-Polarization in the Reaction pK0 "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, 117218, Russia.

Tel: 7(095)129-96-29, Fax: 7(095)883-96-01, E-mail : Dmitry.Svirida@itep.ru

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, 188350, 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/0509032)

Dima Svirida (ITEP)

n(1650) ???(

p or K0)

____________________

* “EPECUR” is the transliteration of the Russian abbreviation for “Experiment for Pentaquark search in the Elastic Scattering (and –pK0 reaction)”

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FA02 PWA allow narrow resonant structures near 1680 and 1730 MeV Theoretical predictions for the mass 1650-1690 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 40o-90o 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 pbeam

range 900-1200 MeV/c (s=1610-1770 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 20oc.m.) bins in the cross-section minimum after 20 days of running

d/d

c.m.

Cross-section minimum 0.2mb/sr

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M=1671 MeV=6 MeVel/=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 TG

T

middle

TG

T

entranceTG

T

exit

Stage II: pK0

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 pK0 + + p

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Kp

KKK

resK

kkl

4

)12(1

pK0 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 150-200 m in order to reliably reconstruct K0 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 K0 and K00 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 K0

lab

TOFpTOF@1m

ns

0 8ns

Stage II: pK0 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 cm2 cell size in the central area of 1x1 m2

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 K00 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)

Milestones passed June 2004 Proposal submitted at ITEP and PNPI September 2004 Proposal approved by ITEP scientific council November 2004 MOU with PNPI was signed, PNPI taking the responsibility for proportional and drift

chambers production; ITEP is responsible for the beam/target issues and the chamber electronics

December 2004 322 beamline at ITEP was resurrected and beam adjustments and tests started, agreement on the LiH target reached between two ITEP groups, technical project of its modification finished

March 2005 Adjustment of beam focusing and tests of the momentum resolution; prototype proportional chamber and electronics production started. Started MC simulations for the elastic setup.

April 2005 LiH target moving to the experiment area started The project is supported by the Russian Fund for Basic Research, grant 05-02-17005

June 2005 Successful tests of prototypes of proportional and drift chambers and their electronics Milestones to pass

October 2005 Start of proportional chambers electronics mass production November 2005 Liquid neon test run of the target December 2005 Installation and tests of the whole set of proportional chambers. March 2006 Liquid hydrogen run of the target. Tests of the full-scale prototype of drift chamber June 2006 Tests of 4 drift chambers for the elastic setup November 2006 The first data run for the elastic scattering March 2007 The second data run for the elastic scattering June 2007 Tests of TOF segmented hodoscope and large drift chamber November 2007 The first data run for KΛ March 2008 The second data run for KΛ

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 pK0 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 pK0 -- 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 05-02-17005

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