Nuclear Theory·nucl-th

Wednesday·May 20, 2020

7 papers—3 primary·4 cross-listed

04
Rare two-body decays of the top quark into a bottom meson plus an up or charm quark
David d'Enterria🇨🇭 · Hua-Sheng Shao🇫🇷
Rare two-body decays of the top quark into a neutral bottom-quark meson plus an up- or charm-quark: $t \to B^{0} + u, c$ ; $t \to B_{s}^{0} + c, u$ ; and $t \to Υ (n S) + c, u$ , are studied for the first time. The corresponding partials widths are computed at leading order in the non-relativistic QCD framework. The sums of all two-body branching ratios amount to $B (t \to B^{0} + jet) \approx B (t \to B_{s}^{0} + jet) \approx 4.2 \cdot 1 0^{- 5}$ and $B (t \to Υ (n S) + jet) \approx 2 \cdot 1 0^{- 9}$ , respectively. The feasibility to observe the $t \to B_{(s)}^{0} + jet$ decay is estimated in top-pair events produced in proton-proton collisions at $s = 14, 100$ TeV at the LHC and FCC, respectively. Combining many exclusive hadronic $B_{(s)}^{0}$ decays, with $J / ψ$ or $D^{0, \pm}$ final states, about 50 (16000) events are expected in 3 (20) ab $^{- 1}$ of integrated luminosity at the LHC (FCC), after typical selection criteria, acceptance, and efficiency losses. An observation of the two-body top-quark decay can also be achieved in the interesting $t \to b (jet) + c (jet)$ dijet final state, where the $B_{(s)}^{0}$ decay products are reconstructed as a jet, with 5300 and 1.4 million signal events above backgrounds expected after selection criteria at the LHC and FCC, respectively. Such unique final states provide a new direct method to precisely measure the top-quark mass via simple 2-body invariant mass analyses.
↳ hep-phhep-exnucl-thJHEP(2020)·3 citations
05
Polarization in low energy kaon-hyperon interaction
Marcelo G. L. Nogueira-Santos🇧🇷 · Celso C. Barros Jr🇧🇷
In this paper, we study the low energy kaon-hyperon interaction considering effective chiral Lagrangians that include kaons, $σ$ mesons, hyperons and the corresponding resonances. The scattering amplitudes are calculated and then we determine the angular distributions and polarizations.
↳ hep-phnucl-thIJMPE(2020)·7 citations
06
A two-neutron halo is unveiled in $^{29}$ F
S. Bagchi🇨🇦 · R. Kanungo🇨🇦 · Y. K. Tanaka🇨🇦 · H. Geissel🇩🇪 · P. Doornenbal🇯🇵 · W. Horiuchi🇯🇵 · G. Hagen🇺🇸 · T. Suzuki🇯🇵 · N. Tsunoda🇯🇵 · D. S. Ahn🇯🇵 · H. Baba🇯🇵 · K. Behr🇩🇪 and 35 other authors
We report the measurement of reaction cross sections ( $σ_{R}^{ex}$ ) of $^{27, 29}$ F with a carbon target at RIKEN. The unexpectedly large $σ_{R}^{ex}$ and derived matter radius identify $^{29}$ F as the heaviest two-neutron Borromean halo to date. The halo is attributed to neutrons occupying the $2 p_{3/2}$ orbital, thereby vanishing the shell closure associated with the neutron number $N = 20$ . The results are explained by state-of-the-art shell model calculations. Coupled-cluster computations based on effective field theories of the strong nuclear force describe the matter radius of $^{27}$ F but are challenged for $^{29}$ F.
↳ nucl-exnucl-thPRL(2020)·96 citations
07
Forward doubly-virtual Compton scattering off the nucleon in chiral perturbation theory: the subtraction function and moments of unpolarized structure functions
Jose Manuel Alarcón (Universidad Complutense de Madrid)🇪🇸 · Franziska Hagelstein (AEC Bern)🇨🇭 · Vadim Lensky🇩🇪 · Vladimir Pascalutsa (JGU Mainz)🇩🇪
The forward doubly-virtual Compton scattering (VVCS) off the nucleon contains a wealth of information on nucleon structure, relevant to the calculation of the two-photon-exchange effects in atomic spectroscopy and electron scattering. We report on a complete next-to-leading-order (NLO) calculation of low-energy VVCS in chiral perturbation theory ( $χ$ PT). Here we focus on the unpolarized VVCS amplitudes $T_{1} (ν, Q^{2})$ and $T_{2} (ν, Q^{2})$ , and the corresponding structure functions $F_{1} (x, Q^{2})$ and $F_{2} (x, Q^{2})$ . Our results are confronted, where possible, with "data-driven" dispersive evaluations of low-energy structure quantities, such as nucleon polarizabilities. We find significant disagreements with dispersive evaluations at very low momentum-transfer $Q$ ; for example, in the slope of polarizabilities at zero momentum-transfer. By expanding the results in powers of the inverse nucleon mass, we reproduce the known "heavy-baryon" expressions. This serves as a check of our calculation, as well as demonstrates the differences between the manifestly Lorentz-invariant (B $χ$ PT) and heavy-baryon (HB $χ$ PT) frameworks.
↳ hep-phhep-latnucl-exnucl-th+1PRD(2020)·18 citations

Affiliations

first authorsco-authorsvia INSPIRE

Rare two-body decays of the top quark into a bottom meson plus an up or charm quark

Polarization in low energy kaon-hyperon interaction

A two-neutron halo is unveiled in 29F

Forward doubly-virtual Compton scattering off the nucleon in chiral perturbation theory: the subtraction function and moments of unpolarized structure functions

Affiliations

A two-neutron halo is unveiled in $^{29}$ F