12 June 2006 1
Sonia Kabana
University of Nantes and Subatech, Nantes, France
MESON2006, 12 June 2006, Krakow
Contents
I Introduction
II Review of pentaquark candidates observed:
+, +, ++, ++, 0c, 0c, --, --, -, -, 0, N0, N0/0, N0, N0/0 I=1/2, Sigma0 I=1/2, Sigma
vis a vis non-observations and theory
III Conclusions and outlook
The pentaquark case: state-of-the-art
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QCD allows for hadronic states other than qqq and qqbar, like:qqqq q-bar (pentaquarks), qq q-bar q-bar (tetraquarks) etc
First ever mentioned: 1964, M. Gell-Mann, PLB 8 (1964) 214. H.J. Lipkin, PLB45 (1973) 267, R.L. Jaffe et al, PLB60 (1976) 201 Etc
First prediction of the mass: 1987, M Preszalowicz, Chiral Soliton
Model, hep-ph/0308114 Mass Z+ (uudds*) = 1530 MeV +- 100 MeV
(error: M. Preszalowicz et al JHEP 0405:002, 2004 )
First prediction of the width: 1997, D. Diakonov, V. Petrov, M. Polyakov,
Z. Phys. A 359(1997)305, Ch. Soliton Model (uudds*, S=1/2, I=0 )
Width < 15MeV (30 MeV)
I Introduction
M. Preszalowicz et al JHEP 0405:002, 2004
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2004
Several recent studies ( F Csikor et al hep-lqt/0503012, K Liu, hep-lat/0510036 etc)don’t find evidence for pentaquarks on the lattice, or masses higher than 1530 MeV (N Ishi hep-lat/0601003) Pentaquarks on the lattice unclear; while ‘the absence of evidence is not evidence of absence’ (hep-lat/0504007) Work in progres
Example of lattice results
Theory:
Quark model, Correlated Quark models, Lattice etc
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II Review of pentaquark candidates observed
+, +, ++, ++, 0c, 0c, --, --, -, -, 0, N0, N0/0, N0, N0/0 I=1/2, S0 I=1/2, S
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++
uudd sbaruudd sbar
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The initial evidence for Pentaquarks
LEPS SAPHIR
CLAS-pHERMES Neutrino
pp ++.
COSY-TOF
DIANA
SVD
CLAS-D
ZEUS
4.6 4.4 5.2 4.8
7.8
~5
6.7
5.6~5
4.6
NA49
6.7 4.2
5-6
1862MeV
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CLAS, S. Stepanyan et al, PRL91 (2003) 252001, hep-ex/0307018 :
exclusive reaction d --> K+ K- p n trigger on p, K+, K-
M(+) = 1542 +- 5 MeV, Width< 21 MeV, S/sqrt(B)= 5.2 +- 0.6 + --> K+ n --> K+K- *(1520) --> pK-
Solid line: fit to S (gauss) +B --> S/sqrt(B)=5.8
Dotted line: MC simulated background --> S/sqrt(B)=4.8
Dashed-dotted: shape of events excluded by a *(1520) rejection cut (m ≠1485-1551 MeV)
CLAS d --> K+ K- p n
Results not confirmed by latest CLAS results
12 June 2006 8
- + production through N*(2400) --> + K- ?
- Mass(theta+)=1555+-10 MeV, Width < 26 MeV,
- S/sqrt(B)=7.8+-1
Pi+
+
Cos *(pi)>0.8
Cos *(K)<0.6
CLAS p -> pi+ K-K+ n
Confirmation of this result with higher statistics by CLAS is planned for 2007
CLAS, V. Kubarovsky et al., hep-ex/0311046, p -> pi+ K-K+ n E( )= 3-5.47 GeV
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LP2005 CLAS 342 , APS Tampa 2005
M(nK+)(GeV)
Cou
nts
/4 M
eV
SAPHIR N(+)/N(*) ~ 9%
CLAS N(+)/N(*) < 0.5% (95% CL)
SAPHIR p K0 ~ 200 (50) nb
CLAS p K0 < 2 nb (95% CL) (1520- 1555 MeV)
< 4 nb (1560 - 1600 MeV)
CLAS 2005 p K0s K+ n
This result disagrees with the SAPHIR observation.
Significance of published Saphir result is very low : 4.8 sigma
The cr. Sect. of this reaction was estimating first 200 nbar in PLB572 (2003)127 without error, updated in the DPG2005 to 50 nbar.
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…..CLAS p K0s K+ n vs theory
The reported non-observation in g p --> theta+ K0
do not disagree with the previous CLAS results on p pi+ K+ K- n
assuming N0* -->theta+ K-
What cross section do we expect ?
S. Nam et al, hep-ph/0403009 estimate 1 nbar for g p --> theta+ K0g p --> theta+ K0 for J^P 1/2+
and a 4 times higher one for n --> theta+ K-
CLAS may not be sensitive enough for the theta+ K0
However: large uncertainty on the theor. Predictions of cr sect.
Isospin asymetry leading to larger cross section for
gamma n than gamma p channel :
Nam, Hosaka and Kim, hep-ph/0505134 , Lipkin and Karliner, hep-ph/0506084
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CLAS 2005 : D K- p K+ n (LP2005 paper 357)
< 5 nb (95% CL)
nosignal
No signal seen. Set upper limits:
This result disagrees with published previous CLAS result (PRL 91, 252001, 2003, hep-ex/0307018).
(LP2005) : In the above PRL result the background is underestimated. New estimate gives a significance of ~3s --> is possibly due to a fluctuation.
CLAS limits of 2nb on the proton and of 5nb on the neutron do not exclude a theta+ with width=1 MeV for JP = 1/2-, 3/2+ (V.Burkert, LP2005)
1/2+ 1/2- 3/2+ 3/2- = 1 MeV
nb
nb
W. Roberts (PRC70, 065201, 2004), effective lagrangian model
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CLAS vs models QNP06
Some model predictions lower than CLAS limits
Model predictions of cr. Sections have large uncertainty
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LEPS new :gamma n K+ K- n (p spectator undetected)
Latest results show peak at 1.53 GeV with higher stat.
-Fermi motion correction done
- Tight phi exclusion cut
- Background from mixed events
- No L(1520) cut
LEPS confirms theta+ observation with increasing statistics
Check reflexions, background estimate, corrections
T Nakano et al, Beijing 16-20 June 2005
LEPS preliminary results confirm the + cand. peak
Candidate peak with 90 counts as compared to 19 in PPRL91 (2003) 012002
T Nakano et al, Pentaquarks2004
PRL91 (2003) 012002
2004
Main contribution to the peak comes from the formation miss. Mom. region 0.42 GeV
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LEPS new: gamma D L(1520) K+ n (Beijing2005)
Nakano et al, 16-20 June 2005 Beijing
Theta+ is indentified by K-p missing mass
Major background process: can be estimated from H target
Excesses are seen at 1.53 and 1.6 GeV
1.53 GeV peak independent of beam momentum (< or > 2.1 GeV) unlikely to be due to kinematic Reflexions
1.6 GeV peak appears only for low beam momenta < 2.1 GeV. Different production mechanism than 1.53 GeV peak.
S=85, B=200
S/sqrt(B)=6
1612 June 2006
Co
un
ts/5
MeV
Sideband subtraction to remove non-resonant background
S = - 0.4
1.50 < M(K - p) < 1.54 1.45 < M(K - p) < 1.50 or 1.54 < M(K - p) < 1.59
LD2 LH2
M(K - p) GeV/c2M(K - p) GeV/c2
(1520) (1520)
MMd(γ,K - p) GeV/c2
LD2
Fluctuations in the sideband spectra are removed by smearing Eg by 10 MeV (nearly equal to the resolution).
1712 June 2006
•Large cross-section compared with(1520).
•Missing Mass resolution is worse.
• No excess at 1.53 GeV nor at 1.6 GeV.
MMd(γ, - p) GeV/c2
Co
un
ts/5
MeV
pre
lim
inar
y
Search for d (1116) +
γ
pn
Θ +
-
p
(1116)
forward angle detection
T Nakano QNP2006
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Results of E522p
- Excess above background observed near 1530 MeV
- Significance about 3
T Nakano QNP2006
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SVD-2 New analysis
pXKpA s
M = 1522 MeV= 12 MeVNevnt = 205
M = 1523 MeV= 12 MeVNevnt = 165
Two independent data set: KS decays inside or outside the Vertex Detector
Ep = 70 GeV
V. Burkert, Lepton Photon 2005
SVD-2 41 87 5.6 3.6SVD-2 370 2000 8.3 7.6Improved analysis
Group Signal Backgr. Significance S/sqrt(S+B)publ. S/sqrt(B)
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Diana 2006
Larger statistics confirms candidate signal of 1st publication with S=60, B=68 S/sqrt(B)=7.3
M=1537+-2 MeV, < 9 MeV
A new estimate of intrinsic width =0.36+-0.11 MeV, (previous value 0.9+-0.3 MeV) do not contradict Belle upper limit
hep-ex/0603017
K+ + Xe -> ++Xe’ -> (K0++p) +Xe’
K+ beam with 850 MeV momentum incident on a liquid
Xenon in a bubble chamber : K+ n K0s p
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Total cross-section is proportional to the decay width
K+ + Xe ++Xe’ (K0++p) +Xe’
DIANA/ITEP
Kaon Scattering
More pictures were analyzed.
hep-ex/0603017
K+
n+
pbeam<445 MeV/c pbeam>525 MeV/c
445<pbeam< 525 MeV/c
Peak appears in mom. range of p(beam)=445-525 MeV consistent with Fermi spearing of a narrow resonance
12 June 2006 22
Non-evidence for Pentaquarks
FOCUS BABARBES
CDF
FOCUS
SPHINX
CDF DELPHI
HyperCPHERA-B
CDF
0c
--
--
+ more
12 June 2006 23
Slope for Pentaquark ?
Slope forbaryons
Slope for p.s. mesons
Slope: Pseudoscalar mesons: ~ 10-2/GeV/c2 (need to generate one qq pair)
Baryons: ~ 10-4 /GeV/c2 (generate two pairs)
Pentaquarks: ~ 10-8 /GeV/c2 (?) (generate four pairs)
Hadron production in e+e- collisions
12 June 2006 24
+ produced mostly at forward rapidity Lab > 0, and Q2 > 20 GeV2.
M(GeV)
ep eK0spX
ZEUS
At HERA ep coll. theta+ candidate is produced in baryon fragmentation
12 June 2006 25
Belle – Limit on + Width
397 fb-1
K+A pK0s Belle limit 90%CL
MeV (90% CL) @ M = 1.525–1.545 GeV
Not inconsistent with previous results.
from K+A pK0sX &
K+D inclusive analysis
Belle: < 0.64 MeV (90% CL) @ M = 1.539 GeV
Cahn,Trilling,PRD69,11501 (2004).
mpKs (GeV/c2)
N /
2 M
eV/c
2
DIANA
T Nakano QNP2006
12 June 2006 26
PDG 2006 : Two stars for theta+
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Theta++
uudusbar
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KppK
(1520)
18.6 M d+Au eventsD+Au Collisions at 200 GeV
pK+ : A 3.5-5.0 sigma signal is seen Mass is ~ 1.53 GeV/c2. Full width ~ 15 MeV. Do we understand the residual background?
KppK
STAR preliminary
After background subtraction
p
Coulomb Interaction
ConversionCoulomb Interaction
H Huang et al
12 June 2006 29
o An excess above background is also seen in AuAu 62.4 GeV data from 20-80% centrality bin, 5.1 M events.o --/++ = 0.47 +- 0.2
++ --
++ plus --
AuAu 62.4 GeV Results
12 June 2006 30
AuAu 62 GeV data20-80% centrality bin5.6 M eventsWeak Signal (3sigma) if any
Au+Au 62 GeVKaon p&pt (0.2, 0.6)Proton p&pt (0.3, 1.5)
STAR preliminary
Au+Au 62 GeV
Au+Au 200 GeV
Year 4 AuAu 200 GeV data
20-80% centrality bin
10.7 M events
No Significant Signal (2)
Au+Au 200 GeV Kaon p&pt (0.2, 0.6) Proton p&pt (0.3, 1.5)
Au+Au results
12 June 2006 31
Year 5 CuCu 62 GeV data0-70% centrality bin16.5 M eventsNo signal at all !!
Kaon p&pt (0.2, 0.6)Proton p&pt (0.3, 1.5)
STAR preliminary
Is There an Obvious Contradiction ?
Cu+Cu 62.4 GeV Run 5 Data
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CLAS theta++
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Comparison to Upper Limits from CLAS
Estimate in STAR for d+Au at sqrt(s) 200 GeV/ ~ 0.35%++/(1520) ~ 5%
New CLAS limit for p K- ++ with ++ pK+ and E(g)=1.8-3.8 GeV ++/(1520) < 0.023% (95% CL) hep-ex/0605001
- CLAS UL ++/ (0.023%) below STAR raw estimate of +/ (3.5%) by ~ 170.
Does this definitely prove the STAR result false ??
There qre null results on theta++pK+ from several experiments e.g. Saphir, Zeus etc
CLAS and STAR study different collision systems, different energy and use different event selection.
The investigated production mechanism of may be different in STAR and CLAS as
-CLAS studies one exclusive reaction. STAR studies inclusive production
For example the mentioned CLAS Upper Limit does not access production with an associated pion (CLAS statement in hep-ex/0605001), while STAR does.
Note that the only still alive and of good significance theta+ signal of CLAS is in this channel (PRL92 032201 2004) to be confirmed with higher stat. In 2007.
12 June 2006 37
0c
uudd cbar
12 June 2006 38
•First evidence for e p --> theta_c^0 (uuddc*) -> D*- p -> (anti-D0 pi-) p -> (K+pi-pi-) p
Mass= 3099 +- 3 +- 5 (syst) MeV Width < 12+-3 MeV
Non observations: Zeus using similar cuts and larger statistics EurPhys J C38 2004 29
hep-ex/0409033, FOCUS (photon+p at Fermilab) hep-ex/0412021
0c
0c candidate and its antiparticle seen by H1
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Xi--, Xi-, Xi^0
Xi-- ssdd ubar
Xi0 duss dbar
Xi- ddss dbar
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• Xi^- (1850) --> Xi* pi- (preliminary) while Xi^+ (1860) --> Xi* pi+ Not seen
• Xi--(1862+-2) --> Xi- pi-
• Xi^0 (1864+-5)--> Xi- pi+ Width<18 MeV
--> Xi^- (and Xi^0) pentaquarks could be from anti-10 or from 8
K. Kadija NA49, JLAB2003NA49 coll., C. Alt et al, PRL92(2004)042003, hep-ex/0310014
Xi--, Xi^0, Xi^-
Walliser,Kopeliovich predicted the Xi(27-plet) mass near 1850 MeV JETP97 433 (2002)
Chir. Sol. Model postdicted the Xi(anti-10) near 1850 MeV (J Ellis et al, hep-ph/0401127)
NA49 pp collisions at sqrt(s)=17 GeV
12 June 2006 41
PDG : 1 star for theta0_c and Xi(1860)
Observed by only one experiment each
12 June 2006 42
N0/Xi0
N0 udsd sbar
Xi0 udss dbar
12 June 2006 43
Au+Au(min.bias, √s=200 GeV)--> K0s
Observation of a possible narrow peak at 1733.6 +-0.5 +- 5 MeV
Cut out upper ~10% of (tot) to suppress background -->
S/(B)=30.6/ ( 35.4)= 5.15, <4.6 +-2.4 MeV
Blue line: mixed event background
STAR Au+Au coll. 200 GeV preliminary
Best Significance obtained in semiperipheral ev.: S/(B)=19.36/ (10.64)=5.93
•N0/Xi0 I=1/2 STAR Coll., S. Kabana et al, hep-ex/0406032
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No cut on centrality
STAR Au+Au coll. 200 GeV preliminary
S/(B)=40.55/ (83.45)= 4.44
STAR Coll., S. Kabana et al, hep-ex/0406032 :
12 June 2006 45
Could fake possibly a peak near 1734 MeV ?
- Difficult to result to a narrow peak ( width ~120 MeV)
--Test 1: Cut more on DCA(p,pi) to primary vertex does not destroy the peak
Test 2: Cut Inv.Mass( p() pi-(K0s) ) out of mass +- 30 MeV does not destroy the peak
STAR Au+Au coll. 200 GeV preliminary
(1232) p() pi-(K0s) + K0s(pi+ pi-) = 1232+497.67 = 1729.7 MeV
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Investigations of systematic errors:
-Split track investigation: Cut on nr of hits(tracks) > 25 (maximal possible 45)
STAR Au+Au coll. 200 GeV preliminary
12 June 2006 47
Split track investigation II :
| MomentumZ(pos. track(Lambda) – MomentumZ(pos. track(K0s) | < 30 MeV
| MomentumZ(neg. track(Lambda) – MomentumZ(neg. track(K0s) | < 30 MeV
| MomentumZ(pos. track(K0s) | < 100 MeV
| MomentumZ(neg. track(Lambda) – MomentumZ(neg. track(K0s) | < 100 MeV
12 June 2006 48
STAR Au+Au coll. 200 GeV preliminary
N0/Xi0(1730) --> Lambda K0s candidate
Seen in 2 decay channels. The Sigma-K+channel tags the strangeness content as ssbar --> N0 candidate (Graal)
Consistent with a partial wave analysis of old data suggesting two narrow N states at 1680 and/or 1730 MeV width < 30 MeV (nucl-th/0312126, R Arndt et al)
S/(B)=5.15S. Kabana et al, hep-ex/0406032
S Kouznetsov et al, Graal, Trento,
Feb 2004
1727 MeV
1750+-18MeV
hep-ex/0504026, P Aslanyan et al
1734+-0.5 MeV
10 GeV beam
12 June 2006 49
Near the lower mass peak of 1680 width < 30 MeV suggested by nucl-th/0312126, R Arndt et al
Could be an N member of the anti-10
S. Kouznetsov, NSTAR2004 and Trento2005
N0(1670) --> eta n candidate
1670 MeV
12 June 2006 50
1980: Sigma(3170) state published and included in PDG
FWHF < 20 MeV (Phys Lett B 89B 1 (1979) 125)
K- p pi- R+
K-p bubble chamber exp.Seen by two experiments
Not ‘searched and not found’
A Sigma pentaquark candidate
12 June 2006 51
+(1530), +(1530), ++(1530), ++(1530), 0c(3099), 0c(3099), - -(1860), - -(1860), -(1850), -(1850), 0(1860), 0(1860),
N0/ N0/ 0 I=1/2(1734)/N0(1727), N0(1680), N0(2400)?, Hyperon(3170)0 I=1/2(1734)/N0(1727), N0(1680), N0(2400)?, Hyperon(3170)
Observed pentaquark candidates:
III Conclusions
Many non observations mainly in high energy collisions, e+e-, hadr. Int.
thetac, Xi(1860) observed only by one experiment each
Study the ‘signal’ where seen with higher statistic, kin. Reflexions studies
comp. to theory and other experiments (UL and signals)
continue Studies of production mechanism of theta+ candidate (e.g. LEPS, Zeus, CLAS)
2006/7: new data from CLAS, LEPS (common acc. LEPS/CLAS), COSY-TOF,
STAR, etc. will allow to answer the question if we have observed (some) narrow pentaquarks.
Maybe part of them, or all of them or non of them correspond to true statesMaybe part of them, or all of them or non of them correspond to true states
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