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
March 3rd, 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, want to look more closely at particles in the target region

4. Visible multiplicity in Breit and hadronic center of mass (HCM) frames
Visible Part
Breit Frame: 90% of hadrons in current region are visible in our detector, where only 30% of target region hadrons are visible.
HCM Frame: No way to measure any particles in proton hemisphere. Photon region has BIG contribution from target region of Breit frame (~80% of what we see)
All Hadrons
Current Region Breit Frame
Proton remnant
Visible Part
All Hadrons
Photon Region HCM Frame
Proton Region HCM Frame

5. 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.
Photon region of HCM frame has BIG contribution from target region of Breit frame

6. Multiplicity vs. W in HCM frame
combination of measurements in the current region of Breit frame and photon hemisphere of the HCM frame compared to Ariadne predictions
Monte Carlo dependant correction for full phase space applied in each bin (Factors: 1.9, 1.5, 1.3)
Ariadne doesn’t fully describe data, possibly because Ariadne doesn’t describe tracks at high W
Behavior of the multiplicities in the two frames is similar
Working on systematics, largest systematic from MC

7. Lepto predictions for HCM frame
Agreement with data is slightly better
One can see the behavior of multiplicity is similar in the two frames
Can’t make the Breit frame measurement at high Q (not enough data at high Q) and can’t measure photon hemisphere at low W for same reason

8. Ariadne extension to high Q2 in current region of the Breit frame
To get a rough estimate of the behavior of the Breit frame multiplicity at high Q2, we run Ariadne at Q2>1250 GeV2
This prediction is presented as pink line
One can conclude that in general even at high Q2, the monte carlo prediction for the behavior of the multiplicity in the current region of the Breit frame is very close to the behavior in the photon hemisphere of the HCM frame vs. W
Based on the monte carlo expectation, it is quite legal to combine these two measurements on one plot

9. Conclusions
Previously we confirmed that we have similar behavior to e+e- and pp in the current region of the Breit frame.
When we move to higher energies we see a disagreement with e+e-
According to the monte carlo prediction for this region the multiplicity in both the current region of the Breit frame and the photon hemisphere of the HCM frame will disagree with the e+e- measurement.
Interesting to see pp data for this high energy region
Keeping in mind that the points in the photon hemisphere include a big portion of hadrons that are close to the proton remnant.

10. 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.
Monte carlo prediction for multiplicity in current region of Breit frame for high Q2 shows same behavior as multiplicity in photon hemisphere HCM frame.
Plans:
Systematics on W points
Second analysis on W points (preliminary check shows good agreement)
Zeus note soon, Paper soon