Tue·Feb 2, 2021Tuesday·February 2, 2021

1. 01*

   Direct Measurements of Neutrino Mass

   Joseph A. Formaggio🇺🇸 · André Luiz C. de Gouvêa🇺🇸 · R. G. Hamish Robertson🇺🇸

   The turn of the 21st century witnessed a sudden shift in our fundamental understanding of particle physics. While the minimal Standard Model predicts that neutrino masses are exactly zero, the discovery of neutrino oscillations proved the Standard Model wrong. Neutrino oscillation measurements, however, do not shed light on the scale of neutrino masses, nor the mechanism by which those are generated. The neutrino mass scale is most directly accessed by studying the energy spectrum generated by beta decay or electron capture -- a technique dating back to Enrico Fermi's formulation of radioactive decay. In this Article, we review the methods and techniques -- both past and present -- aimed at measuring neutrino masses kinematically. We focus on recent experimental developments that have emerged in the past decade, overview the spectral refinements that are essential in the treatment of the most sensitive experiments, and give a simple yet effective protocol for estimating the sensitivity. Finally, we provide an outlook of what future experiments might be able to achieve.

   nucl-exhep-phPhys.Rept.(2021)·149 citations
2. 02*

   The mass radius of the proton

   Dmitri E. Kharzeev🇺🇸

   The mass radius is a fundamental property of the proton that so far has not been determined from experiment. Here we show that the mass radius of the proton can be rigorously defined through the formfactor of the trace of the energy-momentum tensor (EMT) of QCD in the weak gravitational field approximation, as appropriate for this problem. We then demonstrate that the scale anomaly of QCD enables the extraction of the formfactor of the trace of the EMT from the data on threshold photoproduction of $J/\psi$ and ${\rm Y}$ quarkonia, and use the recent GlueX Collaboration data to extract the r.m.s. mass radius of the proton ${\mathrm{R}}_{\mathrm{m}}=0.55\pm 0.03\mathrm{fm}$. The extracted mass radius is significantly smaller than the charge radius of the proton ${\mathrm{R}}_{\mathrm{C}}=0.8409\pm 0.0004\mathrm{fm}$. We attribute this difference to the interplay of asymptotic freedom and spontaneous breaking of chiral symmetry in QCD, and outline future measurements needed to determine the mass radius more precisely.

   ↳ hep-phhep-latnucl-exnucl-thPRD(2021)·143 citations
3. 03*

   Dibaryon with highest charm number near unitarity from lattice QCD

   Yan Lyu🇨🇳 · Hui Tong🇨🇳 · Takuya Sugiura🇯🇵 · Sinya Aoki🇯🇵 · Takumi Doi🇯🇵 · Tetsuo Hatsuda🇯🇵 · Jie Meng🇨🇳 · Takaya Miyamoto🇯🇵

   A pair of triply charmed baryons, ${\Omega }_{ccc}{\Omega }_{ccc}$, is studied as an ideal dibaryon system by (2+1)-flavor lattice QCD with nearly physical light-quark masses and the relativistic heavy quark action with the physical charm quark mass. The spatial baryon-baryon correlation is related to their scattering parameters on the basis of the HAL QCD method. The ${\Omega }_{ccc}{\Omega }_{ccc}$ in the ${}^1{S}_0$ channel taking into account the Coulomb repulsion with the charge form factor of ${\Omega }_{ccc}$ leads to the scattering length $a_0^{\mathrm{C}}\simeq -19\text{fm}$ and the effective range $r_{\mathrm{eff}}^{\mathrm{C}}\simeq 0.45\text{fm}$. The ratio $r_{\mathrm{eff}}^{\mathrm{C}}/a_0^{\mathrm{C}}\simeq -0.024$, whose magnitude is considerably smaller than that of the dineutron ($-0.149$), indicates that ${\Omega }_{ccc}{\Omega }_{ccc}$ is located in the unitary regime.

   ↳ hep-lathep-exhep-phnucl-ex+1PRL(2021)·94 citations
4. 04*

   Energy and mass dependencies for the characteristics of $p_T$ regions observed at LHC energies

   Mais Suleymanov🇦🇿

   The $p_T$ distributions of the $K^0$- and $\varphi$ - mesons produced in the $pp$ collisions at $\sqrt{s}=2.76TeV$ have been analyzed by fitting them using the exponential function. It was observed that the distributions contain several $p_T$ regions similar to the cases with the charged particles, ${\pi }^0$- and $\eta$- mesons produced in the same events. These regions could be characterized using three variables: the length of the region $L_K^c$ and free fitting parameters $a_K^c$ and $b_K^c$. It was observed that the values of the parameters as a function of energy grouped around certain lines and there are jump-like changes. These observations together with the effect of existing the several $p_T$ regions can say on discrete energy dependencies for the $L_K^c$ , $a_K^c$ and $b_K^c$. The lengths of the regions increase with the mass of the particles. This increase gets stronger with energy. The mass dependencies of the parameters $a_K^c$ and $b_K^c$ show a regime change at a mass $\simeq 500MeV/c^2$. According to the phenomenology of string theory, these results could be explained by two processes occurring simultaneously: string hadronization and string breaking. In the experiment we can only measure the spectrum of the hadronized particles, since we cannot access the spectrum of the strings themselves. The string breaking effect could be a signal of string formations and the reason behind the observation of several $p_T$ regions and the jump-like changes for the characteristics of the regions.

   ↳ hep-phnucl-exPhys.Part.Nucl.(2023)·4 citations
5. 05*

   Antikaon-induced $K_1(1270{)}^{+}$ meson production on nuclei near threshold

   E. Ya. Paryev🇷🇺

   We study the inclusive strange axial-vector meson $K_1(1270{)}^{+}$ production in $K^{-}A$ reactions at near-threshold laboratory incident antikaon momenta within a nuclear spectral function approach, which describes incoherent direct $K_1(1270{)}^{+}$ meson production in $K^{-}$ meson--proton $K^{-}p\to K_1(1270{)}^{+}{\Xi }^{-}$ production processes and accounts for three different options for its in-medium mass shift (or for its effective scalar potential) at central density ${\rho }_0$. We calculate the absolute differential and total cross sections for the production of $K_1(1270{)}^{+}$ mesons on ${}^{12}$C and ${}^{184}$W target nuclei at laboratory angles of 0${}^{\circ }$--45${}^{\circ }$ by $K^{-}$ mesons with momenta of 2.5, 2.8 and 3.5 GeV/c, which are close to the threshold momentum ($\approx$ 2.95 GeV/c) for $K_1(1270{)}^{+}$ meson production off the free target proton at rest. The intrinsic properties of carbon and tungsten target nuclei have been described in terms of their spectral functions, which take into account the momenta of target protons and the energies of their separation from the considered nuclei. We show that the differential and total (absolute and relative) $K_1(1270{)}^{+}$ antikaon-induced production cross sections at initial momenta not far from threshold -- at momenta $\sim$ 2.8--3.5 GeV/c, at which there is yet no strong drop in their strength, reveal a distinct sensitivity to changes in the in-medium shift of the $K_1(1270{)}^{+}$ mass, studied in the paper, both in the $K_1(1270{)}^{+}$ meson low-momentum (0.1--1.0 GeV/c) and in its full-momentum ranges. This would permit evaluating this shift. Experimental data necessary for this aim can be obtained in a dedicated experiment at the J-PARC Hadron Experimental Facility.

   ↳ nucl-thhep-phnucl-exNPA(2021)·3 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.