Diquark model [Jaffe, Wilczek]

Transcription

1 E.A.Strokovsky, JINR, and study of narrow exotic baryons Search JINR Nuclotron at E.A.Strokovsky Significance of the problem: why is the "boom"? Experimental observations since 2003 (selected) The newest data and some puzzles How JINR can contribute: the NIS project at Nuclotron Conclusions

2 The problem is not quite new but is more than 40 years old... conclusive results were obtained before the year No After the 1-st steps: from M.Polyakov, COMPASS Workshop, March Bag models [R.L. Jaffe 76, J. De Swart 80] J p =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 J p =1/2 + pentaquark with mass in the range 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

3 year: masses, quantum numbers, widths were 1997 predicted. Θ

4 approach: a number of models were suggested: Conventional by Karliner and Lipkin, "2+2+1"model by Jaffe "3+2"model Wilszek, etc. From M.Polyakov, COMPASS Workshop, March 2004 and Diquark model [Jaffe, Wilczek] No dynamic explanation of Strong clustering of quarks Dynamical calculations suggest large mass [Narodetsky et al.; Shuryak, Zahed] (ud) L=1 s (ud) J P =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 Ξ Θ 200 MeV -> Light Ξ pentaquark

5 soliton: From M.Polyakov, COMPASS Workshop, March 2004 Chiral Quantum numbers Quantum # Coupling of spins, isospins etc. of 3 quarks mean field non-linear system soliton rotation of soliton Quantum # Coherent :1p-1h,2p-2h,... Quantum #

6 check": "Consistency m s m σ πn =3(4M Σ 3M Λ M N ) +4(M Ω M ) }{{}}{{} octet decuplet 4(M Ξ3/2 M Θ +) }{{} antidecuplet From P.Schweitzer, hep-ph/ (20). From this formula: σ πn =(74± MeV 12) From the data: πn σ πn 60 MeV 80 high strangeness content of the nucleon : <N s s N > y=2 <N uū + d d N > 0.6 In particlular, significant consequences follow for nucleon spin problem and OZI rule. the

7 interacts with the Nothing, Something Nothing changes Something... the parallel with the Lamb shift is obvious A interaction of electron with photon vacuum in atoms brings (The the P 1/2 levels under S 1/2.) seems that there is a good piece of physical It in the chiral soliton approach: fluctuations of truth vacuum of fields binding quarks inside hadrons the be taken into account; interaction of constituent must with these fluctuations changes the spectrum quarks baryons etc.; effects depend upon the fluctuations of density/strength...

8 OBSERVATIONS (selected examples)

9 "(dsdsū)": Ξ 3/2 (Ξ π Ξ π + and 2 systems) 1862±2 MeV/c ; Γ < 2 18 MeV/c (instrumental). mass: The "(uudd s)": Θ + (K + and n K 0 systems) p to now - limited statistics: from 20 to 100 events in (up peak). The observable width: instrumental. the than 10 experiments. More Single experiment. "(uudd c)": D p D + p systems 2 and 3099±3±5 MeV/c ; Γ 2 12 ±3MeV/c mass: The (instrumental.) Single experiment. Θ + is expected to be included with rating in the latest PDG Tables.

10 (DIANA coll., K + Xe) and neutrino data from ITEP old BEBC films the Figure 4: Effective mass of the K 0 p system formed in the reaction K + Xe K 0 pxe : (a) for all measured events, (b) for events that pass additional selections aimed at suppressing proton and K 0 reinteractions in nuclear matter (see text). The fit to the expected functional form is depicted by the dashed line.

11 Events/(0.02 GeV/c 2 ) a) Events/(0.02 GeV/c 2 ) b) LEPS data (SPring-8) MM c γk + (GeV/c 2 ) MM c γk (GeV/c 2 )

12 JINR: LHE propan BC inelastic ep (the central Deep region) rapidity JINR, 2m Propane Bubble Chamber (uudd s) 0 C+ C (K p) + X S 4.2 A GeV/c R.Togoo, Ts.Baatar, B.Khurlebaatar, G.Shakhuu, E.N. Kladnitskaya, A.A.Kuznetsov In: Proceedings of the Mongolian Academy of Sciences, v.170, No.4 (2003) 3.

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14 of the two-particle correlations in nuclei: Exploitation for the "cumulative"production typical

15 The Fig. with a special cuts to enhance the applied results... Surprising of the analysis is Systematics LHE Hydrogen Bubble Chamber, D , JINR: et al; np npk + K at 5.2±0.12 GeV/c Yu.A.Troyan signal Several peaks; 3 peaks with > 5σ signinicance First estimation of the spin: J Θ +> 1/2 (!?) not quite clear...

16 The spectrum has been fitted to a (Gaussian + 5 th order polynomial) using an unbinned Likelihood procedure CLAS: a puzzle? γp Θ + K 0, Θ + K + n The spectrum has been compared to MC simulation Yellow: MC bg Blue: MC Θ + Red: Data CLAS preliminary A side-band subtraction method (2 and 4 nearest bins) was applied giving similar results All methods give similar results N peak ± sqrt(n bg ) 22 ± sqrt(30) stat. sig. = (3.9 ± 0.2)σ Mass = /- 5 MeV FWHM ~ 9 MeV N peak ± sqrt(n bg ) 27 ± sqrt(26) stat. sig. = (6.0 ± 0.2)σ Mass = /- 5 MeV FWHM ~ 9 MeV 12) M.Battaglieri - Spectroscopy of Exotic Baryons with CLAS: Search for Ground and First Excited States

17 data for the Θ + mass. Published data with nuclear targets dominate. Note: The systematic uncertainties are included in the error bars Θ mass, MeV/c LHE HBC SPring - 8 CLAS (d ) SAPHIR CLAS (p ) CLAS (1) CLAS (2) Xe BC SVD 2 COSY - TOF LHE propan BC ITEP (BEBC) HERMES ZEUS np γc γd γp K + Xe pp να pa CC ep γ*d (nk + ) (pk 0 S)

18 K 0 p differs from K + n? (1529±6 against 1542±6) CLAS puzzle: γp Θ + K π + one peak γp Θ + K 0 two peaks (?!) CLAS does not observe Ξ in photoproduction. HERA-B and SPHINX (IHEP) do not see the Θ + under conditions similar (apparently!) to SVD-2. PHENIX does not observe Θ + production in d + Au interactions; STAR does not observe in Au + Au. Controversies about (pk + ) system. Other negative signals (WA89, BES etc.) The of Θ + 2 existing kaon data at momenta below 1 : width Γ<1 MeV/c. Theory must adapt to this. demand GeV/c be the exotics are different from the May expected?? theoretically

19 very existence of the exotics is not firmly The at the moment. established if it exists, neither the quark structure is clear Even a matter of a belief) nor the spin/parity/isospin. (is problem is attacked in many Labs over the world. The are coming permanently. But production of the News by hadron beams at intermediate energies can exotics done in the very few places. JINR Nuclotron is the be and the most appropriate for the task. one propose to perform a dedicated search for Θ- We at the Nuclotron using the NIS setup. baryons of the production mechanisms; determination Study of quantum numbers etc...

20 Nuclotron energy is optimal for exclusive experiments. JINR d, p, n beams spin-spin correlations, polarization Polarized determination of J P transfers created mass excess, MeV/c Thresholds accessible at proton accelerators (intermediate energy region) COSY 12 C d Ξ+2K Depolarizing resonanses (Nuclotron, d, extraction) Nuclotron p + Θ Ω+3K φ DC 4-momentum transfer, GeV 2 /c Λ/Σ+K ρ/ω φ COSY 4-momentum transfers at thresholds Ξ+2K Ω+3K tpp tpm tpy p p Nuclotron DC p M Y proton beam energy at lab., Tkin, GeV proton beam energy at lab., Tkin, GeV Energy dependence of the σ prod estimate of J as well

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22 organizations: Participating JINR: LPP, LHE, LNP, LIT, BLTP Jagiellonian University, Cracow, Poland Ludwig Maximilians University, Munich, Germany BINTP, Kiev, Ukraine HEPI TSU, Tbilisi, Georgia countries: Participating Armenia, Georgia, Ukraine, Poland, Germany Russia, stage of the setup is planned for the beam 1-st at the end of this year. tests/calibrations

23 The physical program of the NIS experiment includes: Search for effects of nucleon polarized strangeness in (A) of φ and ω mesons in pp and np scattering close production to thresholds (at ε MeV above the thresholds). Search for production of the Θ + baryons in pp interactions (B) to threshold in reactions: close pp Θ + +K +p+π +, Θ nk + pp Θ + +K +p+π +, Θ pk 0, K 0 S π+ π do this search, the setup is to be enhanced with new trackers To minidrift chambers) installed inside the analyzing magnet. (the attractive option (with additional trackers) is: Very dp Θ + +p S +Λ, Λ pπ The "forward"mdc is of vital importance for this experiment.

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25 production cross section of Θ + in pn, pp, pa reactions at The p lab GeV/c is in the range of µb. = Main components of NIS setup Subsystem Equipment Comment Tracking 2 step, MPWC, 2 mm 2 1 m stations 3 4 sell, MDC, 2 mm m stations 3 PID walls, 40 modules TOF 2 RPC m stations, 3 module 2 each 1 station 5 5 cm start SciFi LH2 target 10 cm thick NIS should detect 1000 reconstructed events/week with > beam of 10 7 /sec, repetition rate of 10 sec and spill duration the of 5 sec (the duty factor 0.5).

26 Preparation for the field map measurements

27 Proportional chambers at the test-bench.

28 RPC modules at the test-bench.

29 modules at the test-bench. The front-end RPC electronics.

30 proof of the new exotic baryons will definitely The in a drastic change of the particle theory. result Present situation is controversial... has contributed using its archives. Maybe there JINR something else. But JINR can and must contribute is more using Nuclotron which has significant much for research in this field. potential The NIS project at Nuclotron meets the challenge.