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Pentaquarks: predictions, evidences & implications

Maxim V. Polyakov Liege Universitiy & Petersburg NPI. Outline: - Predictions - Post-dictions - Implications. Pentaquarks: predictions, evidences & implications. PARIS, March 2. Baryon Families. m s =150 MeV. W −. ?. Gell-Mann, Neeman SU(3) symmetry. q. q. q.

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Pentaquarks: predictions, evidences & implications

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  1. Maxim V. Polyakov Liege Universitiy & Petersburg NPI Outline: - Predictions - Post-dictions - Implications Pentaquarks: predictions, evidences & implications PARIS, March 2

  2. Baryon Families ms=150 MeV W− ? Gell-Mann, Neeman SU(3) symmetry

  3. q q q Quarks are confined inside colourless hadrons Mystery remains: Of the many possibilities for combining quarks with colour into colourless hadrons, only two configurations were found, till now… Particle Data Group 1986 reviewing evidence for exotic baryons states “…The general prejudice against baryons not made of three quarks and the lack of any experimental activity in this areamake it likely that it will be another 15 years before the issue is decided. PDG dropped the discussion on pentaquark searches after 1988.

  4. Baryon states All baryonic states listed in PDG can be made of 3 quarks only * classified as octets, decuplets and singlets of flavour SU(3) * Strangeness range from S=0 to S=-3 • A baryonic state with S=+1 is explicitely EXOTIC • Cannot be made of 3 quarks • Minimal quark content should be , hence pentaquark • Must belong to higher SU(3) multiplets, e.g anti-decuplet observation of a S=+1 baryon implies a new large multiplet of baryons (pentaquark is always ocompanied by its large family!) important Searches for such states started in 1966, with negative results till autumn 2002[16 years after 1986 report of PDG !] …it will be another 15 years before the issue is decided.

  5. Theoretical predictions for pentaquarks 1. Bag models [R.L. Jaffe ‘76, J. De Swart ‘80] Jp =1/2- lightest pentaquark Masses higher than 1700 MeV, width ~ hundreds MeV Mass of the pentaquark is roughly 5 M +(strangeness) ~ 1800 MeV An additional q –anti-q pair is added as constituent 2. Soliton models [Diakonov, Petrov ‘84, Chemtob‘85, Praszalowicz ‘87, Walliser ‘92] Exotic anti-decuplet of baryons with lightest S=+1 Jp =1/2+ pentaquark with mass in the range 1500-1800 MeV. Mass of the pentaquark is rougly 3 M +(1/baryon size)+(strangeness) ~ 1500MeV An additional q –anti-q pair is added in the form of excitation of nearly massless chiral field

  6. The question what is the width of the exotic pentaquark In soliton picture has not been address untill 1997 It came out that it should be „anomalously“ narrow! Light and narrow pentaquark is expected -> drive for experiments [D. Diakonov, V. Petrov, M. P. ’97]

  7. 2003 – Dawn of the Pentaquark Q+first particle which is made of more than 3 quarks ! Particle physics laboratories took the lead Spring-8: LEPS (Carbon) JLab: CLAS (deuterium & proton) ITEP: DIANA (Xenon bubble chamber) ELSA: SAPHIR (Proton) CERN/ITEP: Neutrino scattering CERN SPS: NA49 (pp scattering) DESY: HERMES (deuterium) ZEUS (proton) COSY: TOF (pp-> Q+ S+) SVD (IHEP) (p A collisions) HERA-B (pA) Negative Result

  8. What do we know about Theta ? • Mass 1530 – 1540 MeV • Width < 10-20 Mev, can be even about 1 Mev as it follows from reanalysis of K n scattering data [Nussinov; Arndt et al. ; Cahn, Thrilling] • Isospin probably is zero [CLAS, Saphir, HERMES ] Compatible with anti-decuplet interpretation • Spin and parity are not measured yet

  9. Chiral Symmetry of QCD hadron multiplets No Multiplets Symmetry is sponteneousl broken Symmetry of Lagrangean is not the same as the symmetry of eigenstates QCD in the chiral limit, i.e. Quark masses ~ 0 Global QCD-Symmetry  Lagrangean invariant under:

  10. Three main features of the SCSB • Order parameter: chiral condensate [vacuum is not „empty“ !] • Quarks get dynamical masses: from the „current“ masses of about m=5MeV to about M=350 MeV • The octet of pseudoscalar meson is anomalously light (pseudo) Goldstone bosons.

  11. Spontaneous Chiral symmetry breaking current-quarks (~5 MeV)  Constituent-quarks (~350 MeV) Particles  Quasiparticles

  12. Quark- Model • Three massive quarks • 2-particle-interactions: • confinement potential • gluon-exchange • meson-exchage • (non) relativistisc • chiral symmetry is not respected • Succesfull spectroscopy (?) Nucleon

  13. Chiral Soliton Mean Goldstone-fields (Pion, Kaon) Large Nc-Expansion of QCD Nucleon

  14. Chiral Soliton • Three massive quarks • interacting with each other • interacting with Dirac sea • relativistic field theory • spontaneously broken chiral symmetry is full accounted Nucleon

  15. Quantum numbers Quantum # Coupling of spins, isospins etc. of 3 quarks mean field  non-linear system  soliton  rotation of soliton Quantum # Natural way for light baryon exotics. Also usual „3-quark“ baryons should contain a lot of antiquarks Coherent :1p-1h,2p-2h,.... Quantum # Quark-anti-quark pairs „stored“ in chiral mean-field

  16. Antiquark distributions: unpolarized flavour asymmetry Pobylitsa et al d-bar minus u-bar Soliton picture predicts large polarized flavour asymmetry

  17. Fock-State: Valence and Polarized Dirac Sea Natural way for light baryon exotics. Also usual „3-quark“ baryons should contain a lot of antiquarks Soliton Quark-anti-quark pairs „stored“ in chiral mean-field Quantum numbers originate from 3 valence quarks AND Dirac sea !

  18. Quantization of the mean field Idea is to use symmetries • Slow flavour rotations change energy very little • One can write effective dynamics for slow rotations [the form of Lagrangean is fixed by symmeries and axial anomaly ! See next slide] • One can quantize corresponding dynamics and get spectrum of excitations [like: rotational bands for moleculae] Presently there is very interesting discussion whether large Nc limit justifies slow rotations [Cohen, Pobylitsa, Klebanov, DPP....]. Tremendous boost for our understanding of soliton dynamics! -> new predictions

  19. SU(3): Collective Quantization From Wess-Zumino-term Calculate eigenstates of Hcoll and select those, which fulfill the constraint

  20. SU(3): Collective Quantization Known from delta-nucleon splitting Spin and parity are predicted !!!

  21. General idea: 8, 10, anti-10, etc are various excitations of the same mean field  properties are interrelated Example [Gudagnini ‘84] Relates masses in 8 and 10, accuracy 1% To fix masses of anti-10 one needs to know the value of I2 which is not fixed by masses of 8 and 10

  22. DPP‘97 ~180 MeV In linear order in ms Input to fix I2 Jp =1/2+ Mass is in expected range (model calculations of I2) P11(1440) too low, P11(2100) too high Decay branchings fit soliton picture better

  23. Decays of the anti-decuplet p,K,h All decay constants for 8,10 and anti-10 can be expressed in terms of 3 universal couplings: G0, G1 and G2 In NR limit ! DPP‘97 „Natural“ width ~100 MeV GQ < 15 MeV Correcting a mistake in widths of usual decuplet one gets < 30 MeV [Weigel 98, Jaffe 03]

  24. Where to stop ? The next rotational excitations of baryons are (27,1/2) and (27,3/2). Taken literary, they predict plenty of exotic states. However their widths are estimated to be > 150 MeV. Angular velocities increase, centrifugal forces deform the spherically-symmetric soliton. In order to survive, the chiral soliton has to stretch into sigar like object, such states lie on linear Regge trajectories [Diakonov, Petrov `88] p,K,h p,K,h Very interesting issue! New theoretical tools should be developed! New view on spectroscopy?

  25. X- - CERN NA49 reported evidence forX– - with mass around 1862 MeV and width <18 MeV For X symmetry breaking effects expected to be large [Walliser, Kopeliovich] Update of p N S term gives 180 Mev -> 110 MeV [Diakonov, Petrov] Small width of X is trivial consequence of SU(3) symmetry Are we sure that X is observed ? -> COMPASS can check this! And go for charm

  26. Non strange partners revisited N(1710) is not seen anymore in most recent pi N scattering PWA[Arndt et al. 03] If Theta is extremely narrow N* should be also narrow 10-20 MeV. Narrow resonance easy to miss in PWA. There is a possiblity for a narrow N* at 1680 MeV [Arndt et al. 03] In the soliton picture mixing with usual nucleon is very important. Pi N mode is suppressed, Eta N and pi Delta modes are enhanced. Anti-decuplet nature of N* can be checked by Photoexcitation. It is excited much stronger From the neuteron, not from the proton [Rathke, MVP]

  27. Theory Response to the Pentaquark • Kaon+Skyrmion • Q+ as isotensor pentaquark • di-quarks + antiquark • colour molecula • Kaon-nucleon bound state • Super radiance resonance • QCD sum rules • Lattice QCD P=- • Higher exotic baryons multiplets • Pentaquarks in string dynamics • P11(1440) as pentaquark • P11(1710) as pentaquark • Topological soliton • Q+(1540) as a heptaquark • Exotic baryons in the large Nc limit • Anti-charmed Q+c , and anti-beauty Q+b • Q+ produced in the quark-gluon plasma • ……. More than 130 papers since July 1, 2003. Rapidly developing theory: > 2.3 resubmissions per paper in hep

  28. Constituent quark model If one employs flavour independent forces between quarks (OGE) natural parity is negative, although P=+1 possible to arrange With chiral forces between quarks natural parity is P=+1 [Stancu, Riska; Glozman] • No prediction for width • Implies large number of excited pentaquarks Missing Pentaquarks ? (And their families) Mass difference X -Q ~ 150 MeV

  29. Diquark model [Jaffe, Wilczek] (ud) L=1 s (ud) No dynamic explanation of Strong clustering of quarks Dynamical calculations suggest large mass [Narodetsky et al.; Shuryak, Zahed] JP=3/2+ pentaquark should be close in mass [Dudek, Close] Anti-decuplet is accompanied by an octet of pentaquarks. P11(1440) is a candidate No prediction for width Mass difference X -Q ~ 200 MeV -> Light X pentaquark

  30. Diquark-triquark [Karliner, Lipkin] No dynamic explanation of Strong clustering of quarks u d s JP=1/2+ is assumed, not computed u d No prediction for width

  31. Implications of the Pentaquark • Views on what hadrons “made of” and how do they “work” may have fundamentally changed • - renaissance of hadron spectroscopy • - need to take a fresh look at what we thought we • knew well. • Quark model & flux tube model are incomplete and should be revisited • Does Q start a new Regge trajectory? -> implications for high energy scattering of hadrons ! • Can Q become stable in nuclear matter? -> astrophysics? • Issue of heavy-light systems should be revisited (“BaBar” Resonance, uuddc-bar pentaquarks ). It seems that the chiral physics is important !

  32. Summary • Assuming that chiral forces are essential in binding of quarks one gets the lowest baryon multiplets (8,1/2+), (10, 3/2+), (anti-10, 1/2+) whose properties are related by symmetry • Predicted Q pentaquark is light NOT because it is a sum of 5 constituent quark masses but rather a collective excitation of the mean chiral field. It is narrow for the same reason • Where are family members accompaning the pentaquark Are these “well established 3-quark states”? Or we should look for new “missing resonances”? Or we should reconsider fundamentally our view on spectroscopy?

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