Very Forward Calorimetry at the LHC - Recent results from ATLAS

TL;DR

This paper reports initial results from the ATLAS Zero Degree Calorimeters at the LHC, demonstrating their capability to measure forward neutral particles with high energy resolution and reconstruct pi0's and neutrons in proton-proton collisions.

Contribution

It introduces the first measurements from the ATLAS ZDC, showcasing its unique ability to image electromagnetic and hadronic showers at the LHC.

Findings

Reconstructed pi0's with energies of 0.7-3.5 TeV.

Achieved good time-of-flight resolution for neutrons.

Demonstrated ZDC's coverage of forward neutral particles.

Abstract

We present first results from the ATLAS Zero Degree Calorimeters (ZDC) based on 7~TeV pp collision data recorded in 2010. The ZDC coverage of +/-~350 microradians about the forward direction makes possible the measurement of neutral particles (primarily pi0's and neutrons) over the kinematic region x_F >~0.1 and out to p_T<~ 1.2 GeV/c at large x_F. The ATLAS ZDC is unique in that it provides a complete image of both electromagnetic and hadronic showers.This is illustrated with the reconstruction of pi0's with energies of 0.7-3.5 TeV. We also discuss the waveform reconstruction algorithm which has allowed good time-of-flight resolution on leading neutrons emerging from the collisions despite the sparse (40 MHz) sampling of the calorimeter signals used.