Excited Quarkonia Research Articles

Exclusive photoproduction of excited quarkonia in ultraperipheral collisions

In this paper, we discuss the exclusive photoproduction of ground and excited states of $\psi(1S,2S)$ and $\Upsilon(1S,2S)$ in ultraperipheral collisions (UPCs). Using the potential model in order to obtain the vector meson wave function, we find a good agreement of our calculations with data from the LHC and HERA colliders for $J/\psi (1S,2S) $ and $\Upsilon(1S)$ in $\gamma p$ collisions. We extend the calculations to the nuclear target case applying them to $AA$ UPCs with the use of the shadowing and finite coherence length effects fitted to the data. Our results are compared to the recent LHC data, in both incoherent ($J/\Psi(1S)$ at 2.76 TeV) and coherent ($J/\Psi(1S)$ at 2.76 and 5.02 TeV) processes. We also show the corresponding predictions for the excited states, in the hope that future measurements could provide more detailed information about the vector meson wave functions and nuclear effects.

Results on quarkonia production in Heavy Ion collisions from the ATLAS Experiment

The observed quarkonia states in heavy ion collisions provide a powerful tool to probe the dynamics of the Quark Gluon Plasma. Measurements performed on the ground and excited quarkonia states, as well as their separation into prompt and non-prompt components, reveal the effects of colour screening and colour recombination. In addition, quarkonium production rates and their excited to ground state production ratios in lighter p+Pb collisions are an interesting probe of cold nuclear matter effects. In these proceedings, the latest results of the ATLAS experiment at the LHC on these observables will be presented.

Relative Yields and Nuclear Modification of ψ′ to J/ψ mesons in p+p, p(3He)+A Collisions at [formula omitted], measured in PHENIX

The PHENIX collaboration has measured the ratio of ψ′ to J/ψ in p+p and p(3He)+A collisions at forward and backward rapidity. We find that in p+p collisions, the data are consistent with expectations from a modified color evaporation model of quarkonia formation. In p(3He)+A collisions, in the p(3He)-going direction, the ψ′ to J/ψ ratio is the same as found in p+p within uncertainties. However, in the A-going direction, the weaker bound ψ′ is suppressed by a factor of 2 compared to the J/ψ. Since these states are not fully formed until after they exit the nucleus, interactions between the fully formed charmonia and co-moving matter may be responsible for this effect, consistent with the higher particle density in the A-going direction relative to the p(3He)-going direction. This mechanism may compete with color screening in a deconfined plasma in A+A collisions to produce sequential suppression of excited quarkonia states.

Nuclear Modification of Excited Quarkonia States from SPS to LHC Energies

The study of quarkonia spectroscopy in the presence of hadronic or deconfined medium is a powerful procedure to study density and temperature of different kinds of nuclear matter. Most of the efforts are made with the ground states \(J/\psi \) and \(\Upsilon \)(1S), but excited state quarkonia offers a rich spectrum of binding energies and particle sizes for nuclear medium studies. This report summarizes measurements of several quarkonium excited states in the last three decades by Fermilab, SPS, HERA, RHIC and LHC experiments along with the current understanding on how nuclear medium affects their yields.

Measurement of the relative yields of ψ(2S) to ψ(1S) mesons produced at forward and backward rapidity in p+p , p+Al , p+Au , and He3+Au collisions at sNN=200 GeV

The PHENIX Collaboration has measured the ratio of the yields of $\psi(2S)$ to $\psi(1S)$ mesons produced in $p$$+$$p$, $p$$+$Al, $p$$+$Au, and $^{3}$He$+$Au collisions at $\sqrt{s_{_{NN}}}=200$ GeV over the forward and backward rapidity intervals $1.2<|y|<2.2$. We find that the ratio in $p$$+$$p$ collisions is consistent with measurements at other collision energies. In collisions with nuclei, we find that in the forward ($p$-going or $^{3}$He-going) direction, the relative yield of $\psi(2S)$ mesons to $\psi(1S)$ mesons is consistent with the value measured in \pp collisions. However, in the backward (nucleus-going) direction, the $\psi(2S)$ is preferentially suppressed by a factor of $\sim$2. This suppression is attributed in some models to breakup of the weakly-bound $\psi(2S)$ through final state interactions with comoving particles, which have a higher density in the nucleus-going direction. These breakup effects may compete with color screening in a deconfined quark-gluon plasma to produce sequential suppression of excited quarkonia states.

Holographic heavy quark symmetry

We investigate the heavy quark spin symmetry, i.e. the mass degeneracy of pseudo-scalar and vector quarkonia at heavy quark limit, by using the gauge/gravity correspondence. We allow generic D3-like geometry with a flavor D7-brane, to avoid supersymmetric mass degeneracy. For geometries admitting physical QCD-like properties, we find that the mass degeneracy is generically achieved in a good accuracy, up to a few percent mass splitting. We also compute spectra of excited quarkonia states, and discuss comparisons with experiments and quark-model calculations.

Heavy exotic quarkonia and doubly heavy baryons

During the last three years strong experimental evidence from B and charm factories has been accumulating for the existence of exotic hadronic quarkonia, narrow resonances which cannot be made from a quark and an antiquark. Their masses and decay modes show that they contain a heavy quark-antiquark pair, but their quantum numbers are such that they must also contain a light quark-antiquark pair. The main theoretical challenge has been to determine the nature of these resonances. The main possibilities are that they are either “genuine tetraquarks”, i.e. two quarks and two antiquarks within one confinement volume, or “hadronic molecules” of two heavy-light mesons. In the last few months there is more and more evidence in favor of the latter. In addition, there exist narrow resonances such as X (3872) which are not exotic but are closely related to the exotic states. Most likely such states are a mixture of hadronic molecules and excited quarkonia. I discuss the experimental data and its interpretation and provide fairly precise predictions for masses and quantum numbers of the additional exotic states which are naturally expected in the molecular picture but have yet to be observed. In addition, I provide arguments in favor of the existence of an even more exotic state – a hypothetical deuteron-like bound state of two heavy baryons. I also consider “baryon-like” states QQ′qq′ , which if found will be direct evidence not just for near-threshold binding of two heavy mesons, but for genuine tetraquarks with novel color networks. I also stress the importance of experimental search for doubly-heavy baryons which are intimately connected with doubly heavy exotics.

Intriguing solutions of the Bethe-Salpeter equation for radially excited pseudoscalar charmonia

The purpose of this paper is twofold. The first purpose is to find a fully Poincar\'e invariant solution of the Bethe-Salpeter equation (BSE) for excited quarkonia; however, the second, in fact, major focus is on the relevance of the space-time metric choice and its impact on the correct description of the ground and all excited states. For the first time, we compare the BSE solutions defined independently with the Euclidean and Minkowski metric. For this purpose, the BSE is conventionally defined and solved in Euclidean space with two versions of the propagator: the bare propagator and the confined form of the quark propagator with complex conjugated poles. In both considered cases, there is unexpected doubling of the spectrum when comparing to the experiments as well as to the solutions of the Schr\odinger equation. The quark propagator with complex conjugated singularities allows us to find the BSE solution directly in Minkowski momentum space as well. We find the Minkowski space solution for confining theories is not only numerically accessible but provides a reliable albeit not yet completely satisfactory description of the ground and excited meson states.

Dynamical Quarkonia Suppression from Complex Potentials

I address the effect that a temperature dependent potential has on the suppression of heavy quarkonia states in deconfined hadronic matter. I focus on a simple medium: a homogenous, fixed temperature and deconfined system with a finite lifetime (QGP-brick). Assuming that all the interactions of a heavy quark anti-quark (Q – Q̄) pair with the medium can be recast into an in-medium potential, I solve the time dependent Schrödinger equation to evolve the density matrix which describes the hard pair production and its connection to the final distribution of hadrons after the medium disappears. For those temperatures in which bound states survive in the medium, I find a non-trivial dependence of the production of excited quarkonia states on the in-medium levels, due to the mixing of vacuum and in-medium wave functions. This mixing leads, in particular, to the enhancement of the relative abundance of 2S to 1S states for the case in which the in-medium ground state of the Q – Q̄ system is dissolved.

Dynamical quarkonia suppression in a QGP-brick

I address the effect that a temperature dependent potential has on the suppression of heavy quarkonia states in deconfined hadronic matter. I focus on a simple medium: a homogenous, fixed temperature and deconfined system with a finite lifetime (QGP-brick). Assuming that all the interactions of a heavy quark anti-quark ($Q-\bar Q$) pair with the medium can be recast into an in-medium potential, I solve the time dependent Schr\"odinger equation to evolve the density matrix which describes the hard pair production and its connection to the final distribution of hadrons after the medium disappears. For those temperatures in which bound states survive in the medium, I find a non-trivial dependence of the production of excited quarkonia states on the in-medium levels, due to the mixing of vacuum and in-medium wave functions. This mixing leads, in particular, to the enhancement of the relative abundance of 2S to 1S states for those systems in which the in-medium ground state of the $Q-\bar Q$ system is dissolved or close to threshold. I also explore quarkonia production in a non-homogeneous expanding medium and find that the finite formation time effects arising from the low binding energies of in-medium states lead to the insensitivity of the heavy mesons yield to the hottest part of the system evolution.

Exotic mesons

We discuss possible exotic structure interpretations of the scalar mesons f0(1370), f0(1500) and f0(1710) and the charmonium-like state X(3872). The scalars are shown to result from a scheme where the excited quarkonia QQ̄ configurations mix with the lowest lying glueball. Within an effective chiral Lagrangian approach the strong decays of these states are shown to be consistent within this structure assumption. We also discuss the role of the scalar resonances f0(1370), f0(1500) and f0(1710) in the strong and radiative three-body decays of J/ψ, presenting further tests for this scenario. The charmonium-like X(3872) is assumed to consist dominantly of molecular hadronic components with an additional small admixture of a charmonium configuration. A potential model based on meson exchange is able to generate weak binding of the molecular hadronic components. The observed radiative (γJ/ψ and γψ(2s)) and strong (J/ψ2π and J/ψ3π) decays are shown to be consistent with the molecular structure assumption of the X(3872).

Radial and orbital qq̄ excitations: “higher quarkonia”

Identification of the spectrum of non- qq̄ exotica such as glueballs, hybrids and molecules will require a detailed understanding of radially and orbitally excited quarkonia, since these states are a background to non- qq̄ states. The data likely to become available experimentally on these higher-mass resonances are their total widths and strong branching fractions to dominant modes. We advocate the use of these branching fractions to distinguish quarkonia from exotica; in this contribution we summarize our recent detailed 3 P 0 decay model calculations of the 374 two-body open-flavor decay modes of the 32 lightest nn̄ states above 1S and 1P, which should be useful for this program.