1. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 1 M. Rosin, D. Kçira, and A. Savin University of Wisconsin L. Shcheglova Moscow State University, Institute of Nuclear Physics May 13, 2004 Charged Particle Multiplicity in DIS QCD Group Preliminary Request

2. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 2 Outline Introduction and motivation Data selection & simulation Correction methods: Bin by bin (modified) Matrix vs. M eff with MC predictions In bins of x In bins of x and Q 2 Systematic: LEPTO vs. ARIADNE for correcting in Q 2 and x bins Comparison to second analysis Summary and plan

3. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 3 Motivation  Mean charged multiplicity,, vs. Q shows logarithmic dependence for both e + e - and pp on the effective energy going into hadronization, and dependence is universal  ep points measured in current region of Breit frame (x2), shows nice agreement  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.  Expect that ep (measured in lab frame) and pp (and e+e-) are universal, using a proper scale.

4. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 4 Motivation  Mean charged multiplicity,, vs. Q shows logarithmic dependence for both e + e - and pp on the effective energy going into hadronization, and dependence is universal  ep points measured in current region of Breit frame (x2), shows nice agreement  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.  Expect that ep (measured in lab frame) and pp (and e+e-) are universal, using a proper scale.

5. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 5 Motivation for the use of M eff as energy scale W had M eff M eff : HFS measured in the detector where the tracking efficiency is maximized  Analogous to the pp study, want to measure the dependence of of on it’s total invariant mass. (Energy available for hadronization)  For ep in lab frame, measure visible part of with visible part of energy available for hadronization: should show same universality as total and total energy  Use M eff as scale for comparing to pp (and e + e - ) Lab Frame

6. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 6 1996-97 Data sample Event Selection Scattered positron found with E > 12 GeV A reconstructed vertex with |Z vtx | < 50 cm scattered positron position cut: radius > 25cm 40 GeV < E-p z < 60 GeV Diffractive contribution excluded by requiring η max > 3.2 Track Selection Tracks associated with primary vertex |  | < 1.75 p T > 150 MeV Physics and Kinematic Requirement Q 2 da > 25 GeV 2 y el < 0.95 y JB > 0.04 70 GeV < W < 225 GeV ( W 2 = (q + p) 2 ) 724,958 events after all cuts (38.58 pb -1 )

7. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 7 Ariadne ’97 6v2.4 Matrix elements at LO pQCD O (  s ) Parton showers: CDM Hadronization: String Model Proton PDF’s: CTEQ-4D Event simulation Luminosity of MC : 36.5 pb -1 (Simulates both ’96 and ’97 data; no changes in detector)

8. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 8 Correction to hadron level: bin by bin Part one: correct to hadron level using only hadrons generated with p T > 0.15 GeV Part two: correct for hadrons with lower p T, using ratio of with p T cut to no p T cut in each bin.

9. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 9 Correction to hadron level: bin by bin Correction for detector effects Correction of hadrons of pT > 0.15 to all hadrons

10. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 10 Correction to hadron level: matrix No. of events with p tracks generated when o tracks were observed No. events with o tracks observed M p,o = The matrix relates the observed to the generated distributions in each bin of M eff by:

11. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 11 Comparison of correction methods Better than 3% agreement in all M eff bins

12. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 12 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.  In general data agrees with the MC predictions, LEPTO predicts even higher multiplicities  Check for ep points: does dependence on M eff change depending on scale? ZEUS

13. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 13 vs. M eff 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 mc, in data dependence is stronger Matrix method

14. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 14 vs. M eff in x bins Bin-by-bin method  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.  data agree better with mc than for matrix method, overall weak x dependence

15. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 15 x and Q 2 bins 0.0006 - 0.00120.0012 - 0.00240.0024 - 0.01 0.01 - 0.1 25 -50 50 - 150 150 -1200 Matrix method  No Q 2 dependence observed  for matrix:Data described by ARIADNE, except in high x bins  for bin-by-bin: well decribed by ARIADNE  Bin-by-bin method is more stable against mc, matrix shows some mc dependence  Need to investigate why matrix gives different results in high x bins

16. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 16 x and Q 2 bins 0.0006 - 0.00120.0012 - 0.00240.0024 - 0.01 0.01 - 0.1 25 -50 50 - 150 150 -1200 Bin-by-bin method  No Q 2 dependence observed  for matrix:Data described by ARIADNE, except in high x bins  for bin-by-bin: well decribed by ARIADNE  Bin-by-bin method is more stable against mc, matrix shows some mc dependence  Need to investigate why matrix gives different results in high x bins

17. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 17 LEPTO vs. ARIADNE for corrections  As a systematic, used LEPTO for correction  bin-by-bin method more stable  data agrees with ARIADNE even when corrected using LEPTO

18. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 18 LEPTO vs. ARIADNE for corrections  As a systematic, used LEPTO for correction  bin-by-bin method more stable  data agrees with ARIADNE even when corrected using LEPTO

19. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 19 Comparison to 2 nd analysis in Q 2 and x bins  Agreement between 1 st and 2 nd analysis within 1% for matrix for x and Q 2 bins

20. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 20 Comparison to 2 nd analysis  For full kinematic range, agreement between 1 st and 2 nd analysis is less than 1% for both correction methods.

21. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 21 Summary Shown 3 preliminary plots Measured in x bins, weak x dependence not enough to compensate for difference between ep and pp. Observed difference in dependence of on M eff between ep and pp (and e + e - ) is real Plan Look at Breit frame for consistency check Study diffractive events; combine ARIADNE & RAPGAP

22. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 22 Preliminary plots

23. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 23 Preliminary plots

24. Charged Particle Multiplicity, Michele Rosin U. WisconsinQCD Meeting May 13, 2004 24 Preliminary plots 0.0006 - 0.00120.0012 - 0.00240.0024 - 0.01 0.01 - 0.1 25 -50 50 - 150 150 -1200