 -Polarization in the Reaction   p  K 0   "EPECUR" Experiment Proposal. I.G. Alekseev, P.E. Budkovsky, V.P. Kanavets, M.M. Kats, L.I. Koroleva, V.V. Kulikov, B.V. Morozov, V.M. Nesterov,V.V. Ryltsov, V.A. Sakharov, D.N. Svirida, A.D. Sulimov. Institute for Theoretical and Experimental Physics (ITEP), B. Cheremushkinskaya 25, Moscow, , Russia. Tel: 7(095) , Fax: 7(095) , E.A. Filimonov, V.V. Golubev, A.I. Kovalev, N.G. Kozlenko, V.S. Kozlov, A.G. Krivshich, D.V. Novinsky, V.V. Sumachev, V.Yu. Trautman. Petersburg Nuclear Physics Institute (PNPI), Gatchina, Leningrad district, , Russia. Dima Svirida (ITEP)

 Inspired by  + indications and high interest to the pentaquark matter  Search for the neutral cryptoexotic member of the baryon antidecuplet ½+ based solely on the predictions for it’s small width  No current experimental data can reveal such a resonance with a width of several MeV  Latest detailed investigations of the “modified” “EPECUR”* Proposal (hep-ex/ ) Dima Svirida (ITEP) ____________________ * “EPECUR” is the transliteration of the Russian abbreviation for “Experiment for Pentaquark search in the Elastic Scattering (and  –p  K 0  reaction)” FA02 PWA allow narrow resonant structures near 1680 and 1730 MeV  Theoretical predictions for the mass MeV, width 2-20 MeV  Experiment idea: very precise cross-section measurements with very fine energy steps (  0.6 MeV in terms of invariant mass)  Extremely favorable experimental conditions: large cross-sections, high sensitivity, “ideal” pion beam-line at ITEP

 Weak sensitivity in total elastic cross-section  Yet high effect in differential cross-section in the area of minimum at 40 o -90 o c.m.  Sensitivity estimates from PWA data: 15% effect in d  /d  for  el /  =5% -- coupling to the elastic channel Stage I:   p Elastic Dima Svirida (ITEP)  Measurements in the p beam range MeV/c (  s= MeV)  Beam energy resolution <0.1% in the range  2% at a time  25 cm LiH target  0.5% statistical error in (1 MeV/c  20 o c.m.) bins in the cross-section minimum after 20 days of running d  /d   c.m. Cross-section minimum 0.2mb/sr M=1671 MeV  =6 MeV  el/  =5%

Stage I:   p Elastic Setup Dima Svirida (ITEP)  Beam momentum resolution measured 0.07% in early 70’s  Minimize matter in the beam-line  Beam trigger from proportional chambers  Reasonable Landau widening inside the LiH target  Dipole field measurements with NMR  Mean beam momentum monitored with TOF Proportional chambers PC1–PC3 located in first focus of the ITEP beam-line 322 for the incident pion momentum measurement Proportional chambers PC4–PC6 for the tracking of the incident pions Liquid hydrogen target with 1 mm beryllium cover,  4 cm, 25 cm long Sets of drift chambers DC1–DC4 for the reaction products tracking Beam scintillation counters S1, S2, trigger hodoscopes H2,H3 with TOF features, anti- and beam TOF counter A1. Events TGT middleTGT entrance TGT exit

Stage II:   p  K 0  Dima Svirida (ITEP) Very attractive for search and baryon spectroscopy in general:  Predicted branching  K  /  2*   –p /   Reaction total cross-section is significantly smaller than that of elastic scattering, making the resonant effect more pronounced  Energy range under study close to the reaction threshold – resonant effect enhanced  15% resonant effect in the total reaction cross-section assuming  K  /  =10%,   –p /  =5% In addition:  Pure isotopic state ½  High analyzing power of   p weak decay  =0.642 – important byproduct  polarization measurement Convenient for detection:  Relatively large cross-section ~0.9 mb  Significant fraction 22% of the charged mode   p  K 0    +   + p  

  p  K 0  Detection Features (MC) Dima Svirida (ITEP) Detection of 4 particles in the final state requires rather “hermetic” acceptance With no magnetic field the tracking detector accuracy must be  m in order to reliably reconstruct K 0 and  decay vertices Protons are concentrated in a narrow forward cone, while pions from both decays have wide angular distributions including backward areas Most of the 4-charged events have either all four particles going forward (~20%) or a proton and 2 pions going forward, the third pion at large angle (~80%) The identification of a single proton is highly important for the background suppression as well as for  polarization measurement; TOF technique may be used for this purpose Reliable separation of K 0  and K 0  0 final states can be achieved above  0 production threshold The setup can cover nearly 2  of  production angles in the whole energy range under study protons from  pions from  pions from K 0  lab TOFp  TOF ns 08ns

Stage II:   p  K 0  setup Dima Svirida (ITEP)  The beam part the same as in “Stage I”  4 of 5 middle size drift chambers inherited from “Stage I” (DC1-5)  Additionally need 4 smaller DCs (DC6-9) and one large DC10  XY-segmented hodoscope H1,2 at 2 m from the target for trigger logic and proton TOF identification; need 10x10 cm 2 cell size in the central area of 1x1 m 2  Even with only backward angles lost for tracking, the acceptance for the charged mode is 20-30% Event reconstruction -- no magnetic field, proton identification:  4 unknown momentum absolute values in the final state  4 projections of conservation laws  Overconstraints from 2 vertex information allow background suppression and K 0  0 separation  Naturally  decay angles can be determined for asymmetry measurement

 Polarization – Planned accuracy Dima Svirida (ITEP) 1% statistical accuracy in  tot K  in 1 MeV energy bins in 23 days of running More than twice better accuracy than in NIMROD  polarization data, but in 285 energy bins 10 times better equivalent statistical error Possible resonant singularities in the energy behavior of the  polarization NIMROD Data EPECUR Planned

Milestones and Plans Dima Svirida (ITEP)

Conclusions Dima Svirida (ITEP)  A completely new experimental setup is under construction at the ITEP synchrotron beam-line 322 in collaboration with PNPI  EPECUR experiment has sufficient chances to reveal the cryptoexotic member of the baryon antidecuplet ½+ if it exists  In all cases, new excellent data on   p elastic scattering and   p  K 0  reaction will be obtained, overriding current experimental accuracy by an order of magnitude and more, and significantly contributing to the PWA database   polarization measurement in   p  K 0  -- valuable byproduct of the experiment  Yet the manpower and financial resources of the collaboration are limited, that’s why COLLABORATORS ARE EXTREMELY WELCOME !!! Thanks The authors are grateful to the great number of people who support the proposal and took part in its discussion; special thanks for this to I.I.Strakovsky (GWU) and Ya.I.Azimov (PNPI). The work is partially supported by the RFBR grant