Charged Particle Multiplicity in DIS QCD Group Review Meeting M. Rosin, D. Kçira, A. Savin, and L. Shcheglova University of Wisconsin Feb. 5, 2004

Motivation for the use of Meff as energy scale Similarity of particle production at e+e- and ep colliders Whad Similarity of Whad dependence on <nch> has been observed A common Whad dependence on <nch> implies the production of secondary particles is similar in the different interactions Study the dependence of <nch> of the observed part of the produced HFS on it’s total invariant mass, Meff Whad If you look at hadron production in e+e-, ep and ppbar, what you see is there is a section of the process where the hadrons get produced through a similar process. If you compare e+e- and ep, you see the difference is that in ep I have the proton remnant to contend with. I can test how similar the process is by studying the universality. This can be done by measuring… 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 Whad: HFS measured in full phase space Meff: HFS measured in the detector where the tracking efficiency is maximized

1996 & 1997 Data Selection DIS Event Selection Track Selection Scattered positron found with E > 12 GeV A reconstructed vertex with |Zvtx| < 50 cm scattered positron position cut: |x| > 15 cm or |y| > 15cm (in RCAL) “Box cut” 40 GeV < E-pz < 60 GeV Track Selection Tracks associated with primary vertex || < 1.75 pT > 150 MeV Physics and Kinematic Requirement 25 GeV2 < Q2 da < 1200 GeV2 y el < 0.95 y JB > 0.04 70 GeV < W < 260 GeV ( W2 = (q + p)2 ) For this initial study, I have looked at part of the 1996 data, 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 box cut 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, high track reconstruction efficiency KINEMATIC: Yel<.95 removes photoproduction Yjb>0.04 to guarantee 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

Monte Carlo Study Lab frame Dependence of multiplicity on Meff is the same for restricted regions of phase space

Comparison to 2nd analysis: Q2 2nd Analysis: Dorian Kçira Small data sample Gen level MC Perfect agreement Det level MC Good agreement Data Some small disagreement

Comparison to 2nd analysis: Meff Small data sample Gen level MC Perfect agreement Det level MC Good agreement Data Some small disagreement

Comparison to 2nd analysis: <nch> Small data sample Gen level MC Perfect agreement Det level MC Good agreement Data Some small disagreement

Comparison with second analysis General agreement within statistical errors

Uncorrelated systematics Change % difference in Meff bins Bin 1 Bin 2 Bin 3 Bin 4 Bin 5 Ee’ ± 1 GeV + 1.4% - 1.6% Box cut ± 1cm Q2da ± 2.5 GeV2 - 0.9% yel ± 0.05 +1.2% - 5.6% yjb ± 0.01 + 0.7% E - pz ± 2 GeV |Zvtx| ± 5 cm

Trigger studies by L. Shcheglova Group Run Range #Runs Non-prescaled DIS01 DIS03 1 21186-21631 445 Yes, 12x6 14x14 2 21634-22447 795 - 3 22451-22462 22673-25336 11 427 r >25 4 22466-22662 25344-27899 196 2500 Lydia has investigsated the possibility to go to lower Q2. Because of changing prescales for DIS01 and changing radius for DIS03, must use a weighting scheme Created a mixed sample of DIS01 & DIS03 to get agreement with MC The weighting scheme is described in detail here: http://amzeus.desy.de/~sumstine/trigger_study/weighting_foils.ps

Results Full 96 & 97 data sample Same dependence as 1995 data

Results of reweighting Good agreement between data and MC up to Q2 15 or 10 GeV2 Currently Q2 >25, but it should be possible to go lower

Summary Plans MC studies Started systematics 2nd analysis is on the way; first look: general agreement Trigger study by Lydia Shcheglova Plans Make preliminary work on small differences between 1st and 2nd analysis finish systematics