1 / 31

Experimental Status of Pentaquark States

Phys.Rev.Lett. 91 (2003) 012002. uudds. Experimental Status of Pentaquark States. Introduction Experimental evidence Production mechanisms What do we know about the Q + ? Exotic cascades states. SPring-8. Special Thanks CLAS Collaborators. Mass = 1.54 GeV.

kimberley-cotton
Download Presentation

Experimental Status of Pentaquark States

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Phys.Rev.Lett. 91 (2003) 012002 uudds Experimental Status of Pentaquark States • Introduction • Experimental evidence • Production mechanisms • What do we know about the Q+? • Exotic cascades states SPring-8 Special Thanks CLAS Collaborators Mass = 1.54 GeV

  2. Quarks are confined inside colorless hadrons q q q q Quarks combine to “neutralize” color force q Mystery remains: Of the many possibilities for combining quarks with color into colorless hadrons, only two configurations were found, till now…

  3. What are pentaquarks? Example: uudss, non-exotic Baryon number = 1/3 + 1/3 + 1/3 + 1/3 – 1/3 = 1 Strangeness = 0 + 0 + 0− 1 + 1 = 0 Example: uudds, exotic Baryon number = 1/3 + 1/3 + 1/3 + 1/3 – 1/3 = 1 Strangeness = 0 + 0 + 0 + 0 + 1 = +1 • Minimum quark content is 4 quarks and 1 antiquark • “Exotic” pentaquarks are those where the antiquark has a different flavor than the other 4 quarks • Quantum numbers cannot be defined by 3 quarks alone.

  4. Pentaquarks – two approaches (ud) s L=1 (ud) Soliton: (simplified) Meson fields Quark cluster models, e.g. di-quark description (Jaffe, Wilczek) Chiral soliton model: (Diakonov, Petrov, Polyakov) Pentaquark comes out naturally from these models as they represent rotational excitations of the soliton [rigid core (q3) surrounded by meson fields (qq)] L=1, one unit of orbital angular momentum needed to get J=1/2+ as in cSM Lattice QCD => JP = 1/2-

  5. The Anti-decuplet of SU(3)f Ten observations Null Results? One experiment X5−− X50 (revised version) D. Diakonov, V. Petrov, hep-ph/0310212

  6. Experimental Evidence • Many experiments • No dedicated experiments to date • but,… dedicated experiments are starting to take data For new data from SPring-8 see Hicks Session J2 Sun 10:45 • Walk through the analysis from CLAS • Selected examples from other experiments

  7. Quark lines for the reaction us g K− us K+ Q+ n ddu n ddu Q+ is composed of (uudds) quarks

  8. Production mechanisms g K− K+ (p) n Q+ n K+ (K0) p pspec Control Reactions g g K+ K+ K− K− p n S− L*(1520) p n p− K− p n pspec nspec

  9. JLab accelerator CEBAF • Continuous Electron Beam • Energy 0.8 ─ 5.7 GeV • 200 mA, polarization 75% • 1499 MHz operation • Simultaneous delivery 3 halls

  10. CEBAF Large Acceptance Spectrometer Torus magnet 6 superconducting coils Electromagnetic calorimeters Lead/scintillator, 1296 photomultipliers Liquid D2 (H2)target + g start counter; e minitorus Drift chambers argon/CO2 gas, 35,000 cells Gas Cherenkov counters e/p separation, 256 PMTs Time-of-flight counters plastic scintillators, 684 photomultipliers

  11. gd → p K+K─ (n) in CLAS K+ K- p

  12. Particle identification by time-of-flight

  13. Reaction gd→pK+K-(n) • Clear peak at neutron mass. • 15% non-pKK events within ±3s of the peak. • Almost no background under the neutron peak after event selection with tight timing cut. Reconstructed Neutrons

  14. Deuterium: nK+ invariant mass distribution • Mass = 1.542 GeV • < 21 MeV Significance 5.2±0.6 s NQ= 43 events Q+ Two different Background shapes Distribution of L*(1520) events

  15. Searching for Q+ on a proton target Prominent K*0 K*0 M(nK+) [GeV] gp→p+K- K+ (n) no cuts

  16. Searching for the Q+ on a proton target g Q+ p+ 7.8s p− n Q+ p N* K+ K− cut Eg = 3 – 5.5 GeV gp→p+K-K+(n) Cosq*(p+) > 0.8 • M=1555±10 MeV • < 26 MeV Cosq*(p+) > 0.8 Cosq*(K+) < 0.6 CLAS Collaboration PRL 92, 032001-1 (2004). M(nK+) [GeV]

  17. Q+─N* production mechanism? outside cuts g p+ p− n Q+ p N* K+ K− cuts outside Q+ N* ? • What do p-p scattering data say? • p-p cross section data in PDG have a gap in the mass range 2.3–2.43 GeV. M(nK+K−) [GeV]

  18. Diffractive mechanism? Require forward K0* Cos q*(K−p+) > 0.5 K- g K*0 p+ p Q+

  19. Q+NOT produced in association with K*0 K*0 events Non K*0events

  20. HERMES e+d→(pKs0)X Airapetian et al. Hep-ph/0312044 27.6 GeV positrons M=1528±3.3 MeV G ~ 17±9 MeV Mass (K0p) [GeV]

  21. New results from COSY-TOF COSY-TOF hep-ex/0403011 The TOF spectrometer at the COSY facility in Juelich, Germany found evidence for the Q+ in the reaction: p + p →S++ Q+. pp →S+ K0 p • M=1530±5 MeV • < 18 MeV s ~ 0.4±0.1 mb 2.95 GeV GeV/c2 M(K0p)

  22. From ZEUS at DESY… ZEUS hep-ex/0403051 ep →eKs0p X • M=1521.5±1.5 MeV • ~ 8±4 MeV √s ~ 310 GeV Q2 > 20 GeV2 Mass (K0p) [GeV]

  23. What do we know about this S=+1 state? LEPS : gC→(nK+) K−X DIANA : K+Xe→(pK0) X CLAS-d : gd→(nK+) K−p CLAS-p : gp→(nK+)p+K− SAPHIR : gp→(nK+) K0 Mass (GeV) ITEP : nd,Ne→(pK0) K0 HERMES : e+d→(pK0) X COSY-TOF: pp→(pK0)S+ ZEUS : ep→e (pK0) X SVD-2 : pA→(pK0) X Upper limit or estimate of G (GeV) ( ) Strangeness undetermined Decay products in parenthesis

  24. Search for pentaquarks in HERA-B Q+ ? Q+(1540) < 0.02 L*(1520) HERA-B hep-ex/0403020 L*(1520) M(pK0s) (GeV) M(pK−) (GeV) Null result at HERA-B pA →K0p X √s ~ 41.6 GeV

  25. There is much more to learn • Spin, parity • Chiral soliton model predicts Jp=½+ (p-wave) • Quark model naïve expectation is Jp=½− (s-wave) • Lattice calculations predict Jp=½− • Isospin • Likely I=0, since searches for pK+ partners unsuccessful • Width (lifetime) • Measurements mostly limited by experimental resolution. • Theoretical problem remains why the state is so narrow. • Analysis of existing K+d scattering data indicate that G < 1-2 MeV. • Complete determination of the pentaquark multiplet

  26. A new cousin: observation of exotic X5−− ssddu M=1.862± 0.002 GeV X5−− X50 X5−− X50 Q+ X(1530) NA49 CERN SPS Phys. Rev. Lett. 92 (2004) 042003

  27. But, can it be reproduced?? X−p− + X+p+ X−p+ + X+p− HERA-B hep-ex/0403020 • HERA-B collaboration at DESY (Germany) • Null result with much higher statistics! • They also have a null result for the Q+ X(1530) Mass (GeV/c2)

  28. Predictions depend on dynamics Decay modes are sensitive to dynamical picture Number of states and mass spectra Ss X X5 X5 Ns S N L S Q Q N BR(X5 → K− S−) BR(X5 → p− X−) BR(X5 → p0 X−) BR(X5 → p− X0) Soliton Di-quark Note: Models adjusted to experiment

  29. Search for exotic cascades X5−− and X5− Experiment 04-10, scheduled to run this fall X −−→ p− X− L→ p− p X −→ p− L Electron beam gn→K+K+X5−− • X− ct = 4.9 cm • ct = 7.9 cm Two decay vertices, Negatives bend outwards <gb> ~ 1.5

  30. Current activities at Jlab • Pentaquark experiments in Hall B • g10 (currently taking data) gd → Q+ Eg~1 – 3.5 GeV • g11 (starts in mid-May) gp → Q+ Eg~1 – 3.5 GeV • eg3 (November) gvd→ X5−−, X5− Eg> 3.9 GeV • High energy data gp → Q+, X5 Eg~1.5 – 5.4 GeV • Pentaquark experiment in Hall A • E04-012 (May), search for excited Q++ and Q0 states.

  31. Summary • A key question in non-perturbative QCD is the structure of hadrons. • We have reviewed the evidence for the existence of a new class of colorless hadrons with quantum numbers which cannot be generated from solely three quarks: • There is substantial corroborating evidence for an exotic baryon with S = +1, which would have a minimal quark content of (uudds). • The observation of a doubly negative S=−2 baryon (ddssu) is consistent with a second corner of the anti-decuplet the family of pentaquarks, but needs additional confirmation. • Dedicated experiments are being mounted which should easily establish (or refute) the observations to date.

More Related