Feasibility study to characterize the production of antineutrons in high energy pp collisions through charge exchange interactions

Abstract

Simulations to evaluate the feasibility of antineutron identification and kinematic characterization via the hadronic charge exchange (CEX) interaction n+n¯→p+p¯ are reported. The target neutrons are those composing the silicon nuclei of which inner tracking devices present in the Large Hadron Collider experiments ALICE, ATLAS, and CMS. Simulations of pp collisions in PYTHIA were carried out at different energies to investigate n¯ production and energy spectra. These simulations produced a decreasing power-law n¯ energy spectra. Then, two types of GEANT4 simulations were performed, placing an n¯ point source at the ALICE primary vertex, as a working example. In the first simulation, the kinetic energy E _k was kept at an arbitrary (1 GeV) fix value to develop an n¯ identification and kinematics reconstruction protocol. The second GEANT4 simulation used the resulting PYTHIA at spp=13 TeV n¯ energy spectra. In both GEANT4 simulations, the occurrence of CEX interactions was identified by the unique outgoing p¯ . The simplified simulation allowed to estimate a 0.11% CEX-interaction identification efficiency at E _k = 1 GeV. The p CEX-partner identification is challenging because of the presence of silicon nucleus-fragmentation protons. Momentum correlations between the n¯ and all possible p¯p pairs showed that p CEX-partner identification and n¯ kinematics reconstruction corresponds to minimal momentum-loss events. The use of inner tracking system dE/dx information is found to improve n¯ identification and kinematic characterization in both GEANT4 simulations. The final protocol applied to the realistic GEANT4 simulation resulted in a n¯ identification and kinematic reconstruction efficiency of 0.006%, based solely on p¯p pair observable. If applied to the ALICE minimum-bias RUN2 pp at spp=13 TeV data sample, this technique is found to have the potential to identify and reconstruct the kinematics of 4.3×108n¯ 's, illustrating the feasibility of the method.