charged particle multiplicity in dis
DESCRIPTION
Charged Particle Multiplicity in DIS. Preliminary Request. M. Rosin, D. Kçira, and A. Savin University of Wisconsin L. Shcheglova Moscow State University, Institute of Nuclear Physics June 7th, 2004. Outline. Introduction and motivation Data selection & simulation Control plots - PowerPoint PPT PresentationTRANSCRIPT
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
Charged Particle Multiplicity, Michele Rosin U. Wisconsin Monday Meeting June 7th, 2004 2
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
Charged Particle Multiplicity, Michele Rosin U. Wisconsin Monday Meeting June 7th, 2004 3
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.
Charged Particle Multiplicity, Michele Rosin U. Wisconsin Monday Meeting June 7th, 2004 4
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.
Charged Particle Multiplicity, Michele Rosin U. Wisconsin Monday Meeting June 7th, 2004 5
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
Charged Particle Multiplicity, Michele Rosin U. Wisconsin Monday Meeting June 7th, 2004 6
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)
Charged Particle Multiplicity, Michele Rosin U. Wisconsin Monday Meeting June 7th, 2004 7
• 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
Charged Particle Multiplicity, Michele Rosin U. Wisconsin Monday Meeting June 7th, 2004 8
Kinematic VariablesKinematic Variables
96-97 data compared to
ARIADNE and LEPTO for kinematic variables
Both ARIADNE and LEPTO show good agreement for kinematic variables
Charged Particle Multiplicity, Michele Rosin U. Wisconsin Monday Meeting June 7th, 2004 9
Meff and TracksMeff and Tracks
LEPTO and ARIADNE comparisons to tracks and Meff
Tracks better described by ARIADNE
Meff better described by LEPTO
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Correction to hadron level: bin by bin
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.
Charged Particle Multiplicity, Michele Rosin U. Wisconsin Monday Meeting June 7th, 2004 11
Correction to hadron level: bin by bin
Correction to hadron level: bin by bin
Correction for detector effects
Correction of hadrons of pT > 0.15 to all
hadrons
Charged Particle Multiplicity, Michele Rosin U. Wisconsin Monday Meeting June 7th, 2004 12
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
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Comparison of correction methods
Comparison of correction methods
Better than 2% agreement in all Meff bins
bin-by- bin considered as a systematic
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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%
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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?
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<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
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x and Q2 binsx and Q2 bins
No Q2 dependence observed
Data described by ARIADNE
LEPTO above data
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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
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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.
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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
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Preliminary plotsPreliminary plots
Charged Particle Multiplicity, Michele Rosin U. Wisconsin Monday Meeting June 7th, 2004 22
Preliminary plotsPreliminary plots
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Preliminary plotsPreliminary plots