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Nuclear Theory·nucl-th

Thursday·February 1, 2024

5 papers—2 primary·3 cross-listed

All5Primary2Cross-lists3
  1. 03

    Heavy flavor production under a strong magnetic field

    Shile Chen🇨🇳 · Jiaxing Zhao🇫🇷 · Pengfei Zhuang🇨🇳

    The magnetic field created in high energy nuclear collisions will affect the dynamical processes in the QCD medium, especially the heavy quark production that happens in the initial stage of the collisions. We calculate in a strong magnetic field the heavy quark production cross section for the elementary process gg {\rightarrow} Q{\bar Q} at leading order and the corresponding transverse momentum distribution in nucleus-nucleus collisions. In comparison to the QED process, the heavy quark production is dominated by the unique QCD channel with gluon self-interaction. Due to the dimension reduction of quark phase space in a strong magnetic field, the production is concentrated in a very narrow energy region above the threshold. Since the translation invariance is broken, the production becomes anisotropic in magnetic field.

    ↳ hep-phnucl-thJHEP(2024)·7 citations
  2. 04

    Exclusive photoproduction of a photon-meson pair: A new class of observables to probe GPDs

    Goran Duplančić🇫🇷 · Saad Nabeebaccus🇭🇷 · Kornelija Passek-K.🇭🇷 · Bernard Pire🇫🇷 · Jakob Schönleber🇩🇪 · Lech Szymanowski🇵🇱 · Samuel Wallon🇫🇷

    We discuss the exclusive photoproduction of a photon-meson pair with large as a channel to probe generalised parton distributions (GPDs). Like other exclusive processes, this channel allows us to better study the -dependence of GPDs, in contrast to processes such as Deeply Virtual Compton Scattering (DVCS) which give only "moment-type" information. Moreover, it also gives the possibility to access, at leading twist, the chiral-odd GPDs, which are still completely unknown experimentally. In the first part of these proceedings, we present the computation of the amplitude at leading order and leading twist, for charged pions, and rho mesons of any charge and polarisation. These processes are sensitive to quark GPDs only. We also discuss the possibility of measuring such processes at various experiments, namely JLab, COMPASS, future EIC and LHC in ultra-peripheral collisions. In particular, in collider experiments, the dependence of GPDs at small skewness can be extracted. For the second part, we report on our recent work on the exclusive photoproduction of pair, which, in addition to a quark GPD channel, also has a contribution from gluon GPDs. In the latter case, we demonstrate that a collinear factorisation of the process fails, due to the presence of a Glauber pinch. Our findings also imply that other similar processes, like also suffer from the same issue. On the other hand, we stress that the processes discussed earlier, which are sensitive to the quark GPD channels only, are safe from these factorisation breaking effects.

    ↳ hep-phhep-exnucl-exnucl-thPoS(2024)·4 citations
  3. 05

    Electromagnetic form factors of the transition from the Delta to the nucleon

    Moh Moh Aung (Suranaree U. of Tech., Uppsala U.)🇹🇭 · Stefan Leupold (Uppsala U.)🇸🇪 · Elisabetta Perotti (Uppsala U.)🇸🇪 · Yupeng Yan (Suranaree U. of Tech.)🇹🇭

    The low-energy electromagnetic form factors of the (1232)-to-nucleon transition are derived combining dispersion theory techniques and chiral perturbation theory. The form factors are expressed in terms of the well-understood pion vector form factor and pion-baryon scattering amplitudes. Nucleon and Delta exchange terms and contact terms constitute the input for these pion-baryon amplitudes. The framework is formulated for all form factors. When comparing to experimental data in the spacelike region of scattering, the focus lies on the numerically dominant magnetic dipole transition form factor. Fitting two subtraction constants (one for the scattering amplitude, one for the form factor) yields a very good description of this dominant form factor up to photon virtualities of about 0.6 GeV. After determining the subtraction constants in the spacelike region and at the photon point, respectively, predictions for the timelike region of Dalitz decays are presented.

    ↳ hep-phnucl-thPRD(2025)·8 citations

Affiliations

first authorsco-authorsvia INSPIRE