The prospect of charm quark magnetic moment determination

Abstract

In this paper, we discuss the theoretical framework and the experimental measurements of the magnetic moment of the charmed baryons. We first review the theoretical predictions of the Λ + c magnetic moment and show that the measurements of the magnetic moments of other charmed baryons, such as Ξ c , allow to perform detailed spectroscopy studies. The magnetic moment of the charm quark can be determined using radiative charmonium decay, which can be compared to the Λ + c magnetic moment within theoretical models. The present results show a tension with majority of theoretical predictions. The magnetic moment of the charmed baryons could potentially be measured directly, using bentcrystal experiments at LHC. The possibility to measure precisely the magnetic moments of charmed baryons needs precise measurement of their polarisation and weak decay parameters. In this paper, we revisit the formalism of the angular analysis needed for these measurements and make a detailed evaluation of initial polarisation of deflected Λ c baryons as a function of crystal orientation. We found a special orientation of the crystal that gives the opportunity to measure the Λ c dimensionless electric dipole moment almost with the same precision as its g-factor, which is more than an order of magnitude more efficient than suggested before.

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.…”

“…With the upgraded tracking system of the LHCb detector [48,49], this resolution is about 150 µm [34], and some additional instrumentation after the crystal lens is required to achieve the needed resolution. In the scenario of a dedicated experiment to take place in a different location of the LHC ring [34][35][36]38,40], the design of the tracking system should take this into account.…”

Layouts for fixed-target experiments and dipole moment measurements of short-lived baryons using bent crystals at the LHC

“…Effects due to parity violation [42] that can lead to systematic uncertainties, can be addressed with a single crystal deflecting baryons under study. In particular, a single crystal can deflect two distinct fractions of c with positive and negative polarisation projection on the orthogonal crystallographic plane, as demonstrated in [43]. In any case, this choice has no critical impact on the studies described here and simplifies operational aspects and the overall complexity of the apparatus.…”

“…Thus, the parameters defined here represents a compromise between the ideal case and constraints given by real operations in a particle accelerator. Detailed studies on expected uncertainty on measured precession using parameters defined in this paper are reported in [43].…”

“…An increased target length with the use of germanium crystals can lead to a larger production of c and channeling efficiency, respectively. Increasing the target length from 5 mm to 40 mm and using germanium crystals can reduce the data taking time by a factor 6 and 2.4, respectively, as discussed in [43]. This is mainly due to the increased total c production in the target while keeping low detrimental effects (i.e.…”