Hadron spectroscopy provides direct physical measurements that shed light on the non-perturbative behavior of quantum chromodynamics (QCD). In particular, various exotic hadrons such as the newly observed $T_{cc}^+$ by the LHCb collaboration, offer u
nique insights on the QCD dynamics in hadron structures. In this letter, we demonstrate how heavy ion collisions can serve as a powerful venue for hadron spectroscopy study of doubly charmed exotic hadrons by virtue of the extremely charm-rich environment created in such collisions. The yields of $T_{cc}^+$ as well as its potential isospin partners are computed within the molecular picture for Pb-Pb collisions at center-of-mass energy $2.76~mathrm{TeV}$. We find about three-order-of-magnitude enhancement in the production of $T_{cc}^+$ in Pb-Pb collisions as compared with the yield in proton-proton collisions, with a moderately smaller enhancement in the yields of the isospin partners $T_{cc}^0$ and $T_{cc}^{++}$. The $T_{cc}^+$ yield is comparable to that of the $X(3872)$ in the most central collisions while shows a considerably stronger decrease toward peripheral collisions, due to a threshold effect of the required double charm quarks for $T_{cc}^+$. Final results for their rapidity and transverse momentum $p_T$ dependence as well as the elliptic flow coefficient are reported and can be tested by future experimental measurements.
We give an introduction to the phase structure of QCD matter under rotation based on effective four-fermion models. The effects of the magnetic field on the rotating QCD matter are also explored. Recent developments along these directions are overvie
wed, with special emphasis on the chiral phase transition. The rotational effects on pion condensation and color superconductivity are also discussed.
In 2017, STAR Collaboration reported the measurements of hyperon global polarization in heavy ion collisions, suggesting the subatomic fireball fluid created in these collisions as the most vortical fluid. There remains the interesting question: at w
hich beam energy the truly most vortical fluid will be located. In this work we perform a systematic study on the beam energy dependence of hyperon global polarization phenomenon, especially in the interesting $hat{O}(1sim 10) rm GeV$ region. We find a non-monotonic trend, with the global polarization to first increase and then decrease when beam energy is lowered from $27~rm GeV$ down to $3~rm GeV$. The maximum polarization signal has been identified around $sqrt{s_{NN}} = 7.7~rm GeV$, where the heavy ion collisions presumably create the most vortical fluid. Detailed experimental measurements in the $hat{O}(1sim 10) rm GeV$ beam energy region are expected to test the prediction very soon.
We present a calculation of the heavy quark transport coefficients in a quark-gluon plasma under the presence of a strong external magnetic field, within the Lowest Landau Level (LLL) approximation. In particular, we apply the Hard Thermal Loop (HTL)
technique for the resummed effective gluon propagator, generalized for a hot and magnetized medium. Using the derived effective HTL gluon propagator and the LLL quark propagator we analytically derive the full results for the longitudinal and transverse momentum diffusion coefficients as well as the energy losses for charm and bottom quarks beyond the static limit. We also show numerical results for these coefficients in two special cases where the heavy quark is moving either parallel or perpendicular to the external magnetic field.
The topological structure of vacuum is the cornerstone of non-Abelian gauge theories describing strong and electroweak interactions within the standard model of particle physics. However, transitions between different topological sectors of the vacuu
m (believed to be at the origin of the baryon asymmetry of the Universe) have never been observed directly. An experimental observation of such transitions in Quantum Chromodynamics (QCD) has become possible in heavy-ion collisions, where the chiral magnetic effect converts the chiral asymmetry (generated by topological transitions in hot QCD matter) into an electric current, under the presence of the magnetic field produced by the colliding ions. The Relativistic Heavy Ion Collider program on heavy-ion collisions such as the Zr-Zr and Ru-Ru isobars, thus has the potential to uncover the topological structure of vacuum in a laboratory experiment. This discovery would have far-reaching implications for the understanding of QCD, the origin of the baryon asymmetry in the present-day Universe, and for other areas, including condensed matter physics.
Ultrarelativistic collisions between heavy nuclei briefly generate the quark-gluon plasma (QGP), a new state of matter characterized by deconfined partons last seen microseconds after the Big Bang. The properties of the QGP are of intense interest, a
nd a large community has developed over several decades, to produce, measure and understand this primordial plasma. The plasma is now recognized to be a strongly-coupled fluid with remarkable properties, and hydrodynamics is commonly used to quantify and model the system. An important feature of any fluid is its vorticity, related to the local angular momentum density; however, this degree of freedom has received relatively little attention because no experimental signals of vorticity had been detected. Thanks to recent high-statistics datasets from experiments with precision tracking and complete kinemetic coverage at collider energies, hyperon spin polarization measurements have begun to uncover the vorticity of the QGP created at the Relativistic Heavy Ion Collider. The injection of this new degree of freedom into a relatively mature field of research represents an enormous opportunity to generate new insights into the physics of the QGP. The community has responded with enthusiasm, and this book (to be published as a volume of Lecture Notes in Physics series by Springer) represents some of the diverse lines of inquiry into aspects of strongly interacting matter under rotation.
We study chiral magnetic effect in collisions of AuAu, RuRu and ZrZr at s = 200GeV. The axial charge evolution is modeled with stochastic hydrodynamics and geometrical quantities are calculated with Monte Carlo Glauber model. By adjusting the relaxat
ion time of magnetic field, we find our results in good agreement with background subtracted data for AuAu collisions at the same energy. We also make prediction for RuRu and ZrZr collisions. We find a weak centrality dependence of initial chiral imbalance, which implies the centrality dependence of chiral magnetic effect signal comes mainly from those of magnetic field and volume factor. Our results also show an unexpected dependence on system size: while the system of AuAu has larger chiral imbalance and magnetic field, it turns out to have smaller signal for chiral magnetic effect due to the larger volume suppression factor.
We present a brief overview on recent developments of theory and phenomenology for novel many-body phenomena related to the chirality and magnetic field, with an emphasis on their experimental implications and possible detection in relativistic nuclear collisions.
We report a novel relation between rotation and magnetic field in a charged fluid system: there is naturally a magnetic field along the direction of fluid vorticity due to the currents associated with the swirling charges. This general connection is
demonstrated using a fluid vortex. Applying the idea to heavy ion collisions we propose a new mechanism for generating in-medium magnetic field with a relatively long lifetime. We estimate the magnitude of this new magnetic field in the Au-Au colliding systems across a wide span of collisional beam energy. Such a magnetic field is found to increase rapidly toward lower beam energy and could account for a significant amount of the experimentally observed global polarization difference between hyperons and anti-hyperons.
Recently there have been significant interests in the spin hydrodynamic generation phenomenon from multiple disciplines of physics. Such phenomenon arises from global polarization effect of microscopic spin by macroscopic fluid rotation and is expect
ed to occur in the hot quark-gluon fluid (the ``subatomic swirl) created in relativistic nuclear collisions. This was indeed discovered in experiments which however revealed an intriguing puzzle: a polarization difference between particles and anti-particles. We suggest a novel application of a general connection between rotation and magnetic field: a magnetic field naturally arises along the fluid vorticity in the charged subatomic swirl. We establish this mechanism as a new way for generating long-lived in-medium magnetic field in heavy ion collisions. Due to its novel feature, this new magnetic field provides a nontrivial explanation to the puzzling observation of a difference in spin hydrodynamic generation for particles and anti-particles in heavy ion collisions.
