Charged Particle Multiplicity in DIS

Charged Particle Multiplicity, Michele Rosin U. Wisconsin Monday Meeting June 7th, 2004 1

M. Rosin, D. Kçira, and A. SavinUniversity of Wisconsin

L. ShcheglovaMoscow State University, Institute of Nuclear Physics

June 7th, 2004

Charged Particle Multiplicity in DIS Charged Particle Multiplicity in DIS

Preliminary Request


OutlineOutline

• Introduction and motivation• Data selection & simulation• Control plots• Correction methods:

• Bin by bin (modified)• Matrix

• <nch> vs. Meff • with MC predictions• In bins of x• In bins of x and Q2

• Systematics• Comparison to second analysis• Summary and plan


Motivation Motivation

Mean charged multiplicity, <nch> , vs. Q shows logarithmic dependence for both e+e- and pp on the effective energy going into hadronization, and dependence is universal

For pp and e+e- hadronization is universal when you go to proper scale: √s for e+e- reactions, effective energy going into hadron production, √q2 for pp.


Motivation Motivation

ep points measured in current region of Breit frame (x2) vs. Q, shows nice agreement

Expect that mean charged multiplicity for ep (measured in lab frame) and pp (and e+e-) are universal, when plotted against energy going into hadron production.


Motivation for the use of Meff as energy scale

Motivation for the use of Meff as energy scale

Whad

Meff

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

22222 )()()()(

ei

iz

ei

iy

ei

ix

ei

ieff pppEM

Analogous to the pp study, want to measure the dependence of <nch> of on it’s total invariant mass. (Energy available for hadronization)

For ep in lab frame, measure visible part of <nch> with visible part of energy available for hadronization: should show same universality as total <nch> and total energy

Use Meff as scale for comparing to pp (and e+e-)

Lab Frame


1996-97 Data sample1996-97 Data sample

• 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 )

735,007 events after all cuts(38.58 pb-1)


• Ariadne ’97 6v2.4 • Matrix elements at LO pQCD O(s)

• Parton showers: CDM

• Hadronization: String Model

• Proton PDF’s: CTEQ-4D

Event simulationEvent simulation

Luminosity of MC : 36.5 pb-1


Kinematic VariablesKinematic Variables

96-97 data compared to

ARIADNE and LEPTO for kinematic variables

Both ARIADNE and LEPTO show good agreement for kinematic variables


Meff and TracksMeff and Tracks

LEPTO and ARIADNE comparisons to tracks and Meff

Tracks better described by ARIADNE

Meff better described by LEPTO


Correction to hadron level: bin by bin


Part one: correct to hadron level using only hadrons generated with pT > 0.15 GeV

Part two: correct for hadrons with lower pT, using ratio of <gen> with pT cut to <gen> no pT cut in each bin.




Correction for detector effects

Correction of hadrons of pT > 0.15 to all

hadrons


Correction to hadron level: matrix

Correction to hadron level: matrix

No. of events with p tracks generated when o tracks were observedNo. events with o tracks observed

Mp,o =

The matrix relates the observed to the generated distributions of tracks in each bin of Meff by:

P M Pp p oo

o ,

Matrix corrects tracks to hadron level

ρ corrects phase space to hadron level

ρ = Hadrons passing gen level cutsHadrons passing det level cuts


Comparison of correction methods

Comparison of correction methods

Better than 2% agreement in all Meff bins

bin-by- bin considered as a systematic


Correlated & Uncorrelated Systematics

Correlated & Uncorrelated Systematics

Systematic Change % Difference in Meff bins

Bin 1 Bin 2 Bin 3 Bin 4 Bin 5LEPTO instead of ARIADNE

0.6% 1.5% 3.1% 6.6% 7.2%

Bin-by-bin instead of matrix

1.3% 0.9% 0.6% 0.8% 1.2%

Ee’ ± 1 GeV < 0.5% < 0.5% < 0.5% < 0.5% < 0.5%

Radius Cut ± 1cm < 0.5% < 0.5% < 0.5% < 0.5% < 0.5%

Q2 ± 1.6 GeV2 < 0.5% < 0.5% < 0.5% < 0.5% < 0.5%

yJB± .0006 < 0.5% < 0.5% < 0.5% < 0.5% < 0.5%

Track pT-.03/+.05GeV < 0.5% < 0.5% < 0.5% < 0.5% < 0.5%

Zvtx± 5 cm < 0.5% < 0.5% < 0.5% < 0.5% < 0.5%

W ± 19 GeV < 0.5% < 0.5% < 0.5% < 0.5% < 0.5%

E - pz± 5 GeV < 0.5% < 0.5% < 0.5% < 0.5% < 0.5%

CAL energy scale ± 3 % 1.1% 1.2% 1.1% 0.8% 0.5%


Results with MC predictionsResults with MC predictions

Good agreement with 1995 prelim. points, with smaller statistical, systematic errors

Observe a significant difference between ep, e+e- and pp.

ARIADNE describes data dependence, LEPTO higher than the data

Check for ep points: does <nch> dependence on Meff change depending on scale?


<nch> vs. Meff in x bins<nch> vs. Meff in x bins

if difference is due to quark and gluon distributions, then maybe also x dependence

x range split into similar bins as in

previous multiplicity paper.

weak x dependence in both data and MC observed


x and Q2 binsx and Q2 bins

No Q2 dependence observed

Data described by ARIADNE

LEPTO above data


Comparison to 2nd analysis in Q2 and x bins

Comparison to 2nd analysis in Q2 and x bins

Agreement between 1st and 2nd analysis within 1% for matrix for x and Q2 bins


Comparison to 2nd analysis Comparison to 2nd analysis

For full kinematic range, agreement between 1st and 2nd analysis is less than 1% for both correction methods.


SummarySummary

• Shown 3 preliminary plots

• Measured in x and Q2 bins, weak x dependence not enough to compensate for difference between ep and pp. No Q2 dependence.

• Observed difference in dependence of <nch> on Meff between ep and pp (and e+e-) is real

Plan• Measure <nch> in current region of Breit frame vs. Meff

(instead of Q)

• Study diffractive events; combine ARIADNE & RAPGAP


Preliminary plotsPreliminary plots

Charged Particle Multiplicity in DIS

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