Level-1 trigger rate from beam halo muons in the end-cap

Previous detectors at $p$-$\bar{p}$ machines have experienced problems with high muon trigger rates in the forward region due to muons produced in interactions between the beam and the machine. The se `beam halo' muons typically have a very small angle to the beam direction, and are dominated by muons of several GeV energy and at low radius relative to the beam line. The response of the ATLA S end-cap muon trigger to them has been investigated using a complete simulation of both the LHC machine components and the ATLAS detector and trigger. It is seen that the total flux of such muon s in the end-cap trigger counters is $\sim$ 60 kHz, in high luminosity LHC running, and the acceptance of the Level-1 end-cap muon trigger to these particles is $\sim$1\%. The overall Level-1 trig ger rate from such muons will be small compared to rates from the products of the $p$-$p$ collision. The total rates from low- and high-\pt triggers at 6 and 20 GeV are 250 and 16 Hz respectively. Whilst these rates are negligible in comparison with the total rate from the Level-1 muon system, they are sufficient to enable such triggers to be used for calibration and alignment purposes.