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Charged Particle Multiplicity in DIS

Charged Particle Multiplicity in DIS. ZEUS Collaboration Meeting. Michele Rosin University of Wisconsin June 18, 2003. Universality of dependence of <n ch > on effective energy.

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Charged Particle Multiplicity in DIS

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  1. Charged Particle Multiplicity in DIS ZEUS Collaboration Meeting Michele Rosin University of Wisconsin June 18, 2003

  2. Universality of dependence of <nch> on effective energy • In the current region of the Breit frame, Q for ep reactions corresponds to Whad for e+e- reactions • Mean charged multiplicity, <nch> ,vs. Q shows linear dependence for both e+e- and ep on the effective energy going into hadronization • Universal dependence of <nch> observed in e+e- and ep reactions e+e- ep

  3. Motivation for the use of Meff as energy scale Similarity of particle production at e+e- and ep colliders Whad • A measured portion of the hadronizing string has properties which are derived from the properties of the whole string which forms the hadronic final state (HFS) • linear dependence of <nch> on effective mass Whad Meff Whad: HFS measured in full phase space Meff: HFS measured in the detector where the tracking efficiency is maximized

  4. Study: <nch> vs. Meff CAL within the CDT acceptance CTD Effective Mass • Hadronic final state within  • Charged part seen as tracks • Energy measured by calorimeter

  5. ZEUS Measurement • Lab Frame: Investigation of degree of universality in charged particle production • <nch> consistent with linear dependence vs. ln Meff • <nch> 15% above corresponding e+e- • Data compatible with picture of additional gluon radiation due to color charge in the ep reactions Continuation of work by: L Shcheglova, A. Solomin, S. Zotkin

  6. 1996 Data Sample • DIS Event Selection • Scattered positron found with E > 12 GeV • A reconstructed vertex with |Zvtx| < 50 cm • scattered positron position cut: |x| > 15 cm or |y| > 15cm (in RCAL) “Box cut” • 40 GeV < E-pz < 60 GeV • Track Selection • Tracks associated with primary vertex • || < 1.75 • pT > 150 MeV • Physics and Kinematic Requirement • Q2 da > 25 GeV2 • y el < 0.95 • y JB > 0.04 This Analysis done with ORANGE! 8,700,692 events before cuts 208,550 events after all cuts

  7. Event Simulation • Ariadne ’97 v4.08 • No changes in detector from ’96 to ‘97 • Matrix elements at LO pQCD O(s) • Parton showers: CDM • Hadronization: String Model • Proton PDF’s: CTEQ-4D Need more Monte Carlo 747,003 events before cuts 50,884 events after all cuts

  8. Zeus ’96 Data vs. Ariadne Vertex Position X & Y vertex • MC simulates transverse vertex well Z vertex • Longitudinal vertex is generally well described

  9. Energy and Angle of Scattered Positron Polar Angle Scattered Positron Energy Corrected for dead material and non-uniformities

  10. Virtuality & Inelasticity Yel Q2 double angle method Yjb

  11. hmax shows diffractive events • These are diffractive events that are not simulated by the Ariadne Monte Carlo • Only max>3.2 is described by Ariadne • 15545 events out of total data sample (208,550 events) 7.5% Note: Log Scale • Strategy: • (current) Cut out diffractive events • (later) Use mixture of diffractive & non-diffractive Monte Carlo. Normalized above max= 3.2

  12. Tracking: # of Charged Tracks • Number of tracks well described by Ariadne model over four orders of magnitude • Validation of model & CTD tracking simulation

  13. Tracking:  & pT acceptable agreement for correcting for detector effects

  14. ’96 Data Ariadne Effective Mass • First look at Ariadne vs. Meff • needs further study

  15. Mean Charged Multiplicity vs. Meff Average number of charged tracks vs. effective mass <nch> • first look data sample • uncorrected ZEUS ’96 data compared to Ariadne • proportional to ln (Meff) • improvement expected

  16. Statistical errors only ZEUS Measurement • Lab Frame: Investigation of degree of universality in charged particle production • <nch> consistent with linear dependence vs. ln Meff • <nch> 15% above corresponding e+e- • Data compatible with picture of additional gluon radiation due to color charge in the ep reactions Continuation of work by: L Shcheglova, A. Solomin, S. Zotkin

  17. Summary • First look at Multiplicity Distributions in DIS at HERAusing 1996 data • Progress in understanding event kinematics and tracking • Plan • Increase statistics to include 1997 data • generate Monte Carlo • Investigate diffractive effects • Measure multiplicities vs. Q in the current and target region of the Breit frame • Measure momentum spectra • Compare different models for parton showers and hadronization to data • Evaluate systematic uncertainties • Interest in second analysis: Lydia Shcheglova

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