Nuclear Theory·nucl-th

Friday·July 12, 2019

9 papers—2 primary·7 cross-listed

03
[Submitted on 10 Jul 2019] (cross-list from hep-ph)
Deciphering the $z_{g}$ distribution in ultrarelativistic heavy ion collisions
Paul Caucal🇫🇷 · Edmond Iancu🇫🇷 · Gregory Soyez🇫🇷
Within perturbative QCD, we develop a new picture for the parton shower generated by a jet propagating through a dense quark-gluon plasma. This picture combines in a simple, factorised, way multiple medium-induced parton branchings and standard vacuum-like emissions, with the phase-space for the latter constrained by the presence of the medium. We implement this picture as a Monte Carlo generator that we use to study two phenomenologically important observables: the jet nuclear modification factor $R_{AA}$ and the $z_{g}$ distribution reflecting the jet substructure. In both cases, the outcome of our Monte Carlo simulations is in good agreement with the LHC measurements. We provide basic analytic calculations that help explaining the main features observed in the data. We find that the energy loss by the jet is increasing with the jet transverse momentum, due to a rise in the number of partonic sources via vacuum-like emissions. This is a key element in our description of both $R_{AA}$ and the $z_{g}$ distribution. For the latter, we identify two main nuclear effects: incoherent jet energy loss and hard medium-induced emissions. As the jet transverse momentum increases, we predict a qualitative change in the ratio between the $z_{g}$ distributions in PbPb and pp collisions: from increasing at small $z_{g}$ , this ratio becomes essentially flat, or even slightly decreasing.
Comments:
49 pages, 23 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1907.04866 [pdf]
JHEP(2019)·115 citations
04
[Submitted on 11 Jul 2019] (cross-list from hep-ph)
Charmed baryon $-$ nucleon interaction
H. Garcilazo🇲🇽 · A. Valcarce🇪🇸 · T.F. Carames🇪🇸
We present a comparative study of the charmed baryon $-$ nucleon interaction based on different theoretical approaches. For this purpose, we make use of i) a constituent quark model tuned in the light-flavor baryon $-$ baryon interaction and the hadron spectra, ii) existing results in the literature based both on hadronic and quark-level descriptions, iii) (2+1)-flavor lattice QCD results of the HAL QCD Collaboration at unphysical pion masses and their effective field theory extrapolation to the physical pion mass. There is a general qualitative agreement among the different available approaches to the charmed baryon $-$ nucleon interaction. Different from hadronic models based on one-boson exchange potentials, quark $-$ model based results point to soft interactions without two-body bound states. They also support a negligible channel coupling, due either to tensor forces or to transitions between different physical channels, $Λ_{c} N - Σ_{c} N$ . Short-range gluon and quark-exchange dynamics generate a slightly larger repulsion in the $^{1} S_{0}$ than in the $^{3} S_{1}$ $Λ_{c} N$ partial wave. A similar asymmetry between the attraction in the two $S$ waves of the $Λ_{c} N$ interaction also appears in hadronic approaches. A comparative detailed study of Pauli suppressed partial waves, as the $^{1} S_{0} (I = 1/2)$ and $^{3} S_{1} (I = 3/2)$ $Σ_{c} N$ channels, would help to disentangle the short-range dynamics of two-baryon systems containing heavy flavors. The possible existence of charmed hypernuclei is discussed.
Comments:
25 pages, 8 figures, to appear in Eur. Phys. J. C
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1907.05022 [pdf]
EPJC(2019)·14 citations
05
[Submitted on 11 Jul 2019] (cross-list from hep-ph)
The angular momentum decomposition in the scalar diquark model
D. A. Amor-Quiroz🇫🇷 · M. Burkardt🇺🇸 · C. Lorcé🇫🇷
One of the challenges of hadronic physics is to fully understand the structure of the proton. In particular, there is nowadays a great interest in the decomposition of its total angular momentum into orbital angular momentum and intrinsic spin, as well as identifying contributions from valence quarks, sea quarks and gluons. The most common decompositions of angular momentum are the Jaffe-Manohar (canonical) and Ji (kinetic) decompositions, which differ in the way contributions are attributed to quarks and gluons. Using perturbation theory, explicit one-loop calculations found that the difference between such decompositions vanishes. We justify within the diquark model in QED that the difference appears at two-loop level, supporting the interpretation of such a difference as originating from the torque exerted by the spectator system on the struck quark.
Comments:
DIS conference 2019
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1907.05268 [pdf]
PoS(2019)·2 citations
06
[Submitted on 11 Jul 2019] (cross-list from hep-ph)
One pion exchange and the quantum numbers of the Pc(4440) and Pc(4457) pentaquarks
Manuel Pavon Valderrama🇨🇳
The LHCb collaboration has recently discovered three pentaquark-like states --- the $P_{c} (4312)$ , $P_{c} (4440)$ and $P_{c} (4457)$ --- close to the $D ˉ Σ_{c}$ and the $D ˉ^{*} Σ_{c}$ meson-baryon thresholds. The standard interpretation is that they are heavy antimeson-baryon molecules. Their quantum numbers have not been determined yet, which implies two possibilities for the $P_{c} (4440)$ and $P_{c} (4457)$ : $J^{P} = \frac{1}{2}^{-}$ and $J^{P} = \frac{3}{2}^{-}$ . The preferred interpretation within a contact-range effective field theory is that the $P_{c} (4440)$ is the $J^{P} = \frac{1}{2}^{-}$ molecule, while the $P_{c} (4457)$ is the $J^{P} = \frac{3}{2}^{-}$ one. Here we show that when the one pion exchange potential between the heavy-antimeson and heavy-baryon is taken into account, this conclusion changes, with the contrary identification being as likely as the original one. The identification is however cutoff dependent, which suggests that improvements of the present description (e.g. the inclusion of subleading order corrections, like two-pion exchanges) are necessary in order to disambiguate the spectroscopy of the molecular pentaquarks.
Comments:
9 pages, 5 tables
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1907.05294 [pdf]
PRD(2019)·88 citations
07
[Submitted on 11 Jul 2019] (cross-list from hep-ph)
Electrical conductivity and Hall conductivity of hot and dense quark gluon plasma in a magnetic field: a quasi particle approach
Arpan Das🇮🇳 · Hiranmaya Mishra🇮🇳 · Ranjita K. Mohapatra🇮🇳
We estimate here the electrical and Hall conductivity using a quasiparticle approach for quark matter. We use a Boltzmann kinetic approach in presence of external magnetic field. We confront the results of model calculations with Lattice QCD simulations for vanishing magnetic field. In general electrical conductivity decreases with magnetic field. The Hall conductivity on the other hand can show a non monotonic behaviour with magnetic field due to an intricate interplay of behaviour of relaxation time and strength of the magnetic field. We argue for vanishing quark chemical potential Hall conductivity vanishes and quark gluon plasma with finite quark chemical potential can show Hall effect. Both electrical conductivity and Hall conductivity increases with increasing quark chemical potential.
Comments:
15 pages, 7 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1907.05298 [pdf]
PRD(2020)·54 citations
08
[Submitted on 11 Jul 2019] (cross-list from hep-ph)
Five-flavor pentaquarks and other light- and heavy-flavor symmetry partners of the LHCb hidden-charm pentaquark
Fang-Zheng Peng🇨🇳 · Ming-Zhu Liu🇨🇳 · Ya-Wen Pan🇨🇳 · Mario Sánchez Sánchez🇫🇷 · Manuel Pavon Valderrama🇨🇳
The discovery of three pentaquark peaks -- the $P_{c} (4312)$ , $P_{c} (4440)$ and $P_{c} (4457)$ -- by the LHCb collaboration has a series of interesting consequences for hadron spectroscopy. If these hidden-charm objects are indeed hadronic molecules, as suspected, they will be constrained by heavy-flavor and SU(3)-flavor symmetries. The combination of these two symmetries will imply the existence of a series of five-flavor pentaquarks with quark content $b ˉ cs d u$ and $b c ˉ s d u$ , that is, pentaquarks that contain each of the five quark flavors that hadronize. In addition, from SU(3)-flavor symmetry alone we expect the existence of light-flavor partners of the three $P_{c}$ pentaquarks with strangeness $S = - 1$ and $S = - 2$ . The resulting structure for the molecular pentaquarks is analogous to the light-baryon octet -- we can label the pentaquarks as $P_{Q^{'} Q ˉ}^{N}$ , $P_{Q^{'} Q ˉ}^{Λ}$ , $P_{Q^{'} Q ˉ}^{Σ}$ , $P_{Q^{'} Q ˉ}^{Ξ}$ depending on their heavy- and light-quark content (with $N$ , $Λ$ , $Σ$ , $Ξ$ the member of the light-baryon octet to which the light-quark structure resembles and $Q^{'}$ , $Q ˉ$ the heavy quark-antiquark pair). In total we predict $45$ new pentaquarks from heavy- and light-flavor symmetries alone, which extend up to $109$ undiscovered states if we also consider heavy-quark spin symmetry. If an isoquartet ( $I = 3/2$ ) hidden-charm pentaquark is ever observed, this will in turn imply a second multiplet structure resembling the light-baryon decuplet: $P_{Q^{'} Q ˉ}^{Δ}$ , $P_{Q^{'} Q ˉ}^{Σ^{*}}$ , $P_{Q^{'} Q ˉ}^{Ξ^{*}}$ , $P_{Q^{'} Q ˉ}^{Ω}$ .
Comments:
13 pages, 4 tables, corresponds to published version
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1907.05322 [pdf]
NPB(2022)·28 citations
09
[Submitted on 11 Jul 2019] (cross-list from hep-ph)
Scattering amplitudes and contour deformations
Gernot Eichmann🇵🇹 · Pedro Duarte🇵🇹 · M. T. Peña🇵🇹 · Alfred Stadler🇵🇹
We employ a scalar model to exemplify the use of contour deformations when solving Lorentz-invariant integral equations for scattering amplitudes. In particular, we calculate the onshell 2 -> 2 scattering amplitude for the scalar system. The integrals produce branch cuts in the complex plane of the integrand which prohibit a naive Euclidean integration path. By employing contour deformations, we can also access the kinematical regions associated with the scattering amplitude in Minkowski space. We show that in principle a homogeneous Bethe-Salpeter equation, together with analytic continuation methods such as the Resonances-via-Padé method, is sufficient to determine the resonance pole locations on the second Riemann sheet. However, the scalar model investigated here does not produce resonance poles above threshold but instead virtual states on the real axis of the second sheet, which pose difficulties for analytic continuation methods. To address this, we calculate the scattering amplitude on the second sheet directly using the two-body unitarity relation which follows from the scattering equation.
Comments:
21 pages, 25 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1907.05402 [pdf]
PRD(2019)·42 citations

Affiliations

first authorsco-authorsvia INSPIRE

Deciphering the zg​ distribution in ultrarelativistic heavy ion collisions

Charmed baryon−nucleon interaction

The angular momentum decomposition in the scalar diquark model

One pion exchange and the quantum numbers of the Pc(4440) and Pc(4457) pentaquarks

Electrical conductivity and Hall conductivity of hot and dense quark gluon plasma in a magnetic field: a quasi particle approach

Five-flavor pentaquarks and other light- and heavy-flavor symmetry partners of the LHCb hidden-charm pentaquark

Scattering amplitudes and contour deformations

Affiliations

Deciphering the $z_{g}$ distribution in ultrarelativistic heavy ion collisions

Charmed baryon $-$ nucleon interaction