Progress in developing a spiral fiber tracker for the J-PARC E36 experiment

TL;DR

This paper details the development and testing of a spiral fiber tracker for the J-PARC E36 experiment, aiming to improve charged particle detection for testing lepton flavor universality in kaon decays.

Contribution

The paper introduces a novel spiral fiber tracker design with high detection efficiency, integrated into the upgraded E36 apparatus for precise particle tracking.

Findings

Prototype two-layer ribbon shows 99.6% detection efficiency.

Successful assembly of the SFT around the target holder.

Enhanced capability for charged particle detection in the experiment.

Abstract

This paper reports the recent progress made in developing a spiral fiber tracker (SFT) for use in the E36 experiment scheduled at the Japan Proton Accelerator Research Complex (J-PARC). The primary goal of this positive kaon decay experiment, which uses a stopped kaon beam, is to test lepton flavor universality to search for physics beyond the Standard Model of particle physics. For this experiment, we are currently upgrading the E246 apparatus, which consists of the superconducting toroidal spectrometer previously used at the High Energy Accelerator Research Organization (KEK), Japan. Conducting high-precision measurements will rely on efficiently detecting and tracking charged particles (i.e., positive muons and positrons) from kaon decays. Combined with the three existing layers of multiwire proportional chambers, the SFT comprises four layers of ribbons, with each layer containing 1-mm-diameter double-clad plastic scintillating fibers; the ribbons are spirally wound in two helicities around the kaon stopping target at the center of the detector system. Scintillation photons are read out by multipixel photon counters connected to the scintillating fibers by clear optical fiber extensions. A preliminary bench test shows that a prototype two-layer fiber ribbon exhibits 99.6% detection efficiency at the 1-photoelectron threshold. Finally, the SFT was successfully assembled around the target holder.