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Main Pentaquark 04: Proceedings of International Workshop, Spring-8, Japan, 20-23 July 2004 (Proceedings..
The papers collected in this book represent an exciting contribution to the growing body of experimental and theoretical research into exotic hadrons. The prime focus of the volume is the latest work on pentaquark baryons. The in-depth experimental reports cover both positive and negative evidence for the existence of various combinations of particles, and photo-electro production, hadronic production and high-energy processes are discussed in detail. Important theoretical areas of current interest are considered, including chiral solitons, constituent quarks, the QCD sum rule, lattice QCD, production reactions, and the determination of spin and parity. The volume features the work of two pioneering theorists, H Lipkin and D Diakonov, among the comprehensive coverage of the latest theoretical ideas in the field.
Copyright 0 2005 by World Scientific Publishing Co. Re. Ltd.
exclusively on the pentaquark baryons and related exotic hadrons.
an experimental issue. However, the understanding is a theoretical issue.
far from the final goal.
was made possible in this workshop at the Spring-8 site.
conclusion but also to make another step toward new developments.
particle consisting of 5 quarks was f i s t confirmed.
year for Spring-8. Hearing this news, I was very pleased. I did not understand the details but I felt that something very new took place: extraordinary science that provides a big breakthrough has been done.
discovery of the pentaquark particle fulfills this expectation.
contributed to the present big discovery.
PANIC02 held in Osaka in 2002. The paper was published in Phys. Rev.
was made to all the world.
I sincerely hope that the symposium is fruitful to all the participants.
approach gives mass bounds for other pentaquarks.
1. Introduction What can QED teach us about QCD?
but by quasiparticles related to electrons by a complicated transformation.
quasiparticles related to current quarks by a complicated transformation?
need another Laughlin to tell us what constituent quarks are?
- ME = -0.61 n.m.
2.2. Two Hadron Spectrum puzzles -Why qqq and qa ?
and baryons differently. A vector interaction gives equal and opposite forces; a scalar or tensor gives equal attractions for both.
have been observed; e.g. no T+T+ or K + N bound states.
interaction with the color-factor of one-gluon exchange.
M 2 MeV binding normal hadrons.
We don’t know what these quarks are and the low-lying hadron spectrum provides no direct experimental information on (ijq)a and (qq)f3 interactions needed for multiquark exotic configurations.
the right theory without going through that stage’.
observable as hadron resonances? What does quark model say?
look for possible bound states.
on the two-body density matrix are relaxed .
open that this stable bound pentaquark exists and needs a better search.
hyperfme interaction. This led to the diquark-triquark mode14v5..
short-range color-magnetic interaction produces binding.
search for H dibaryon uuddss.
interaction is always repulsive between flavor-symmetric pairs.
Costs 300 MeV relative to nucleon with only one.
Only two same-flavor pairs feel short range repulsion.
(2) Pentaquark search. (uudst?) pentaquark has same binding as H.
Ashery’s E791 search for &uds found events”; not convincing enough.
vertex detectors and particle ID8.
Any proton emitted from secondary vertex is interesting. One goldplated event not a known baryon is enough; No statistical analysis needed.
4. The 8+ was found! What can it be?
has no simple connection with quarks except by another “wrong model”.
The l/Nc expansion invented13 pre-QCD to explain absence of free quarks.
N. M 1 This is NOT A SMALL PARAMETER!
triquark color-spin coupling minimizing color-magnetic energy 4*5.
color-magnetic energy leads naturally to a two-state model14.
Let 101) and 1 0 2 ) denote an orthonormal basis for the two diquarktriquark states with different triquark color-spin couplings.
into K N is forbidden.
are produced without suppression by K* exchange.
(2) Assume 0+and E-- are degenerate in S U ( 3 ) f limit.
color couplings unchanged in H.
where we have substituted eq. (12) for the SV(3)f breaking piece of H.
Is an experiment or one of our assumptions wrong?
(i) O+ and Z-- not pentaquarks uud& and ssddii?
(ii) O+ and E-- not degenerate in the SV(3)f limit?
(iii) Is our SU(3)-breaking model wrong?
We have the same light quark system and a different flavored antiquark.
There is the same color electric field and a mass change.
15 140 MeV the 0,is stable against strong decays.
Vh,,(B) with one quark in a kaon?
Some experiments see the pentaquark 17&hers definitely do not". No theoretical model addresses why certain experiments see it and others do not.
Comprehensive reviewlg analyzes different models.
1. Ya.B. Zeldovich and A.D. Sakharov, Yad. Fiz 4(1966)395; Sov. J. Nucl. Phys.
4. M. Karliner and H. J. Lipkin, hep-ph/0307243.
5. M. Karliner and H.J. Lipkin, Phys. Lett. B575, 249 (2003).
6. Y. Nambu, in Preludes in Theoretical Physics, edited by A. de Shalit, H.
10. E.M. Aitala et al.,FERMILAB-Pub-97/118-E, Phys. Lett. B448,303 (1996).
13. Harry J. Lipkin, in: ”Physique Nucleaire, Les Houches 1968,” edited by C.
14. M. Karliner and H. J. Lipkin, Phys.Lett. B586, 303 (2004) hep-ph/0401072.
15. M. Karliner and H. J. Lipkin, hep-ph/0402008.
16. M. Karliner and H.J. Lipkin, hep-ph/0307343.
19. Byron K. Jennings and Kim Maltman, hep-ph/0308286.
20. L. G. Landsberg, Phys.Rept.320 223 (1999); hep-exf9910048.
language of the Dirac theory. It becomes clear why the naive quark models overestimate pentaquark masses by some 500 MeV and why in the Mean Field Approximation to baryons pentaquarks are light.
built of an indefinite number of quark-antiquark (QQ) pairs l .
implies that all lattice simulations for the “real” QCD are at present running with inherent strings between quarks, which do not exist in nature!
or that the artifact strings are not too relevant for most of the observables.
zero quark modes in the vacuum is probably here to stay.
Figure 1. Dynamical quark mass M ( p ) from a lattice simulation6 . Solid curve: obtained from instantons two decades before lattice measurements4 .
set to zero) the pseudoscalar mesons are exactly massless as they correspond to going along the “Mexican hat” valley, which costs zero energy.
massless, there is no gap between the positive and negativeenergy Dirac continua.
is given in the second paper under Ref. l. A more fresh example is provided in Ref.
the constituent quark idea has been a useful guideline for 40 years.
tensor) meson masses in the interacting case as well.
their mass is roughly 2 M .
energy and a quark with negative energy, hence their mass is roughly zero.
but there is a more neat way to understand it.
be already mixed with the gluonium.
Without spontaneous chiral symmetry breaking, the nucleon would be either nearly massless or degenerate with its chiral partner, N(1535, f-).
an opportunity to talk about it recently and shall not repeat it here.
and which one is weaker and can be disregarded in the first approximation.
few percent from the true wave function at N, = 3.
relativistic invariance and all symmetries following from QCD.
field, as compared to the free one.
functions of the octet and decuplet baryons, and there are few antiquarks 12.
the reality, although shares with reality some qualitative features.
prediction largely motivated the first experiments. Both circumstances lightness and narrowness - are puzzles for naive quark models.
the pure glue world, which I find very natural - see the beginning.
started to be done, and the results are, to my mind, remarkable.
model parameters fixed from the 3Q baryons, and obtained the Q+ mass.
It turns out to be 510MeV heavier than 1540 MeV.
diquarks and still heavier if diquarks are not exactly massless b.
8 has positive parity. It gives more than 2 GeV. This is the starting point.
may reduce the starting mass, but has to pay back the kinetic energy.
vacuum, i. e. the pseudoscalar meson(s).
4M = 1400MeV mass but it is 400 MeV lighter, actually close to 2 m ~ .
two quasi-Goldstone bosons where all four M’s are eaten up.
field as well, third, because its coupling to the K N state is very weak.
supported in part by the US Department of Energy under contract DEAC05-84ER40150.
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CTheidea of the KnN and n(800)N bound states has been put forward in Ref.
pilot study shows that there is a mild attraction.
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and by Oset to these Proceedings.
prospects of the experimental study on the O+ at LEPS are reported.
A hadron with a combination of qqqqq is a pentaquark, and it is called exotic if the flavor of the antiquark is different from those of the other quarks.
Backward-Compton scattering of laser photons with the 8-GeV electrons.
momentum analyzed by a forward angle spectometer and kaons were identified by a time-of-flight measurement '.
which may be attributed to the exotic 5-quark baryon proposed as the Q+.
narrow resonances in the past.
high energy must be heavily suppressed with respect to normal baryons.
non-existence of the @+ experimentally.
event selection for both the Q+ and the A(1520) was a q5 exclusion cut.
K - missing mass distribution.
spectrum only by using a small number ( m 1000 events) of the sample.
kinematical reflections, or their combinations.
1. D. Diakonov, V. Petrov, and M. Polyakov, Z. Phys. A359,305 (1997).
2. T. Nakano et al. (LEPS Collaboration), Phys. Rev. Lett. 91, 012002 (2003).
3. K.T. Knopfle, M. Zavertyaev, and T. Zivko (HERA-B Collaboration), J. Phys.
4. J.Z. Bai et al. (BES Collaboration), Phys. Rev. D 70, 012004 (2004).
5. C. Pinkenburg (for the PHENIX Collaboration), J. Phys. G30, S1201 (2004).
6. M. Longo et al. (Hyper-CP Collaboration), arXiv:hep-ex/0410027.
7. E. Gottschalk (FNAL-E690 Collaboration), in the presentation of this workshop.
8. M.J. Wang (CDF Collaboration), in these proceedings.
measured up to now are inconsistent with expectations for charmonium states.
into charmed particles (see Fig.l(b) and (c)).
meson decay producing charmed mesons (b), and charmonium (c).
0.589 GeV/c2 peak corresponding to well known @'(3686) is clearly visible.
beam energy, all in the e+e- c.m. system.
distribution tends to cluster near p, although not conclusive.
orbital angular momentum (large contrifugal barrier).
2 , 23P1 (xL1,1++), and 3lS0 ($, 0-+) for C = +l.
r + r - J / $ > , and I'($"'(3770) + n+n-J/$~)are all equal. We conservatively set I?(+"
to be a few times larger than r(&t r+r- J/$J).
disfavoring the $3 asignment for X(3872).
less than 0.4(90%CL). disfavoring the xLl asignment for X(3872).
Figure 5. Helicity distribution for X(3872) ---t nnJ/$ decay. Solid line shows expectation for hh hypothesis. Dotted line is background estimation.
-+ yxcl,X(3872) + yxcl candidates, respectively.
these two states being the missing O+ and 1+ members of L = 1 multiplet.
transition thresholds and the D,~(2317)+ Ds7ro,0 , ~ ( 2 4 5 7 )+ D,*.rrotransitions are isospin-violating which are known to be highly suppressed.
state with 2632 MeV mass and decays into DZv and D°K+ modes 13.
Br(2573 + DoK+) < 1.1%(9O%CL) where the corresponding SELEX ratio is 0.56 f 0.27. Search for D,Qmode is under study.
Figure 7. Predicted masses for L = 1 states in the potential model, and the masssplitting calculation between (0-, 1-) and ( O + , I+) multiplets.
third errors come from PDG errors.
4 for B- -+ A$A--(1600), 5 for B- + A:A--(2420).
is shown in Fig. 7(b).
rBw = 0.15 f 0.05 GeV.
(b) The Afp invariant mass distribution.
We face a difficulty for asigning X(3872) to vacant charmonium states.
improved measurements of radiative decays for X(3872) are also important.
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2. CDF Collaboration, G. Bauer, et al. hep-ex/0312021.
3. DO Collaboration, V.M. Abazov, et al. hepex/0405004.
4. BaBar Collaboration, B. Aubert, et al. hep-ex/0406022.
5. Belle Collaboration, R. Chistov, et al. hep-ex/0307061.
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an indication of enhancements at the same mass.
addition to the exotic states Ec (uussd) and E,5-(ddss.ii).
depending on the track length and topology.
sensitive to most of the inelastic cross section of 31.8 mb.
reduced the data sample to 3.75 M events.
detected via the G+T+ and Z+T- decay channels, respectively.
Figure 1. E-T- and E-n+ invariant mass spectra The cuts are explained in the text.
invariant mass spectrum the only clearly visible resonance is the E(153O)O.
absolute mass scale below 0.001 GeV/c2.
directon at the main vertex.
Figure 2. The combined 2-n- + 8+nf and =-a+ B+n- spectra after the final cut.
The insert shows background subtracted spectra with the result of Gauss fit.
are now seen in all cases.
position of 1.862 f0.002 GeV/c2 and 1.864 f0.005 GeV/c2, respectively.
Table 1. Rejected invariant mass ranges for combinations of the negative primary tracks with positive tracks.
additional cuts. The peak in E-s- spectra remains clearly visible.
Figure 5d finally shows the results, with the primary T - dE/dx within 1 (T.
fluctuations were observed in the resulting invariant mass distributions6.
rejected (b) in addition, primary pions that can contribute (under different mass hypotheses) to the known remnances were excluded.
at several high statistics experiements (for the references see8).
have a production mechanism which is poorly understood.
reactionlo. In the E-r+ channel a number of resonances are visible, including a prominent state at 1860 MeV and a less significant one at 1760 MeV.
8-* in the K+K+ missing mass spectra from the 7 p d K + K f S - * reaction.
with the above mentioned two experiments.
NA49 to try t o resolve this issue.
Figure 5. 8-a- NA49 invariant mass distribution for progresively better 8-a- selection. See text for details.
spectra show indication of enhancements at the same mass.
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system. Nothing similar is present in the eta-proton spectrum.
photoproduction of mesons in Hydrogen and Deuterium.
production of another particle like a no.
reproduces very well the result obtained with simulated events.
clearly correspond to the masses of the no and q.
polar angle of the nucleon and that calculated from the q kinematics.
values of the gamma-ray energy and the q center of mass angle. Upper curves for reaction 1 (quasifree proton) and lower curves for reaction 2 (quasi-free neutron).
the momentum of the q .
direction. Two curves for selected intervals of gamma ray energy and q centerof-mass angle €), are reproduced in Figure 3.
calculated values of the gamma-ray beam polarization.
for a free proton in Hydrogen and a quasi-free proton in Deuterium.
photoproduction on free (grey points) and quasi-free protons (black points).
between quasi-fiee proton and quasi-free neutron is indicated in Figure 6 .
photoproduction on quasi-free protons (grey points) and quasi-free neutrons (black points).
same is not true for no photoproduction where T=3/2 channels are present.
reaction. More data are necessary to clarify this problem.
photoproduction cross sections measured for the free proton.
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pentaquark state have driven a rebirth of the experimental activity in this field.
and perspective for experiments using proton targets are discussed.

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