Search for T in the ?3He??K0pp reaction at CLAS

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Search for T in the ?3He??K0pp reaction at CLAS
S. Niccolai, IPN Orsay

• Motivation
• The reaction
• Experimental setup
• Data analysis
• Preliminary results

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Motivation

• Evidence for exotic pentaquark state with
  1.52ltMlt1.55 GeV/c2 shown by several experiments.
• In all cases production of T associated to K.
• Production mechanism not yet clearly understood.

Necessary to study different reactions
?3He??Tp

• Final state clean
• No kinematic reflections possible
• Low E? threshold (0.8 GeV)
• CLAS data available

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?3He??Tp the reaction
(n)
(K)
Decay modes studied T?K0p ??pp- K0 ?
pp- T?Kn
??pp-
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The CLAS detector at JLab
Experiment 93-044 Electron beam energy 1.645
GeV Beam current 10 nA
Bremsstrahlung photon tagger
Target R2 cm, L 18 cm, liquid 3He
at T3 K
E? 0.35 1.55 GeV
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Analysis technique

• 3 different topologies mutually exclusive
  analyzed
• 1) pppp- detected, missing ?
• 2) pp p- pp- detected, missing p
• 3) ppKp- detected, missing n (case T?nK)

Results of analyses of 3 topologies can be
combined

• Increase statistics
• Reduce systematic uncertainties

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1) Case pppp- detected

• p2 spectator (p p2 lt0.4GeV/c)
• ? detected by missing mass

E?gt1.05 GeV
?misslt90
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1) Case pppp- detected

• p2 spectator (p p2 lt0.4GeV/c)
• ? detected by missing mass
• K0 reconstructed from pp-
• invariant mass

pp-lt0.45 GeV/c
pplt0.45 GeV/c
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1) Case pppp- detected

• p2 spectator (p p2lt0.4GeV/c)
• ? detected by missing mass
• K0 reconstructed from pp-
• invariant mass
• p1K0 invariant mass

CLAS preliminary
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1) Case pppp- detected
MC ?3He?T?p (phase space) ?3He?pK0?p (phase
space)
DATA
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2) Case ppp-pp- detected

• 3rd proton (spectator) detected
• by missing mass

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2) Case ppp-pp- detected

• 3rd proton (spectator) detected
• by missing mass
• K0 reconstructed from pp-
• invariant mass

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2) Case ppp-pp- detected

• 3rd proton (spectator) detected
• by missing mass
• K0 reconstructed from pp-
• invariant mass
• ? reconstructed from pp-
• invariant mass

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2) Case ppp-pp- detected

• 3rd proton (spectator) detected
• by missing mass
• K0 reconstructed from pp-
• invariant mass
• ? reconstructed from pp-
• invariant mass
• p2K0 invariant mass

CLAS preliminary
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2) Case ppp-pp- detected

• 3rd proton (spectator) detected
• by missing mass
• K0 reconstructed from pp-
• invariant mass
• ? reconstructed from pp-
• invariant mass
• pK0 invariant mass

CLAS preliminary
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3) Case ppp-K detected (T?nK)
n detected by missing mass
CLAS preliminary
? identified by pp- invariant mass
nK invariant mass
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Sum of the 3 topologies
CLAS preliminary
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Sum of the 3 topologies
CLAS preliminary
no pp and ?miss cuts on case 1
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Conclusions

• ?3He??pK0p and ?3He??pKn measured for the first
  time, with CLAS
• 3 independent topologies studied
• final state cleanly reconstructed
• low statistics in each topology, but agreement
  in presence and position of the peak
• the sum of the 3 analyses shows a peak in the nK
  invariant mass spectrum at M1.55 GeV/c, with
  statistical significance of 5s