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  • Thomas S. Bauer - NIKHEF

  • QThomas S. Bauer - NIKHEF

  • Q with ?sSome questions and critical remarks to the recently reported exotic states:+ = { u u d d s } at 1.540 GeV and X - - = { u d d s s } at 1.862 GeV.

  • Present experimental status several experiments reporting positive results; all reported signals are not very strong; revisiting an intensively studied domain;

    several critical remarks published; possibly other origins of observed effects;

  • Present experimental status several experiments reporting positive results; all reported signals are not very strong; revisiting an intensively studied domain;

    several critical remarks published; possibly other origins of observed effects; but : no discussion of other results than mass and width; (almost) no comparison with existing data; no assessment of consistency of results; experiments without result refrain to publish ...

  • List of experiments: SPring-8 (Japan) hep-ex/0301020 08 Jul. 2003 CLAS (TJLab) hep-ex/0307018 10 Dec. 2003 SAPHIR (Bonn) hep-ex/0307083 30 Sep. 2003 Hermes (HERA) hep-ex/0312044 22 Jan. 2004 n-data (BEBC and Fermilab)hep-ex/0309042 25 Sep. 2003 Diana (ITEP)hep-ex/0304040 18 Sep. 2003 SVD-2 (Protvino) hep-ex/0401024 22 Jan. 2004 NA49 (CERN) hep-ex/0310014 8 Oct. 2003 ZEUS (HERA) ...

    ggge-scatt.

    (K+ + Xe)(p + A)(p + p)e-p scatt.

    WA89;Graal;H1;CoSy;Hera-B...

  • L and S resonancesdecays to n K + and to p K 0

  • X resonancesX - - {ssddu}decays to X - p -

  • SPring-8

  • SPring-8 (LEPS) ( g + 12C) Some salient features: new experiment, optimized for f-physics *) ; uses real photons from Synchr. Radiation Source; Eg < 2.4 GeV; LH2 target and 12C target - only 12C used; PID through ToF and magnetic field; recoiling protons via Si-strip detector; correction for Fermi-motion.

    *) new = 2001. No printed publication except 2 conference contributions + PQ paper.

  • SPring-8 (LEPS)first evidence for Q+-state;

    produced in : + n Q+ + K-; Q+ K+ + n;used C-target;

    19 events in peak.

  • SPring-8 (LEPS)Particle Identification: magnetic field + Time of Flight ( + Cherenkov )

    possible problem: 43 * 106 triggers8000 events with K+ K-,final signal = 19 events need purity of 10-6 !! (including other cuts)

  • SPring-8 (LEPS)A closer look at Fermi motion: due to nuclear target; correlated with Q-value; correction crucial for final result!However measured width of Q+ n K+ much smaller than width of S !! (20 MeV vs. 42 MeV)

    by the way: shouldnt the width rather be correlated to momentum in cms ...?which would make things worse.

  • SPring-8 (LEPS)Identification of Q+ state relies heavily on absence of (fast) proton:

    the Si-strip detector is used as VETO -- this relies crucially on (very) high efficiency. (no info on this found in the available SPRING-8 documents). (Questions: strip efficiency, coincidence between layers, etc.) The Veto condition is checked at 45 mm around the presumed impact of the proton. this requires knowledge of the complete kinematics which is not available!

  • SPring-8 (LEPS)(from Nakano et al.)

  • SPring-8 (LEPS)Question:removing 5 events destroys peak.

    (from Nakano et al.)

  • SPring-8 (LEPS)Question:removing 5 events destroys peak.Thus: how can we gain trust in result ?

    Answer: Use data on LH2: must be able to see Q+ p + K0s; no problem with proton-veto ; no problem with Fermi-motion.(from Nakano et al.)Note: SPring-8/LEPS can (in principle) trigger on pions of K0s decay.

  • CLAS

  • CLAS ( g + 2D, g + 1H ) Some salient features: Large acceptance experiment, several years of operation; domain: Baryon resonances; Eg < 2.9 GeV and < 5 GeV , (respectively) H2 target and 2D target ; PID through ToF and magnetic field; Correction for Fermi-motion (when needed).

  • CLASattempt: analyze D-target data, assuming g + n Q+ + K- , Fermi correction treated as by SPring-8 collaboration:

    Problem: No statistical significant result obtained! andCLAS ... unfavorable... for direct Q+ photoproduction detection(Luminita Todor, Seminar@JLAB, Aug. 15, 2003)

    --- how to proceed ???

  • CLAS require double scattering process to eject proton;

    measurement kinematically complete

    Goal: n + g Q+ + K- ;Problem: no free neutron target ;

    apply trick : use n in D-target;

  • CLAS Prize for re-scattering:yield goes down (later called quenching) .(implicit claim CLAS: ~50 % )reported yields:f: 124 L1520 : 228Q+: 42 Attention: difficult to compare: acceptances not known, presumably not equal. yield Q/yield L1520 0.4 probably even larger!

    Need Monte Carlo in order to determine acceptance and cross section.

  • CLAS -- new data apparently not yet available, though shown at workshop in Trento, Febr. 12, 2004 two peaks, at 1.528 and 1.578 GeV yield of 1.578 GeV peak is ~2 times stronger

  • SAPHIR

  • SAPHIR (Elsa-Bonn) ( g + 1H ) 133 M events (taken ~5 years ago)trigger = 2 charged trackssignal: ~ 50 eventscorresponds to production cross section of s ~ 200 nb.this is 20 % of L, S and L1520 cross sections and decreasing with time .rising with energy

  • X-- another member of the anti-decuplet...Q+ = { u u d d s }

  • NA49

  • NA49 (p-p, s = 17 GeV)p-p scattering at s = 17 GeVsignals for X-- :combining X- and p- cross check with other charge combinations.

    can use X0*1530 as benchmark.

  • NA49Remarks:

    opening angle Qlab > 4.5

  • NA49Remarks:

    opening angle Qlab > 4.5 Qlab is not a physical parameter !!!

  • NA49Remarks:

    opening angle Qlab > 4.5 Qlab is not a physical parameter !!!

    X*01530 visible, but weaker than X- -(1860)

    (due to some cuts... total X*01530 signal is ~150 evts.)

  • NA49 versus NA49 Criticism:(Thanks to H.G. Fischer and S. Wenig, CERN, hep-ex / 0401014 12 Jan 2004)

    NA49 used 1640 X- and 551 X+ eventsNA49 sees a total of ~ 150 X*01530

    S.N. Gangule et al. (NP. B128-408, (1977) report ~ 800 X*01530 from S.N. Gangule et al. Nucl.Phys. B128, 408, (1977)

  • NA49 (p-p, s = 17 GeV) X--

  • NA49 versus (?) WA89 *)*) taken from Pochodzalla, Mainz, talk at JLab, Oct 2003

  • What is hidden beyond 1.8 GeV in WA89 ??total: ~150 X0*

  • NA49 Q+ nK+

    what has NA49 to say about Q+?

  • NA49 Q+ nK+nK+ inv. mass spectrum;

    deviation from polynomial;

  • NA49 Q+ nK+nK+ inv. mass spectrum;

    deviation from polynomial;

    30 % of L1520 added as a hypothetical Q+ ;

    statistical significance of added signal.

    note: different E-scale!

  • Hermes

  • Hermes (e-A, Ee = 27 GeV)quoted signal: 54 ... 59 16

  • Hermes (e-A, Ee = 27 GeV)First: one can do much more with 33 datapoints...

  • Hermes (e-A, Ee = 27 GeV)

  • Hermes (e-A, Ee = 27 GeV)

  • Hermes (e-A, Ee = 27 GeV)

  • Hermes (e-A, Ee = 27 GeV)note: width L1670 small (25 ~ 50 MeV/c2)width L1690 small (50 ~ 70 MeV/c2)L-channel

  • Hermes -- another regard on these datafrom Hermes publication:

  • other work R. A. Arndt, I.I. Strakovsky and R.L. Workman:(nucl-th/0311030, 10 Nov. 2003) reexamine existing K+p and K+d database;how could such a state have been missed?

    The lack of structure in database implies:

    a width of an MeV or less , assuming a state exists near 1540 MeV.

  • Hera-B

  • Hera-B (p-A, s = 42 GeV) finally, a signal which one would like to believe...

  • Hera-B (p-A, s = 42 GeV) finally a signal which we can enhance...

  • Hera-B (p-A, s = 42 GeV) finally a signal which we can enhance... and let shrink

  • Hera-B (p-A, s = 42 GeV) and let come back...

  • Hera-B (p-A, s = 42 GeV) if only we couldnt make it come and go...... a signal which we would like to believe...? ? ? ? ? ? ? ?let me explain:

  • Ks proton as artefact: 1. take the Armenteros-Podolanski plot for Ks and L

  • Ks proton as artefact:3. add third particle (proton) with momentum to one of the pions. Result: This is a MCgenerated peak!

  • Hera-B (p-A, s = 42 GeV) this Q+ signal appears if :

    - L-Ks ambiguity not 100 % removed; clones not 100 % removed protons not 100 % identified

  • Hera-B (p-A, s = 42 GeV) REAL RESULTp likelihood > 0.95No evidence of resonances in the mass region around 1.530 GeV.

  • NA49 versus Hera-BX*0X--

  • NA49 versus Hera-Bnote: Resolution Hera-B 3.5 MeVnote: different scales!

  • Yields and s (taken from publications)

  • Summary by now, >8 experiments claim positive signals; all signals are weak:
  • Problems SPring-8: correction for Fermi motion ? Particle identification ? proton veto through SSD, and only in region where proton expected.

  • Problems - 2 CLAS:

    Quenching through rescattering process likely to be strongly underestimated; Newest results show two peaks: 1.528 GeV and 1.578 GeV first peak agrees with other experiments

    SPring-8 Fermi motion c

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