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

12 June 2006 2

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

12 June 2006 3

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

12 June 2006 4

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

12 June 2006 9

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

12 June 2006 21

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

12 June 2006 28

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

12 June 2006 32

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

12 June 2006 39

Xi--, Xi-, Xi^0

Xi-- ssdd ubar

Xi0 duss dbar

Xi- ddss dbar

12 June 2006 40

• 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

12 June 2006 44

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

12 June 2006 46

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