Precision Experiment with CLAS Search for the pentaquark

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Precision Experiment with CLASSearch for the
pentaquark

Latifa Elouadrhiri Jefferson Lab
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Outline

• Precision search for the pentaquark with CLAS
• Requirements
• Increase luminosity by factor 10
• Dedicated setup for precise energy measurement
• Control masses of hadrons to lt 2 MeV
• Data analysis/Results
• Summary

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Evidence for Pentaquark States

• First evidence for a possible Q(1540) was
  reported by the LEPS/Spring-8 Collaboration in
  photoproduction off nuclei
• Corroborated by several experiments ( CLAS,
  COSY-TOF, DIANA, HERMES, JINR, NOMAD, nBC, SAPHIR
  , SVD-2, ZEUS) using different probes and targets
• Positive results have limited event samples in
  the observed structures
• Comparison of results from different experiments
  shows discrepancies in the observed masses by up
  to 20 MeV
• Null results have been recently presented
  (ALEPH, BABAR, BELLE, BES, CDF, COMPASS, DELPHI,
  E690, FOCUS, HERA-B, PHENIX, SPHINX)

Definitive confirmation from high statistics/
high resolution experiments is needed to resolve
the controversy about the existence of the
Q(1540) pentaquark
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Search for Pentaquarks at CLAS
A comprehensive program to search for pentaquarks
with high statistics and high resolution
photoproduction experiments is in progress at
Jefferson Lab
New experiments seeking evidence of pentaquarks
with the CLAS detector were approved in 2003-2004
with the goal of confirming previous results and
explore new kinematics with at least a factor 10
increase in statistics
g10 deuteron Eg 1.0-3.5 GeV
data taking completed in 2004 g11
proton Eg 1.6-3.8 GeV data
taking completed in 2004 eg3 deuteron
Eg 4.0-5.4 GeV data taking
completed in 2005 g12 proton Eg 3.8
5.7 GeV planned for 2006
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Experiment 04-021 Spectroscopy of Exotic Baryons
with CLAS Search for Ground and First Excited
States
M. Battaglieri R. De Vita V. Koubarovsky and
the CLAS Collaboration

• Bremsstrahlung photon beam
• 4 GeV, 60-65 nA electron beam (94)
• 5 GeV, 60-65 nA electron beam (6)
• X/X08?10-5 radiator
• Hall B photon tagger 0.2 - 0.95 (1.6-3.8 (4.7)
  GeV)

Beam conditions
CLAS set-up

• 40 cm LH2 target and new Start Counter
• In bending torus field (0.5 Bmax)

• Commissioning 3 days
• Data taking 55
• Maintenance 7 days

Total Time 5/22 - 7/26 2004
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The CEBAF Large Acceptance Spectrometer CLAS
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G11 Statistics

• DAQ rate 3kHz (80 live time)
• 400 runs (20M triggers each)
• 10k bos files (20 TB)
• Luminosity (1.8 lt Eg lt 3.8 GeV) 76 pb-1
• L(1.8 lt Eg lt 2.3 GeV) 25 pb-1
• (10 times the g1c analysis !!)

Maintenance period

• Data Calibration and processing
• Started during the run
• Calibration completed in October 2004
• Data Processing completed on February 9th

L. Elouadrhiri (JLab) Analysis Coordinator M.
Ungaro (U.Conn) as 'chef' L. Guo (JLab)
TAGGER/Start Counter J. Goett(RPI) DC
calibration N. Baltzell (SCU) TOF calibration
D. Dale (KU), E.Pasyuk (ASU) Normalization
M.Ostrick (Bonn) EC timing calibration C.Smith
(UVA) EC energy calibration S. Stepanya (JLab),
L. Guo (JLab) Tagger Energy Calibration R.
Devita (INFN) and V. Koubarovski (RPI) General
Data quality checks
The Team
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Start Counter
Channels 24 Length 651.8 mm Width 29
mm Thickness 2.0 mm

• Needed
• For triggering at high luminosity
• Long target
• Full coverage in polar and azimuthal angle

• Calibration procedure developed
• TDC conversion measured
• Time walk correction applied
• Light propagation velocity extracted from data
  different values for leg and nose part
• Overall time resolution 350ps
• Implemented in CLAS software

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Start Counter Schedule
January 15 Experiment apporved January 31
Design finalized May 16 Assembly
completed May 23 Commissioning and
trigger studies May 27 Start production
data taking
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Start Counter Performance
LEG NOSE
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Tagger Energy Variations

• The first observation of nonlinearities in the
  tagger energy spectrum in the search for
  pentaquarks in the g2a data (S. Stepanyan et
  al.). Empirical corrections were derived using
  the exclusive reaction gd? ppp-(n)
• Later similar results have been obtained by M.
  Williams et al. from the analysis of g1c data
  (higher statistics, full focal plane).
• These finding were explained by the effects of
  gravitational sag and various possible
  misalignmets of the tagger focal plane (D. Sober
  et al.).

S. Stepanyan CLAS Analysis Note 03-105 D. Sober
et al., CLAS-NOTE 2004-019
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Tagger Energy Calibration
Trigger detector
pair spectrometer magnet
Photon converter target
Bo
Tagging system
e
0.5Bo
radiator
Microstrip detectors 20x20 mm, 50mm pitch
e-
electrons
Trigger detector
Tagger focal plane energy counters
endpoint
Note In reality pair spectrometer deflects in
horizontal plane. Shown here as vertical
deflection, for clarity.
Nee-
E counter
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Final Energy Correction
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End point Energy Measurement

• Normalized yield of ee- as a function of Ec.
• For 4 different acceptances of ee- detection the
  ratio of beam energy to the defined end point
  energy was within 0.1.

Ee.p.

• EB for this measurements was 3.7765 GeV (from
  accelerator and Hall A beam energy measurements).
• Ee.p. is defined as a mid point of the falling
  edge of the ee- coincidence rate, and is 3.784
  GeV.

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Data Quality
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Data Analysis Example
1 of statistics
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All known masses are within 1.5 MeV from the
nominal value!
DM PDG - Exp
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Cross Section Extraction
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Summary