15 pages, 8 figures, Invited talk at the Workshop "Saturation, the Color Glass Condensate and Glasma: What Have we Learned from RHIC?", BNL, May 10-12, 2010
Nuclear effects for J/Psi production in pA collisions are controlled by the coherence and color transparency effects. Color transparency onsets when the time of formation of the charmonium wave function becomes longer than the inter-nucleon spacing. In this energy regime the effective break-up cross section for a c-cbar dipole depends on energy and nuclear path length, and agrees well with data from fixed target experiments, both in magnitude and energy dependence. At higher energies of RHIC and LHC coherence in c-cbar pair production leads to charm quark shadowing which is a complement to the high twist break up cross section. These two effects explain well with no adjusted parameters the magnitude and rapidity dependence of nuclear suppression of J/Psi observed at RHIC in dAu collisions, while the contribution of leading twist gluon shadowing is found to be vanishingly small. A novel mechanism of double color filtering for c-cbar dipoles makes nuclei significantly more transparent in AA compared to pA collisions. This is one of the mechanisms which make impossible a model independent "data driven" extrapolation from pA to AA. This effect also explains the enhancement of nuclear suppression observed at forward rapidities in AA collisions at RHIC, what hardly can be related to the produced dense medium. J/Psi is found to be a clean and sensitive tool measuring the transport coefficient characterizing the dense matter created in AA collisions. RHIC data for pT dependence of J/Psi production in nuclear collisions are well explained with the low value of the transport coefficient q_0-hat<0.5 GeV^2/fm.
We argue that the s-channel cut contribution to J/psi hadroproduction can be significantly larger than the usual cut contribution of the color-singlet mechanism, which is known to underestimate the experimental measurements. A scenario accounting for intermediate $c\bar(c)$ interactions is proposed that reproduces the data at low- and mid-range transverse momenta P_T from the Fermilab Tevatron and BNL Relativistiv Heavy Ion Collider. The J/psi produced in this manner are polarized predominantly longitudinally.
We propose a new explanation for the longstanding puzzle of the tiny branching fraction of psi' -> rho pi relative to that for J/psi -> rho pi. In the case of J/psi, we argue that this decay is dominated by a higher Fock state in which the ccbar pair is in a color-octet ^3S_1 state and via annihilate process ccbar -> qqbar. In the case of the psi', we argue that the probability for the ccbar pair in this higher Fock state to be close enough to annihilate is suppressed by a dynamical effect related to the small energy gap between the mass of the psi' and the DDbar threshold.
We examine the so-called rho-pi puzzle of the psi(2S) decay by incorporating two inputs: One is the relative phase between the one-photon and the gluon decay amplitude, and the other is a possible anomaly in the inclusive nonelectromagnetic decay rate of psi(2S). We propose the possibility that in the psi(2S) decay a hadronic decay process of long distance origin is important in addition to the short-distance decay process. The amplitude of this additional process should nearly cancel the three-gluon amplitude in the exclusive psi(2S)---> 1-0- and turn the sum dominantly real in contrast to th…
A new explanation for the longstanding puzzle of the tiny branching fraction of psi' --> rho pi relative to that for J/psi --> rho pi was proposed. In the case of J/psi, we argue that this decay is dominated by a higher Fock state in which the c cbar pair is in a color-octet ^3S_1 state and annihilates via the process c cbar --> q qbar. In the case of the psi', we argue that the probability for the c cbar c pair in this higher Fock state to be close enough to annihilate is suppressed by a dynamical effect related to the small energy gap between the mass of the psi' and the D Dbar threshold.
We present a collection of selected phenomena observed in J/Psi production from proton-nucleus and heavy ion collisions at energies, ranging between the SPS and LHC. The emphasis is placed on the related theoretical ideas or techniques, which are either not widely known, or offer an alternative explanation to the observed nuclear effects.
Based on the non-relativistic quantum chromodynamics factorization formalism, the polarization parameters $λ_{θϕ}$ and $λ_ϕ$ of $J/ψ$ hadroproduction are analyzed in helicity frame and calculated at QCD next-to-leading order for the first time. For prompt $J/ψ$ production, we take into account the feeddown contributions from $χ_{cJ}$ and $ψ(2S)$ decays. The theoretical predictions for the polarization parameters $λ_{θϕ}$ and $λ_ϕ$ of $J/ψ$ are presented. With the theoretical results we have done the fit to the experimental measurements on yield and polarization for $J/ψ$ hadroproduction simult…
In order to understand the J/psi suppression arising from the possible occurrence of the quark-gluon plasma in high-energy heavy-ion collisions, it is necessary to have a comprehensive picture how the J/psi and its precursors are produced, what their properties after production are, and how the J/psi and its precursors propagate inside nuclear matter. There are unresolved questions in the descriptions of J/psi production and propagation. We outline some of these questions and discuss the approaches for their resolution.
The theoretical explanations about the ``Rho-pi puzzle'' in charmonium decays are reviewed extensively, and the comparison of theoretical predications with experimental data is made whenever possible. Three methods to estimate the ratio of the branching fractions of J/psi and psi' decays are also discussed. It is pointed out that in order to understand the Rho-pi puzzle, and the dynamics of charmonium decays, systematic studies should be made in theory, phenomenology and experiment aspects.
We calculate the inclusive J/Psi production in heavy ion collisions including the effects of gluon saturation in the wave functions of the colliding nuclei. We argue that the dominant production mechanism in proton--nucleus and nucleus--nucleus collisions for heavy nuclei is different from the one in hadron-hadron interactions. We find that the rapidity distribution of primary J/Psi production is more peaked around midrapidity than the analogous distribution in elementary pp collisions. We discuss the consequences of this fact on the experimentally observed J/Psi suppression in Au-Au collision…
We point out that non-leptonic B decays driven by b-->ccbar s should provide a favourable environment for the production of hidden charm diquark-antidiquark bound states that have been suggested to explain the resonances with masses around 4 GeV recently observed by BaBar and BELLE. Studying their relative abundances in non-leptonic B decays can teach us novel lessons about their structure and the strong interactions. Through their decay into psi they can provide a natural explanation of the excess of B-->psi X observed for p_psi < 1 GeV. Other phenomenological consequences are mentioned as we…
The hierarchy among the radiative $γ$($π^0$, $η$, $η^{\prime}$) decay channels for the $ψ^{\prime}$ looks quite different from the $J/ψ$ one. The fate of charm, namely an ultimate survival of on-shell $c \bar{c}$ intermediate states, might give us the clue for this new puzzle in exclusive charmonium decays. A similar self-preservation has already been invoked in the past to solve the so-called $ρπ$ puzzle.
We estimate the $D$, $\overline{D}$ and $J/Ψ$ meson potentials in nuclei. $J/Ψ$-nuclear potential (self-energy) is calculated based on the color-singlet mechanism, by the $DD$ and $DD^*$ meson loops. This consistently includes the in-medium properties of $D$ and $D^*$ mesons. The potential obtained for the $J/Ψ$ meson is attractive, and it is complementary to the attraction obtained from the color-octet gluon-based mechanism. We predict that the $D^-$ and $J/Ψ$ mesons will be bound in nuclei under proper conditions.
With nonrelativistic QCD factorization, we present a full next-to-leading order computation of the polarization observable for $J/psi$ production at hadron colliders including all important Fock states, i.e. $^3S_1[1,8]$, $^1S_0[8]$, and $^3P_J[8]$. We find the $^3P_J[8]$ channel contributes a positive longitudinal component and a negative transverse component. So the $J/psi$ polarization puzzle may be understood as the transverse components canceling between $^3S_1[8]$ and $^3P_J[8]$ channels, which results in mainly the unpolarized (even slightly longitudinally polarized) $J/psi$. This may g…
Nonrelativistic QCD provides a systematic approach for inclusive decays and productions of a quarkonium. By taking color-octet components into account, the approach can explain the $ψ'$-anomaly at Tevatron, where the measured production rate at large transverse momentum $p_\perp$ is in order of magnitude larger than the predicted with color-singlet components only. With the approach one can predict that the produced $J/ψ$ and $ψ'$ at large $p_\perp$ will be transversely polarized. But the prediction fails in confronting with experimental measurements and this generates a puzzle. We examine the…
The observed pT-dependence of nuclear effects for J/Psi produced in heavy ion collisions at RHIC might look puzzling, since the nuclear suppression seems to fade at large pT. We explain this by the interplay of three mechanisms: (i) attenuation of J/Psi in the hot medium created in the nuclear collision; (ii) initial state shadowing of charmed quarks and attenuation of a c-cbar dipole propagating through the colliding nuclei; (iii) a strong Cronin effect for J/Psi caused by saturation of gluons in the colliding nuclei. All three effects are well under control and calculated in a parameter free…
One observes strong suppression effects for hard probes, e.g. the production of J/psi or high-pT particles, in nucleus-nucleus (AA) collisions at RHIC. Surprisingly, the magnitude of the suppression is quite similar to that at SPS. In order to establish whether these features arise due to the presence of a thermalized system of quarks and gluons formed in the course of the collision, one should investigate the impact of suppression mechanisms which do not explicitly involve such a state. We calculate shadowing for gluons in the Glauber-Gribov theory and propose a model invoking a rapidity-depe…
The nonlinear effect of gluon depletion in the collision of large nuclei can be large. It is due to multiple scatterings among comoving partons initiated by primary scattering of partons in the colliding nuclei. The effect can give rise to substantial suppression of $J/ψ$ production in very large nuclei, even if the linear depletion effect is insignificant for the collisions of nuclei of smaller sizes. This mechanism offers a natural explanation of the enhanced suppression in the Pb-Pb data recently observed by NA50.
The nuclear effects in J/psi hadro- and electroproduction on nuclei are considered in framework of reggeon approach. It is shown that screening regime which holds for electroproduction at x_F > 0.7 and for hadroproduction at x_F > -(0.3-0.4) is changed with anti-screening regime for smaller x_F values.
The long-standing puzzle of the quenched $g_A$ in nuclei -- and in dense matter -- is shown to have a simple resolution in a scale-symmetric HLS chiral Lagrangian at the Fermi-liquid fixed point. This resolution exposes scale-chiral symmetry, hidden in QCD in the vacuum, emerging in nuclear matter from low density to high compact-star density. It has important implications on "first principles" approaches to nuclear physics, such as the role of multi-body exchange currents in Gamow-Teller matrix elements in nuclei and in neutrinoless double $β$ decays for going Beyond the Standard Model.
We consider the $J/Ψ$ suppression at a high energy heavy ion collision. An ideal gas of massive hadrons in thermal and chemical equilibrium is formed in the central region. The finite-size gas expands longitudinally in accordance with Bjorken law. The transverse expansion in a form of the rarefaction wave is taken into account. We show that $J/Ψ$ suppression in such an environment, when combined with the disintegration in nuclear matter, gives correct evaluation of NA38 and NA50 data in a broad range of initial energy densities.
We review the production of high-mass lepton pairs in fixed-target experiments, including both Drell-Yan (DY) and heavy quarkonium (J/Psi and Upsilons) production.
In this work we investigate the photoproduction of radially excited vector mesons off nuclei in heavy ion relativistic collisions. In particular, we analyze the exclusive photoproduction of psi(2S) off nuclei, evaluating the coherent and the incoherent contributions to that process. The theoretical framework used in the present analysis is the light-cone dipole formalism and predictions are done for PbPb collisions at the CERN-LHC energy of 2.76 TeV. The theoretical uncertainties are analyzed and comparison is also done to the recent ALICE Collaboration data for the psi(1S) state photoproducti…
We present new results based on an improved version of the Glauber model, used to describe the nuclear absorption of J/psi in reactions between nuclei at high energy. The excitation of the colour degrees of freedom of nucleons, due to collisions mediated by one-gluon exchange, is taken into account. It is found that the proposed mechanism leads to larger nuclear absorption of J/psi than previously considered.
We present a complete evaluation for $\jpsi(\psip)$ prompt production at the Tevatron and LHC at next-to-leading order in nonrelativistic QCD, including color-singlet, color-octet, and higher charmonia feeddown contributions. The short-distance coefficients of $\pj$ at next-to-leading order are found to be larger than leading order by more than an order of magnitude but with a minus sign at high transverse momentum $p_T$. Two new linear combinations of color-octet matrix elements are obtained from the CDF data, and used to predict $\jpsi$ production at the LHC, which agrees with the CMS data. …
We present a summary of the recent results obtained with the novel hadron resonance gas model with the multicomponent hard-core repulsion which is extended to describe the mixtures of hadrons and light (anti-, hyper-)nuclei. A very accurate description is obtained for the hadronic and the light nuclei data measured by STAR at the collision energy $\sqrt{s_{NN}} =200$ GeV and by ALICE at $\sqrt{s_{NN}} =2.76$ TeV. The most striking result discussed here is that for the most probable chemical freeze-out scenario for the STAR energy the found parameters allow us to reproduce the values of the exp…
We study the J/Psi production from nuclei near the kinematic threshold within the collision model, based on the nuclear spectral function, for incoherent primary proton-nucleon charmonium creation processes. The model takes into account the initial proton and final J/Psi absorption, target nucleon binding and Fermi motion, the formation length of J/Psi mesons as well as the effect of their nuclear mean-field potential on these processes. We calculate the A dependences of the absolute and relative (transparency ratio) charmonium yields as well as its excitation function within the different sce…
We calculate the coherent charmonium photoproduction at intermediate energies accounting for the physics of the charmonium bound states and the dependence of the cross section on the region occupied by color using a correspondingly adjusted generalized vector dominance model (GVDM). In the photon energy domain where the coherence lengths are comparable to the average internucleon distances in nuclei and the nuclear radii we found that significant oscillations of the total and forward photoproduction cross sections governed by the longitudinal nuclear form factor are strongly modified by the ch…
Interpreting the J/psi suppression reported in nucleus--nucleus collisions at SPS and RHIC requires the quantitative understanding of cold nuclear matter effects, such as the inelastic rescattering of J/psi states in nuclei or the nuclear modification of parton densities. With respect to our former Glauber analysis, we include in the present work the new PHENIX d--Au measurements, and analyze as well all existing data using the EPS08 nuclear parton densities recently released. The largest suppression reported in the new PHENIX analysis leads in turn to an increase of sigma from 3.5 +/- 0.3 mb …
We present predictions for the J/psi and rho meson production in the heavy ion ultraperipheral collisions (UPC) for the current energy 2.76 TeV at the LHC. Both total cross sections and cross sections with the neutron emission from one or both nuclei are presented. We also analyse the RHIC rho meson photoproduction data and emphasize importance of these data to test the current model for nucleus break up in UPC.
The J/psi-hadron interaction is a key ingredient in analyzing the J/psi suppression in hot hadronic matter as well as the propagation of J/psi in nuclei. As a first step to clarify the J/psi-hadron interactions at low energies, we have calculated J/psi-pi, J/psi-rho and J/psi-nucleon scattering lengths by the quenched lattice QCD simulations with Wilson fermions for beta=6.2 on 24^3*48 and 32^3*48 lattices. Using the Luscher's method to extract the scattering length from the simulations in a finite box, we find an attractive interaction in the S-wave channel for all three systems: Among others…
Energy dependence of heavy quarkonia production in hadron-nucleus collisions is studied in the framework of the Glauber-Gribov theory. We emphasize a change in the space-time picture of heavy-quark state production on nuclei with energy. Longitudinally ordered scattering of a heavy-quark system takes place at low energies, while with increasing energy it transforms to a coherent scattering of projectile partons on the nuclear target. The characteristic energy scale for this transition depends on masses and rapidities of produced particles. For J/psi, produced in the central rapidity region, th…
We propose to investigate the properties of nuclear matter by measuring the elastic scattering of J/ψon nuclei with high precision. The J/ψmesons are produced from the photons emitted in high energy electron-proton or electron-nucleus scattering in the low-x region. The measurement could be performed at the future ENC, EIC or LHeC facilities.
We report that, unlike most inclusive quarkonium-production processes, the production rate for p p -> J/psi+Upsilon+X dominantly depends on two not well-known long-distance nonrelativistic QCD matrix elements, <O_8^{J/psi}(^3S_1)> and <O_8^{Upsilon}(^3S_1)> at leading order in the strong coupling constant, which account for the transition probabilities of the color-octet spin-triplet heavy-quark-antiquark pairs c\bar{c}_8(^3S_1) -> J/psi and b\bar{b}_8(^3S_1) -> Upsilon, respectively. With the integrated luminosity ~ 100 fb^{-1} at the center-of-momentum energy sqrt{s}=14 TeV we expect that ap…
Recent measurements have established the sensitivity of ultracentral heavy-ion collisions to the deformation parameters of non-spherical nuclei. In the case of ${}^{ 129}$Xe collisions, a quadrupole deformation of the nuclear profile led to an enhancement of elliptic flow in the most central collisions. In ${}^{ 208}$Pb collisions a discrepancy exists in similar centralities, where either elliptic flow is over-predicted or triangular flow is under-predicted by hydrodynamic models; this is known as the $v_2$-to-$v_3$ puzzle in ultracentral collisions. Motivated by low-energy nuclear structure c…
We consider a novel mechanism for J/Psi production in nuclear collisions arising due to the high density of gluons. We calculate the resulting J/Psi production cross section as a function of rapidity and centrality. We evaluate the nuclear modification factor and show that the rapidity distribution of the produced J/Psi's is significantly more narrow in AA collisions due to the gluon saturation effects. Our results indicate that gluon saturation in the colliding nuclei is a significant source of J/Psi suppression that can be disentangled from the quark-gluon plasma effects.
The contribution of the QCD Pomeron to the process AA -> AA J/Psi J/Psi is discussed. We focus on the photon-photon collision, with the quasi-real photon coming from the Weizsacker - Williams spectrum of the nuclei. We calculate the cross section for this process considering the solution of the LLA BFKL equation at zero momentum transfer using a small-t approximation for the differential cross section of the subprocess. Furthermore, the impact of non-leading corrections to the BFKL equation is also analyzed. In both cases the cross section is found to increase with the energy, predicting consi…
The studies of heavy quarkonium inclusive production and polarization at LHC are becoming crucial to solve the puzzle of hadron formation. The results by CMS and the other LHC experiments are compactly presented for the five S-wave states J/Psi, Psi(2S) and Y(nS) (n=1,2,3) and briefly discussed especially in comparison to the theoretical predictions provided by Non Relativistic QCD.
Gluons at small x in high-energy nuclei overlap in the longitudinal direction, so the nucleus acts as a single source of gluons, like higher Fock components in a single nucleon, which contribute to inelastic collisions with a high multiplicity of produced hadrons. This similarity helps to make a link between nuclear effects in pA and high-multiplicity pp collisions. Such a relation is well confirmed by data for the J/Psi production rate in high-multiplicity pp events measured recently in the ALICE experiment. Broadening of J/Psi transverse momentum is predicted for high-multiplicity pp collisi…
The production rate of prompt $ψ'$'s at large transverse momentum at the Tevatron is larger than theoretical expectations by about a factor of 30. As a solution to this puzzle, we suggest that the dominant $ψ'$ production mechanism is the fragmentation of a gluon into a $c \bar c$ pair in a pointlike color-octet S-wave state, which subsequently evolves nonperturbatively into a $ψ'$ plus light hadrons. The contribution to the fragmentation function from this process is enhanced by a short-distance factor of $1/α_s^2$ relative to the conventional color-singlet contribution. This may compensate f…
We compare the coherent and quasielastic J/psi photoproduction in the peripheral heavy ion collisions in kinematics of RHIC. Our improved estimate of the total coherent cross section is a factor of two smaller than the earlier ones. We find that the counting rate of quasielastic J/psi photoproduction tagged by neutrons emitted due to cascading of the recoiled nucleon within the residual nucleus exceeds the rate of the coherent events. We argue that measurements of this process can be used to learn about the dynamics of color dipole-nucleon interactions in nuclei in the wide effective range of …
The creation of loosely bound objects in heavy ion collisions, e.g. light clusters, near the phase transition temperature $\left(T_{\rm ch} \approx 155 \, \rm{MeV} \right)$ has been a puzzling observation that seems to be at odds with Big Bang nucleosynthesis suggesting that deuterons and other clusters are formed only below a temperature $T\approx 0.1-1 \, \text{MeV}$. We solve this puzzle by showing that the light cluster abundancies in heavy ion reactions stay approximately constant from chemical freeze-out to kinetic freeze-out. To this aim we develop an extensive network of coupled reacti…
The remarkable discrepancy between theory and data on the p_t distribution of J/psi polarization in the process pp -> J/psi+X has been standing as a puzzle for a long time. Our early work indicates that if only considering the color-singlet state, NLO corrections may drastically change the distribution, but are not sufficient to accommodate the data. The color-octet intermediate state was suggested to make up the gap. Therefore a direct motivation is to evaluate if the NLO corrections to the J/psi production via a color-octet can indeed remedy the problem. Unfortunately, our results show that …
We describe a precursor in heavy quarkonium production in terms of a coherent admixture of states of different color, spin, and angular momentum quantum numbers, and obtain the production amplitudes for different quarkonium bound states by projecting out this precursor state onto these bound states. The precursor is absorbed in its passage through a nucleus in a pA reaction, and the total cross section between this precursor with a nucleon can be calculated with the two-gluon model of the Pomeron. Such a description of coherent precursors and their subsequent interactions with nucleons can exp…
In order to examine a muon excess observed by the Pierre Auger Observatory, detailed Monte Carlo simulations were carried out for primary protons, iron nuclei and strangelets (hypothetical stable lumps of strange quark matter). We obtained a rough agreement between the simulations and the data for ordinary nuclei without any contribution of strangelets in primary flux of cosmic rays. Our simulations suggest that the shower observables are dominated by details of hadronic interaction models.
The gluon density in nuclei, G^A(x), is poorly constrained at all x from the current DIS and Drell-Yan data. In this paper, we point out that J/psi production measured in proton-nucleus collisions at sqrt(s)=38.8 GeV by the E866 collaboration puts stringent constraints on the x-dependence of the G^W/G^Be ratio in the x=0.02-0.1 range. The E866 data suggest a rather mild x-dependence of G^W/G^Be, and consequently tend to favour DS and HKM sets, rather than the DSg, EKS, and EPS parametrizations which exhibit a large shadowing and anti-shadowing.
We point out that dissociation of J/Psi by partons (mostly gluons) present in the intermediate stage of heavy-ion collisions can explain J/Psi suppression observed recently by the NA-50 Collaboration at the CERN-SPS in Pb-Pb interactions. Suppression by intermediate stage gluons represents an additional multiplicative factor to that given by Gerschel-Hufner mechanism. The agreement with data on J/Psi suppression both in light- ions induced nuclear collisions and in Pb-Pb interactions requires that the life-time of intermediate gluons increases with nucleon numbers of colliding nuclei. In our m…
We study eta_c and J/psi hadroproduction induced by multiple scattering off fixed centres in the target. We determine the minimum number of hard scatterings required and show that additional soft scatterings may be factorized, at the level of the production amplitude for the eta_c and of the cross section for the J/psi. The J/psi provides an interesting example of soft rescattering effects occurring inside a hard vertex. We also explain the qualitative difference between the transverse momentum broadening of the J/psi and of the Upsilon observed in collisions on nuclei. We point out that resca…
We examine the production of J/$Ψ$ mesons in high energy hadron-nucleus collisions using models that account for both the initial state modification of parton distributions in nuclei and the final state interaction of the produced $c\bar c$ pairs. We show that, at the energies of current fixed target experiments, J/$Ψ$ production through quark-antiquark annihilation gives the largest contribution at $x_F > 0.5$, while gluon-gluon fusion dominates the production at smaller $x_F$. The observed J/$Ψ$ suppression at large $x_F$ is directly connected to nuclear shadowing in deeply inelastic scatter…
Prompt gluons are an additional source for charmonium suppression in nuclear collisions, in particular for nucleus-nucleus collisions. These gluons are radiated as bremsstrahlung in N-N collisions and interact inelastically with the charmonium states while the nuclei still overlap. The spectra and mean number <n_g> of the prompt gluons are calculated perturbatively and the gluon-Psi inelastic cross section is estimated. The integrated cross sections for AB --> J/Psi (Psi')X for p-A and A-B collisions and the dependence on transverse energy for S-U and Pb-Pb can be described quantitatively with…
This work investigates the exclusive photoproduction of $ψ(2S)$ meson off nuclei evaluating the coherent and the incoherent contributions. The theoretical framework used in the present analysis is the light-cone dipole formalism and predictions are done for PbPb collisions at the CERN-LHC energy of 2.76 TeV. A comparison is done to the recent ALICE Collaboration data for the $ψ(1S)$ state photoproduction.
The charmonium yields are expected to be considerably suppressed if a deconfined medium is formed in high-energy heavy-ion collisions. In addition, the bottomonium states, with the possible exception of the Upsilon(1S) state, are also expected to be suppressed in heavy-ion collisions. However, in proton-nucleus collisions the quarkonium production cross sections, even those of the Upsilon(1S), are also suppressed. These "cold nuclear matter" effects need to be accounted for before signals of the high density QCD medium can be identified in the measurements made in nucleus-nucleus collisions. W…
Quarkonium suppression in heavy ion collisions is a potential signature of the formation of the quark-gluon plasma. After a very brief review of the J/psi result at CERN, we restrict our discussion to the effects of the high-energy multiple scattering of the quark pair in the colliding nuclei.
Ultra High Energy Cosmic Rays (UHECR) map at 60 EeV have been found recently by AUGER group spreading anisotropy signatures in the sky. The result have been interpreted as a manifestation of AGN sources ejecting protons at GZK edges mostly from Super-galactic Plane. The result is surprising due to the absence of much nearer Virgo cluster. Moreover, early GZK cut off in the spectra may be better reconcile with light nuclei (than with protons). In addition a large group (nearly a dozen) of events cluster suspiciously along Cen-A. Finally, proton UHECR composition nature is in sharp disagreement …
Coherence effects are important in the description of collisions with extended objects as nuclei. At fixed target energies and small x_F, the coherence length of the fluctuation containing the $c\bar c$ is small and the usual nuclear absorption model is valid. However, at higher energies and/or x_F the nucleus is seen as a whole by the fluctuation. In this case, the total, not the absorptive, $c\bar c-N$ cross section controls the suppression and also shadowing of gluons appears. We propose that the growth of the coherence length can explain the x_F-dependence of present experimental data. For…
We calculate the yields of quarkonia in heavy ion collisions at RHIC and the LHC as a function of their transverse momentum. Based upon non-relativistic quantum chromodynamics, our results include both color-singlet and color-octet contributions and feed-down effects from excited states. In reactions with ultra-relativistic nuclei, we focus on the consistent implementation of dynamically calculated nuclear matter effects, such as coherent power corrections, cold nuclear matter energy loss, and the Cronin effect in the initial state. In the final state, we consider radiative energy loss for the…
The production of J/Psi's in nuclei is re-examined and the critical role of Feynman x distributions in the study of photoproduction and hadronic production of both J/Psi's and Drell-Yan dimuons is expatiated. The need to consider both initial and final state interactions and the key effect of initial state interactions on the total J/Psi cross section are demonstrated. We use a Woods-Saxon Monte Carlo simulation to obtain distributions of the numbers of collisions prior and subsequent to the charmonium production. With those results we relate the mean number of nucleon-nucleon collisions, $<n>…
We discuss the formation of $Δ$ isobars in neutron star matter. We show that their threshold density strictly correlates with the density derivative of the symmetry energy of nuclear matter, the $L$ parameter. By restricting $L$ to the range of values indicated by recent experimental and theoretical analysis, i.e. $40$ MeV $\lesssim L \lesssim 62$ MeV, we find that $Δ$ isobars appear at a density of the order of 2$÷$3 times nuclear matter saturation density, i.e. the same range for the appearance of hyperons. The range of values of the couplings of the $Δ$s with the mesons is restricted by the…
