Search for narrow pion-proton states in s-channel at EPECUR: experiment status

TL;DR

The EPECUR experiment searches for narrow pion-proton states in the 1610-1770 MeV range using a precise s-channel scan with a specialized setup, aiming to identify cryptoexotic pentaquark members and measure cross sections with high accuracy.

Contribution

This work reports the first physics run of a novel experiment designed to detect narrow states in pion-proton interactions with high precision and minimal background interference.

Findings

Successful assembly and initial testing of the experimental setup.

Collection of 0.5 billion triggers covering pion beam momenta 940-1135 MeV/c.

First physics data acquired for invariant mass and cross section measurements.

Abstract

An experiment EPECUR, aimed at the search of the cryptoexotic non-strange member of the pentaquark antidecuplet, started its operation at a pion beam line of the ITEP 10 GeV proton synchrotron. The invariant mass range of the interest (1610-1770) MeV will be scanned for a narrow state in the pion-proton and kaon-lambda systems in the formation-type experiment. The scan in the s-channel is supposed to be done by the variation of the incident pi- momentum and its measurement with the accuracy of up to 0.1% with a set of 1 mm pitch proportional chambers located in the first focus of the beam line. The reactions under the study will be identified by a magnetless spectrometer based on wire drift chambers with a hexagonal structure. Because the background suppression in this experiment depends on the angular resolution, the amount of matter in the chambers and setup is minimized to reduce multiple scattering. The differential cross section of the elastic pi-p-scattering on a liquid hydrogen target in the region of the diffractive minimum will be measured with statistical accuracy 0.5% in 1 MeV steps in terms of the invariant mass. For KLambda-production the total cross section will be measured with 1% statistical accuracy in the same steps. An important byproduct of this experiment will be a very accurate study of Lambda polarization. The setup was assembled and tested in December 2008 and in April 2009 we had the very first physics run. About 0.5x10^9 triggers were written to disk covering pion beam momentum range 940-1135 MeV/c.