Nuclear Theory·nucl-th

Tuesday·June 25, 2019

9 papers—4 primary·5 cross-listed

01
Local spin polarization in high energy heavy ion collisions
Hong-Zhong Wu🇨🇳 · Long-Gang Pang🇺🇸 · Xu-Guang Huang🇨🇳 · Qun Wang🇨🇳
We revisit the azimuthal angle dependence of the local spin polarization of hyperons in heavy-ion collisions at 200 GeV in the framework of the (3+1)D viscous hydrodynamic model CLVisc. Two different initial conditions are considered in our simulation: the optical Glauber initial condition without initial orbital angular momentum and the AMPT initial condition with an initial orbital angular momentum. We find that the azimuthal angle dependence of the hyperon polarization strongly depends on the choice of the so-called "spin chemical potential" $Ω_{μν}$ . With $Ω_{μν}$ chosen to be proportional to the temperature vorticity, our simulation shows qualitatively coincidental results with the recent measurements at RHIC for both the longitudinal and transverse polarization. We argue that such a coincidence may be related to the fact that the temperature vorticity is approximately conserved in the hot quark-gluon matter.
nucl-thPhys.Rev.Research.(2019)·121 citations
02
Nuclear modification of jet shape for inclusive jets and $γ$ -jets at the LHC energies
Ning-Bo Chang🇨🇳 · Yasuki Tachibana🇺🇸 · Guang-You Qin🇨🇳
With our coupled jet-fluid model, we study the nuclear modifications of full jets and jet structures for single inclusive jets and $γ$ -jets in Pb+Pb collisions at $5.02$ ~ATeV and $2.76$ ~ATeV. The in-medium evolution of full jet shower is described by a set of coupled transport equations including the effects of collisional energy loss, transverse momentum broadening and medium-induced splitting process. The dynamical evolution of bulk medium is simulated by solving relativistic hydrodynamic equation with source term which accounts for the energy and momentum deposited by hard jet shower to soft medium. Our study demonstrates that the hydrodynamic medium response to jet propagation significantly enhances the broadening of jet shape at large angles and is essential for the cone-size dependence of jet energy loss and nuclear modification factor of inclusive jet production. It is also found that the nuclear modification pattern of jet shape is sensitive to jet energy but has weak dependence on the flavor of the parton that initiates the jet. Our result can naturally explain the different nuclear modification patterns of jet shape functions for single inclusive jet and $γ$ -jet events as observed by the CMS Collaboration, and can be tested in the future by measuring the jet shape function over a wider range of jet energies in heavy-ion collisions.
nucl-thhep-phnucl-exPLB(2020)·60 citations
03
Finite size of hardons and HBT interferometry for hydrodynamic sources
Yong Zhang🇨🇳 · Hong-Jie Yin🇨🇳 · Weihua Wu🇨🇳
Hadrons formed in heavy-ion collisions are not point-like objects, they cannot occupy too close space-time points. When the two bosons are too close to each other, their constituents start to mix and they cannot be considered as bosons subjected to Bose-Einstein statistics, this effect is called excluded volume effect. We study the volume effect on HBT for the sources with various sizes. The effect on HBT was shown in out, side and long directions, and it is more obvious for the source with a narrow space-time distribution. The correlation functions for high transverse momenta are more suppressed by the volume effect. Hence the incoherence parameter may be more suppressed by the volume effect for high transverse momenta in small collision systems.
nucl-thhep-phIJMPE(2020)·0 citations
04
Radiative corrections to Gamow-Teller decays
Leendert Hayen🇧🇪 · Nathal Severijns🇧🇪
Radiative corrections in the electroweak sector constitute an essential component in the ability to disentangle Beyond Standard Model physics from experimental data. This is particularly relevant for strongly bound systems undergoing weak decays such as nuclear $β$ decay, where its contribution to top-row CKM unitarity tests is essential. In this Letter we note the need for an additional radiative correction to the Gamow-Teller form factor in allowed decays. It concerns a combination of electrostatic final state interactions and QCD-induced currents. We review the basic derivation and report analytical results. Due to differences in their theoretical treatment in the literature, effects on the neutron and mirror systems are distinct. Significant consequences appear for a comparison of the former with lattice QCD, while changes occur in the $∣ V_{u d} ∣$ extraction in the latter. We discuss new limits on right-handed currents and provide a new value for $∣ V_{u d} ∣$ from mirror decays.
nucl-thnucl-ex16 citations
05
Aspects of heavy flavor jet physics in heavy ion collisions
Ivan Vitev🇺🇸
n these proceedings I discuss several recent developments in the physics of heavy flavor jets in heavy ion collisions. i) The dijet mass modification in nucleus-nucleus reactions has been proposed as a new observable with enhanced sensitivity to parton energy loss in nuclear matter. It also enables more precise studies of heavy quark mass effects on parton shower formation. ii) Computational techniques from soft-collinear effective theory have allowed us to bridge the gap between high energy and heavy ion QCD phenomenology. I show the first application of the semi-inclusive jet function formalism to heavy flavor jet production in proton-nucleus and nucleus-nucleus collisions at the LHC. iii) Last but not least, central to the theoretical calculations of heavy flavor jets is the accurate theoretical description of in-medium parton showers. A formalism to compute branching processes in nuclear matter to any desired order in opacity has been developed and illustrative numerical results are presented.
↳ hep-phnucl-thPoS(2020)·1 citation
06
Perspectives of photon physics at future colliders
M. Klasen🇩🇪
We review current results on physics with photons at the LHC and discuss realistic perspectives of photon physics at future colliders. In particular, we focus on Standard Model (SM) measurements with photons at the upcoming high-luminosity and a possible high-energy LHC as well as jet measurements at an Electron-Ion Collider (EIC) to be constructed either at BNL or at JLAB and their potential to constrain nuclear parton densities. We also discuss future searches for physics beyond the SM with photons in the high-luminosity phase of the LHC.
↳ hep-phhep-exnucl-exnucl-thFrascati Phys.Ser.(2019)·3 citations
07
Prompt $J / ψ$ -pair production at the LHC: impact of loop-induced contributions and of the colour-octet mechanism
Jean-Philippe Lansberg🇫🇷 · Hua-Sheng Shao🇫🇷 · Nodoka Yamanaka🇫🇷 · Yu-Jie Zhang🇨🇳
Prompt double- $J / ψ$ production at high-energy hadron colliders can be considered as a golden channel to probe double parton scatterings (DPS) --in particular to study gluon-gluon correlations inside the proton-- and, at the same time, to measure the distribution of linearly-polarised gluons inside the proton. Such studies however require a good control of both single and DPS in the respective regions where they are carried out. In this context, we have critically examined two mechanisms of single parton scatterings (SPS) that may be kinematically enhanced where DPS are thought to be dominant, even though they are either at higher orders in the strong-coupling or velocity expansion. First, we have considered a gauge-invariant and infrared-safe subset of the loop-induced contribution via Colour-Singlet (CS) transitions. We have found it to become the leading CS SPS contributions at large rapidity separation, yet too small to account for the data without invoking the presence of DPS yields. Second, we have surveyed the possible Colour-Octet (CO) contributions using both old and up-to-date non-perturbative long distance matrix elements (LDMEs). We have found that the pure CO yields crucially depend on the LDMEs. Among all the LDMEs we used, only two result into a visible modification of the NRQCD (CS+CO) yield, but only in two kinematical distributions measured by ATLAS, those of the rapidity separation and of the pair invariant mass. These modifications however do not impact the control region used for their DPS study.
↳ hep-phhep-exnucl-exnucl-thEPJC(2019)·29 citations
08
Relativistic invariance in Euclidean formulations of quantum mechanics
Gohin Shaikh Samad🇺🇸 · Wayne Polyzou🇺🇸
Relativistic invariance in Euclidean formulations of quantum mechanics is discussed. Relativistic treatments of quantum theory are needed to study hadronic systems at sub-hadronic distance scales. Euclidean formulations of relativistic quantum mechanics have some computational advantages. In the Euclidean representation the physical Hilbert space inner product is expressed in terms of Euclidean space-time variables with no need for any analytic continuation. The identification of the complex Euclidean group with the complex Poincaré group relates the infinitesimal generators of both groups. In this work explicit representations of the Poincaré generators in Euclidean space-time variables for all positive-mass positive-energy irreducible representations of the Poincaré group are derived. The commutation relations are checked, both hermiticity and self-adjointness are established, and reflection positivity of the kernels is verified.
↳ math-phhep-thmath.MPnucl-th0 citations
09
The contact in the unitary Fermi gas across the superfluid phase transition
S. Jensen🇺🇸 · C. N. Gilbreth🇺🇸 · Y. Alhassid🇺🇸
A quantity known as the contact plays a fundamental role in quantum many-body systems with short-range interactions. The determination of the temperature dependence of the contact for the unitary Fermi gas of infinite scattering length has been a major challenge, with different calculations yielding qualitatively different results. Here we use finite-temperature auxiliary-field quantum Monte Carlo (AFMC) methods on the lattice within the canonical ensemble to calculate the temperature dependence of the contact for the homogeneous spin-balanced unitary Fermi gas. We extrapolate to the continuum limit for 40, 66, and 114 particles. We observe a dramatic decrease in the contact as the superfluid critical temperature is approached from below, followed by a gradual weak decrease as the temperature increases in the normal phase. Our results are in excellent agreement with the most recent precision ultracold atomic gas experiments. We also present results for the energy of the unitary gas as a function of temperature in the continuum limit.
↳ cond-mat.quant-gascond-mat.supr-conhep-latnucl-thPRL(2020)·26 citations

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