Helium identification with LHCb

TL;DR

This paper presents a method for identifying helium nuclei at LHCb using ionisation and timing measurements, achieving high background rejection and enabling new physics studies involving light nuclei.

Contribution

The paper develops and demonstrates a novel helium identification technique at LHCb with high efficiency and near-zero background, expanding the experiment's physics capabilities.

Findings

Approximately 100,000 helium and antihelium candidates identified

Helium identification efficiency around 50%

Background rejection rate up to 10^12

Abstract

The identification of helium nuclei at LHCb is achieved using a method based on measurements of ionisation losses in the silicon sensors and timing measurements in the Outer Tracker drift tubes. The background from photon conversions is reduced using the RICH detectors and an isolation requirement. The method is developed using $pp$ collision data at $\sqrt{s}=13\,{\rm TeV}$ recorded by the LHCb experiment in the years 2016 to 2018, corresponding to an integrated luminosity of $5.5\,{\rm fb}^{-1}$. A total of around $10^5$ helium and antihelium candidates are identified with negligible background contamination. The helium identification efficiency is estimated to be approximately $50\%$ with a corresponding background rejection rate of up to $\mathcal O(10^{12})$. These results demonstrate the feasibility of a rich programme of measurements of QCD and astrophysics interest involving light nuclei.