1. SPIN 2012, Dubna, September 17-22, 2012 I.G. Alekseev a,*, V.A. Andreev b, I.G. Bordyuzhin a, D.A. Fedin a, Ye.A. Filimonov b, V.V. Golubev b, A.B. Gridnev b, E.A. Konovalova b, L.I. Koroleva a, N.G. Kozlenko b, V.S. Kozlov b, A.G. Krivshich b, B.V. Morozov a, V.M. Nesterov a, D.V. Novinsky b, V.V. Ryltsov a, M. Sadler c, A.D. Sulimov a, V.V. Sumachev b, D.N. Svirida a, V.I. Tarakanov b, V.Yu. Trautman b a Institute for Theoretical and Experimental Physics, B. Cheremushkinskaya 25, Moscow, Russia. b Petersburg Nuclear Physics Institute, Gatchina, Leningrad district, Russia c Abilene Christian University, Abilene, Texas, USA * igor.alekseev@itep.ru High precision measurements of the pion-proton elastic scattering and kaon-lambda production in the EPECUR experiment

2. Pentaquark antidecuplet 2 ? Original prediction – N***(1710) From modified PWA – 1680 or 1730 1 1 ) R. Arndt et al., Phys.Rev. C69 (2004) 035208 SPIN’2012 Igor Alekseev (ITEP, Moscow)

3. N(1685) 3 NNR’2009, Edinburg, June 8-10, 2009 http://2009physicsevents.org η-photoproduction off neutron GRAAL: SPIN’2012 Igor Alekseev (ITEP, Moscow)

4. SPIN’2012 4Igor Alekseev (ITEP, Moscow) M.J Amaryan et al. Phys.Rev. C85 (2012) 035209 MC MC cor The same CLAS statistics of 2004 (g11a run period) as in R. De Vita et al., [CLAS Collaboration], Phys. Rev. D74, 032001 (2006) A narrow structure at K S missing mass M X (K S ) = 1.543 GeV with a Gaussian width = 0.006 GeV for the reaction γp→pK S K L when M(K S K L ) = m ϕ and −t Θ <0.45 GeV 2 with 5.4σ statistical significance. S+MC cor

5. S. Naohito @ SPIN 2010

6. 6Igor Alekseev (ITEP, Moscow) Resonance parameters within safe reach by the experiment: This provides a good coverage of both theoretical and experimental expectations. and “Formation” – type experiment. Extremely high invariant mass resolution (~0.6 MeV), provided by high momentum resolution of the magneto-optic channel 0.1%. High statistical precision: 0.5% for elastic scattering and 1% for K  -production. Magnetless spectrometer with drift chambers. Liquid hydrogen target. Very small amount of matter on the particle paths. EPECUR: Not narrow resonances only … Precise cross section measurements:   p    p: d  /d  – 0.5% statistical precision and 1 MeV momentum step   p  K 0  :  REAC – 1% statistical precision and the same step  Very important data for PWA “Usual” resonace P11 N(1710)***  -polarization in the reaction   p  K 0  - an order of magnitude better precision then the best data available now - NIMROD (78) SPIN’2012

7. Setup for elastic scattering 7Igor Alekseev (ITEP, Moscow)  Proportional chambers with 1mm pitch and 40 um aluminum foil potential electrode in the first focus (1FCH1-4) and in front of the target (2FCH1-4). Momentum of each incident pion is tagged with the precision better 0.1%.  Liquid hydrogen target with beryllium outer shell and mylar hydrogen container. The target diameter is 40 mm and the length along the beam ~250 mm.  8 modules of drift chambers with hexagonal structure to measure tracks of particles produced.  Trigger scintillation counters S1, S2, A1.  NMR system for measurement field in the magneto-optic channel dipoles with precision better 0.1%.  Triggers: Main = S1∙1FCH ∙S2 ∙2FCH ∙(!A1) With prescale: Mom1F = S1∙1FCH ∙S2 ∙2FCH BeamPos = S1∙1FCH∙2FCH ∙ A1  p  p SPIN’2012

8. I.G Alekseev (ITEP) 8 Drift chambers Proportional chambers Hodoscope Liquid hydrogen target heat exchanger Engineering run (December 2008) 7 millions of triggers were written with the liquid hydrogen target 8Igor Alekseev (ITEP, Moscow) SPIN’2012

9. 9 Statistics so far 2.97 billion triggers P beam, MeV/c N trg, mln. Many thanks to ITEP accelerator! SPIN’2012 Igor Alekseev (ITEP, Moscow)

10. 10 Elastic events selection Hypothesis – pion scattered to the left arm θ цм =84 о The hypothesis is true The hypothesis is false SPIN’2012 Igor Alekseev (ITEP, Moscow)

11. Track reconstruction efficiency We require 3 hits on the track out of 4 possible in each projection 100% 99% 11 SPIN’2012 Igor Alekseev (ITEP, Moscow)

12. Preliminary Corrected to the acceptance, efficiency and decays 12Igor Alekseev (ITEP, Moscow) SPIN’2012 Statistical errors only

13. Preliminary Corrected to the acceptance, efficiency and decays 13Igor Alekseev (ITEP, Moscow) SPIN’2012 Statistical errors only

14. Preliminary Corrected to the acceptance, efficiency and decays 14Igor Alekseev (ITEP, Moscow) SPIN’2012 Statistical errors only

15. Preliminary Corrected to the acceptance, efficiency and decays 15Igor Alekseev (ITEP, Moscow) SPIN’2012 Statistical errors only

16. Resonances and channel thresholds in the differential cross section Resonance influence on the cross section Other channel threshold influence on the cross section π - p→K 0 Σ 0 – M inv =1690.2 MeV P beam = 1033 MeV/c π - p→K + Σ - – M inv =1691.1 MeV P beam = 1035 MeV/c π - p→ωn – M inv =1722.3 MeV P beam = 1092 MeV/c π + p→K + Σ + – M inv =1683.1 MeV P beam = 1021 MeV/c S-wave only Any wave N(1685) – M inv =1685 МэВ → P beam = 1024 MeV/c Energy 16Igor Alekseev (ITEP, Moscow) A.I. Baz, ZETF 33 (1957) 923 SPIN’2012

17. 17Igor Alekseev (ITEP, Moscow) Preliminary Statistical errors only

18. SPIN’2012 18Igor Alekseev (ITEP, Moscow) Preliminary Statistical errors only

19. SPIN’2012 19Igor Alekseev (ITEP, Moscow) Preliminary Statistical errors only

20. Some irregularity is seen in the region of the most interest (1020-1040 MeV) in several θ CM bins Only one half of the statistics in this region was already analyzed We plan to get more statistics in the narrow energy range SPIN’2012 20Igor Alekseev (ITEP, Moscow) Preliminary Statistical errors only

21. SPIN’2012 21Igor Alekseev (ITEP, Moscow) Preliminary Statistical errors only

22. SPIN’2012 22Igor Alekseev (ITEP, Moscow) Preliminary Statistical errors only

23. SPIN’2012 23Igor Alekseev (ITEP, Moscow) Preliminary Statistical errors only

24. SPIN’2012 24Igor Alekseev (ITEP, Moscow) Preliminary Statistical errors only

25. –pK0S +––p–pK0S +––p We keep the target and the beam equipment The drift chambers we already have New wide-aperture drift chambers New hodoscopes Most of the events have either all 4 particles going forward or 3 particles including the proton going forward and one pion going in some other direction SPIN’2012 25Igor Alekseev (ITEP, Moscow)

26. 26Igor Alekseev (ITEP, Moscow) The new wide-apperture drift chamber tests at PNPI SPIN’2012

27. Status and plans 27Igor Alekseev (ITEP, Moscow) Elastic scattering  Detector EPECUR for precision measurement of elastic πp-scattering was built and comissioned: track efficiency in the drift chambers > 99% beam momentum tagging is better 0.1%  We took 4 physics runs and 2.97 billions of triggers are collected. The analysis is under way.  The preliminary results show some irregularity at P beam =1020-1040 MeV/c.  We plan to take more data in the narrow region of interest as well as extend the measurement till 2 GeV/c  The beam composition will be determined using Cherenkov counter and Monte-Carlo simulations K 0 Λ-production  The first out of 4 required wide-aperture drift chambers is manufactured and is being tested at PNPI  We have full front-end and DAQ electronic  Engineering of mechanical structure as well as of TOF forward hodoscope is under way. SPIN’2012