Searches for Pentaquark Production at LEP

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Searches for Pentaquark Production at
LEP Steve Armstrong (ALEPH Collaboration) Brook
haven National Laboratory 29 June 2004 6th
International Conference on Hyperons, Charm
Beauty Hadrons (BEACH04) Illinois Institute of
Technology Chicago, Illinois, USA June 27 July
3 2004
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OUTLINE

• MOTIVATION FOR LEP PENTAQUARK SEARCHES
• THE LEP EXPERIMENTAL PROGRAM AT CERN
• SEARCHES FOR PENTAQUARK PRODUCTION
• SUMMARY

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PENTAQUARK MOTIVATION THEORY
_

• QCD does not forbid more complicated color
  singlet hadron states other than qq mesons and
  qqq baryons

• Various quark models as well as Skyrme and chiral
  soliton models predict SU(3) J 1/2
  anti-decuplet 10 of exotic baryons
• Diakonov et al. predict an isosinglet lowest mass
  member with mass near 1.53 GeV/c2 with a narrow
  width of 15 MeV/c2 and valence quark
  configuration of uudds (i.e., S 1) now
  denoted as Q which is in astonishing agreement
  with compelling experimental evidence

_
_

• Miraculously, the anti-decuplet also contains
  exotic X states (X-- and X0) consistent with NA49
  observations of X states near 1.86 GeV/c2
• A natural consequence would be the replacement of
  anti-strange quark(s) with anti-charm or
  anti-beauty ? heavy flavour pentaquarks (i.e., Q
  and Q)

b
c
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PENTAQUARK MOTIVATION EXPERIMENT (g N REACTIONS)






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PENTAQUARK MOTIVATION EXPERIMENT





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OUTLINE

• MOTIVATION FOR LEP PENTAQUARK SEARCHES
• THE LEP EXPERIMENTAL PROGRAM AT CERN
• SEARCHES FOR PENTAQUARK PRODUCTION
• SUMMARY

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LEP PROGRAM AT CERN
Large Electron Positron (LEP) Collider at
CERN LEP1 Starting in 1989 at Ecm 91 GeV
(MZ) LEP2 Starting in 1995, sucessive upgrades
to higher Ecm
LEP1 (1989 1995) 200 pb1 per experiment
Terminated in November 2000 Accelerator Lattice
and Experiments dismantled (for LHC)
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THE ALEPH DETECTOR
Muon Chambers
Hadron Calorimeter
Electromagnetic Calorimeter
Time Projection Chamber
Superconducting Magnet Coil
Inner Tracking Chamber
Silicon Vertex Detector
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THE DELPHI DETECTOR
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THE L3 DETECTOR
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HADRON SYNTHESIS IN ELECTRON-POSITRON
INTERACTIONS
Hadronic Z Decays
Two Photon Interactions
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OUTLINE

• MOTIVATION FOR LEP PENTAQUARK SEARCHES
• THE LEP EXPERIMENTAL PROGRAM AT CERN
• SEARCHES FOR PENTAQUARK PRODUCTION
• HADRONIC Z DECAYS (ALEPH DELPHI)
• TWO PHOTON (L3)
• SUMMARY

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DATA AND MONET CARLO SAMPLES

• ALEPH Hadronic Z decays between 1991 1995
  (LEP1)
• DELPHI Hadronic Z decays recorded during 1994
  and 1995 during which Time Projection Chamber and
  Ring Imaging Cherenkov detectors were functioning
  optimally
• L3 1998-2000 (LEP2) data with Two Photon
  preselection for Wgg gt 5 GeV
• Hadronic Z Based on JETSET with parameters tuned
  to agree with well-established measurements
• Two Photon PYTHIA with jet hadronization
  simulated with JETSET
• Simulated only octet and decuplet Baryons
• Full detector simulation

DATA
MONTE CARLO
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ALEPH PARTICLE IDENTIFICATION
To identify particles of type i, cuts are placed
on pull of dE/dx from Time Projection Chamber
1.3x106 proton candidates selected 52 purity in
high momentum range 96 purity in low momentum
range
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DELPHI PARTICLE IDENTIFICATION
Pions Kaons Protons
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ALEPH NON-EXOTIC pK MASS SPECTRA
Smooth deviation from simulated pK mass spectrum
observed at few percent level. Understood to be
caused by imperfect simulation of dE/dx for
spatially close track pairs. Corrected from
doubly charged combinations.
Excess pK fit to L(1520) and eight established
S resonances
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ALEPH NON-EXOTIC pK RESULTS

• Simultaneous fit to the strengths of eight more
  or less established resonances over background
  results in an L(1520) excess of 2814
  293 combinations.
• If L(1520) excess is counted in 30 MeV/c2 window
  around 1.520 GeV/c2, result is 400
  combinations lower ? conservatively taken as
  systematic error
• Average acceptance of 0.10 obtained from
  simulation as well as BR(L(1520)?pK) 22.5

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ALEPH EXOTIC pK0 SPECTRA
s
K0 are selected from kinematic fit to two
opposite charged pions emerging from secondary
vertex ? 1.2 x 106 K0 candidates with 93 purity
s
s

• Seach for maximum number of excess combinations
  in sliding window of width 20 MeV/c2 over smooth
  3rd degree polynomial fit to data
• Mass resolution is 5 MeV/c2
• Maximum excess in interval of 1.525 to 1.545
  GeV/c2 is 57 combinations over background of 2840
• Corresponding 95 confidence level upper limit on
  excess is 195 combinations

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ALEPH EXOTIC pK0 RESULTS
s

• Use average acceptance of 0.063 and BR(Q ? p K0)
  ¼
• 95 Confidence Level upper limit on the
  multiplicity of Q (plus its antiparticle) in
  hadronic Z decays
• Ratio of Q to L(1520) production is Z decays
• This limit is roughly a factor of 20 lower than
  the ratio in gd reactions measured by HERMES

NQ lt 0.0030
NQ/NL(1520) lt 0.13
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DELPHI pK MASS SPECTRA AND RESULTS
pK
pK0
pK
s
No excess NQ lt 0.006 (95 C.L.)
No excess NQ lt 0.015 (95 C.L.)
306 55 events NL(1520) 0.0224 0.0027
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L3 pp and pK0 MASS SPECTRA(TWO PHOTON
INTERACTIONS)
s
pK0
pp
s
NL (1.57 0.11) x 10-2 per ee- ? ee-
hadrons s(ee- ? ee-LX) 197.8 13.8 pb
No excess observed 95 C.L. limit set s(ee- ?
ee-QX) lt 20 pb
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ALEPH SEARCH FOR Xp RESONANCES MASS SPECTRA
Sample of 3350 X- candidates with a purity of 76
within a mass window of 7 MeV/c2
No excess observed 95 C.L. limit set
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ALEPH SEARCH FOR Xp RESONANCES RESULTS

• Mass spectrum of doubly-charged combinations
  (X--) is well fitted by linear background from
  1.62 to 2.1 GeV/c2
• In NA49 signal region (1.835 to 1.885 GeV/c2)
  observed excess is 2 combinations over
  background of 436
• Using acceptance of 0.021 and systematic
  uncertainty of 8, a 95 Confidence Level upper
  limit is obtained

NX(1862)- - BR(X(1862) ? Xp) lt 4 x 104

• For neutral combinations, X(1530)0 multiplicity
  is found to be
• in good agreement with previous ALEPH and OPAL
  results

NX(1530)0 NX(1530)0 (70 8 6) x 104

• 95 Confidence Level upper limit on
  Exotic/Non-Exotic X

NX(1862)- - BR(X(1862) ? Xp)/NX(1530)0 lt
0.06
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ALEPH SEARCH FOR CHARM RESONANCES D0p and Dp
MASS SPECTRA
No compelling excess observed 95 C.L. limit set
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ALEPH SEARCH FOR CHARM RESONANCES Dp MASS
SPECTRA
No excess observed 95 C.L. limit set
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ALEPH SEARCH FOR CHARM RESONANCES RESULTS

• No excess in Dp channel 2 combinations between
  3.09 and 3.11 GeV/c2 (3.5 combinations
  expects from Monte Carlo)
• Dp channel (not covered by H1), an slight excess
  is observed of 5.2 3.7 combinations

or
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OUTLINE

• MOTIVATION FOR LEP PENTAQUARK SEARCHES
• THE LEP EXPERIMENTAL PROGRAM AT CERN
• SEARCHES FOR PENTAQUARK PRODUCTION
• SUMMARY

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SUMMARY

• No evidence of light pentaquark production
  Q(1530) observed in Hadronic Z Decays and Two
  Photon Interactions in ALEPH, DELPHI, L3 data

NQ lt 0.0030
s(ee- ? ee-QX) lt 20 pb
NQ/NL(1520) lt 0.13

• No evidence of light pentaquark production
  X(1862) observed in Hadronic Z Decays in ALEPH
  data

NX(1862)- - BR(X(1862) ? Xp) lt 4 x 104

• No evidence of heavy flavour pentaquark
  production Qc(3100)0 observed in Hadronic Z
  Decays in ALEPH data