1. Charged Particle Multiplicity in DIS
Request for Preliminary
M. Rosin, D. Kçira, and A. Savin
University of Wisconsin
L. Shcheglova
Moscow State University, Institute of Nuclear Physics
July 5th, 2004

2. Introduction Details: http://www-zeus.desy.de/~sumstine/multip
short introduction to the method
new measurement in Breit Frame
Plots for preliminary
The analysis was presented many times to the group and to the collaboration, the last presentation was given by Dorian Kcira at ZEUS week just 10 days ago, so I won’t go into all the detail of the analysis here. The details can be found on the analysis web page. Today I would like to give an overview of the method and show all the plots we would like to make preliminary, four of which have been previously shown and one new one.

3. Charged Hadrons & Effective Mass: experimental method
Measure HFS within  for best CTD acceptance
Measure # charged tracks, reconstruct number of charged hadrons
Measure invariant mass of the system (Meff) in corresponding delta eta region.
Energy is measured in the CAL
I’ll start by explaining the experimental method. We want to measure the HFS within delta eta which corresponds to region of best CTD acceptance. We measure the number of charged tracks in the CTD because we want to reconstruct the number of charged hadrons. We measure the invariant mass of the system, Meff . Meff is calculated like this, using Energy measured in the corresponding delta eta region of the calorimeter. So then we can study the dependence of the number of charged hadrons on Meff.
CAL within the CTD acceptance
Study: <nch> vs. Meff
CTD

4. The use of Meff as energy scale
For ep in lab frame, measure visible part of <nch> vs. visible part of energy available for hadronization: Meff
Previously shown in e+e- and pp that the number of charged particles vs. invariant mass of the system is universal
Based on previous studies in e+e-, one can assume that the visible part of the system behaves as the total, maybe excluding the remnants
We compare our measurement to e+e- and pp
For ep in lab frame, measure visible part of <nch> vs. visible part of energy available for hadronization: Meff
Whad
Meff
Lab Frame
Visible part
energy scale for the analysis is Meff, then Can look at just part of the string: assumed to give final state particles proportional to logarithm of mass
Meff : the effective mass of a part of the produced multi-hadronic final state measured in the detector, unlike Whad, which corresponds to the hadronic final state measurement in full phase space
Meff: HFS measured in the detector where the tracking efficiency is maximized

5. 1996-97 Data sample 735,007 events after all cuts (38.58 pb-1)
Event Selection
Scattered positron found with E > 12 GeV
A reconstructed vertex with |Zvtx| < 50 cm
Scattered positron position cut: radius > 25cm
40 GeV < E-pz < 60 GeV
Diffractive contribution excluded by requiring ηmax> 3.2
Track Selection
Tracks associated with primary vertex
|| < 1.75
pT > 150 MeV
Physics and Kinematic Requirement
Q2 da > 25 GeV2
y el < 0.95
y JB > 0.04
70 GeV < W < 225 GeV ( W2 = (q + p)2 )
And I used the following criteria to select my events.
EVENT SELECTION:
To ensure that the kinematic variables can be reconstructed with sufficient accuracy,
I required a good positron be found coming from the vertex,
I used a radius to ensure that the positron is fully contained in the detector,
And required the total E-pz to be near 55 Gev
TRACK SELECTION:
Trks associated with primary vtx,
<+/-1.75, ensure tracks are in a region of high CTD acceptance, where detector response & systematics are well understood
Pt>150, to ensure the track makes it thru the layers of the CTD
KINEMATIC:
Yel<.95 removes photoproduction
Yjb>0.04 to guarentee accuracy for DA method (which is used to reconstruct Q2)
The hadron angle depends on yjb, and the measurement of yjb is distorted bu Uranium noise in the cal for low yjb
NOTES:
E-pz. For e+ E=27.5, pz = since E2-p2=m2 and m=0, so = 55, for the proton, Ep=920, p=920, =0
Total e-pz = 55 GeV
E-pz removes photoproduction (scattered e is missing, q2 is low=0, electron goes in beam pipe, Ee=0.)
removes evnts w/ large radiative corrections (electron looses energy by radiating a big photon, so Ee is less than 27.5)
E-pz calculated from cells
Q2da calculated from cells
Yjb calculated from cells
735,007 events
after all cuts
(38.58 pb-1)

6. Event simulation Ariadne ’96-’97 4.08 Lepto 6.5.1
Matrix elements at LO pQCD O(s)
Parton showers: CDM
Hadronization: String Model
Proton PDF’s: CTEQ-4D
Lepto 6.5.1
Including SCI
Also used Lepto without SCI
Proton PDF’s are parameterized from experimental data
Detector simulation besed on JAY-AUNT
Luminosity of MC : 36.5 pb-1

7. Kinematic Variables, Meff and Tracks
96-97 data compared to ARIADNE and LEPTO w/SCI
Both ARIADNE and LEPTO show good agreement for kinematics, Meff & tracks

8. Comparison of e+e-, pp, & ep
agreement between e+e- and pp for <nch> vs. invariant mass.
<nch> * 2 vs. Q for ep measured in the current region of the Breit frame (CRBF) agree with e+e- and pp for higher Q
Lab frame points lie above e+e- and pp, and above the previous ZEUS measurement in CRBF.
ARIADNE describes data dependence, LEPTO higher than the data, LEPTO w/ SCI even higher. Used both for correcting data: systematic errors small
Agree with 1995 preliminary measurement of <nch> vs. Meff in lab frame
Request for preliminary
Here we see mean number of charged hadrons for three different systems, ep, e+e- and pp. plotted vs. their corresponding invariant mass. Here are the e+e- points and here are pp points and one can see they the points lie on top of one another. Here we see mean number of charged hadrons times 2 for ep points measured in the CRBF and plotted vs Q, one can see that they agree with the e+e- and pp for higher values of Q. (One should keep in mind that Q is only an approximation of invariant mass) Here are the points from the current measurement in the lab frame vs. Meff, with statistical and systematic errors. One can see that they lie above the e+e- and pp points. They are also lying above the previos BF measurement. ARIADNE describes the data well, while LEPTO is lying slightly above, and LEPTO lies even further above the data. We used both ARIADNE and LEPTO SCI to correct the data, to test the sensitivity to the MC. The absolute predictions differ, but the systematics are very small, and can’t be seen here. It was shown by Dorian at ZEUS week that these points agree with the previous ZEUS preliminary measurement done in 1995 of multiplicity vs. Meff in the Lab frame. This plot is intended to be made preliminary.

9. Lab frame: <nch> vs. Meff in x bins
Check if ep vs. e+e- and pp difference is due to quark and gluon distributions: study x and Q2 dependence
x range split into similar bins as in previous multiplicity paper.
weak x dependence in both data and MC observed not sufficient to explain difference
Request for Preliminary
Q2 dependence? => next page

10. Lab frame: x and Q2 bins Data described by ARIADNE LEPTO above data
No Q2 dependence observed
Request for preliminary

11. Breit Frame - Change to scale Meff
Using Meff agreement between:
Lab frame
Breit Frame Current Region
Breit Frame Target Region
Number of charged hadrons plotted vs. Meff shows similar behavior for the lab frame, and current & target region of Breit frame
Request for Preliminary
We want to understand why our points don’t lie on top of e+e-, so tried moving to BF and looking at the mean number of charged hadrons vs. invariant mass for both the current and target regions. Read slide. So plotting number of hadrons vs. Meff for CRBF doesn’t yeild agreement with e+e-.

12. Invariant Mass in the Current Region
Look closer at current region of Breit frame (CRBF) try to find better way to compare to e+e-
Shown here is invariant mass for the CRBF
Invariant mass calculated as before using the total energy in the CRBF
Current Hemisphere PL PT
Invariant Mass
Want to look closer at the current region of the Breit Frame, and try to find a better way to compare to e+e-. Keeping in mind One hemisphere of CRBF for ep is analogous to one hemisphere of e+e-. So here is shown the invariant mass for the current region of the BF, with inv. Mass calculated as before the using the total energy in the CRBF.

13. Invariant Mass Calculationθ E E
θ = π E
θ = 0
With the same energy of the particles, one gets very different invariant mass of the system depending on the system configurations.
Let me take a second to remind you of some details of the calculation of invarant Mass. Here we have two particles each with energy E, the invariant mass of the systemdepends on the energies of the particles and the angle between them, so that when you have two particles with the same E, back to back, the inv.Mass is 2E, but when the angle between them goes to 0, the inv mass also goes to 0. The invariant mass can change drastically from one system to another even if the energy stays the same.

14. Invariant Mass Construction
Current region Breit Frame
universality is not observed between e+e- and ep
Assume universality may be broken because system not uniform but rather collimated
Expect inv. Mass of CRBF to change significantly if we “mirror” each particle, with another particle with the same energy but opposite momentum.
M2 = (Eobs+Emirrired)2-(pobs+pmirrored) M = 2E
Total number of particles increased by 2
“Mirrored” invariant mass
So, if you don’t assume the universality of the hadronizaton vs inv mass, since we don’t show same behavior as e+e-, and if we assume the system is not uniform but rather collimated, like so, we can expect that inv mass of the crbf will change significantly if you just mirror it to make this configuration to be similar to what we have in e+e-. So one should kim that the inv mass that will appear due to this mirroring is not real because it doesn’t exist in our case. So now for each particle we create 1 antiparticle with the same energy but with opposite momentum in this case the inv mass of such a system will be equal E+E-p-p or just 2*Ebreit, where 2*E breit are the total energy of all particles observed in crbf. The total num part will be increased by fact of 2, Lets see what happens if we use this approx to compare our data to e+e-.
collimated

15. Breit Frame - Change to scale Meff
Points lie slightly above the e+e- points.
This approximation of invariant mass partially takes into account the real distribution of the particles.
Similar studies for target region are hampered by the fact that the analogy between our target region and the target region in pp is a bit more complex.
Request for Preliminary
Now we see that our points lie only slightly above ee points. This approx is much better than used previously in ‘99 publucation where they used q, because it partially takes into account the real distribution of the particles. Unfortunately we cant make similar studies for the target region becaue the analogy btwm out tr and the tr in pp is a bit more complex.

16. Correlated & Uncorrelated Systematics
Change
% Difference in Meff bins
Bin 1
Bin 2
Bin 3
Bin 4
Bin 5
matrix instead of bin-by-bin
1.3%
0.9%
0.6%
1.2%
LEPTO instead of ARIADNE
< 0.5%
Ee’
± 1 GeV
Radius Cut
± 1cm Q2
± 1.6 GeV2
yJB
± .0006
Track pT
-.03/+.05GeV
Zvtx
± 5 cm W
± 19 GeV
E - pz
± 5 GeV |
CAL energy scale
± 3 %
1.1%
1.2%
0.8%
0.5%

17. Comparison to 2nd analysis
Agreement between 1st and 2nd analysis within 1% for all preliminary plots:
Lab Frame

18. Comparison to 2nd analysis
Agreement between 1st and 2nd analysis within 1% for all preliminary plots:
Lab Frame
Current Region Breit Frame

19. Comparison to 2nd analysis
Agreement between 1st and 2nd analysis within 1% for all preliminary plots:
Lab Frame
Current Region Breit Frame
Target Region Breit Frame

20. Comparison to 2nd analysis
Agreement between 1st and 2nd analysis within 1% for all preliminary plots:
Lab Frame
Current Region Breit Frame
Target Region Breit Frame
X bins

21. Comparison to 2nd analysis
Agreement between 1st and 2nd analysis within 1% for all preliminary plots:
Lab Frame
Current Region Breit Frame
Target Region Breit Frame
X bins
X and Q2 bins

22. Comparison to 2nd analysis
Agreement between 1st and 2nd analysis within 1% for all preliminary plots:
Lab Frame
Current Region Breit Frame
Target Region Breit Frame
X bins
X and Q2 bins
Current Region Breit Frame vs. 2*E

23. Summary Request 5 plots for preliminary:
Including all 96 Data will increase my statistics an order of magnitude
Total luminosity for my study 0.06 pb-1; total for 1996 ~12pb-1
Diffraction:
Events with low momentum transferred to the hadron.

24. Summary Request 5 plots for preliminary:
Including all 96 Data will increase my statistics an order of magnitude
Total luminosity for my study 0.06 pb-1; total for 1996 ~12pb-1
Diffraction:
Events with low momentum transferred to the hadron.

25. Summary Request 5 plots for preliminary:
Including all 96 Data will increase my statistics an order of magnitude
Total luminosity for my study 0.06 pb-1; total for 1996 ~12pb-1
Diffraction:
Events with low momentum transferred to the hadron.

26. Summary Request 5 plots for preliminary:
Including all 96 Data will increase my statistics an order of magnitude
Total luminosity for my study 0.06 pb-1; total for 1996 ~12pb-1
Diffraction:
Events with low momentum transferred to the hadron.

27. Summary Request 5 plots for preliminary:
Including all 96 Data will increase my statistics an order of magnitude
Total luminosity for my study 0.06 pb-1; total for 1996 ~12pb-1
Diffraction:
Events with low momentum transferred to the hadron.