Preliminary Request: Mean Charged Multiplicity in DIS M. Rosin, D. Kçira, and A. Savin University of Wisconsin ZEUS Monday meeting Preliminary request April 18th, 2005 http://www-zeus.desy.de/~sumstine/multip

Multiplicity: e+e- and pp pp(ISR) vs. √q2had pp(ISR) vs. √spp e+e- multiplicity plotted vs √se+e- compared to pp multiplicity plotted vs 3 different values of √spp Remove the leading particles from the pp reactions and plot pp vs √qhad2 Agreement between e+e- and pp when plotted vs. pp invariant mass Current analysis: Compare multiplicity measurements in ep to e+e- and pp Start with mean multiplicity for e+e- and pp. Here is e+e- annhilation, and a plot of multiplicity for ee vs. the scale is sqrt s, (inv. Mass of ee collisions). In pp tried sqrt of s using whole energy of incoming protons, plotted number charged particles vs this scale, for three different values of sqrt s. Points are below ee data. So, tried to correct for leading effects: A certain amt of energy doesn’t contribute, and it is taken out by leading protons. Q2 had as shown here corresponds to inv. Mass of system that was created within the detector, (one should keep in mind the sqrt s for e+e- is also inv. Mass). And when multiplicity for pp is plotted against q2had, the data lie on top pf the e+e- points So based on this study it was suggested that hadronization has universal behvior for the inv. Mass (energy). To check: is it still true in ep collision.

ep measurements in the current region of Breit frame Previous ZEUS analysis compared e+e- (vs √se+e-) to ep in current region of the Breit Frame (vs. Q). Agreement for higher Q This analysis: repeat the ep measurement in current region of Breit frame using 2*Ecurrent as scale. Better overall agreement with e+e- and pp. This method compensates for gluon migration into the target hemisphere. These points are already preliminary Current region understood  look more closely at particles in the target region

Visible multiplicity in Breit and hadronic center of mass (HCM) frames Visible Part Breit Frame: 90% of hadrons in current region visible in detector, only 30% of target region hadrons are visible HCM Frame: Particles in proton hemisphere unseen in detector. Photon region dominated by contribution from target region of Breit frame (~80% of visible hadrons) All Hadrons Current Region Breit Frame Proton remnant Visible Part All Hadrons Photon Region HCM Frame Proton Region HCM Frame

Moving to the hadronic center of mass (HCM) frame Using HCM frame is intuitive because all interactions in e+e- and pp happen in the center of mass frame. Photon region of HCM frame has BIG contribution from target region of Breit frame To be consistent with Breit frame measurement we measure 2<nch> vs. 2*E of correspondent hadronic system

2*Ephoton region = W in HCM frame Measure total energy in photon hemisphere of hadronic center of mass frame. By definition the total energy in each hemisphere is W/2. Plot 2*E / W vs. W & fit to line slope: 0.12 x10-4 intercept: 1.00062 2*Ephoton region= W in HCM frame slope: 0.12 x10-4 intercept: 1.00062

Control Plots:W & Tracks Data compared to both Ariadne and Lepto for W and Tracks W: Both Lepto and Ariadne show general agreement with data, some disagreement at lower W. Tracks: Lepto simulates track distribution and gives better description of tracks than Ariadne. W: LOG SCALE W: LINEAR SCALE TRACKS: LINEAR SCALE TRACKS: LOG SCALE

Control Plots: Tracks in W bins Ariadne shows disagreement in two highest W bins ARIADNE ARIADNE ARIADNE W bin 1 W bin 2 W bin 3 disagreement in highest W bin Lepto has better overall agreement than Ariadne LEPTO LEPTO LEPTO

Multiplicity vs. W in HCM frame (data and both Lepto and Ariadne) Measurements in current region of Breit frame and photon hemisphere of HCM frame compared to both Lepto and Ariadne predictions Disagreement between predictions and data in highest W due to poor simulation of track distributions at high W. Lepto & Ariadne predictions agree well with each other in both frames Number of observed hadrons is multiplied by Monte Carlo estimated corrections applied in each W bin (Factors: 1.9, 1.5, 1.3) Largest systematic from MC (5% in highest W bin), Lepto points are above Ariadne  plot data on average

Significant Systematics Change % Difference in W bins W bin 1 W bin 2 W bin 3 Lepto vs. Ariadne <0.5% 3.1% 5.4% Matrix vs. Bin-by-bin 0.6% 0.8% CAL energy scale +/- 3% Electron energy cut +/- 1 GeV Q2 cut +/- 1.6 GeV Vertex cut +/- 5 cm E-pz cut +/- 5 GeV Electron radius cut +/- 1 cm yjb +/- 0.0006 Track pT +0.05/-0.03 GeV

Comparison to second analysis Current region hadronic center of mass frame vs. W Monte carlo: Ariadne on left, Lepto on right  Agreement between 2 analysis good for both Ariadne and Lepto Second analysis done by D. Kçira

Multiplicity in current region of Breit and HCM frames compared to e+e- and pp Measurement in current region of Breit frame agree with e+e- and pp points. Measurement in photon hemisphere of HCM frame agrees with LEP points. Request for preliminary

Summary Request for preliminary:

Comparison to second analysis (Matrix method) Current region hadronic center of mass frame vs. W Monte carlo: Ariadne on left, Lepto on right Correction method: Matrix method  Agreement between 2 analysis good for both Ariadne and Lepto