1. Mean Charged Multiplicity in DIS, Michele Rosin U. WisconsinZEUS Collaboration Meeting, Oct. 21st 2004 1 Analysis Update: Mean Charged Multiplicity in DIS M. Rosin, D. Kçira, and A. Savin University of Wisconsin L. Shcheglova Moscow State University, Institute of Nuclear Physics ZEUS Collaboration Meeting Padova, Italy October 21st, 2004 http://www-zeus.desy.de/~sumstine/multip

2. Mean Charged Multiplicity in DIS, Michele Rosin U. WisconsinZEUS Collaboration Meeting, Oct. 21st 2004 2 Outline & Status Status of analysis: Plots made preliminary for QFTHEP04 (also shown at ICHEP and HS04) (these will be reviewed in this talk) measurement in current region of Breit frame Lab frame measurement of vs. M eff vs. M eff in Breit Frame Agreement with second analysis achieved All systematics completed (except systematics on the boost) Checks Testing the sensitivity of the dependence of on M eff to the configuration of the final state

3. Mean Charged Multiplicity in DIS, Michele Rosin U. WisconsinZEUS Collaboration Meeting, Oct. 21st 2004 3 Comparing ep and e + e - using current region of Breit Frame  e+e-: boson with virtuality √s produces (in LO) 2 quarks & hadronization is between 2 colored objects q and q to produce final state  ep: boson with virtuality Q produces 1 quark: the 2 nd quark comes from the interaction between the photon and the proton  current region of Breit frame for ep similar to one hemisphere of e+e-  If we use Q as scale to compare the current region of the Breit frame to e+e-, multiply hadrons by 2

4. Mean Charged Multiplicity in DIS, Michele Rosin U. WisconsinZEUS Collaboration Meeting, Oct. 21st 2004 4 Previous ZEUS Measurement vs. Q compared to e + e -  multiplicity vs. center of mass energy (√s) for different e+e- experiments: data agree with one another  Attempt to compare multiplicity in current region of Breit frame vs. Q, for ep, to multiplicity vs. √s for e+e-.  Multiplicity for e+e- has been scaled down by factor of 2  Consistent with e+e- data for high Q 2  Idea of current analysis: Understand current and target multiplicity and compare to e+e- European Physics Journal C11 (1999) 251-270

5. Mean Charged Multiplicity in DIS, Michele Rosin U. WisconsinZEUS Collaboration Meeting, Oct. 21st 2004 5 Closer look at current region  ep: Split into Current and Target Region – one string two segments.  In ep we have a color field between 2 colored objects the struck quark and the proton remnant  When we use Q as a scale we are assuming the configuration in ep is as symmetric as it is in e+e-, but it isn’t  This asymmetric ep configuration leads to migration of particles from the current region to the target region Breit Frame diagram

6. Mean Charged Multiplicity in DIS, Michele Rosin U. WisconsinZEUS Collaboration Meeting, Oct. 21st 2004 6 Gluon radiation, Q, and 2*E Breit q q g q q g Soft ContributionHard Contribution QCD Compton  In hard and soft processes gluon radiation occurs  These radiated gluons can migrate to target region  Total energy in the current region of Breit frame and multiplicity are decreased due to these migrations (Q 2 is not)  Effect is more pronounced for low Q 2 : more low energy gluons  Must use 2*E Breit and 2*N ch for comparing with e+e- No migrations: With migrations: N < N expected

7. Mean Charged Multiplicity in DIS, Michele Rosin U. WisconsinZEUS Collaboration Meeting, Oct. 21st 2004 7 Multiplicity vs. 2*E Breit  Measure multiplicity dependence on 2*E Breit and compare to previous ZEUS measurement vs. Q, and to e+e- vs. √s e+e-.  Points agree with the e + e - points  This approximation of invariant mass partially takes into account the real distribution of the particles.  Current region understood, would like to use some energy scale to compare target region for ep to e+e-  Start by looking at comparison of e+e- and pp where agreement in the multiplicity dependence has been observed

8. Mean Charged Multiplicity in DIS, Michele Rosin U. WisconsinZEUS Collaboration Meeting, Oct. 21st 2004 8 Multiplicity: e + e - and pp Based on this study it was suggested that hadronization has universal behavior for the invariant mass.  Check: Is it true for ep? e+e-e+e- pp Inv. mass of pp e+e-:e+e-: pp vs. √q 2 had pp vs. √s pp Agreement between e+e- and pp plotted vs. pp inv. mass

9. Mean Charged Multiplicity in DIS, Michele Rosin U. WisconsinZEUS Collaboration Meeting, Oct. 21st 2004 9 Charged Hadrons & Effective Mass: experimental method CAL within the CTD acceptance Study: vs. M eff CTD  Measure hadronic final state within  for best acceptance in the central tracking detector (CTD)  Measure # charged tracks, in η range, reconstruct number of charged hadrons  Measure invariant mass of the system (Meff) in corresponding delta eta region.  Energy is measured in the Calorimeter (CAL)

10. Mean Charged Multiplicity in DIS, Michele Rosin U. WisconsinZEUS Collaboration Meeting, Oct. 21st 2004 10 The use of M eff as energy scale M eff : HFS measured in the detector where the tracking efficiency is maximized  repeat what was done in the pp measurement for ep in the lab frame.  Effectively cut out part of the final state and measure number of charged particles there along with the corresponding invariant mass  Previously shown in e+e- and pp that the number of charged particles vs. invariant mass of the system is universal  For ep in lab frame, measure visible part of vs. visible part of energy available for hadronization: M eff Difference between ep and pp: ep is more asymmetric W had Lab Frame M eff Visible part 1 remnant 2 remnants

11. Mean Charged Multiplicity in DIS, Michele Rosin U. WisconsinZEUS Collaboration Meeting, Oct. 21st 2004 11 Current lab frame measurement  Agreement between data* and ARIADNE  LEPTO describes data but when including the soft color interactions LEPTO-SCI deviates from data  Agreement with 2 nd analysis <1% (Dorian Kçira) *1996-97 Inclusive DIS data 38 pb -1 Q 2 >20 GeV 2 70 GeV < W < 225 GeV ( W 2 = (q + p) 2 ) Diffractive events excluded Normal track requirements

12. Mean Charged Multiplicity in DIS, Michele Rosin U. WisconsinZEUS Collaboration Meeting, Oct. 21st 2004 12 Previous results in lab frame: vs. M eff compared to e + e - and pp  ZEUS 1995 preliminary results  plotted vs. M eff for ep, vs. q had for pp and vs. √s for e+e-.  Present analysis consistent with previous results  for ep is ~15% higher than that for e+e- and pp.   Checked x and Q 2 dependence: no Q 2 dependence, weak x dependence not enough to explain difference  Investigate this difference: look at visible charged multiplicity vs. M eff for current and target regions of the Breit frame.

13. Mean Charged Multiplicity in DIS, Michele Rosin U. WisconsinZEUS Collaboration Meeting, Oct. 21st 2004 13 Detector acceptances for current and target regions The visible part of the multiplicity is very different for the current and target region of the Breit Frame.  Observed portion of hadrons from total number generated is 90% for current region & only 30% for target region.  When comparing visible part of the current and target regions we compare total current region with only the part of the target region that is far from the proton remnant Visible Part Proton remnant

14. Mean Charged Multiplicity in DIS, Michele Rosin U. WisconsinZEUS Collaboration Meeting, Oct. 21st 2004 14 Breit frame: vs. M eff  Visible multiplicity as function of Meff show similar dependence for current and target regions of Breit frame  Target multiplicity is higher than current multiplicity and can reach higher values of Meff  combined current and target region (black lab frame points) show same behavior as target region

15. Mean Charged Multiplicity in DIS, Michele Rosin U. WisconsinZEUS Collaboration Meeting, Oct. 21st 2004 15 Check: Compare to e+e- & pp using ep dijet events QCD Compton Boson-Gluon Fusion  Try to mimic final state of e+e- and pp by looking at ep dijet events  Require events with only 2 jets, one in the current region of the Breit Frame an one in the Target region e+e- annihilation pp collision  remnant jet

16. Mean Charged Multiplicity in DIS, Michele Rosin U. WisconsinZEUS Collaboration Meeting, Oct. 21st 2004 16 vs. M eff for events with 2 jets  First look at dijet events  A simple test of the sensitivity of this dependence vs. the configuration of the final state: higher dijet E T  more collimated events  more similar to pp and e+e- final state  M eff increases with increasing dijet E T  Events with 2 jets of E T >10 GeV show similar dependence to pp &e+e-  Next check: Look at hadronic center of mass frame

17. Mean Charged Multiplicity in DIS, Michele Rosin U. WisconsinZEUS Collaboration Meeting, Oct. 21st 2004 17 Summary  The hadronic final state has been investigated in DIS ep scattering in terms of the mean charged multiplicity and respective invariant mass of the charged and neutral particles, M eff  in current region of the Breit frame show same dependence as e+e- if 2*E Breit is used as the scale  vs. M eff show similar dependence for visible part of the current and target regions of the Breit frame  Lab frame 15% above e+e- and pp & shows no strong dependence on x or Q 2  Study using dijet events to better mimic pp collision is underway and shows dependence similar to that of e+e- and pp when dijet E T is increased Other tests: move to γP center of mass frame, use HERWIG to correct data to hadron level Plans :  Finish systematics of the boost  Paper before the end of the year (1 st draft started)