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
QCD Review meeting
January 27th, 2005

2. Multiplicity: e+e- and pp
pp vs. √q2had
pp 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
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.

3. ep measurements in the current region of Breit frame
Previous ZEUS analysis compared the e+e- (vs √se+e-) to ep in the current region of the Breit Frame (vs. Q.) Agreement for higher Q
Redid the ep measurement in the current region of the 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.
Current region understood , need to find a scale for comparisons of the target region

4. 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.
Measure ep multiplicity in photon hemisphere of HCM and plot it vs W.
Same as for the current region of the Breit frame (use 2*E as a scale), must take into account migrations of particles out of the frame.
Small correction of W to 2*E
Hadron level Ariadne

5. Multiplicity vs. W in HCM
Monte carlo dependant correction for full phase space applied in each bin
Factors: 1.9, 1.5, 1.3
8% correction for definition of hadrons applied
Ariadne doesn’t describe data, Ariadne doesn’t describe tracks (showed last time)
Working on systematics, largest systematic from MC

6. Ariadne predictions for HCM frame
Ariadne predictions for photon and target hemispheres of HCM frame, as well as for the total HCM frame.

7. Summary
Measurement in current region of the Breit frame show same dependence as e+e- if 2*Ecurrent is used as the scale
Measured multiplicity as a function of W in photon hemisphere on HCM frame. Points are below the LEP points.
Plans:
Systematics on W points
Second analysis on W points
Continue study mentioned in previous QCD review meeting using dijet events
Zeus note soon, Paper soon