Pentaquark04 Workshop Summary

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Pentaquark04 Workshop Summary

• Ken Hicks
• Ohio University / RCNP
• 23 July 2004

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Emotional Issues

• The existence of the pentaquark is, at the
  present time, an experimental issue.
• But theory can give us guidance.
• In the past, Ive often suggested that we need to
  be cautious and patient as we wait for new data.
• In the end, the truth will emerge.
• But should we be optimistic or pessimistic?

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Reasons to be Optimistic

• Over a dozen independent measurements show
  positive evidence.
• Even if a few of these are statistical
  fluctuations, there is still a lot of positive
  evidence.
• The new deuterium result from SPring-8 is very
  encouraging.
• Some highlights will be reviewed in this talk.
• Several new results are on the horizon.

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Reasons to be Pessimistic

• The ee- collider data give null results.
• Belle, BaBar, ALEPH, DELPHI, etc.
• High-energy protons give null results.
• HERA-B, E690, CDF, D0, HyperCP, etc.
• The backgrounds are largely unknown in the
  low-energy data (kin. reflections, etc.)
• Lack of a generally accepted theoretical model
  for a resonance with G 1 MeV.

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E690 pKs and pK- (Preliminary)
1540 MeV
Monte Carlo pKs mass resolution (s) at 1540 MeV
is 1.5 MeV.
Yield of narrow (pKs) at 1540 MeV is less than 25
events (95 CL).
5000 L(1520) above background FWHM 14 MeV
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(No Transcript)
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Slope for mesons
Slope for baryons
Slope for pentaquarks??
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Titov inclusive production (fragmentation
region)
fast
slow
Ratio pentaquark to baryon production


Regge exchange dominates
(2 diquarks as quasipartons)
K
U.Kashon ZEUS
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Possible Interpretation

• Fragmentation likely dominates the production of
  hadrons in high-energy proton-proton and ee-
  collisions.
• The sensitivity of detection versus mass of the
  hadron drops rapidly in fragmentation.
• The pentaquark may be further suppressed in these
  reactions based on parton counting estimates.

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A critical look at experiments

• If one requires reactions where the strangeness
  in the final state is known, and there is
  reasonable understanding of the shape of the
  background, we have
• DIANA (K Xe)
• CLAS-proton data
• COSY-TOF (?)
• LEPS-deuterium
• Only 3-4 positive experiments remain!

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A critical look at high-energy

• The ee- data what should we expect?
• How do get 5q5q from the initial state?
• Need to calculate (or estimate) this rate.
• The high-energy proton data background?
• Can one calculate the signal/noise ratio?
• Is this a string-fragmentation process?
• None of these results are published! (How
  preliminary are these data??)

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A critical look at theory

• Chiral soliton are there limitations?
• Where are J3/2 states? What about the higher
  rotational states of the soliton?
• Quark models CS, FS or KMT?
• CS problems with L1. FS fails for mesons.
  KMT predicts a low-lying penta-singlet.
• Lattice gauge quenched approximation?
• are there dynamical pion cloud effects?

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Experimental Highlights

• As usual, I make the standard apology that it is
  impossible to show the results from everyones
  talk, and that the results I show obviously
  reflect my own bias.
• I will focus on the newest data
• LEPS-deuterium (with background estimate)
• A possible narrow N at GRAAL
• HERMES improved signal-to-background
• Whats happening at CLAS?

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LEPS f background
Ratio of Real data to MC(f)
Realistic MC f event generator.
Events
Real data
Ratio
MC(f)
Invariant mass (KK-) (GeV)
Invariant mass (KK-) (GeV)
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Energy dependent f exclusion cut
R0.20
R0.05
Invariant mass (KK-) (GeV)
R0.01
Cut on the ratio of the data to MC
Eg (GeV)
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LEPS missing mass of gd?KK-X
deuteron mass
LH2
LD2
MMgKK- (GeV)
MMgKK- (GeV)
Remove gd?KKd coherent production by requiring
MMd(g,KK)gt1.89 GeV
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LEPS Fermi motion correctionsfor L(1520)
resonance
MMgK (GeV)
MMgK (GeV)

• No large difference among the three Fermi motion
  correction methods
• Same conclusion for Q.

MMgK (GeV)
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LEPS Q spectrum, no L(1520)

• The excess above the BG level is 90 events.
• The peak position, width, significance strongly
  depends on the BG shape.

MMgK- (GeV)
Background estimate from LH2 target mixed-event
analysis.
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GRAAL gd ? hN(N)

• Detector can measure exclusive final state
• tells whether the h produced from p or n
• Prediction from Polyakov and Rathke (03)
• N8 ? N10 suppressed on p, allowed on n
• same result follows from u-spin (see Lipkin)
• N10 should be narrow, big ss decay branch
• Phase shifts (nucl-th/0312126) suggest possible
  narrow N at 1680 or 1730 MeV.

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The Revised Anti-decuplet
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GRAAL possible narrow N
neutron
proton
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HERMES Q vs S

• Is peak a new S or a pentaquark state?
• If peak is S ? also see a peak in M(Lp)
• if member of baryon octect b.r.(Lp)/(pKs) ?
  3/2
• if member of decuplet
  3/2 (M. Polyakov)

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HERMES Q mass with additional p

• standard cuts applied
• K and L veto
• signal/background 21

• signal/background 13

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Proposal SP-8 convention

• In the future, experiments should not quote the
  naïve statistical significance.
• This underestimates the statistics probability
• It is confusing when different experiments use
  the words statistical significance that are
  calculated in different ways.
• We should agree on a common convension of N/dN
  where dN comes from the fit errors.

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Whats up at CLAS?

• CLAS has received criticism that they did not
  study the background shape enough.
• Someone once said Extraordinary claims require
  extraordinary proof.
• The CLAS collaboration has decided that results
  will be presented only when final.
• Normally, preliminary results would be shown, but
  these are not normal circumstances.
• Final results of the high-statistics run are
  expected near the end of 2004.

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Theoretical Highlights

• Titov estimate for high-energy Q prod.
• Praszalowicz possible Q nearby?
• Lipkin narrow width due to Q, Q mixing?
• Diakonov overlap of Q and N?
• Suganuma narrow width in string model?

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Praszalowicz. Exotics in ChQSM
M.Diakonov, V.Petrov, M.Polyakov, Z.Phys. A359
(1997) 305
ChQSM
M.Karliner, H.J. Lipkin hep-ph/0402008 ? excluded
NA49
27 -plet
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Praszalowicz Full Mixing
Vibrational states (not rotation)
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Dmitrasinovic Quark model states
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Lipkin mixing of 2 Q states
Consider mixing of two states which are close in
mass
K
N
For degenerate states, loop dominates ? mass
eigenstates
Then one state decouples from decay to KN final
state
and the other state is broad (100 MeV decay
width)
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Diakonov small Q width?
In the infinite momentum frame
Crude estimate give G 0.7 MeV
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Suganuma string model(zero momentum frame!)
The ordinary string model describes mesons and
glueballs as open strings and closed strings,
respectively.
glueballs
mesons
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Suganuma baryons
baryons
antibaryons
Example of decay of a qq pair to NN has a large
branching ratio
meson
excited meson
baryon-antibaryon
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Suganuma pentaquarks
Note that string breaking just creates a
baryon-(2q2q) system
previous connection
pentaquark
The string must be excited and then recombination
to reach the baryon-meson final state.
gluon-excited
This process requires a barrier through which it
must pass ? narrow width.
baryon-meson decay
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Experimental Outlook

• New results expected in the near future
• CLAS high-statistics proton data (just done)
• HERMES gt double statistics (now running)
• COSY-TOF statistics x 5 (end of 2004)
• KEK E559 pp ? K-(Q) run in May 2005.
• Possibly BNL using rare-kaon decay detector

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From BEACH04 Summary

• Treat each state as a separate entity. Dont use
  the non-existence or confusion about higher mass
  states to cast doubt on Q and vice versa Joel
  Butler (Fermilab)

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Summary

• I choose to be optimistic rather than pessimistic
  regarding the Q existence.
• Hopefully, we will not need to wait too long for
  new experimental results.
• The high-energy null results do not invalidate
  the exclusive reactions at lower energies.
• The Q, if it exists, is a new class of hadron,
  so our intuition of the production mechanism for
  baryons may not extend here.

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We will publish proceedings. The volume will
become an important issue not only to RCNP and
Spring-8, but also to all participants! Length
40 min talk 10 pages 30 min
25 min talk 8 pages
20 min takk 4 pages We will send more details
to speakers as soon as possible. Thanks a
lot!
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On behalf of the organizers,
Hiroshi Toki (Chair, RCNP, Osaka)Schin Date'
(Scientific Secretary, Spring-8)Atsushi Hosaka
(Scientific Secretary, RCNP, Osaka)Kenneth Hicks
(Ohio)Tomoaki Hotta (RCNP, Osaka)Ken-ichi Imai
(Kyoto)Noritaka Kumagai (SPring-8)Takashi
Nakano (RCNP, Osaka)Yuji Ohashi
(Spring-8)Makoto Oka (Tokyo Inst. Tech.)
We want to thank Professor Atsushi Hosaka and
Conference Secretary Natsuko Arimoto for a nicely
organized workshop.
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And finally,

• We look forward to Pentaquark 2005 to be held in
  Genova, Italy.
• Hosts will be the INFN group
• By then, CLAS results will be ready!
• Date perhaps June or July, 2005.