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Hadron Production in Jets: CDF Insights on MLLA and LPHD in High-Energy Collisions

This paper presents findings from the CDF collaboration on bulk hadron production in jets from p+p- collisions at a center of mass energy of 1.8 TeV. The study employs the Modified Leading Log Approximation (MLLA) and Local Parton-Hadron Duality (LPHD) to analyze charged hadron production in jets with energies ranging from 40 to 300 GeV. Results indicate that MLLA effectively describes the momentum distribution of partons within jets and provides experimental predictions that align with data. The work emphasizes the need for further tests across broader energy ranges.

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Hadron Production in Jets: CDF Insights on MLLA and LPHD in High-Energy Collisions

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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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