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Hadron production in jets at CDF

Hadron production in jets at CDF. Anthony Timmins, Wayne State University. Phys. Rev. D 68 (2003) 012003. CDF’s last big paper on bulk hadron production in jets p + +p - collisions at CM 1.8 TeV Jet energies 40  300 GeV with || <~ 1

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Hadron production in jets at CDF

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  1. Hadron production in jets at CDF Anthony Timmins, Wayne State University

  2. Phys. Rev. D 68 (2003) 012003 • CDF’s last big paper on bulk hadron production in jets • p++p- collisions at CM 1.8 TeV • Jet energies 40  300 GeV with || <~ 1 • Paper showed that MLLA assuming LPHD describes charged hadron production in jets well…

  3. What are MLLA and LPHD? • MLLA = Modified Leading Log Approximation • For an initial parton Ejet, uses pQCD to describe shower evolution analytically • Implements Angular Ordering • Constrains sequentially emitted partons to successively smaller angles WRT initial parton. • Mimics destructive coherence effects not accounted in pQCD • Predicts momentum distribution of partons in jet • Needs a cut-out parameter Qeff • Branching at this momentum • Predicts ratio of parton multiplicities in quark/gluon jets • ~ 9/4 q g q q q g Initial q with Ejet

  4. What are MLLA and LPHD? • LPHD = Local Parton Hadron Duality • Assumes when partons hadronise, one-one correspondence between hadron and parton multiplicities…. • Assumes momentum distribution of partons is similar to that of the hadrons • Allows MLLA (parton calculation) to be compared to the data (hadron measurement) • Has an experimentally verifiable quantity, the KchargedLPHD factor.. • KchargedLPHD = Ncharged hadrons/Npartons = 2/3….

  5. The CDF detector • Has Electromagnetic and Hadronic Calorimeters to measure jet energy Jet energy res. 7-10% • CTC (Central Tracking Chamber) detects charged hadrons… • Momentum distribution of hadrons expressed in   = log(Ejet/phadron)

  6. MLLA fits to  distributions • Lines show MLLA fits to data • Two free parameters, Qeff and K Higher order QCD corrections Ratio of quark/gluon jet multiplicities Fraction of gluon jets

  7. Characterising the K Factor • Using the above, KchargedLPHD andrcan be extracted • FnMLLAare g are known from theory • LPHD predicts KchargedLPHD =2/3 • MLLA predicts r = 9/4 = 2.25 • Data consistent with those predictions • Errors are large though…

  8. Extraction of Qeff • In MLLA, maximum position in  related to Qeff 0= Y + √Yc - c where Y = log(Ejet sin / Qeff) • Extracted value consistent with fits shown two slides ago

  9. Eur. Phys. J. C55 (2008) 293 Ideas for ALICE? • Test theory in much larger energy range… • CDF p+p =1.8 TeV • LHC p+p = 7 TeV • ATLAS and CMS also have QCD groups • and have hadronic calorimetry • ALICE has superior PID • More useful to look at identified particles in jets? • MLLA predictions exist for p+p and Pb+Pb • Currently doing this at STAR • Measurements not finished :-(

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