Abstract
The flux of cosmic ray antiprotons is a powerful tool for indirect detection of dark matter. The sensitivity is limited by the uncertainty on the predicted antiproton flux from scattering of primary rays on the interstellar medium. This is, in turn, limited by the knowledge of production cross‐sections, notably in p–He scattering. Thanks to its internal gas target, the LHCb experiment performed the first measurement of antiproton production from collisions of LHC proton beams on He nuclei at rest. The results and prospects are presented.
Highlights
The flux of cosmic ray antiprotons is a powerful tool for indirect detection of dark matter
The LHCb detector (Alves et al 2008) is a single-arm forward spectrometer covering the pseudorapidity range 2 < η < 5, designed for the study of particles containing b or c quarks, which are predominantly produced at high η in p–p collisions at the Large Hadron Collider (LHC)
The forward geometry and excellent vertexing, tracking, and particle identification (PID) capabilities (Aaij et al 2015), which are key features for the reconstruction of heavy flavor decays, make it an ideal tool to study interactions of the LHC beams with a fixed target. Such a target is provided by the SMOG (System for Measuring Overlap with Gas) device (Barschel 2014), through which tiny amounts of a noble gas (He, Ne, Ar) can be injected inside the primary LHC vacuum around the LHCb vertex detector (VELO)
Summary
Particles with negative charge in the kinematic range of interest were selected after applying quality requirements on the reconstruction of the track and of the collision primary vertex (PV). The reconstruction efficiency for prompt antiprotons, determined in three-dimensional bins of p, pT, and z, ranges from 40% to 80%. Antiprotons were identified through the response of the RICH detectors, from which two variables are built, DLL(p − π) and DLL(p − K), representing the difference of the log likelihood between the proton and pion and the proton and kaon hypotheses, respectively. The fraction of antiprotons among the negative tracks was determined from a two-dimensional extended binned maximum likelihood fit to the DLL variable distributions, where templates for the different particle species were obtained from calibration samples in data and simulation. The DLL distributions for data and calibration samples, illustrating the RICH performance, are shown in Figure 1 for an arbitrary kinematic bin
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