abstract

In this article, we construct the \([sc]_{\mathrm {A}}[\bar {s}\bar {c}]_{\mathrm {V}}-[sc]_{\mathrm {V}}[\bar {s}\bar {c}]_{\mathrm {A}}\)-type tensor current to study the mass and width of the \(X\)(4274) with the QCD sum rules in detail. The predicted mass \(M_{X}=(4.27\pm 0.09)\) GeV for the \(J^{PC}=1^{++}\) tetraquark state is in excellent agreement with the experimental data \(4273.3 \pm 8.3 ^{+17.2}_{-3.6}\) MeV from the LHCb Collaboration. The central value of the width \({\mit \Gamma }(X(4274)\to J/\psi \phi )=47.9\) MeV is in excellent agreement with the experimental data \(56 \pm 11 ^{+8}_{-11}\) MeV from the LHCb Collaboration. The present work supports assigning the \(X\)(4274) to be the \(J^{PC}=1^{++}\) \([sc]_{\mathrm {A}}[\bar {s}\bar {c}]_{\mathrm {V}}-[sc]_{\mathrm {V}}[\bar {s}\bar {c}]_{\mathrm {A}}\) tetraquark state with a relative \(P\)‑wave between the diquark and antidiquark constituents. Furthermore, we obtain the mass of the \([sc]_{\mathrm {A}}[\bar {s}\bar {c}]_{\mathrm {V}}-[sc]_{\mathrm {V}}[\bar {s}\bar {c}]_{\mathrm {A}}\)-type tetraquark state with \(J^{PC}=1^{-+}\) as a byproduct.

abstract

Prior proposed observing approaches using event mixing technique for the Bose–Einstein correlations (BEC) measurements in exclusive reactions with very low multiplicities are still unsatisfactory due to the problems of sample reduction and introducing extra and unnecessary fitting parameters. We propose here an event mixing method with a new mixing cut, named energy sum range (ESR) cut, to investigate the two-pion Bose–Einstein correlations in reactions with only two identical pions among three final-state particles. This mixing method employs two-pion energy sum characteristic to control the mixing procedures, with no requirement on eliminating any original events. Numerical simulations are performed to show the viability of this new BEC observing method.

abstract

Semi-classical particle rotor model calculation has been carried out for the magnetic dipole bands in \(^{60}\)Ni to understand the possible existence of the shears mechanism in this nucleus. The reduced transition probability of the magnetic dipole transitions belonging to the candidate magnetic rotational bands has been calculated. Results of the present work have been discussed in the light of the earlier theoretical works on this nucleus.

abstract

In previous papers, it was shown that in a quasi-spherical Szekeres (QSS) metric, impulses of gamma radiation can arise that have several properties in common with the observed gamma-ray bursts. This happens when the bang-time function \(t_{\mathrm {B}}(r)\) has a gate-shaped hump around the origin of the QSS region. The gamma rays arise along two preferred directions of the QSS geometry (coincident with dipole extrema when axially symmetric, otherwise unrelated). In these directions, the rays of the relic radiation are blueshifted rather than redshifted. The blueshift is generated in a thin region between the Big Bang (BB) and the extremum-redshift hypersurface (ERH). However, the Szekeres models can describe the real Universe only forward in time from the last-scattering hypersurface (LSH) because the matter in them has zero pressure. The ERH is tangent to the BB at the origin, so in a neighbourhood thereof the ERH lies earlier than the LSH and no blueshift is generated in the physical region. The question thus arose whether the BB and ERH can be “unglued” if the QSS region has no origin, but the areal radius function \({\mit \Phi }\) has a local maximum or minimum somewhere. In the present paper, it is demonstrated that this is indeed the case. If the hump in \(t_{\mathrm {B}}(r)\) is centred around the minimum of \({\mit \Phi }\), then the BB and ERH in general do not coincide there and a stronger blueshift is generated on rays passing nearby. It follows that a lower and narrower hump on the BB set can generate sufficient blueshift to move the initial frequencies of the relic radiation to the gamma range. These facts are demonstrated by numerical calculations in an explicit example of a QSS region.