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Charged Particle Multiplicity in DIS

This presentation by Michele Rosin details the universality of charged particle multiplicity dependence on effective energy in deep inelastic scattering (DIS) processes, comparing e+e- and ep interactions. The fit reveals a linear relationship between mean charged multiplicity and effective energy, emphasizing consistent behavior across both reaction types. The analysis includes extensive data from HERA, focusing on event characteristics, kinematics, and Monte Carlo simulations. Future work aims to enhance statistical significance and investigate differences in diffractive and non-diffractive events.

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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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