Part 1: Have Pentaquark States been seen?

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Part 1 Have Pentaquark States been seen?
New Hadrons Facts and Fancy
Volker D Burkert Jefferson Lab
EINN 2005 19 - 20 September, Milos, Greece
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The initial evidence for the Q
CLAS-D
DIANA
4.4?
5.2?
4.8?
4.6?
CLAS-p
Neutrino
SVD
HERMES
7.8?
6.7?
5.6?
5?
ZEUS
KN -gtX
5?
4.6?
3?
3
Non-evidence for Pentaquarks
BABAR
BES
X--
DELPHI
X--
Q0c
4
The Q width
U. Meissner

• Measured width dominated by
• experimental resolution

• Analysis of KA data give limit of
• few MeV.

KD -gt X
U. Meissner
KD , KXe X
Sibirtsev et al. GQ lt 1 MeV

• Very narrow for a hadronically
• decaying particle with mass 100 MeV
• above threshold
• Q(1540) -gt nK, pK0

From selected data sample

• What can we say about event rates?
• Kn -gt Q gt G1MeV,
• K-p -gt L gt G16 MeV.
• s(Q)/s(L) 1.4 for formation.

GQ 0.9 /-0.3 MeV
W. Gibbs, Phys.Rev.C70, 054208 (2004)
5
Are the results on Q consistent?
Low energy effective degrees of freedom,
meson-baryon coupling High energy quark
degrees of freedom, fragmentation

• Can the positive low statistics results be
  reproduced with
• high statistics, e.g. LEPS, CLAS_d, CLAS_p,
  SAPHIR, COSY,
• HERMES,..?

• Is fragmentation at high energy an efficient way
  of generating
• pentaquarks? Why do some experiment (ZEUS,
  HERMES, SVD)
• see a signal while others dont?

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Pentaquark talks at Workshop

• C. Alexandrou - Pentaquarks on the Lattice
• Paul Stoler - Searches for Pentaquarks on proton
  targets at JLab
• R. Mizuk - Limit of the Q width from KN
  scattering at Belle
• S. Niccolai - Searches for Pentaquark baryons on
  deuterium with CLAS
• N. Muramatsu - Studies of Q with LEPS at SPring8
• A. Geiser - Study of Q and other Pentaquark
  searches at HERA
• J. M. Izen - Search for Pentaquark baryons at
  BaBaR
• S. Kabana - Search for exotic baryons at RHIC
• U. Meissner - What do we know about the width of
  Q ?
• Discussion - Where are we and what to do next in
  the Pentaquark search?

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C. Alexandrou
Takahashi et al., Pentaquark04 and
hep-lat/0503019 JKN and JKN on spatial lattice
size 1.4, 1.7, 2.0 and 2.7 with a larger number
of configurations
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Summary of LQCD
C. Alexandrou
Group Method of analysis/criterion Conclusion
Alexandrou and Tsapalis Correlation matrix, Scaling of weights Can not exclude a resonance state. Mass difference seen in positive channel of right order but mass too large
Chiu et al. Correlation matrix Evidence for resonance in the positive parity channel
Csikor et al. Correlation matrix, scaling of energies First paper supported a pentaquark , second paper with different interpolating fields produces a negative result
Holland and Juge Correlation matrix Negative result
Ishii et al. Hybrid boundary conditions Negative result in the negative parity channel
Lasscosk et al. Binding energy Negative result
Mathur et al. Scaling of weights Negative result
Sasaki Double plateau Evidence for a resonance state in the negative parity channel.
Takahashi et al. Correlation matrix, scaling of weights Evidence for a resonance state in the negative parity channel.
J. Negele, Lattice 2005 Correlation matrix, scaling of weights Maybe evidence for a resonance state?
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Upper limit on the Q cross section (95c.l.)
Paul Stoler
s g p ? Q K0 lt 1.25 nb _at_ 1.54 GeV/c2
CLAS gp -gt K-K0n
Fit with a sum of smooth function and a Gaussian
with fix width and centroid.
g
K0
Results put stringent limits on possible
production mechanism, e.g. implies very small
coupling to K
K
n
p
Q
K
10
P Stoler
Comparison with SAPHIR results
SAPHIR
Observed Yields SAPHIR N(Q)/N(L)
10 CLAS N(Q)/N(L) lt 0.2
(95CL) Cross Sections SAPHIR sg p ? Q K0
300 nb reanalysis 50 nb (unpublished) CLAS
sg p ? Q K0 lt 2 nb
Counts
Counts
cosqCM(K0) gt 0.5
cosqCM(K0) gt 0.5
M(nK) (GeV)
M(nK0) (GeV)
g11_at_CLAS
Counts
Counts
L(1520)
cosqCM(K0) gt 0.5
preliminary
cosqCM(K0) gt 0.5
Q(1540) ?
M(nK) (GeV)
M(nK0) (GeV)
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Silvia Niccolai
Upper limit on Q production with CLAS.
G10
G2
Background from G10

• In previous result the background is
  underestimated. New estimate of
• the original data gives a significance of 3s,
  possibly due to fluctuations.

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Upper limit on GQ from CLAS Results
Theoretical cross section are for GQ1 MeV
Publication  Reaction   Jp     Experimental width
    1/2- 1/2 3/2- 3/2  GQ
M. Guidal et al.,  0.01nb 0.22nb      lt5.7 MeV
hep-ph/0507180 0.2nb 1nb 55nb  10nb  lt 4 MeV
S. Nam et al.,   (2.7)nb  8nb (1)nb  lt(0.5) MeV
hep-ph/0505134   2.7nb  200nb 25nb  lt 1.7 MeV
Y. Oh et al., NP A745 0.4nb  1.6(100)nb      lt 0.8 MeV 
hep-ph/0412363  1.7nb 8.7(75)nb     lt 0.5 MeV 
C.M. Ko and W. Liu   15(30)nb     lt 0.08 MeV 
nucl-th/0410068   15(30)nb      lt 0.25 MeV 
W. Roberts  2nb 5.2(10)nb 15.4nb 1.8nb lt 0.24 MeV 
nuc-th/0408034 3.5nb  11.2(20)nb  48nb  4.nb lt 0.4 MeV 
( ) with K exchange
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Old and New Signal from LEPS/SPring8
N. Muramatsu
gD -gt K-X

• Mix K, K-, ? from different events in LH2 data.
• ?(1520) contribution was removed from the sample.

?
?(1520)
preliminary
preliminary
MMC(?,K) GeV/c2
MMC(?,K-) GeV/c2
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K-p missing mass spectrum
N. Muramatsu
? fitted in MMlt1.52 GeV/c2
5s excess at 1.53 GeV/c2 corresponding ? 1.6
GeV bump was also seen.
?
preliminary
1.6 GeV bump
Counts/5 MeV
preliminary
Counts/5 MeV
?
from sidebands
MMd(?,K-p) GeV/c2
MMd(?,K-p) GeV/c2
Signal emerges with selection of L(1520) in
M(K-p)
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Pentaquark Studies at HERA
A. Geiser
ep -gt eK0spX
High energy production mechanism?
ZEUS
gt Signal seen at medium Q2 and forward rapidity
in both pKs and pKs
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ZEUS Cross section on Q
A. Geiser
M(GeV)
Q/L 5 (independent of Q2)
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Pentaquark in fragmentation?
Quark fragmentation
u
u
d
q
Q
e
Pentaquark strongly suppressed ?
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BELLE Low energy KN scattering
R. Mizuk
ee- -gt K/- X, K/-A -gt pK0, pK-
Detector Tomography
momentum spectra of K and K-
1 / 50MeV
momentum, GeV/c
Momentum range possibly contributing to Q
formation.
gt Determine resonance width
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Belle Limit on Q Width
R. Mizuk
GQ from KA -gt pK0sX KD -gt inclusive analysis
KA -gt pK0s
Belle limit 90CL
397 fb-1
DIANA
No
no signal
Belle G lt 0.64 MeV (90 CL) _at_ M 1.539 GeV
G lt 1 MeV (90 CL) _at_ M 1.5251.545 GeV
Cahn,Trilling,PRD69,11501 (2004).
Not inconsistent with previous results.
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Upper limit on cross section ratio
epK epKs
NT N?
B(?(1520)? pK-) B(T(1540) ? pK0) B(K0? KS? pp-)
s(KN? T(1540) X) s(KN? ?(1520) X)

lt2.5 at the 90 C.L.
epKs/epK from MC assuming that T and ?(1520)
kinematics is similar.
Comparison with other experiments
Experiment Reaction Energy s(T)/s(?)
CDF pp?TX 1960 GeV lt3
HERA-B pA?TX 42 GeV lt2
SPHINX pA?TX 12 GeV lt2
Belle KA?TX ?2 GeV lt2.5
LEPS ?A?TX ?2 GeV ?60
HERMES eD?TX 7 GeV ?200
Consistent with lt1 MeV width.
?
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Hadron production in ee- collisions
J.M. Izen
Baryons 10-4 /GeV/c2 (generate two pairs)
Pentaquarks 10-8 /GeV/c2 (?) (generate four
pairs)
G 1Mev
G 1MeV BR(X-- ?X-p-)0.5
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Tomography with pKs0 Vertices
BaBar Preliminary233 fb1 ee data
Y cm
Y cm
Vetobeamspot R ? 2 cm
e
e
SVT
X cm
X cm
SVT support tube
DCH inner wall
Beampipe
z profile
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e-Be Electroproduction
Preliminary233 fb1 ee data
(quasi-real photoproduction)
HERMES (ed?KS0p X)
HERMES
HERMES/BaBaR comparison disturbing. ZEUS High
Q2, no signal for Q2lt1 BaBaR Quasi-real photons
HERMES acceptance loss in low mass region? (PID
requires p(p) gt4.1 GeV/c p(KS0)gt3 GeV/c)
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STAR d-Au results
S. Kabana
Possible mechanism for production of multi-q/g
states Coalescence of out of QGP?
STAR Preliminary
?
M (GeV/c2)
A Q candidate ?
Also a Q candidate ??
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SVD-2 New Analysis
Private info from SVD group
Two independent data set KS decays inside or
outside the Vertex Detector
Ep 70 GeV
M 1522 MeV s 12 MeV Nevnt
205

• New analysis improves Q signal by factor 8. The
  results maybe in
• conflict with new WA89 results (to be published
  shortly).

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Cascade Pentaquark X5--(1862) ?
HERA-B
CDF

• State not produced in quark
• fragmentation or is severely suppressed.

gA
FOCUS
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Charmed Pentaquark Q0c(3100) ?

• Signal also in photo-
• production
• Claim kinematical
• uniqueness.
• Possible production
• mechanism - PGF.

• FOCUS experiment claims
• incompatibility with H1.

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Pentaquark Status _at_ EINN 2005

• Group Signal Backgr. Significance
• publ. Comments
• --------------------------------------------------
  --------------------
• SPring8 19 17 4.6s 3.2s
• SPring8 90 260 4.8s
• SAPHIR 55 56 4.8s 5.2s
• DIANA 29 44 4.4s 3.4s
• CLAS(d) 43 54 5.2s 4.4s
• CLAS(p) 41 35 7.8s 4.7s
• ? 18 9
  6.7? 3.5s
• HERMES 51 150 4.3-6.2? 3.6s
• ZEUS 230 1080 4.6?
  6.4s
• COSY 57 95
  4-6? 4.7s
• SVD 41 87
  5.6? 3.6s
• SVD-2 370 2000 7.5s Improved analysis
• NA49 38 43
  4.2? 4.2s
• H1 50.6 51.7
  5-6? 5.0s

? BELLE
Q
? BABAR
X5
Q0c
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Concluding comments
Q(1540)

• Two high statistics experiments on protons and
  deuterium (CLAS)
• contradict results that observed 5s signals
  with same kinematics.
• Within hadronic models the new CLAS results put
  limits on the widths.
• For most models GQ lt 0.5 MeV. New limit from
  Belle not (yet?) in
• contradiction with 1 MeV limit. Increase in
  statistics could change that.
• Need to examine if gD and gA experiments with
  lower statistics
• are consistent with CLAS cross section limit
  on neutrons .
• Sensitivity to Q at high energy appears in
  baryon fragmentation
• not in quark fragmentation. This could explain
  some of the null results
• at high energies.
• Babar is challenging the HERMES results on Q.
• New data/analysis from LEPS, SVD-2, and STAR,
  support Q observations.

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Outlook

• The Q pentaquark is not in good health, but it
  is
• still alive.
• - new analyses underway from COSY, SVD-2,
  SPring8
• - measurements planned at SPring8, JLab
• - H1, ZEUS, HERMES high luminosity run until
  2007
• - higher statistics data from STAR, PHENIX
• - more statistics and analyses from B-factories
  
• Should the Q pentaquark not survive the next few
  years of
• intense scrutiny we will have to examine why
  so many
• experiments observed the signal in the first
  place.