Pentaquark Searches on Protons Targets at JLab

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Pentaquark Searches on Protons Targets at JLab

• Paul Stoler
• Rensselaer Polytechnic Institute, Troy NY
• For the CLAS Collaboration

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Yogi Berra

• It aint over til its over.

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This talk Discuss four experiments.

• 1. CLAS g6 ?p???K-?(published 2004)
• 2. Hall A search for ?.
• 3. ?p?K0? (recently completed),
• 4. CLAS g12 ?p???K-?, ????????

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Photoproduction on hydrogenExperiment g6
?p??K-K(n)

• Data 1999 and 2000 runs
• Tagged photons Eg 3 - 5.5 GeV.
• Target 18 cm LH2.
• Reaction ?p??K- ?
• p, K, K- and ?detected.
• neutron identified by missing mass.

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Jefferson Lab Electron Accelerator Facility
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CEBAF Large Acceptance Spectrometer - CLAS
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Real Photons with CLAS
n
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gd ? p KK- (n) in CLAS
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Possible Q production mechanisms
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CLAS ?pg ?K-? ? gnK
V. Kubarovsky et al., PRL, Jan.04
(?)
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CLAS-gp Indication for a heavy N(2430)?
N ?
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CLAS ?pg ?K-? ? gnK
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Experiment g6 Revisited
The published data is the sum of data obtained in
three experiments, all run at different times
under very different conditions.
Eg Torus Current (A) Tgt.Pos.(cm)
g6a 3.2-3.8 3375 1 0 0.90 (260)
g6b 4.6-5.2 3375 1 0 0.80 (370)
g6c 4.8-5.5 1690 2.7 -100 cm 0.94 (200)
Consider each separately
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The published data is the sum of data obtained in
three experiments, all run at different times
under very different conditions.
Eg Torus Current (A) Tgt.Pos.(cm)
g6a 3.2-3.8 3375 1 0 0.90 (260)
g6b 4.6-5.2 3375 1 0 0.80 (370)
g6c 4.8-5.5 1690 2.7 -100 cm 0.94 (200)
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• The Current Status of g6
• The g6a and g6b show very little statistical
  significance.
• The published data is totally dominated by g6c.
• Independent analyses show the the peak in g6c is
  very strong.
• It cannot be reduced by different simple analysis
  schemes.
• An in-depth scrutiny of all the accepted g6c
  events is currently underway.

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• Second round of Jlab experiments
• Designed specifically for comprehensive
  pentaquark searches,
• With orders of magnitude more statistics than
  previously presented.
• Hall A A search ????and????? on proton at high
  resolution.
• Results presented.
• CLAS g10 Attempt to verify result of first
  published Jlab result on neutron.
• First round of analysis complete. See talk of
  Sylvia Niccolai
• CLAS g11 Attempt to verify SAPHIR published
  experiment and suggestions of possible ????
  peaks at CLAS on proton target
• Initial results presented .
• CLAS eg3 Search for ??????members of
  anti-decuplet on neutron.
• Data taking complete. See talk of Sylvia
  Niccolai
• CLAS g12 6 GeV run. Verify published result of
  g6 and search for ????on proton. Data taking
  expected late 2006.

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CLAS - G11
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New Start Conter trigger PID

• Specifications
• Extended target cell coverage (40 cm)
• 2mm thick scintillator light guide
• Higher azimuthal segmentation (4 x 6)
• Time resolution lt 1ns (200 ps in rec)

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CLAS - G11
7109 triggers recorded Luminosity
70 pb-1 gt10 times the statistics of previous
measurements Eg 1.6 3.8 GeV ?Mpeak 2
MeV Obtain??T and d?/dt
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CLAS - G11 online plots
p
K0
?-
?0
?0
?(1520)
?
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1 of statistics
CLAS-g11
n
?(1116)
0
(1192)
?

?(1116)
??(1197)
??(1520)
0


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Cascades in g11
X-(1530)
X0(1315)
X-(1320)
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Cross Section Extraction
?p ? p ?
?(mb)

• Different final states are measured
• simultaneously in the CLAS detector
• Cross section for known reactions
• have been extracted to test the
• accuracy of the analysis procedure
• 1 of statistics

• CLAS g11
• preliminary
• world data

• WORLD data

Eg(GeV)
?p ? K?
?(mb)
?p ? p ?

• CLAS g11
• preliminary
• SAPHIR

• CLAS g11
• preliminary
• SAPHIR

Eg(GeV)
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Search for the ? (1540)

Counts
KS

• final state is identified
• using the missing mass technique
• the K0 is detected via its KS component decaying
  into p p-
• strangeness is tagged detecting the K
• using the full statistics (70 pb-1) a total of
  320000 events are selected

M (pp-)(GeV)
Counts
n
Mx(pp-K X)(GeV)
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Hyperon Production

M(nK)
?

(1520)
?
K
?p
Counts



X)
K
(
?
M
p
Counts
X
NL 91300 NS 36200 NS- 26800
?

-
)
M(n
?
)
M(n
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nK Mass Spectrum
Counts/4 MeV
preliminary
M(nK)(GeV)

• the nK mass spectrum is smooth

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nK Mass Spectrum
M(nK)
Counts/4 MeV
preliminary
cosqCM
M(nK)
K0
Counts
qCM
g
p
Q

• mass vs. CM angle distribution shows coverage of
  the whole kinematics
• no evidence for a structure is found for
  different CM angle ranges

cosqCM
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Evaluation of an Upper Limit on the Q Yield
Counts/4 MeV
Counts/4 MeV
-0.8 lt cosqCM lt -0.6
preliminary
M(nK)(GeV)
Counts/4 MeV
0.6 lt cosqCM lt 0.8
M(nK)(GeV)
M(nK)(GeV)
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Upper Limit on the Q(1540) Cross section
energy and angular dependence

• L - luminocity
• BR (Q? nK)50
• CLAS detection efficiency evaluated using
  different Q production models

preliminary
ds/dcosq (nb) (95CL)
cosqCM
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Q(1540)/?(1520) ratio
preliminary
N(Q) (95CL) lt 210
95 CL
N(L) 91000
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Upper Limit on the Q Cross sectionmass
dependence
(95 CL) s g p ? Q K0 lt 2 nb
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Comparison with SAPHIR results for same
kinematics.
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Comparison with SAPHIR results for same
kinematics.
SAPHIR
Observed Yields SAPHIR N(Q)/N(L) 63/630
10 CLAS N(Q)/N(L) lt110/53000 lt0.2
(95CL) Cross Sections SAPHIR sg p ? Q K0
300 nb reanalysis 50 nb CLAS sg p
? Q K0 lt 2 nb (95CL)
Counts
Counts
cosqCM(K0) gt 0.5
cosqCM(K0) gt 0.5
M(nK) (GeV)
M(nK0) (GeV)
g11_at_CLAS
Counts
Counts
L(1520)
preliminary
cosqCM(K0) gt 0.5
cosqCM(K0) gt 0.5
Q(1540) ?
M(nK) (GeV)
M(nK0) (GeV)
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High resolution Hall A Studies
E04-012 a search for ? partners
Look for missing mass in reaction H(e, e K ) X
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Viewgraphs from J-O. Hansen (Jlab)
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CLAS - Search for ?5 Pentaquark States

• The search for narrow X5 states can be approached
  
• in at least two ways
• Missing mass technique.
• Reconstruction of all decay particles.
• Both channels will be explored.

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CLAS missing mass technique
Data from run at Eg lt 3.8 GeV

• Good missing mass
• resolution and low
• background.
• Needs Eg gt 5 GeV,
• new start counter

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Yogi Berra (redux)
When you come to a fork in the road
. take it !
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To Come Late 06

• g6 gpgKK-pp
• E g6 GeV
• Repeat published result with 10x statistics
• Search for K0
• Search for exotic narrow Xs

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Yogi Berra (yet again)

• It aint over until the fat lady sings.

Paul Stoler
The fat lady aint sung yet!
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CLAS X5 Searches (approved experiment)
Electron beam
gn?KK?--

• X0 ct 8.7 cm
• X- ct 4.9 cm
• ct 7.9 cm
• Ks ct 2.7 cm

Measure 3p- and one proton
gb 1.5
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CLAS-?d Exclusive reaction

• Exclusive photoproduction on deuterium

• Experimental data from 1999 run
• Tagged photons with up to 3 GeV energy
• Target 10 cm long liquid deuterium

Possible reaction mechanism

• No correction for Fermi smearing is needed.
• Aids significantly to reduce the background.

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CLAS
M 1.542 GeV ??lt 21 MeV (?M9 MeV) Stat.sig.
5.2? (4.6-5.8)
?
Gaussian background
Simulated background
Distribution of ?(1520) events
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CLAS gd Exclusive Reaction

• Exclusive photoproduction on deuterium
• ???K-K n

• 1999 run
• E 1g3 GeV
• Target 10 cm long liquid deuterium

Possible reaction mechanism

• No correction for Fermi smearing is needed.
• Aids significantly to reduce the background.

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CLASExclusive photoproduction on
deuterium?dgpK-K n
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CLAS-gd results
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Ongoing G10 analysis for the ?

• Independent analysis of several reactions by
  different groups.
• Particles detected

Fermi momentum correction

• Issues of reflections, statistical
  fluctuations, particle miss identifications, mass
  determination, pK0 vs. nK will be addressed.
• Preliminary results are in the collaboration
  review.

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Comparison with published data

• The same photon beam energy spectrum, the same
  event selection criteria reaction ?d?pKK-(n).

New (g10) data
Published spectra
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?n? p?- cross section

• p ?- detected in CLAS, proton in the deuterium is
  spectator.
• High statistics, simple kinematics
• Many measurements (e.x., Hall-A).

g10, 3375A
g10, 3375A
MC(Bonn potential)
Events
Events
proton
rejected
Missing momentum (?,p?-)X (GeV/c)
MM(?,p?-) (GeV/c2)
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?n? p?- cross section

1.00 lt Eg lt 1.20 GeV
1.05 lt Eg lt 1.15 GeV
g10 2250A g10 3375A
g10 preliminary (3375A) World data
ds/dWCM (mb/sr)
ds/dWCM (mb/sr)

• Consistency between high field and low field
  data.
• g10 data agree with world data.
• 0.5 of statistics

Cos?CM(?-)
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g6a Npeak11
g6b Npeak14
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g6b Npeak9
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g6a Npeak5.4
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g6a Npeak5.5
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Preliminary Results from the ?5 Search
?(?5) / ?(1520) lt 1.7
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0

Q
?
g
K
p
Effective Lagrangian method (hep-ph/0505134)
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Total cross section from proton and neutron
Total cross section from proton and neutron do
not show differences
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Upper Limit on the Q Cross sectionmass
dependence
Upper limit (95 CL) s g p ? Q K0 lt 2 nb
preliminary