Charged Particle Multiplicity, Michele Rosin, U. Wisconsin QCD Review Meeting February 5,2004

M. Rosin, D. Kçira,A. Savin, and L. Shcheglova

University of WisconsinFeb. 5, 2004

Charged Particle Multiplicity in DIS Charged Particle Multiplicity in DIS Charged Particle Multiplicity in DIS Charged Particle Multiplicity in DIS

QCD Group Review Meeting

Charged Particle Multiplicity, Michele Rosin, U. Wisconsin QCD Review Meeting February 5,2004

Motivation for the use of MMotivation for the use of Meffeff as as energy scaleenergy scale

Motivation for the use of MMotivation for the use of Meffeff as as energy scaleenergy scale

Similarity of particle production at e+e- and ep colliders

Whad

Whad

Meff

Whad: HFS measured in full phase space

Meff: HFS measured in the detector where the tracking efficiency is maximized

22222 )()()()(

ei

iz

ei

iy

ei

ix

ei

ieff pppEM

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

Charged Particle Multiplicity, Michele Rosin, U. Wisconsin QCD Review Meeting February 5,2004

• DIS Event 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 )

1996 & 1997 Data Selection1996 & 1997 Data Selection1996 & 1997 Data Selection1996 & 1997 Data Selection

Charged Particle Multiplicity, Michele Rosin, U. Wisconsin QCD Review Meeting February 5,2004

Monte Carlo StudyMonte Carlo StudyMonte Carlo StudyMonte Carlo Study

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

Lab frame

Charged Particle Multiplicity, Michele Rosin, U. Wisconsin QCD Review Meeting February 5,2004

Comparison to 2nd analysis: QComparison to 2nd analysis: Q22Comparison to 2nd analysis: QComparison to 2nd analysis: Q22

2nd Analysis: Dorian Kçira

Small data sampleGen level MC

Perfect agreementDet level MC

Good agreementData

Some small disagreement

Charged Particle Multiplicity, Michele Rosin, U. Wisconsin QCD Review Meeting February 5,2004

Comparison to 2Comparison to 2ndnd analysis: M analysis: MeffeffComparison to 2Comparison to 2ndnd analysis: M analysis: Meffeff

Small data sampleGen level MC

Perfect agreementDet level MC

Good agreementData

Some small disagreement

Charged Particle Multiplicity, Michele Rosin, U. Wisconsin QCD Review Meeting February 5,2004

Comparison to 2Comparison to 2ndnd analysis: <n analysis: <nchch>>Comparison to 2Comparison to 2ndnd analysis: <n analysis: <nchch>>

Small data sampleGen level MC

Perfect agreementDet level MC

Good agreementData

Some small disagreement

Charged Particle Multiplicity, Michele Rosin, U. Wisconsin QCD Review Meeting February 5,2004

Comparison with second analysisComparison with second analysisComparison with second analysisComparison with second analysis

General agreement within statistical errors

Charged Particle Multiplicity, Michele Rosin, U. Wisconsin QCD Review Meeting February 5,2004

Uncorrelated systematicsUncorrelated systematicsUncorrelated systematicsUncorrelated systematics

Systematic Change % difference in Meff binsBin 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

- 0.9%

+ 0.7%

E - pz± 2 GeV

|Zvtx| ± 5 cm

Charged Particle Multiplicity, Michele Rosin, U. Wisconsin QCD Review Meeting February 5,2004

Trigger studies by L. ShcheglovaTrigger studies by L. ShcheglovaTrigger studies by L. ShcheglovaTrigger studies by L. Shcheglova

Group Run Range #Runs Non-prescaled DIS01 DIS03

1 21186-21631 445 Yes, 12x6 14x14

2 21634-22447 795 - 14x14

3

3

22451-22462

22673-25336

11

427

Yes, 12x6

Yes, 12x6

r >25

r >25

4

4

22466-22662

25344-27899

196

2500

-

-

r >25

r >25

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

Charged Particle Multiplicity, Michele Rosin, U. Wisconsin QCD Review Meeting February 5,2004

ResultsResultsResultsResults

Full 96 & 97 data sample

Same dependence as 1995 data

Charged Particle Multiplicity, Michele Rosin, U. Wisconsin QCD Review Meeting February 5,2004

Results of reweightingResults of reweightingResults of reweightingResults 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

Charged Particle Multiplicity, Michele Rosin, U. Wisconsin QCD Review Meeting February 5,2004

SummarySummarySummarySummary

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