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Pentaquarks : dead or alive? . T ome Anticic, K. Kadija, Tanja Sus a. Rudjer Boskovic Institute. NA61, feb 201 1, Warsaw. What are pentaquarks?. d. −1/3. u. s. +1/3. +2/3. d. u. −1/3. +2/3. New form of quark matter : baryons whose - PowerPoint PPT Presentation
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Pentaquarks: dead or alive?
Tome Anticic, K. Kadija, Tanja Susa
Rudjer Boskovic Institute
NA61, feb 2011, Warsaw
What are pentaquarks?
• New form of quark matter: baryons whose minimum quark content is 5 (qqqqq)
• “Non-exotic” pentaquarks The antiquark has the same flavor as one of the other quarks Difficult to distinguish from 3-quark baryons
s+1/3
d−1/3u
+2/3
d−1/3u
+2/3
Baryons with S = +1 cannot be made by qqq !!!!!
• “Exotic” pentaquarks (qqqqQ) The antiquark has a different flavor from the other 4 quarks Quantum numbers different from any 3-quark baryon
Example: uudds (exotic): Baryon number = 1/3 + 1/3 + 1/3 + 1/3 - 1/3 = 1 Strangeness = 0 + 0 + 0 + 0 + 1 = +1
The pentaquark anti-decupletExperimental searches were motivated by predictions of chiral soliton model Diakonov, Petrov, Polyakov, Z.Physics A359 (1997). Jaffe and
Wilczek had a quark-diquark model.
S = +1
S = 0
S = -1
S = -2
: exotic states
I=-3/2 I=-1/2 I=1/2 I=3/2I=1I=-1 I=0
+ (1539)
N(1650-1690)
(1760-1810)
(1862)
uudds
ddssu uussd
narrow width (few MeV)
decay modesnK+,pK0
J=1/2+
can be detected
experimentally!!
First evidence for
H1
LEPS at Spring-8Spring-8
Narrow peak observed in K- missing mass spectrum
M = 1.54 ± 0.01GeV/c2
≤ 0.025 GeV/c2
S=19 B=17 Significance: S/√B = 4.6
+
n→K+K-(n) (the neutron is bound inside 12C)
Positive signals
Spring8 ELSA
JLab-p
HERMES
ITEP
pp ++.
COSY-TOF
DIANA
SVD/IHEP
JLab-d
ZEUSCERN/NA49H1
Positive experimental results
Experiment Energy Reaction Mass Width Significance (GeV) (MeV) (MeV)
+
c+
3/2
LEPS 1.5 - 2.4 C→K+K-X 1540 ± 10 < 25 4.6
CLAS 3 d→K+K-p(n) 1542 ± 5 < 21 5.2 ± 0.6
CLAS 3 – 5.47 p→ +K+K-(n) 1555 ± 10 < 26 7.8 ± 1.0
SAPHIR 0.87 – 2.63 p→K0sK+(n) 1540 ± 4 < 25 4.8
HERMES 27.6 e+d→pK0s X 1528 ± 3 19 ± 5 4 - 6
ZEUS √s =300 e+p→pK0s X 1522 ± 2 8 ± 4 3.9 – 4.6
COSY-TOF 2.95 pp→pK0s + 1530 ± 5 < 18 ± 4 3.7 – 5.9
JINR 10 p(C3H8)→pK0sX 1540 ± 8 9 ± 2 5.5
SVD 70 pA→pK0sX 1526 ± 3 < 24 5.6
DIANA 0.85 K+Xe→K0pXe’ 1539 ± 2 < 9 4.4
BC 40,50,110,140 A→pK0sX 1533 ± 5 < 20 6.7
NOMAD 24.3 A→pK0sX 1529 ± 3 < 9 4.3
H1 √s =300, 320 ep D*-pX 3099 ± 3 < 20 5.4
NA49 158 pp →X 1862 ± 2 < 17 5.8
Negative eksperimental results
L3
ALEPH
DELPHI
BES
BaBar
BaBar
Belle
Belle
CDF
FOCUS
E690
HyperCP
SELEX
HERA-B
SPHINX
WA89
COMPASS
LASS
PHENIX
ZEUS
HERMES
W > 5
√s = 10.58
800
120 – 220
70
e+e- → e+e- → pK0s X
Z boson hadronic decays
Z boson hadronic decays
e+e- → J/ ((2S)) →
e+e- → (4S) → PX
eBe → PX
e+e- → B0B0 → PX
KN → PX
pp → PX
p→ PX
pp→ PX
(+,K+,p)Cu → PX
(, p,)p → PX
pA → PX
pC(N) → +C(N)
-N → PX
+(6LiD) → PX
K+p → K+n+
AuAu → P X
e+p→PX
e+d→pK0s X
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Orig/New NA49 X-- analysis
M()
M(--)[GeV/c2] E
ntri
es
550 Xi1530 new analysis
~180 Xi1530 old analysis
prelim X– signal with new analysis??
old analysis
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eff
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Critical Comments
For many experiments, the background shape is not clearly known.
Some experiments have harsh angle cuts that could affect the mass spectra.
In all cases, the signal is weak compared with standard resonances.
Cuts are necessary to lower background.
Several experiments retracted data with more data/further analysis
But, some (not many…) positive results remain…
New DIANA & LEPS results
M 1.537 ± 0.002 GeV/c2
= 0.00036 ± 0.00011GeV/c2
K+Xe KS p Xe’
s/√s+b = 5.3
Statistics nearly doubledd pn
LEPS
M 1.524 ± 0.002 GeV/c2
GeV/c2
Significance: 5.1
DIANA
New SVD-2 results
pN
M 1.523 ± 0.002 GeV/c2
≤ 0.014 GeV/c2
KS p X
Two independent K0s samples (inside & outside vertex)
Sample ISample II
Combined significance: s/√s+b = 8.0
Conclusion/NA61 steps
Pentaquarks, although knocked down, not completely dead yet, as there are a few experiments with consistently positive results.
Seems/perhaps pp and pA low energy a possible channel for them.
NA61, with improved statistics and analysis methods, could easily explore, across different energies and in pp, pA, and AA, for both particles and antiparticles:
• p K0s
•
And publish a paper, either with positive or negative results for the pentaquark searches
5-- -K-, - n (BR = 99.848 %)
Reconstruction
5-- --
- (BR = 99.887 %)
p- (BR= 63.9 %)
more stringent selection
1.850 < M < 1.8725 GeV/c2
Peak in the -- distribution candidate
for the 5-- state
Indications of a peak in +-,+- ,++
distributions candidates for
the 50,5
0,5++ state
M 1.86 GeV/c2
Width and position of the peak
M = 1.862 0.002 GeV/c2
= 0.017 0.003 GeV/c2
M = 1.862 0.002 GeV/c2
= 0.017 0.003 GeV/c2M = 1.864 0.005 GeV/c2
= 0.019 0.003 GeV/c2
M = 1.864 0.005 GeV/c2
= 0.019 0.003 GeV/c2
1.8 < M() < 1.9 GeV/c2
Systematic studies and checks
• Analiza MC analysisAnaliza MC analysis
• Background Background candidate candidates
• Resonance reflectionResonance reflection
• Changing cuts
-: all negative particles
-: negative pions
RecRec VENUS VENUS p+p p+p eventsevents
New analysis
• Improve geometry and residual corrections (Millepede)Improve geometry and residual corrections (Millepede) • Several bugs in chain correctedSeveral bugs in chain corrected
- - R3D correctedR3D corrected (outlier removal not used, (outlier removal not used, 2 2 not in a not in a
common block)common block) - - TPC error, ….TPC error, …. • Different Different finder finder, , fitter developed (13-par fit) fitter developed (13-par fit)• Improve main vertex determinationImprove main vertex determination
old and new data
J.M. Gago et al., “ Production in K- p Interactions at 14.3 GeV/c”Ecole-Polytechnique-Saclay-RHEL Collaboration,(CERN/EP/PHYS 76-50)
J.W.Price,J.Ducote,J.Goetz,B.M.K.Nefkens, “Photoproduction of the double-strange hyperons” For the CLASS Collaboration,(arXiv:nucl-ex/0402006)
Hyperon results overview
First clear signal at SPS energies in p-p collisions
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