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 http://www-zeus.desy.de/~sumstine/multip

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.

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

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

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 = -27.5 since E2-p2=m2 and m=0, so 27.5- - 27.5 = 55, for the proton, Ep=920, p=920, 920-920 =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)

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

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

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.

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

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

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-.

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.

Invariant Mass Calculation θ 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.

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)2 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

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.

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 -1.1291978359 -1.3515368700 -1.2803798914 -0.3391644061 0.3264250159| CAL energy scale ± 3 % 1.1% 1.2% 0.8% 0.5%

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

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

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

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

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

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

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.

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.

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.

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.

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.