Charged Particle Multiplicity in DIS

1
Charged Particle Multiplicity in DIS

• Request for Preliminary

M. Rosin, D. Kçira, and A. Savin University of
Wisconsin L. Shcheglova Moscow State University,
Institute of Nuclear Physics July 5th,
2004 http//www-zeus.desy.de/sumstine/multip
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Introduction

• Details http//www-zeus.desy.de/sumstine/multip
  
• short introduction to the method
• new measurement in Breit Frame
• Plots for preliminary

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Charged Hadrons Effective Mass

• Measure HFS within ?? for best CTD acceptance
• Measure charged tracks, reconstruct number of
  charged hadrons
• Measure invariant mass of the system (Meff) in
  corresponding delta eta region.
• Energy is measured in the CAL

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The use of Meff as energy scale

• For ep in lab frame, measure visible part of
  ltnchgt vs. visible part of energy available for
  hadronization Meff

Whad
Meff
Lab Frame
Visible part
Meff HFS measured in the detector where the
tracking efficiency is maximized
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1996-97 Data sample

• Event Selection
• Scattered positron found with E gt 12 GeV
• A reconstructed vertex with Zvtx lt 50 cm
• Scattered positron position cut radius gt 25cm
• 40 GeV lt E-pz lt 60 GeV
• Diffractive contribution excluded by requiring
  ?maxgt 3.2
• Track Selection
• Tracks associated with primary vertex
• ? lt 1.75
• pT gt 150 MeV
• Physics and Kinematic Requirement
• Q2 da gt 25 GeV2
• y el lt 0.95
• y JB gt 0.04
• 70 GeV lt W lt 225 GeV ( W2 (q p)2 )

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

• Ariadne 96-97 4.08
• Matrix elements at LO pQCD O(?s)
• Parton showers CDM
• Hadronization String Model
• Proton PDFs CTEQ-4D
• Lepto 6.5.1
• Including SCI
• Also used Lepto without SCI

Luminosity of MC 36.5 pb-1
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Kinematic Variables, Meff and Tracks

• 96-97 data compared to ARIADNE and LEPTO
  w/SCI
• Both ARIADNE and LEPTO show good agreement
  for kinematics, Meff tracks

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Comparison of ee-, pp, ep

• agreement between ee- and pp for ltnchgt vs.
  invariant mass.
• ltnchgt 2 vs. Q for ep measured in the current
  region of the Breit Frame (CRBF) agree with ee-
  and pp for higher Q
• Lab frame points lie above ee- and pp, and above
  the previous ZEUS measurement in CRBF.
• ARIADNE describes data dependence, LEPTO higher
  than the data, LEPTO w/ SCI even higher. Used
  both for correcting data systematic errors small
• Agree with 1995 preliminary measurement of ltnchgt
  vs. Meff in lab frame
• Request for preliminary

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Lab frame ltnchgt vs. Meff in x bins

• Check if ep vs. ee- and pp difference is due to
  quark and gluon distributions study x and Q2
  dependence
• x range split into similar bins as in previous
  multiplicity paper.
• weak x dependence in both data and MC observed
  not sufficient to explain difference
• Request for Preliminary
• Q2 dependence? gt next page

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Lab frame x and Q2 bins

• Data described by ARIADNE
• LEPTO above data
• No Q2 dependence observed
• Request for preliminary

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Breit Frame - Change to scale Meff

• Using Meff agreement between
• Lab frame
• Breit Frame Current Region
• Breit Frame Target Region
• Number of charged hadrons plotted vs. Meff
  shows similar behavior for the lab frame, and
  current target region of Breit frame
• Request for Preliminary

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Invariant Mass in the Current Region
Current Hemisphere
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Invariant Mass Calculation
With the same energy of the particles, one gets
very different invariant mass of the system
depending on the system configurations.
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Invariant Mass Calculation
With the same energy of the particles, one gets
very different invariant mass of the system
depending on the system configurations.
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Invariant Mass Construction
Current region Breit Frame

• Assume system is collimated
• Expect inv. Mass of CRBF to change significantly
  if we mirror each particle, with another
  particle with the same energy but opposite
  momentum.
• M2 (EobsEmirrired)2-(pobs-pmirrored)2
  2E
• Total number of particles increased by 2

collimated
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Breit Frame - Change to scale Meff

• Points lie slightly above the ee- points.
• This approximation of invariant mass partially
  takes into account the real distribution of the
  particles.
• Similar studies for target region are hampered by
  the fact that the analogy between our target
  region and the target region in pp is a bit more
  complex.
• Request for Preliminary

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Correlated Uncorrelated Systematics
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Comparison to 2nd analysis

• Agreement between 1st and 2nd analysis within 1
  for all preliminary plots
• Lab Frame
• Current Region Breit Frame
• Target Region Breit Frame
• X bins
• X and Q2 bins
• Current Region Breit Frame vs. 2E

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Summary

• Measured mean charged multiplicity in the Lab and
  Breit frame. Compared to predictions, to other
  ZEUS data, and ee-
• Difference ep vs. ee- and pp
• not due to experimental measurement.
• not due to the choice of frame (Lab Breit).
• not due to quark/gluon distributions.
• is due to choice of scale (Q vs. Meff)
• Plans for the future
• Finish checks in the Breit frame.
• Run on Lepto without SCI
• Make results preliminary soon!

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Invariant Mass Calculation
Isotropic configuration
Configuration with leading particles
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Multiplicity ee- and pp
ee-
ee-
pp vs. vq2had pp vs. vspp
pp
Invariant mass of pp

• Agreement between ee- and pp plotted vs. pp
  invariant mass