A Luminosity Spectrometer for the Zeus Experiment at HERA

TL;DR

This paper introduces a novel luminosity spectrometer for the ZEUS experiment at HERA that mitigates damage and pile-up issues in luminosity measurement, achieving a systematic uncertainty of 1.4%.

Contribution

It presents a new spectrometer design that counts bremsstrahlung photon conversions with reduced radiation damage and pile-up effects.

Findings

Achieved a systematic uncertainty of 1.4%.

Reduced impact of synchrotron radiation damage.

Effective counting of bremsstrahlung photon conversions.

Abstract

The HERA luminosity upgrade is expected to generate two major problems in the current method of luminosity determination which is based on counting brehmsstrahlung photons: damage of the calorimeter monitor due to high primary synchrotron radiation and large multiple event (pile-up) corrections. The luminosity spectrometer presented in this talk, is a novel method that reduces the impact of these problems in the luminosity measurement and is expected to yield a total systematic uncertainty of 1.4%. The spectrometer counts brehmsstrahlung photon conversions in the beam pipe exit window using two small calorimeters (former ZEUS beam pipe calorimeters) symmetrically placed away from the synchrotron radiation plane. The photon conversion rate is measured by counting electron-positron (ep) coincidences in the calorimeters. The ep acceptance is measured using a third calorimeter (6 meter tagger) which tags the brehmsstrahlung electrons. The electron-positron pair is separated by a small dipole magnet.