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Soft QCD Phenomena in High-E T Jet Events at CDF

Soft QCD Phenomena in High-E T Jet Events at CDF. Andrey Korytov. (for the CDF Collaboration). 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

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Soft QCD Phenomena in High-E T Jet Events at CDF

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  1. Soft QCD Phenomena in High-ET Jet Events at CDF Andrey Korytov (for the CDF Collaboration) • 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-ET Jet Events • with the CDF Detector

  2. Soft QCD Phenomena in High-ET Jet Events • Anatomy of events with high ET 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

  3. LHC MinBias Why bother? • Jet Fragmentation: • Jet development physics: • Parton shower stage—challenge for pQCD calculations at the very soft limit (kT~LQCD) • Hadronization stage—still remains a mystery • Many high-ET 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 kT=1 GeV/c

  4. Results presented in this talk • Jets: • Momentum distribution of charged particles in jets vs. 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 jets vs. MC • Charged particle multiplicity flow away from jets vs. MC • Momentum distribution of away-from-jet charged particles vs. MC

  5. Jets: doing fragmentation analytically • Jet fragmentation: • parton shower development: MLLA’ Modified Leading Log Approximation with one kT-cutoff parameter Qeff=Qcutoff=LQCD • hadronization: LPHD Hypothesis of Local Parton Hadron Duality with one parameter KLPHD=Nhadrons/Npartons • MLLA+LPHD: cannot describe all details… but all analytical… and works surprisingly well… • Momenta of charged particles in jets: • Qeff = 230  40 MeV • KLPHD() = 0.56  0.10 CDF Charged particle momentum spectra (cone=0.47) and MLLA+LPHD fit

  6. Jets: gluon vs quark jet differences • Ratio r = Nhadrons(gluon jet) / Nhadrons(quark jet) • recent calculations (for partons): extensions of NLLA, r=1.4-1.7 (Q=10-100 GeV) • lots of results from LEP, not all self-consistent: r = 1 to 1.5 jet-ID biased, model-dependent, few “unbiased/model-independent”

  7. Jets: gluon vs quark jets at CDF • di-jet events (~60% gluon jets) and g-jet events (~80% quark jets) • di-jet or g-jet center of mass frame: Ejet = ½Mjj or ½Mgj • Nch multiplicity in cones with opening angle q from ~0.3 to ~0.5 rad • Energy scale Q=Ejetq • Results • Ratio: r=1.60.2, almost energy scale independent • multiplicities in quark and gluon jets: see plot

  8. Run II CDF preliminary Jets: Energy flow inside jets (vs MC) • Jet shape: fractional energy flow Y(r) = ET(0:r) / ET(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

  9. 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 h and  the smaller jet’s ET, the larger the disagreement • Is it real or do we have simulation problems with the new plug calorimeter? • expand tracker analysis to higher h region… • any D0 data? ?

  10. 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=d2N / dfdh • PT spectrum of particles in direction transverse to leading jet: dn/dPT • Average Energy summed over charged particles in transverse direction: d2ET/dfdh • Confront data and MC: • Identify importance of various MC knobs/parameters ET(jet) • Charged tracks: • d2N/dfdh • d3N/dfdhdPT • d2ET/dfdh “transverse” particles as a probe of the underlying event

  11. Charged Particle Density h f "Transverse" Charged Particle Density: dN/d d 1.0E+01 1.00 CDF Preliminary h | |<1 CDF Data Pythia 6.206 (default) 1.0E+00 MSTP(82)=1 data uncorrected theory corrected PARP(81) = 1.9 GeV/c 0.75 Min-Bias Data, 1.8 TeV dPT (1/GeV/c) 1.0E-01 f d "Transverse" Charged Density 1.0E-02 h 0.50 HW "Soft" Min-Bias 1.0E-03 at 0.63, 1.8, and 14 TeV Charged Density dN/d 0.25 1.0E-04 h 1.8 TeV | |<1.0 PT>0.5 GeV 0.00 1.0E-05 0 5 10 15 20 25 30 35 40 45 50 PT(charged jet#1) (GeV/c) 1.0E-06 0 2 4 6 8 10 12 14 CTEQ3L CTEQ4L CTEQ5L CDF Min-Bias CDF JET20 PT (GeV/c) UE: data vs. default Pythia and Herwig • Default Pythia and Herwig fail to reproduce data one way or another, e.g.: • Pythia 6.206 underestimates number of tracks in transverse direction… • Herwig 6.4 gives too soft spectrum for particles in transverse direction, especially in events with small ET jets (missing MPI now have been added)

  12. Pythia: CDF Tune A vs. Default 6.206 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 … UE: tune Pythia to match CDF data

  13. "Transverse" Charged Particle Density 1.0E+00 CDF Preliminary data uncorrected theory corrected 1.0E-01 PYTHIA Tune A 1.96 TeV dPT (1/GeV/c) 70 < PT(chgjet#1) < 95 GeV/c f 1.0E-02 d h 1.0E-03 Charged Density d3N /d 1.0E-04 30 < PT(chgjet#1) < 70 GeV/c 1.0E-05 0 2 4 6 8 10 12 14 16 18 20 PT(charged) (GeV/c) UE: Pythia Tune A describes Data

  14. Summary • Jet fragmentation • Momenta of charged particles in jets are well described by NLLA pQCD: • MLLA kT-cutoff Qeff=230  40 MeV • LPHD Nhadrons/Npartons = KKLPHD() = 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-h 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?

  15. A few backup slides follow this page…

  16. 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 ms • Max luminosity: 2x1031 50x1031 cm-2 s-1 • Integrated luminosity: 0.1  15 fb-1 • (before LHC turn-on) • As of May 2003: • Peak luminosity so far: 4.5x1031 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

  17. 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 pT>1.5 GeV/c • Faster Front End Electronics • 3d vertex coverage: |h|<2 • Tracking coverage: |h|<2 • Calorimeter coverage: |h|<3.6 • Mini-plug calorimeter: 3.6<|h|<5.1 • Muon coverage:|h|<1.5

  18. 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

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