Search for Fractional Charges in Niobium and Tungsten

Abstract

We have searched in niobium and tungsten for fractionally charged particles with effective nuclear charge Z = 7V+y (where TV = 0,1,2,3, . . .). In addition, we have looked for fractionally charged particles with Z concentration limits are reported.j-and y in the same materials. No positive signal was observed, and PACS numbers: 14.80. Dq, The reported observation 1 of fractional charge on superconducting niobium spheres has stimulated much experimental 2,3 and theoretical 4,5 work in the past few years. Aside from Ref. 1, the experiments that search in niobium 2 all assumed that the fractionally charged particles (FCP) will diffuse out of the sample as a positive ion when the sample is heated. The efficiency of this diffusion process is difficult to estimate. The effects observed by the authors of Ref. 1 could imply the existence of fractional charges (modulo \e) at a concentration level of 2xlO~1 8 /Nb atom, and possibly that the fractional charge is transferred from tungsten during annealing of the niobium sample. Since most of the residual charges observed corresponded to + \e (rather than -}e) a fractionally charged particle with an effective nuclear charge of Z = TV 4-y (where 7V = 0, 1,2,3,. . .) is more likely than those with Z = N+\. We define the quantity Z as the charge that would remain on the FCP if all of the atomic electrons were removed.We have performed an experimental search to test this hypothesis, and report the initial results in this Letter. Our technique is sensitive to FCP with Z = JV+| (7V = 0,1,2,3, . . .) which would form negative ions of charge -y, as well as FCP with Z = y or y which would form negative ions of charge -y. A detailed paper describing the apparatus and technique will be published elsewhere.The method we employed involves four steps (see Fig. 1): (a) extraction of the FCP from the host sample and formation of a negative ion (see below); (b) acceleration of negative FCP and stripping of an electron in a tandem electrostatic accelerator; (c) deflection of the (now positively charged) FCP in a transverse electric field; and (d) measurement of the kinetic energy in a particular detector. The acceleration and deflection of nonrelativistic charged particles from rest in purely electrostatic fields yields trajectories which are mass independent (stray magnetic fields and relativistic effects limit our sensitivity to FCP with mass > 200 MeV/c 2 ). The efficiency for the transmission of particles through the accelerator to a particular final charge state is primarily determined by the stripping efficiency, which drops off for masses greater than several hundred GeV/c 2 . The transmission efficiencies and mass independence of trajectories were determined by use of integrally charged ion beams (1 GeV/c 2 < m < 200 GeV/c 2 ) from both the FCP source and a conventional sputter ion source.The charge measurement results from steps (c) and (d).Step (c) selects ions with the desired ratio of kinetic energy to charge (the "electric rigidity") to an FCP sputter source , charge exchange cana...

A relativistic two-nucleon model for reaction

“…This reflects directly the nature of the Dirac spinors for the bound states which involve several maxima in the region of large momentum transfer. In case of the light target 4 He, however, the differential cross section still peaks near the zero degree as in this case the momentum transfers are in the region where the bound state spinors are smoothly decreasing with momentum. The energy dependence of the calculated total production cross section follows closely that of the pp → pΛK + reaction.…”

“…In summary, we have made a study of the A(p, K + ) Λ B reaction on 4 He, 12 C, and 40 Ca targets within a fully covariant general two-nucleon mechanism where in the initial collision of the incident proton with one of the target nucleons, N * (1710), N * (1650), and N * (1720) baryonic resonances are excited which subsequently propagate and decay into the relevant channel. The initial nucleonnucleon collisions are mediated by pion and also by rho and omega exchange mechanisms.…”

“…The value of the parameter α is taken to be 1.61 fm, 2.37 fm and 3.52 fm for 4 He, 12 C and 40 Ca targets, respectively [61]. In Table 3, we show the values of the total attenuation |S(E)| 2 for the three targets discussed in this paper.…”

“…Λ hypernuclei are the most familiar hypernuclear systems which have been studied extensively by stopped as well as in-flight (K − , π − ) reaction [1,2,3] and also by (π + , K + ) reaction [4,5]. The kinematical properties of the (K − , π − ) reaction allow only a small momentum transfer to the nucleus (at forward angles), thus there is a large probability of populating Λ-substitutional states (Λ assume the same orbital angular momentum as that of the neutron being replaced by it).…”

Hypernuclei

“…In associated production, a non-strange particle hits a nucleon and creates a hyperon (S = -1) and a meson K+ (S = + 1). An example of such a process is the reaction: π + + η -K+ + Λ (1) which has been used very efficiently at Brookhaven National Laboratory, USA, to produce A-hypernuclear states [4].…”