2013
Beam Conditions Monitor – ATLAS safety & luminosity
by
→
Pacific/Honolulu
417A (Watanabe hall)
417A
Watanabe hall
Description
Beam conditions and the potential detector damage resulting from their
anomalies have pushed the LHC experiments to implement their own
monitoring devices. In ATLAS the role of beam protection is handled by
the Beam Conditions Monitor (BCM). It is aimed at resolving background
from collision particles by sub-ns time-of-flight measurement. It uses
16 1×1 cm^2 0.5 mm thick polycrystalline chemical vapor deposition
(pCVD) diamond sensors arranged in 8 positions at a radius r ≈ 55 mm, ∼
1.9 m up- and down- stream the interaction point. Time measurements at
2.56 GHz sampling rate are performed to distinguish between collision
and shower particles from beam incidents. A FPGA-based readout system
performs real-time data analysis and interfaces the results to ATLAS and
the LHC systems. The system was employed in various modalities from the
first physics LHC run in November 2009, and is adapting its performance
to balance between the need to protect the sensitive ATLAS Inner
Detector, and yet allow efficient operation of the collider. Though
initially designed as a safety system its properties make it well suited
also for physics measurements. Its appropriate acceptance, timing
performance and data-purity have been exploited further by extending the
system into a luminosity monitoring device. Though secondary
functionality, this has proved to provide even bigger contribution to
the ATLAS experiment.
In the presentation the diamond sensors, the detector modules and their
readout system will be described. Results of performance with LHC beams
will be given, showing timing separation of collisions from beam related
background. On this basis the beam-abort system will be presented and
appropriate algorithms discussed. In the second part the focus will turn
to luminosity infrastructure, calibration and final measurement results.