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Register a new userThe production of doubly charmed exotic hadrons in heavy ion collisions
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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 unique 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.
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We study the production of multi-charmed hadrons by recombination in heavy ion collisions by focusing on the production of $Xi_{cc}$, $Xi_{cc}^*$, $Omega_{scc}$, $Omega_{scc}^*$, $Omega_{ccc}$ baryons and X(3872) mesons. Starting from the estimation of yields for those hadrons at chemical freeze-out in both the statistical and coalescence model, we evaluate their transverse momentum distributions at mid-rapidity in the coalescence model. We show that yields of multi-charmed hadrons in heavy ion collisions at RHIC and LHC are large enough, and thereby not only multi-charmed hadrons observed so far, e.g., the $Xi_{cc}$ but also those which have not been observed yet, can be discovered sufficiently in heavy ion collisions. We also find that the transverse momentum distribution ratio between various multi-charmed hadrons sensitively reflects the interplay between quark contents of corresponding hadrons as well as the transverse momentum distribution of charm quarks at the hadronization point, and therefore we insist that studying both the transverse momentum distributions of multi-charmed hadrons themselves and transverse momentum distribution ratios between various multi-charmed hadrons provide us with useful information on hadron production mechanism involving charm quarks in heavy ion collisions.
Heavy ion collisions (HIC) at high energies are excellent ways for producing heavy hadrons and composite particles. With upgraded detectors at RHIC and LHC, it has become possible to measure hadrons beyond their ground states. Therefore, HIC provide a new method for studying exotic hadrons that are either hadronic molecular states or compact multiquark systems. Because their structures are related to the fundamental properties of QCD, studying exotic hadrons is currently one of the most active areas of research in hadron physics. Experiments carried out at various accelerator facilities have indicated that some exotic hadrons may have already been produced. The present review is a summary of the current understanding of a selected set of exotic particle candidates that can be potentially measured in HIC. It also includes discussions on the production of exotic hadrons in HIC based on the coalescence and statistical models. A more detailed discussion leads to the conclusion that the yield of a hadron is typically an order of magnitude smaller when it is a compact multiquark state than that of an excited hadronic state with normal quark numbers and/or a molecular configuration. Attention is also given to some of the proposed heavy exotic hadrons that could be produced with sufficient abundance in HIC because of the significant numbers of charm and bottom quarks produced at RHIC and LHC, making it possible to study them in these experiments. Further included in the discussion are the general formalism for the coalescence model that involves resonance particles and its implication on the present estimated yield for resonance production. Finally, a review is given on recent studies to constrain the hadron-hadron interaction through correlation measurements in HIC and their implications on the interpretation and the possible existence of exotic states in hadronic interactions.
We investigate the possibilities of using measurements in present and future experiments on heavy ion collisions to answer some longstanding problems in hadronic physics, namely identifying hadronic molecular states and exotic hadrons with multiquark components. The yields of a selected set of exotic hadron candidates in relativistic heavy ion collisions are discussed in the coalescence model in comparison with the statistical model. We find that the yield of a hadron is typically an order of magnitude smaller when it is a compact multiquark state, compared to that of an excited hadronic state with normal quark numbers. We also find that some loosely bound hadronic molecules are formed more abundantly than the statistical model prediction by a factor of two or more. Moreover, due to the significant numbers of charm and bottom quarks produced at RHIC and even larger numbers expected at LHC, some of the proposed heavy exotic hadrons could be produced with sufficient abundance for detection, making it possible to study these new exotic hadrons in heavy ion collisions.
Recent data on the production of $D$ mesons and $Lambda_c^+$ baryons in heavy ion collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider exhibit a number of striking characteristics such as enhanced yield ratios $D_s^+/D^0$, $Lambda_c^+/D^0$ and their transverse momentum dependences. In this paper, we derive the momentum dependence of open charm mesons and singly charmed baryons produced in ultra-relativistic heavy ion collisions via the equal-velocity quark combination. We present analytic expressions and numerical results of yield ratios and compare them with the experimental data available. We make predictions for other charmed hadrons.
This paper investigates the electromagnetic production of lepton pairs with low transverse momentum in relativistic heavy ion collisions. We estimate the initial photons transverse momentum contributions by employing models where the average transverse momentum squared of the incoming photon can be calculated in the equivalent photon approximation. We further derive an all order QED resummation for the soft photon radiation, which gives an excellent description of the ATLAS data in ultra-peripheral collisions at the LHC. For peripheral and central collisions, additional $p_T$-broadening effects from multiple interaction with the medium and the magnetic field contributions from the quark-gluon plasma are also discussed.
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