Nuclear Theory·nucl-th

Friday·October 12, 2018

12 papers—6 primary·6 cross-listed

07
Decay rate and asymmetries of $Σ^{+} \to p μ^{+} μ^{-}$
Xiao-Gang He🇹🇼 · Jusak Tandean🇹🇼 · German Valencia🇦🇺
The LHCb Collaboration has recently reported evidence for the rare hyperon decay $Σ^{+} \to p μ^{+} μ^{-}$ that is consistent with the standard model expectation. Motivated by this new result we revisit the calculation of this mode including both long and short distance contributions. In the standard model this mode is completely dominated by long distance physics and thus subject to large uncertainties. We present a range of predictions for the rate, the dimuon invariant mass spectrum, and a muon polarization asymmetry that covers these uncertainties as well as known constraints. We study the interplay between short and long distance contributions which could result in additional asymmetries, but we find that they are negligible within the standard model. We propose a parameterization of these asymmetries in terms of a couple of constants that can arise from new physics.
↳ hep-phhep-exnucl-thJHEP(2018)·29 citations
08
Strangeness Enhancement due to String Fluctuations
H.J. Pirner🇩🇪 · B.Z. Kopeliovich🇨🇱 · K. Reygers🇩🇪
We study string fragmentation in high multiplicity proton-proton collisions in a model where the string tension fluctuates. These fluctuations produce exponential pion spectra which are fitted to the transverse momentum distributions of charged particles for different multiplicities. For each multiplicity the so obtained hadronic slope parameter defines the magnitude of the string fluctuations which in turn determines the produced ratio of strange to light quarks. PYTHIA string decay simulations are used to convert each ratio of strange to light quarks to the appropriate ratio of strange hadrons to pions.
↳ hep-phnucl-thPRD(2020)·7 citations
09
Precise measurement of $α_{K}$ and $α_{T}$ for the 39.8-keV $E$ 3 transition in $^{103}$ Rh: Test of internal-conversion theory
N. Nica · J.C. Hardy · V.E. Iacob · V. Horvat · H.I. Park · T.A. Werke · K.J. Glennon · C.M. Folden III · V.I. Sabla · J.B. Bryant · X.K. James · M.B. Trzhaskovskaya
Neutron-activated sources of $^{103}$ Ru and $^{103}$ Pd both share the isomeric first-excited state in $^{103}$ Rh as a daughter product. From independent measurements of both decays, we have measured the $K$ -shell and total internal conversion coefficients, $α_{K}$ and $α_{T}$ , for the 39.8-keV $E$ 3 transition, which de-excites that state in $^{103}$ Rh, to be 141.1(23) and 1428(13), respectively. When compared with Dirac-Fock calculations, our new results disagree with the version of the theory that ignores the $K$ -shell atomic vacancy, which is consistent with our conclusion drawn from a series of measurements on high multipolarity transitions in nuclei with higher $Z$ . Calculations that include the atomic vacancy indicate that the transition actually has a small $M$ 4 component with mixing ratio $δ$ = 0.023(5).
↳ nucl-exnucl-thPRC(2018)·3 citations
10
Nucleon Transversity Distribution at the Physical Pion Mass from Lattice QCD
Yu-Sheng Liu🇨🇳 · Jiunn-Wei Chen🇹🇼 · Luchang Jin🇺🇸 · Ruizi Li🇺🇸 · Huey-Wen Lin🇺🇸 · Yi-Bo Yang🇺🇸 · Jian-Hui Zhang🇩🇪 · Yong Zhao🇺🇸
We report a state-of-the-art lattice calculation of the isovector quark transversity distribution of the proton at the physical pion mass. Within the framework of large-momentum effective theory (LaMET), we compute the transversity quasi-distributions using clover valence fermions on 2+1+1-flavor (up/down, strange, charm) HISQ-lattice configurations with boosted proton momenta as large as 3.0~GeV. The relevant lattice matrix elements are nonperturbatively renormalized in regularization-independent momentum-subtraction (RI/MOM) scheme and systematically matched to the physical transversity distribution. With high statistics, large proton momenta and meticulous control of excited-state contamination, we provide the best theoretical prediction for the large- $x$ isovector quark transversity distribution, with better precision than the most recent global analyses of experimental data. Our result also shows that the sea quark asymmetry in the proton transversity distribution is consistent with zero, which has been assumed in all current global analyses.
↳ hep-lathep-phnucl-exnucl-th82 citations
11
Effects of nucleon resonances on $η$ photoproduction off the neutron reexamined
Jung-Min Suh🇰🇷 · Sang-Ho Kim🇰🇷 · Hyun-Chul Kim🇰🇷
We investigate $η$ photoproduction off the neutron target, i.e., $γ n \to η n$ , employing an effective Lagrangian method combining with a Regge approach. As a background, we consider nucleon exchange in the $s$ -channel diagram and $ρ$ - and $ω$ -meson Regge trajectories in the $t$ channel. The role of nucleon resonances given in the Review of Particle Data Group in the range of $W \approx 1500 - 2100$ MeV and the narrow nucleon resonance $N (1685, 1/ 2^{+})$ is extensively studied. The numerical results of the total and differential cross sections, double polarization observable $E$ , and helicity-dependent cross sections $σ_{1/2}$ , $σ_{3/2}$ are found to be in qualitative agreement with the recent A2 experimental data. The predictions of the beam asymmetry are also given.
↳ hep-phhep-exnucl-exnucl-thPRD(2019)·11 citations
12
Initial-state energy loss in cold QCD matter and the Drell-Yan process
François Arleo🇫🇷 · Charles-Joseph Naïm🇫🇷 · Stephane Platchkov🇫🇷
The effects of parton energy loss in nuclear matter on the Drell-Yan process in pA and $π$ A collisions at fixed-target energies are investigated. Calculations are based on the Baier-Dokshitzer-Mueller-Peigné-Schiff (BDMPS) framework embedded in a next-to-leading order calculation, using the transport coefficient extracted from $J / ψ$ measurements. Model calculations prove in good agreement with preliminary measurements by the E906 experiment, despite a slightly different magnitude, supporting a consistent picture between Drell-Yan and $J / ψ$ data. Predictions for the COMPASS future measurements in $π$ A collisions at $s = 18.9$ ~GeV are also performed. At higher collision energy ( $s = 38.7$ ~GeV), Drell-Yan measurements are only slightly affected by energy loss effects. On the contrary, the E906 results turn out in clear disagreement with nuclear PDF effects alone. The comparison of E772, E866, and E906 measurements indicates for the first time a clear violation of QCD factorization in Drell-Yan production in pA collisions.
↳ hep-phhep-exnucl-exnucl-thJHEP(2019)·24 citations

Affiliations

first authorsco-authorsvia INSPIRE

Decay rate and asymmetries of Σ+→pμ+μ−

Strangeness Enhancement due to String Fluctuations

Precise measurement of αK​ and αT​ for the 39.8-keV E3 transition in 103Rh: Test of internal-conversion theory

Nucleon Transversity Distribution at the Physical Pion Mass from Lattice QCD

Effects of nucleon resonances on η photoproduction off the neutron reexamined

Initial-state energy loss in cold QCD matter and the Drell-Yan process

Affiliations

Decay rate and asymmetries of $Σ^{+} \to p μ^{+} μ^{-}$

Precise measurement of $α_{K}$ and $α_{T}$ for the 39.8-keV $E$ 3 transition in $^{103}$ Rh: Test of internal-conversion theory

Effects of nucleon resonances on $η$ photoproduction off the neutron reexamined