Title: AFTER @ LHC: A Fixed Target ExpeRiment on the LHC beams

Speaker: Prof. Jean-Philippe Lansberg (IPNO - Paris-Sud U. - CNRS/IN2P3)

Time: 10:00AM, March 1st (Thursday)

Place: Theory Division，319

Abstract: We discuss the possibility of the conception of a multi-purpose fixed-target experiment with the proton or lead ion LHC beams extracted by bent crystals. As simple as it seems, the multi-TeV LHC beams will allow for the most energetic fixed-target experiments ever performed. Such an experiment, tentatively named AFTER for A Fixed-Target ExperRiment, gives access to new domains of particle and nuclear physics complementing that of collider experiments, in particular that of Brookhaven’s Relativistic Heavy Ion Collider (RHIC) and the projects of Electron-ion colliders (EIC). We have already evaluated that the instantaneous luminosity achievable with AFTER using typical targets would surpass that of RHIC by more than 3 orders of magnitude. Beam extraction by bent crystals off ers an ideal way to obtain a clean and very collimated high-energy beam, without decreasing the performance of the LHC. This technique is now becoming mature with successful tests at SPS (450 GeV) and at the Tevatron (900 GeV) and with future tests at the LHC (3.5 or 7 TeV). The fixed-target mode also has the advantage to allow for spin measurements with polarized target and for an access over the full backward rapidity domain up to xF ~-1.

The aim of such an experiment is to perform novel studies of rare configurations of the proton wave function which contain gluon or heavy-quarks with high momentum fraction; the gluon content in the deuteron and neutron in a wide momentum-fraction range; the correlation between the proton spin and the gluon angular momentum through the Sivers e ect and novel spin correlations; the production of W and Z bosons in their threshold domain; the deconfinement dynamics in the target-rest frame in heavy-ion collisions and the melting of excited heavy-quark bound states in the deconfined QCD phase; the nucleus structure function for momentum fractions close to and above unity; and ultra-peripheral collisions in a fixed-target mode. In this seminar, we will focus on the physics part related to quarkonia in pp, pd, pA and AA collisions.