First observation of magnetic moment precession of channeled particles in bent crystals

Abstract

Spin precession of channeled particles in bent crystals has been observed for the first time. Polarized I"*" were channeled using bent Si crystals. These crystals provided an effective magnetic field of 45 T which resulted in a measured spin precession of 60° ±17°. This agrees with the prediction of 62° ± 2° using the world average of Z"*" magnetic moment measurements. This new technique gives a I"*" magnetic moment of (2.40 ± 0.46 ± 0.40)/X7v, where the quoted uncertainties are statistical and systematic, respectively. We see no evidence of depolarization in the channeling process. PACS numbers: 13.40.Fn, 14.20.Jn, 61.80.MkChanneling of high-energy particles in bent crystals has been observed in the momentum range [1-5] of 1.7-800 GeV/c. This technique has already found applications [3][4][5] in the deflection of high-energy beams. Another possibly important application of channeling is the precession of the spin of a polarized particle. This may allow the measurement of magnetic moments in distances of only a few cm. The lifetimes [6] of baryons containing charm quarks are so short that they travel only a few centimeters even at the highest available accelerator energies. Because of these short lifetimes, classical spin precession techniques using conventional magnets would produce negligibly small spin precession angles.It was pointed out by Baryshevskii [7] and Pondrom [8] that the magnetic moments of particles should precess if they were channeled in a bent crystal. The detailed precession theory has been developed by Lyuboshits [9] and Kim [10]. In a curved crystal the electrostatic field of the atomic planes deflecting the particle transforms into a magnetic field in the particle's rest frame. Thus the spin precession angle ^ is [9] <P = r<o^g-2)/2 forr»l, (1) where / is the Lorentz factor, g is the gyromagnetic ratio, and ft) is the deflection angle of the channeled particle. From a measurement of ^ and (o of the channeled particle, we can determine g and hence the particle's magnetic moment,where e, m, and S are the charge, mass, and spin of the particle, respectively. We expect [11] that channeling could be preserved for equivalent magnetic fields up to ^ 1000 T, thus off*ering the potential of significant precession angles even when the length of the bent crystal is as small as I cm.Modern hyperon beams [12] provide a tool for testing this concept [13]. Using a beam of polarized 1"*" hyperons, we measured their spin precession in bent Si single crystals. With this result we determine the IL^ magnetic moment. The measurements [14] were performed as part of Fermilab experiment E761 which was designed to measure the asymmetry parameter [15] in the decay of polarized I"*" -/?/, Figure 1(a) shows the relevant parts of the E761 apparatus [14,15] used in these measurements. The same components were used as in the asymmetry-parameter measurement [15] but some of the relative spacings were changed. The apparatus consists of a hyperon spectrometer (one dipole magnet and three 3286

Feasibility of measuring the magnetic dipole moments of the charm baryons at the LHC using bent crystals

“…Because of the extremely short lifetime of charmed baryons in comparison with the Σ + hyperon, in our case it is not possible to prepare a beam of polarized baryons in advance and to measure the degree of their initial polarization, as was done in the Fermilab experiment [42]. In our case, as explained below, the crystal could be used as a beam collimator.…”

“…The first experimental realization of such method was carried out in Fermilab [42] at the 800 GeV proton beam. The strange Σ + (uus) baryons (with lifetime 0.8×10 −10 s) produced on the Cu target had average momentum 375 GeV/c and the absolute value of polarization (12 ± 1) %.…”

Channeling of high-energy particles in bent crystals – Experiments at the CERN SPS

“…So, since the distance over which it will precess through a given angle in a crystal is drastically shortened compared to in a magnet, one may use this eect to measure magnetic moments of shortlived particles. This eect has been used in a proof-of-principle experiment to measure the magnetic moment of the R [89], a hyperon with l 2X46l N and a short lifetime in its rest-system, cs 2X4 cm [90], see also [91].…”

Spin rotation and oscillations of high energy particles in a crystal and possibility to measure the quadrupole moments and tensor polarizabilities of elementary particles and nuclei

“…Nowadays this effect has been experimentally discovered [4,5,6]. It has been also shown that the similar experiments are beneficial for measuring the magnetic moments of short-lived particles [7] and, particularly, Λ c particle [8].…”