet Fragmentation:  Jet development physics: Parton shower stage—challenge for pQCD calculations at the very soft limit (k T ~  QCD ) Hadronization stage—still remains a mystery  Many high-E T physics analyses depend on good understanding of jet properties Underlying Event:  UE physics is poorly understood: MC Generators implement UE differently and often with many (too many?) parameters Even when tuned to match the accessible data, MC predictions for LHC vary wildly  UE pollutes many analyses  source of systematic errors LHC MinBias k T =1 GeV/c

Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen Results presented in this talk Jets:  Momentum distribution of charged particles in jetsvs. NLLA  Multiplicities of charged particles in g- and q-jets vs. NLLA  Energy flow in jets (jet shapes)vs. MC Underlying Event:  Energy flow away from jetsvs. MC  Charged particle multiplicity flow away from jetsvs. MC  Momentum distribution of away-from-jet charged particlesvs. MC

Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen Jets: doing fragmentation analytically Jet fragmentation:  parton shower development: MLLA’ Modified Leading Log Approximation with one k T -cutoff parameter Q eff =Q cutoff =  QCD  hadronization: LPHD Hypothesis of Local Parton Hadron Duality with one parameter K LPHD =N hadrons /N partons  MLLA+LPHD: cannot describe all details… but all analytical… and works surprisingly well… Momenta of c harged particles in jets:  Q eff = 230  40 MeV  K LPHD(  ) = 0.56  0.10 CDF Charged particle momentum spectra (  cone =0.47) and MLLA+LPHD fit

Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen Jets: gluon vs quark jet differences Ratio r = N hadrons (gluon jet) / N hadrons (quark jet)  recent calculations (for partons): extensions of NLLA, r= (Q= GeV)  lots of results from LEP, not all self-consistent: r = 1 to 1.5 jet-ID biased, model-dependent, few “unbiased/model-independent”

Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen Jets: gluon vs quark jets at CDF  di-jet events (~60% gluon jets) and  -jet events (~80% quark jets)  di-jet or  -jet center of mass frame: E jet = ½M jj or ½M  j  N ch multiplicity in cones with opening angle  from ~0.3 to ~0.5 rad  Energy scale Q=E jet   Results Ratio: r=1.6  0.2, almost energy scale independent multiplicities in quark and gluon jets: see plot

Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen Jets: Energy flow inside jets (vs MC) Run II CDF preliminary  Jet shape: fractional energy flow  (r) = E T (0:r) / E T (0:R), where R=1  In central region, do it with Calorimeter towers ( ● ) Charged tracks ( ○ )  Either way—shapes are nearly identical  Herwig and Pythia practically coincide and agree with data

Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen Run II CDF preliminary Jets: Energy flow inside jets (vs MC)  In forward region, do it with Calorimeter towers only  Data vs MC discrepancy:  the higher jet  and  the smaller jet’s E T, the larger the disagreement  Is it real or do we have simulation problems with the new plug calorimeter? expand tracker analysis to higher  region… any D0 data? ?

Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen UE studies with charged tracks  Event sample: min-bias, jet events (central jets)  Measure: Average Number of particles in direction transverse to leading jet: n=d 2 N / d  d  P T spectrum of particles in direction transverse to leading jet: dn/dP T Average Energy summed over charged particles in transverse direction: d 2 E T /d  d   Confront data and MC: Identify importance of various MC knobs/parameters “transverse” particles as a probe of the underlying event E T (jet) Charged tracks: d 2 N/d  d  d 3 N/d  d  dP T d 2 E T /d  d 

Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen UE: data vs. default Pythia and Herwig Default Pythia and Herwig fail to reproduce data one way or another, e.g.:  Pythia underestimates number of tracks in transverse direction…  Herwig 6.4 gives too soft spectrum for particles in transverse direction, especially in events with small E T jets (missing MPI now have been added) "Transverse" Charged Particle Density: dN/d  d  PT(charged jet#1) (GeV/c) "Transverse" Charged Density CTEQ3LCTEQ4LCTEQ5LCDF Min-BiasCDF JET TeV |  | 0.5 GeV Pythia (default) MSTP(82)=1 PARP(81) = 1.9 GeV/c CDF Data data uncorrected theory corrected

Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen UE: tune Pythia to match CDF data PYTHIA and CDF Tune A (CTEQ5L) ParameterDefaultTuneDescription PARP(67)1.04.0Scale factor that governs the amount of initial-state radiation. MSTP(81)11Turns on multiple parton interactions (MPI). MSTP(82)14Double Gaussian matter distribution. PARP(82)1.92.0Cut-off for multiple parton interactions, P T0. PARP(83)0.5 Warm Core: 50% of matter in radius 0.4. PARP(84)0.20.4Warm Core: 50% of matter in radius 0.4. PARP(85) Probability that the MPI produces two gluons with color connections to the "nearest neighbors". PARP(86) Probability that the MPI produces two gluons either as described by PARP(85) or as a closed gluon loop. The remaining fraction consists of quark-antiquark pairs. PARP(89)1,000.01,800.0Determines the reference energy E 0. PARP(90) Determines the energy dependence of the cut-off P T0 as follows P T0 (Ecm) = P T0 (Ecm/E 0 ) PARP(90). Pythia: CDF Tune A vs. Default Enhanced initial state radiation Smoothed out probability of Multi-Parton Interactions (vs. impact) MPIs are more likely to produce gluons than quark-antiquark pairs and MPI gluons are more likely to have color connection to p-pbar remnants …

Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen UE: Pythia Tune A describes Data "Transverse" Charged Particle Density 1.0E E E E E E P T (charged) (GeV/c) Charged Density d 3 N /d  d  dP T (1/GeV/c) CDF Preliminary data uncorrected theory corrected PYTHIA Tune A 1.96 TeV 30 < PT(chgjet#1) < 70 GeV/c 70 < PT(chgjet#1) < 95 GeV/c

Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen Summary Jet fragmentation  Momenta of charged particles in jets are well described by NLLA pQCD: MLLA k T -cutoff Q eff =230  40 MeV LPHD N hadrons /N partons = K KLPHD(  ) = 0.56  0.10  Multiplicities in gluon and quark jets and their ratio r = 1.6  02 agree with extended NLLA pQCD and recent LEP data  Jet shapes mostly agree with PYTHIA and HERWIG, but more studies/tuning are needed for high-  jets Underlying event  Run II and Run I data agree, Run II analysis is being expanded  MC generators with default parameters do not quite work, but can be tuned to match data…  insights into UE physics?

Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen A few backup slides follow this page…

Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen Tevatron upgrade: Run II vs. Run I Original Plan: Run I  Run II CM energy: 1.8  1.96 TeV Bx spacing: 3.5  0.4  s Max luminosity: 2x10 31  50 x10 31 cm -2 s -1 Integrated luminosity: 0.1  15 fb -1 (before LHC turn-on) As of May 2003: Peak luminosity so far: 4.5x10 31 cm -2 s -1 Total delivered (incl. commissioning): 0.24 fb -1 On tape (CDF, incl. commissioning): 0.18 fb -1 Good for physics (CDF) >0.13 fb -1 CDF current data taking efficiency ~90% Long-term plan (by end of 2008): Base goal: 6 fb -1 Stretch goal: 11 fb -1

Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen CDF upgrade: what is new Retained from CDF I:  Solenoid  Central Calorimeters  Central Muon System Brand new in CDF II:  5-layer 3D vertex Si detector  Intermediate Si layers  Central Drift Tracker  Plug Calorimeter  Mini-plug calorimeter  Time of Flight System  Expanded Muon Coverage  TRIGGER, now includes: displaced vertex track p T >1.5 GeV/c  Faster Front End Electronics 3d vertex coverage:  <2 Tracking coverage:  <2 Calorimeter coverage:  <3.6 Mini-plug calorimeter: 3.6<  <5.1 Muon coverage:  <1.5

Andrey Korytov, University of Florida EPS 2003 July 17-23, 2003, Aachen Jets: Gluon vs Quark jets at CDF Momentum distributions of charged particles in gluon and quark jets  Ratio reaches max and flattens for soft part of spectrum at ~1.8  0.2  Same pattern was observed at LEP