Charged Particle Multiplicity in DIS

1
Charged Particle Multiplicity in DIS

• QCD Group Review Meeting

M. Rosin, D. Kçira, A. Savin, and L.
Shcheglova University of Wisconsin Feb. 5, 2004
2
Motivation for the use of Meff as energy scale
Similarity of particle production at ee- and ep
colliders
Whad

• Similarity of Whad dependence on ltnchgt has been
  observed
• A common Whad dependence on ltnchgt implies the
  production of secondary particles is similar in
  the different interactions
• Study the dependence of ltnchgt of the observed
  part of the produced HFS on its total invariant
  mass, Meff

Whad
Meff
Whad HFS measured in full phase space Meff HFS
measured in the detector where the tracking
efficiency is maximized
3
1996 1997 Data Selection

• DIS Event Selection
• Scattered positron found with E gt 12 GeV
• A reconstructed vertex with Zvtx lt 50 cm
• scattered positron position cut x gt 15 cm or
  y gt 15cm (in RCAL) Box cut
• 40 GeV lt E-pz lt 60 GeV
• Track Selection
• Tracks associated with primary vertex
• ? lt 1.75
• pT gt 150 MeV
• Physics and Kinematic Requirement
• 25 GeV2 lt Q2 da lt 1200 GeV2
• y el lt 0.95
• y JB gt 0.04
• 70 GeV lt W lt 260 GeV ( W2 (q p)2 )

4
Monte Carlo Study
Lab frame

• Dependence of multiplicity on Meff is the
  same for restricted regions of phase space

5
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

6
Comparison to 2nd analysis Meff

• Small data sample
• Gen level MC
• Perfect agreement
• Det level MC
• Good agreement
• Data
• Some small disagreement

7
Comparison to 2nd analysis ltnchgt

• Small data sample
• Gen level MC
• Perfect agreement
• Det level MC
• Good agreement
• Data
• Some small disagreement

8
Comparison with second analysis

• General agreement within statistical
  errors

9
Uncorrelated systematics
10
Trigger studies by L. Shcheglova
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
11
Results

• Full 96 97 data sample
• Same dependence as 1995 data

12
Results of reweighting
Good agreement between data and MC up to Q2 15 or
10 GeV2 Currently Q2 gt25, but it should be
possible to go lower
13
Summary

• 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