During the night, at 1:30 am, LHCb recorded the first proton-lead ion collisions at the LHC. The proton-lead physics data taking is planned to take place in January and February 2013. Today the LHC operational team made tests of collisions in order to prepare the set-up of the LHC collider and the LHC experiments for next year. Note that collisions of protons with lead ions are more difficult than proton-proton or lead-lead collisions. In fact the speed of protons and lead ions is slightly different, even though it is close to the speed of light at LHC. The LHC operators succeeded in making the proton path length inside LHC ring slightly longer than the lead-ion path length in order to compensate for this difference.
click the image for higher resolution
A typical proton-lead collision event at LHCb is shown in the left image above. Note that the lead ions arrive at the LHCb collision point from the right hand side and the protons from the left hand side. The right image shows the invariant mass spectrum of the decay products of Λ and Λ particles indicating excellent prospects for physics analysis of p-lead collision data early next year.
Read also the CERN Courier article.