Charged Particle Multiplicity in DIS

1. Charged Particle Multiplicity in DIS Preliminary Request M. Rosin, D. Kçira, and A. Savin University of Wisconsin L. Shcheglova Moscow State University, Institute of Nuclear Physics June 7th, 2004

2. Outline • Introduction and motivation • Data selection & simulation • Control plots • Correction methods: • Bin by bin (modified) • Matrix • <nch> vs. Meff • with MC predictions • In bins of x • In bins of x and Q2 • Systematics • Comparison to second analysis • Summary and plan

3. Motivation • Mean charged multiplicity, <nch> , vs. Q shows logarithmic dependence for both e+e- and pp on the effective energy going into hadronization, and dependence is universal • For pp and e+e- hadronization is universal when you go to proper scale: √s for e+e- reactions, effective energy going into hadron production, √q2 for pp.

4. Motivation • ep points measured in current region of Breit frame(x2) vs. Q, shows nice agreement • Expect that mean charged multiplicity for ep (measured in lab frame) and pp (and e+e-) are universal, when plotted against energy going into hadron production.

5. Motivation for the use of Meff as energy scale • Analogous to the pp study, want to measure the dependence of <nch> of on it’s total invariant mass. (Energy available for hadronization) • For ep in lab frame, measure visible part of <nch> with visible part of energy available for hadronization: should show same universality as total <nch> and total energy • Use Meff as scale for comparing to pp (and e+e-) Whad Meff Lab Frame Meff: HFS measured in the detector where the tracking efficiency is maximized

6. 1996-97 Data sample • Event Selection • Scattered positron found with E > 12 GeV • A reconstructed vertex with |Zvtx| < 50 cm • Scattered positron position cut: radius > 25cm • 40 GeV < E-pz < 60 GeV • Diffractive contribution excluded by requiring ηmax> 3.2 • 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 • 70 GeV < W < 225 GeV ( W2 = (q + p)2 ) 735,007 events after all cuts (38.58 pb-1)

7. Event simulation • Ariadne ’97 6v2.4 • Matrix elements at LO pQCD O(s) • Parton showers: CDM • Hadronization: String Model • Proton PDF’s: CTEQ-4D Luminosity of MC : 36.5 pb-1

8. Kinematic Variables • 96-97 data compared to ARIADNE and LEPTO for kinematic variables • Both ARIADNE and LEPTO show good agreement for kinematic variables

9. Meff and Tracks • LEPTO and ARIADNE comparisons to tracks and Meff • Tracks better described by ARIADNE • Meff better described by LEPTO

10. Correction to hadron level: bin by bin Part one: correct to hadron level using only hadrons generated with pT > 0.15 GeV Part two: correct for hadrons with lower pT, using ratio of <gen> with pT cut to <gen> no pT cut in each bin.

11. Correction to hadron level: bin by bin Correction for detector effects Correction of hadrons of pT > 0.15 to all hadrons

12. No. of events with p tracks generated when o tracks were observed Mp,o = No. events with o tracks observed Correction to hadron level: matrix The matrix relates the observed to the generated distributions of tracks in each bin of Meff by: • Matrix corrects tracks to hadron level • ρ corrects phase space to hadron level Hadrons passing gen level cuts ρ = Hadrons passing det level cuts

13. Comparison of correction methods • Better than 2% agreement in all Meff bins • bin-by- bin considered as a systematic

14. Correlated & Uncorrelated Systematics

15. Results with MC predictions • Good agreement with 1995 prelim. points, with smaller statistical, systematic errors • Observe a significant difference between ep, e+e- and pp. • ARIADNE describes data dependence, LEPTO higher than the data • Check for ep points: does <nch> dependence on Meff change depending on scale?

16. <nch> vs. Meff in x bins • if difference is due to quark and gluon distributions, then maybe also x dependence • x range split into similar bins as in previous multiplicity paper. • weak x dependence in both data and MC observed

17. x and Q2 bins • No Q2 dependence observed • Data described by ARIADNE • LEPTO above data

18. Comparison to 2nd analysis in Q2 and x bins • Agreement between 1st and 2nd analysis within 1% for matrix for x and Q2 bins

19. Comparison to 2nd analysis • For full kinematic range, agreement between 1st and 2nd analysis is less than 1% for both correction methods.

20. Summary • Shown 3 preliminary plots • Measured in x and Q2 bins, weak x dependence not enough to compensate for difference between ep and pp. No Q2 dependence. • Observed difference in dependence of <nch> on Meff between ep and pp (and e+e-) is real • Plan • Measure <nch> in current region of Breit frame vs. Meff (instead of Q) • Study diffractive events; combine ARIADNE & RAPGAP

21. Preliminary plots

22. Preliminary plots

23. Preliminary plots