LHCf: ready to go

Reinstalled in the tunnel at the end of 2014, the two detectors of the LHCf experiment are now ready for operation. The first data should be taken in May.


LHCf’s Arm1 detector.

The Large Hadron Collider forward (LHCf) experiment measures neutral particles emitted at nearly zero degrees from the proton beam direction. Because these "very forward" particles carry a large fraction of the collision energy, they are important for understanding the development of atmospheric air-shower phenomena produced by high-energy cosmic rays. To measure these particles, two detectors, Arm1 and Arm2, sit along the LHC beamline, at 140 metres either side of the ATLAS collision point.

In July 2010, after a 9-month operation, the LHCf collaboration removed the two detectors from the tunnel to avoid severe radiation damage. The Arm2 detector was reinstalled in the tunnel for data-taking with proton–lead collisions in 2013, while Arm1 was being upgraded to be a radiation-hard detector using gadolinium orthosilicate (Gd2SiO5) scintillators. After completion of the upgrades, the performance of the detectors was tested at the Super Proton Synchrotron fixed beam line in Prévessin in October 2014. Both Arm1 and Arm2 were then reinstalled in the LHC tunnel, on 17 and 24 November 2014 respectively.

At the beginning of 2015, LHCf restarted activity to relaunch its data-acquisition system. The experiment is now ready for the dedicated operation period, starting in May. At 13 TeV, the new energy of the LHC, the proton-proton collisions correspond to interactions in the atmosphere of cosmic rays with an energy of 0.9 × 1017 eV. This is the energy at which the origins of the cosmic rays are believed to switch from galactic to extragalactic, and a sudden change of the primary mass is expected. Based on these new highest-energy LHC data, cosmic-ray physicists expect to confirm this standard scenario.

The full version of this article is available in the January 2015 edition of the CERN Courier (Volume 55).

by CERN Bulletin