First Experimental Determination of the Charge Radius ofRb74and Its Application in Tests of the Unitarity of the Cabibbo-Kobayashi-Maskawa Matrix

Abstract

Collinear-laser spectroscopy with bunched-beams technique was used for the study of neutron deficient Rb isotopes, out to 74 Rb (N = Z = 37) at TRIUMF. The measured hyperfine coupling constants of 76,78m Rb were in agreement with literature values. The nuclear spin of 75 Rb was confirmed to be I = 3/2, and its hyperfine coupling constants were measured for the first time. The mean-square charge radius of 74 Rb was determined for the first time. This result has improved the isospin symmetry breaking correction term used to calculate the Ft value, with implications for tests of the unitarity of the Cabibbo-Kobayashi-Maskawa matrix.The unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix is one of the cornerstones of the Standard Model of particles and fields. Therefore, the value of all its matrix elements should be measured as accurately and as precisely as possible for the search of new physics phenomena, such as the existence of right-handed currents, extra Z bosons or another quark generation [1]. Indeed, over the years, the value of these matrix elements have been independently determined from different experiments. Superallowed Fermi transitions of nuclear beta decays (0 + → 0 + ) provide the most competitive method to determine the up-down quark matrix element V ud [2]. Assuming the Conserved Vector Current (CVC) hypothesis, which states that the vector coupling constant of semileptonic weak interactions G V remains unchanged in all superallowed beta transitions, this matrix element can be obtained from V ud = G V /G F , where G F is the weak interaction constant for leptonic muon decay, and G V is defined in terms of the corrected F t value of the beta decay [3],.The f t value is related to the measured half-lives, branching ratios and the Q value of the beta decay. The terms δ ′ R and δ N S are transition-dependent theoretical corrections, and δ C is the isospin symmetry breaking term [4]. The latter is purely nuclear structure dependent, the error of which normally dominates the uncertainty on the F t value. The term ∆ V R is transition-independent and K is a constant. Evaluations of the isospin symmetry breaking correction involve the 13 most precisely measured superallowed beta emitters which span a wide Z range (6 ≤ Z ≤ 37) [4]. Within the existing theoretical approaches used to determine δ C [5] the leading source of uncertainty stems from the incomplete knowledge of the radial extension of the charge distribution of the parent and daughter isotopes. Where experimental data are unavailable, the nuclear structure input is based on extrapolations of the existing models. For the lighter elements, shell model calculations with a Saxon-Woods potential provide a more consistent framework from which this information can be reliably extracted. However, with higher Z, the orbitals of the f p shell are filled and shell model calculations become computationally difficult, due to the larger model space required. In addition, effective interactions become less reliable [6]. There have been many theoretical ef...

Superallowed0+→0+nuclearβdecays: 2014 critical survey, with precise results forVud

“…18 Ne, 34 Ar and 38m K. In addition, more recently, collinear-laser spectroscopy on the neutron-deficient Rb isotopes enabled the charge radius of 74 Rb to be determined from its hyperfine splitting [198]. For these four cases, therefore, we have recomputed the δ C2 correction.…”

Precision mass measurements at TITAN with radioactive ions

“…Unlike for other beam cooler and bunchers at ISOLTRAP [18], LEBIT [19], JYFLTRAP [20], or SHIPTRAP [21], the RF for the TITAN RFQ is generated with a digital driver to permit higher RF amplitudes and therefore a larger space-charge limit. The TITAN RFQ has additional symmetry to permit not only forward extraction of the bunched beam to subsequent ion traps but also reverse extraction to other experiments, most notably the collinear laser spectroscopy experiment [22]. In forward extraction, SCI are transported at variable energy, typically 2 keV, either directly to the measurement Penning trap for the mass measurement or to the EBIT for charge breeding.…”

Laser spectroscopy of radioactive isotopes: Role and limitations of accurate isotope-shift calculations

“…These nuclei are produced at radioactive ion beam facilities and the spectroscopy is performed in situ. Two common forms exist: the "collinear beams" method [17,22,27,28], which achieves the highest precision, and the "insource" method [29,30] which is currently applicable to lower atom fluxes. One or the other is generally used and these are discussed below, with a schematic overview in Fig.…”

“…In addition, the migration of the energy gaps themselves, with a proton or neutron number, is of interest as it gives information on the internucleon interactions. Halo structure [20], parity nonconservation [21], and unitarity tests of the Cabibbo-Kobayashi-Maskawa (CKM) matrix [22] are all phenomena where δ r 2 plays a key role.…”