contents 2 j-parc e19 collaboration 3 pentaquark search 4 genuine exotic hadron (uudds bar ) m =...
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Pentaquark Q+ search experiment at J-PARC
M. Moritsu( Kyoto University RCNP, Osaka University )
for the J-PARC E19 collaboration
Baryons2013 @ Glasgow, 2013/06/24
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Contents
1. Introduction2. J-PARC E19 experiment– Overview of the experiment– New result of E19-2nd run
3. Summary
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J-PARC E19 Collaboration
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Pentaquark search
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• Genuine exotic hadron (uuddsbar )• M = ~1540 MeV/c2 (decay Q+ KN)
Situation is still controversial ...
Pentaquark Q+
Historical background• Q+ pentaquark was first predicted by Diakonov et al. in 1997.• SPring8/LEPS group reported the evidence for Q+ in 2003.• Dozen experimental groups published supporting evidence for the Q+,• followed by a number of experiments with no evidence.
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Physics Motivation• Distinctive feature of Q+ pentaquark
– Need some mechanism to suppress decay.
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Narrow Width
Meson-Baryon molecule Diquark structure(Need quark rearrangement for KN decay)
( < a few MeV )
Useful tool to understand low energy QCD dynamics !!
R.Jaffe, F.Wilczek (2003)
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Our Approach ( J-PARC E19 )
1. Pion induced reaction– Complementary to photo-production (LEPS/CLAS).– Expect sizable production cross section. => High statistics
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p- + p → K- + Q+
2. High resolution missing mass spectroscopy– K1.8 beam line & SKS = DM < 2 MeV (FWHM)
2.6s
KEK-PS E522Miwa et al., PLB 635, 72.
DM ~ 13.4 MeV
(FWHM)
Previous experiment
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Our Approach ( J-PARC E19 )
1. Pion induced reaction– Complementary to photo-production (LEPS/CLAS).– Expect sizable production cross section. => High statistics
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p- + p → K- + Q+
2. High resolution missing mass spectroscopy– K1.8 beam line & SKS = DM < 2 MeV (FWHM)
Conclusive result by higher sensitivity !!
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Experimental setup
J-PARC K1.8
p- beam
1.92/2.00 GeV/c
Dedicated to the (p,K) reaction spectroscopy
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History of E19
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Comment Beam Momentum
Beam intensity
p’s on Target
2009/10 ~ K1.8 beam line & detector commissioning start
2010/10-111st RUN
examine the 2.6s bump structure observed in E522
1.92 GeV/c
1.0 M /spill
7.8 x 1010
2012/022nd RUN
new data at the highest beam momentum at K1.8
2.00 GeV/c
1.7 M /spill
8.7 x 1010
This presentation
Shirotori et al., PRL 109, 132002 (2012).• Q+ Peak was not observed.• We concluded that E522 bump was not the signal
by 10 times higher sensitivity.
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Note on Q+ decay width
PV Fs 500MeV
PV Fc 1800MeV
1800 2000 2200 2400 26000
2
4
sqrt(s) [MeV]
s [m
b]
Jp=1/2+, G +Q = 1MeV
Theoretical calculations :T. Hyodo et al., PRC 72, 055202 (2005),
PTP 128, 523 (2012).
plab=2.0 GeV/c
plab= 1.92 GeV/c
• Higher beam momentum provides higher sensitivity.
2.0 GeV/c ( = Max. of K1.8 B.L.) Even if no peak, stronger
constraint on the Q+ decay width will be obtained.
s-channel dominance GQ g∝ 2
KNQ ∝ s
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Result of the E19-2nd run
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SKS spectrometer
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K
Scattered particle M2
pp
M2 [GeV2]
SKS system : pK
PID counters– Timing counter– Aerogel Cherenkov (K/p) : n=1.05– Lucite Cherenkov (K/p) : n=1.49Tracking– MWDCs : 3 mm pitch– DCs : 10 mm pitch, 2m×1m size
Good momentum reconstruction and PID !!
We can separate only K very clearly.
Example of analysis 1
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Vertex-ZVertex-(X vs Y)
Vertex Reconstruction
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LH
2 T
arge
t ce
ll
f67.8 × 120 mm
pK
Target cell is clearly identified !!
Consistent with horizontally oblate beam shape.
window window
Beam
LH2 targetEmpty target (scaled)
Example of analysis 2
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Consistency check with previous exp.
p+ + p → K+ + S+ @ 1.37 GeV/c Missing mass resolution: DMS = 1.92 MeV
(FWHM)– Equivalent to the 1st run.
Cf.) 1.86±0.08 MeV @ E19-1st
S+ Missing Mass
DM = 1.92 ±0.05 MeV
p+ + p → K+ + S+ @ 1.37 GeV/c
S+
E19-2nd
Preliminary
Preliminary
DMQ = 1.74 MeV (FWHM)
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p+ + p → K+ + S+ @ 1.37 GeV/c Missing mass resolution: DMS = 1.92 MeV
(FWHM)– Equivalent to the 1st run.
Cf.) 1.86±0.08 MeV @ E19-1st
S+ Differential Cross Section
Preliminary
Differential cross section– Almost consistent with 1st run
and reference data.– Good understanding of
efficiencies and acceptance.
p+ + p → K+ + S+ @ 1.37 GeV/c
Consistency Check OK
Consistency check with previous exp.
DMQ = 1.74 MeV (FWHM)
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E19-2nd Preliminary
Analysis Result of E19-2nd run
• No peak structure was observed.• Upper limit on differential cross section averaged from 2 to 15 deg:
< 0.28 mb/sr @ 1.50 – 1.57 GeV/c2
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p- + p → K- + X @ pp = 2.0 GeV/c
An example of fitting result @ 1.535 GeV/c2
Fitting results of each mass and Upper limit (90%C.L.)
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Upper limit on decay width
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• 0.61 MeV for ½+• 3.7 MeV for ½-
gKNQ
• Considering about theoretical uncertainty (coupling scheme and form factor), we chose the most conservative case as the upper limit.
GQ g∝ 2KNQ ∝ s
T. Hyodo et al., PTP 128, 523 (2012).
Upper Limit on GQ for JPQ
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Summary• J-PARC E19 is a pentaquark Q+ search experiment with
high statistics and high resolution.– p- p → K- Q+ reaction– J-PARC K1.8 B.S. and SKS
• New result of E19-2nd run was presented. – Consistency with the 1st run was checked. O.K.– Q+ missing mass resolution of 1.74 MeV was evaluated.– No peak structure was observed in MM spectrum.– Upper limit for Q+ production cross section was obtained to be
0.28 mb/sr @ 1.50 – 1.57 GeV/c2
– This corresponds to upper limit on Q+ decay width of 0.61 and 3.7 MeV for JP = ½+ and ½-, respectively.
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BACKUPS
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1st run result of E19
• No prominent peak structure• Upper limit: < 0.26 mb/sr
@ 1.51-1.55 GeV/c2
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p- + p → K- + X @ 1.92 GeV/c
E19-1stdatabackground(sim.)
s-channel dominance GQ g∝ 2
KNQ ∝ sUpper limit of decay width
• 0.72 MeV for ½+• 3.1 MeV for ½-
Shirotori et al., PRL 109, 132002 (2012).
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Comparison with background simulation
Simulation with measured cross section using angular distributions• f production : uniform (S-wave)• L(1520) : 1+cos∝ 2qcm (D-wave)
BG reactions• p- p → fn→K- K+ n(s = 30±8 mb)
• p- p → L(1520) K0
→K- K0 p(s = 21±5 mb)
• p- p →K- K+ n• p- p →K- K0 p(s ~25 mb)
O. I. Dahl et al . Phys. Rev. B 163, 1377 (1967).(Bubble chamber data)
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Cut condition : NpK = 1
2 < q < 15 deg Vertex-(X2+Y2) < 252 mm2
-60 < Vertex-Z < 60 mm0.15 < m2 < 0.4 GeV2
c2 cut : Local tracking c2 < 20 (BcOut c2 < 10)SKS, K18 tracking c2 < 30
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Previous experiments at KEK-PSE522 : p- p → K- Q+ @ 1.92 GeV/c E559 : K+ p → p+ Q+ @ 1.20 GeV/c
K. Miwa et al., PLB 635, 72 (2006).
K. Miwa et al., PRC 77, 045203 (2008).
2.6s
Bump structure (2.6s) Not enough to claim the existence
Upper limit: s < 3.9 mb (90% C.L.)
No peak structure Upper limit: s < 3.5 mb/sr (90% C.L.)
p--induced
K+-induced
Prev. Exp.
1.53 GeV
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Positive Results (~2005)LEPS DIANA CLAS-d
HERMES
ITEP
COSY-TOF
ZEUS
SVD
SAPHIR
CLAS-p
4.33.43.2 5.1
3.6
4.93.6
4~5
4.74.4
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[CAUTION]Significances ware recalculated by significance = S/√(S+B) or S/dS
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Positive Results (updated)LEPS
DIANA
HERMES
ITEP
ZEUS
SVD
CLAS-p
5.55.1
3.6
4.93.6
4~6
5.825
CLAS-d< 0.3 nb
COSY-TOF< 0.15 mb Some confirmed their evidence,
but others did not...[CAUTION]Significances ware recalculated by significance = S/√(S+B) or S/dS
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Negative Results26
FOCUS
BABAR
SPHINXCDF
BES
BELLE
LEP
HERA-B
HyperCP
PHENIX (Q-)_
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J-PARC Hadron facility
High-p
K1.1BR
K1.8BR
K1.8
Primaryproton beam
T1 target
KL
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GC BH1BC1 BC2
K1.8 Beam Spectrometer
SKS Spectrometer
MS2
Q10 Q11
Q12
Q13
D4
SDC3SDC4 TOF
LC
AC1AC2
SDC2SDC1
BC4BC3 BH2
Target
2009 Oct
28
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2011 Sep.
Injection angle : 30 15 deg.• Higher-momentum acceptance.• For future experiments.
Rotation of SKS
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Recovery from the earthquake
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Setup difference of 1st and 2nd run
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E19-1st run (2010) E19-2nd run (2012)
30 deg.
injection
15 deg.injection