Electromagnetic dipole moment and time reversal invariance violating interactions of high energy short-lived particles in bent and straight crystals

Abstract

A particle, which moves in a crystal, experiences weak interactions with electrons and nuclei alongside with electromagnetic interaction. Measuring the polarization vector and the angular distribution of charged and neutral particles scattered by axes (planes) of an unbent (straight) crystal enables to obtain restrictions for the EDM value and for magnitudes of constants describing Todd (CP-odd) interactions Beyond the Standard Model. Spin rotation and polarization conversion from vector to tensor one and vice versa for a channelled in a crystal Ω ± hyperon enable measuring hyperon's quadrupole moment that is not possible to measure by use of laboratory available noncrystalline electric fields.

Improved experimental layout for dipole moment measurements at the LHC

“…In the proposed experiment, based on the plain-crystal scheme [14,15,[34][35][36][37], part of the protons from the LHC beam halo are deflected at an angle of about 100 µrad with a crystal kicker positioned about 100 m upstream of the target, creating a secondary beamlet within the LHC beam pipe.…”

“…A net electromagnetic field deflects their trajectory and induces the precession of the + c magnetic moment around the magnetic field, as seen in the reference frame of the particle. Any change on the polarization in the perpendicular direction to the main precession, i.e around electric field, signals the presence of a nonzero EDM, at least at the sensitivity level of the planned experiments [37]. At the crystal exit, these + c particles reach an angle with respect to the proton beam sufficient for its decay products to enter in the detector acceptance, whereas other products of the proton-target interactions are produced in the forward direction, and are contained within the LHC beam pipe.…”

“…The spread of particle directions at the crystal exit would allow to precisely determine the channel of each particle due to the excellent angular resolution on these events [34]. This would also allow to determine the initial x component of the + c polarization for each event [36,37] (defined as the direction perpendicular to the plane of magnetic precession, see e.g. Ref.…”

Improved experimental layout for dipole moment measurements at the LHC

“…In the proposed experiment, based on the plain-crystal scheme [12,13,[32][33][34][35], part of the protons from the LHC beam halo are deflected by O(100 µrad) with a crystal kicker positioned about 100 m upstream of the target, creating a secondary beamlet within the LHC beam pipe. Accurate simulations of the beam optics project these protons to be about 4 mm away from the main beam when they arrive to the fixed-target setup [36], positioned either before the LHCb detector or at the IR3 interaction region, in a future dedicated experiment.…”

“…A net electromagnetic field deflects their trajectory and induces the precession of the Λ + c magnetic moment around the magnetic field, as seen in the reference frame of the particle. Any change on the polarization in the perpendicular direction to the main precession, i.e around electric field, signals the presence of a nonzero EDM, at least at the sensitivity level of the planned experiments [35]. At the crystal exit, these Λ + c particles reach an angle with respect to the proton beam sufficient for its decay products to enter in the detector acceptance, whereas other products of the proton-target interactions are produced in the forward direction, and are contained within the LHC beam pipe.…”