Abstract
Electromagnetic dipole moments of short-lived particles are sensitive to physics within and beyond the Standard Model of particle physics but have not been accessible experimentally to date. To perform such measurements it has been proposed to exploit the spin precession of channeled particles in bent crystals at the LHC. Progress that enables the first measurement of charm baryon dipole moments is reported. In particular, the design and characterization on beam of silicon and germanium bent crystal prototypes, the optimization of the experimental setup, and advanced analysis techniques are discussed. Sensitivity studies show that first measurements of $\Lambda_c^+$ and $\Xi_c^+$ baryon dipole moments can be performed in two years of data taking with an experimental setup positioned upstream of the LHCb detector.
Highlights
Electromagnetic dipole moments are static properties of particles that are sensitive to physics within and beyond the Standard Model (SM) of particle physics
An experimental setup based on bent crystals and a W target placed upstream of the LHCb detector is studied
The germanium crystal provides enhanced sensitivity to magnetic dipole moment (MDM) and electric dipole moment (EDM) compared to the silicon crystal, especially when cooled down at 77 K [19]
Summary
Electromagnetic dipole moments are static properties of particles that are sensitive to physics within and beyond the Standard Model (SM) of particle physics. By exploiting the phenomenon of particle channeling in bent crystals, the electric and magnetic dipole moments of short-lived particles can be measured by studying the spin precession induced by the intense electric field between the crystal atomic planes, first proposed by Baryshevsky in 1979 [24]. The Λþc and Ξþc charm baryons, produced by interactions of the 7 TeV LHC proton beam on a fixed target, are allowed to have initial polarization perpendicular to the production plane, due to parity symmetry conservation in strong interactions. A germanium crystal allows for enhanced sensitivity to MDM and EDM with respect to the silicon crystal [18,29] due to the higher electric field between crystal atomic planes. The main improvements with respect to previous studies [18] include a full amplitude analysis for optimal determination of baryon polarization, a more realistic polarization model [19], an optimized target thickness, CRYSTALRAD Monte Carlo simulations for particle channeling for cryogenic temperatures [30], and additional charm baryon decay modes
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