1. 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

2. 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.

3. 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

4. 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

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.
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

6. 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:
2*Ephoton region= W in HCM frame
slope: 0.12 x10-4
intercept:

7. 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

8. 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

9. 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

10. 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 +/
Track pT
+0.05/-0.03 GeV

11. 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

12. 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

13. Summary
Request for preliminary:

14. 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