J/psi->VP decays and the quark and gluon content of the eta and eta'
R. Escribano
备注：
7 pages, 1 figure, uses svjour style. Comments on the relationship between J/psi to VP and V to Pgamma decays and on the neglected contributions together with an asymmetric treatment of errors are included
The $η$-$η^\prime$ pseudoscalar mixing angle and the gluonium content of the $η^\prime$ meson are deduced from an updated phenomenological analysis of $J/ψ$ decays into a vector and a pseudoscalar meson. In absence of gluonium, the value of the mixing angle in the quark-flavour basis is found to be $ϕ_P=(40.7\pm 2.3)^\circ$. In presence of gluonium, the values for the mixing angle and the gluonic content of the $η^\prime$ wave function are $ϕ_P=(44.6\pm 4.4)^\circ$ and $Z^2_{η^\prime}=0.29^{+0.18}_{-0.26}$, respectively. The newly reported values of $B(J/ψ\toρπ)$ by the BABAR and BES Collaborations are crucial to get a consistent description of data.
We present an effective field theory based extraction of the eta_c mass and width from a recent measurement by CLEO of the photon line shape in J/Psi -> eta_c gamma decay.
We proceed for the first time to the evaluation of the Born cross section for J/psi+eta(c) production, namely via g+g -> J/psi+eta(c)+g, and show that it has a harder P_T spectrum than the J/psi-pair yield at Born level. If one stuck to a comparison at Born level, one would conclude that J/psi+eta(c) production would surpass that of J/psi+J/psi at large P_T. This is nonetheless not the case since J/psi-pair production, as for single J/psi, receives leading-P_T contributions at higher orders in alpha_s. We also present the first evaluation of these leading-P_T next-to-leading order contribution…
The eta(1835) is confirmed clearly in new BESIII data for J/Psi -> gamma (eta'-pi-pi); the angular distribution of the photon is consistent with a pseudoscalar. This makes it a candidate for an s-sbar radial excitation of eta' and eta(1440) (or one or both of eta(1405) and eta(1475)). However, a conspicuous feature of the BES III data is the absence of evidence for eta(1440) -> eta'-pi-pi while it is well known that eta(1440) appears in eta-pi-pi. Can these facts be reconciled? There is in fact a simple explanation. The channel eta(1440) -> eta-pi-pi may be explained by the two-step process et…
The $η$-$η^\prime$ mixing angle is deduced from an updated phenomenological analysis of $J/ψ$ decays into a vector and a pseudoscalar meson. Corrections due to non-ideal $ω$-$ϕ$ mixing are confirmed to be crucial to find $θ_P=(-16.9\pm 1.7)^\circ$, in agreement with most recent analyses. The newly reported values of $B(J/ψ\toρπ)$ by the BABAR and BES Collaborations make more difficult a reasonable description of data.
We study the effects of final state interactions on the eta(b) => J/psi J/psi decay. In particular, we discuss the effects of the annihilation of eta(b) into two charmed meson and their rescattering into J/psi J/psi. We find that the inclusion of this contribution may enhance the short-distance branching ratio up to about 2 orders of magnitude.
Light quark masses are important fundamental parameters of the Standard Model. The decays psi'-->J/psi pi^0 (eta) were widely used in determining the light quark mass ratio m_u/m_d. However, there is a large discrepancy between the resulting value of m_u/m_d and the one determined from the light pseudoscalar meson masses. Using the technique of non-relativistic effective field theory, we show that intermediate charmed meson loops lead to a sizeable contribution to the decays and hence make the psi'-->J/psi pi^0 (eta) decays not suitable for a precise extraction of the light quark mass ratio.
It is shown that difficulties in reconciling the values of the cross section e+e- -> J/psi+eta_c measured at BELLE and calculated within non-relativistic QCD (NRQCD) are caused not by some misinterpretation of the data or other exotic explanations, but by poor applicability of NRQCD to such processes. We use general theory of hard exclusive processes in QCD together with more realistic models of charmonium wave functions, and show that the BELLE result can be naturally explained.
Estimates of the branching ratios for B_{d,s}->J/psi eta and B_{d,s}->eta l+l- are obtained by SU(3) relation to B_d->J/psi K and B_d->K l+l-, respectively, as functions of the eta mixing parameter, theta_P. Based on these estimates, a discussion of the prospects for HERA-B, CDF-II, and ATLAS on these processes is given. The CP violation in B_{d,s}-> J/psi eta is analyzed in depth and a method to extract the angle gamma of the unitarity triangle is discussed. Finally, a possible method to constrain the Wilson coefficient C_{10A} from measurements on semileptonic B decays such as B_d->J/psi K a…
We show that in the transitions psi' -> h_c π^0 and eta_c' -> chi_{c0} pi^0 the contributions from charmed meson loops are highly suppressed, in contrast to various other charmonium decays. We calculate the width of the psi' -> h_c pi^0, which agrees with the recent BES-III data, and predict the width of the eta_c' -> chi_{c0} pi^0, Γ(eta_c' -> chi_{c0} pi^0) = 1.5\pm0.4 keV. A confirmation of this prediction would also provide additional support for a recent analysis of psi' -> J/psi pi^0 (eta), where loops are claimed to play a prominent role.
It has been argued long ago that eta(b) could be observed through the eta(b) => J/psi(=> mu+ mu-) J/psi(=> mu+ mu-) decay chain. Recent calculations indicate that the width of eta(b) into two J/psi is almost three order of magnitude smaller than the one into the D D*. We study the effects of final state interactions due to the D D* intermediate state on the J/psi J/psi final state. We find that the inclusion of this contribution may enhance the short distance branching ratio of about two orders of magnitude.
The Bc --> J/psi pi, etac pi decays are studied with the perturbative QCD approach. It is found that form factors and branching ratios are sensitive to the parameters w, v, f_J/psi and f_etac, where w and v are the parameters of the charmonium wave functions for Coulomb potential and harmonic oscillator potential, respectively, f_J/psi and f_etac are the decay constants of the J/psi and etac mesons, respectively. The large branching ratios and the clear signals of the final states make the Bc --> J/psi pi, etac pi decays to be the prospective channels for measurements at the hadron colliders
We review selected recent Belle results in quarkonium physics, that include precision measurement of the eta_b(1S) parameters, evidence for the eta_b(2S); evidence for the psi_2(1D); observation of the psi(4040) and psi(4160) transitions to J/psi eta with anomalously high rates; observation of the Upsilon(5S) transitions to Upsilon(1D)pi+pi- and Upsilon(1S,2S)eta. The low excitations of charmonium and bottomonium are in agreement with the Lattice QCD and effective theories calculations, while high excitations show unexpected properties.
The composition of the eta and eta' mesons has long been a source of discussion and is of current interest with new experimental results appearing. We investigate what can be learnt from a number of different processes: V to P gamma and P to V gamma (V and P are light vector and pseudoscalar mesons respectively), P to gamma gamma, J/psi,psi' to P gamma, J/psi,psi' to P V, and chi_{c0,2} to PP. These constrain the eta-eta' mixing angle to a consistent value, phi approx 42 degrees; we find that the c cbar components are lesssim 5% in amplitude. We also find that, while the data hint at a small g…
We compute the decay constants of the lowest ccbar-states with quantum numbers J(PC)=0(-+) [eta_c], 1(--) [J/psi], and 1(+-) [hc] by using lattice QCD and QCD sum rules. We consider the coupling of J/psi to both the vector and tensor currents. Lattice QCD results are obtained from the unquenched (Nf=2) simulations using twisted mass QCD at four lattice spacings, allowing us to take the continuum limit. On the QCD sum rule side we use the moment sum rules. The results are then used to discuss the rate of eta_c --> gamma gamma decay, and to comment on the factorization in B --> X K decays, with …
The $η$-$η^\prime$ pseudoscalar mixing angle and the gluonium content of the $η^\prime$ meson are deduced from an updated phenomenological analysis of $J/ψ$ decays into a vector and a pseudoscalar meson. The values for the mixing angle and the gluonic content of the $η^\prime$ wave function are $ϕ_P=(44.5\pm 4.3)^\circ$ and $Z^2_{η^\prime}=0.28\pm 0.21$, respectively.
We evaluate the form factors describing the semileptonic decays $\bar{B^0}\to J/ψ(η_c) D^+ \ell^- \bar ν_\ell$, within the framework of a QCD relativistic potential model. This decay is complementary to $\bar{B^0}\to J/ψ(η_c) D^+ π^-$ in a phase space region where a pion factors out.We estimate the branching ratio for these semileptonic and nonleptonic channels, finding $\mathcal{BR}(\bar{B^0} \to J/ψ(η_c) D^+ \ell ν_\ell) \simeq 10^{-13}$, $\mathcal{BR}(\bar{B^0} \to J/ψD^+ π^-) = 3.1 \times 10^{-8}$ and $\mathcal{BR}(\bar{B^0} \to η_c D^+ π^-) = 3.5 \times 10^{-8}$.
The inclusive and exclusive B decays into the eta' meson plus others are investigated in a model based on the QCD anomaly. The invariant mass distribution is discussed. The constraint of the effective coupling is obtained from the data of the exclusive decay modes. The branching ratio of J/psi -> eta'eta gamma is predicted to be as large as 5.4*10^{-5}, which can be tested in the forthcoming CLEO-c experiments.
We estimate the quantity |f_eta'^(c)| which is associated with the charm content of eta' meson from the experimentally known ratio R=B(psi ->eta' gamma )/B(psi ->eta_c gamma). It is shown that due to the off-shellness of the c\bar c component of eta', which has been overlooked so far, f_eta'^(c) is further suppressed. Assuming that psi ->eta' gamma decay is dominated by psi ->eta_c transition, we obtain |f_eta'^(c)| = 2.4 MeV which could imply that the (b -> c\bar cs) mechanism does not play a major role in the B -> K eta' decay mode.
Following searches for photinos and very light gravitinos in invisible decays of psi and Upsilon, we discuss new limits on Light Dark Matter and U bosons, from psi and Upsilon decays, as well as rare decays of K+ and invisible decays of pi0, eta and eta' ... . The new limits involving the vector couplings of the U to quarks turn out, not surprisingly, to be much less restrictive than existing ones on axial couplings, from an axionlike behavior of a light U boson, tested in psi --> gamma U, Upsilon --> gamma U and K+ --> pi+ U decays (or as compared to the limit from parity-violation in atomic …
We compute the O(alpha_s^2) correction to the decay rate eta_c --> gamma gamma and discuss its implications for precision quarkonium physics. We study the suitability of the ratio Gamma(J/psi --> e+e-)/Gamma(eta_c --> gamma gamma), in which the non-perturbative or soft effects cancel at O(alpha_s^{0,1}), for extracting fundamental parameters of QCD at low energies. We show that the QCD-based theory of charmonia is not capable of predicting this ratio with any degree of confidence.
The large rate of the $J/ψ+η_c$ production observed by the Belle collaboration has posed a serious challenge to our understanding of the quarkonium. We examine a scenario that there exists a light scalar boson around 5 GeV, with an enhanced coupling solely to the charm quark. Such a scenario would explain the Belle anomaly. It also predicts a significant increase in $J/ψ$ plus open charm pair production. An immediate test for the scalar boson is to look for a peak around 5 GeV in the recoil mass spectrum of $J/ψ$, because the scalar boson can also be produced in association with the $J/ψ$. Fin…
The octet-singlet mixing angle $θ_P$ in the pseudoscalar meson nonet is deduced from the rich set of accurate data on $J/ψ$ decays into a vector and a pseudoscalar meson. Corrections due to non-ideal $ω$-$ϕ$ mixing have been included for the first time and turn out to be crucial to find $θ_P = -16.9 \pm 1.7$ degrees, which is appreciably less negative than previous results coming from similar analyses.
It is pointed out that the decay of the recently observed charmonium eta_c^prime resonance, eta_c^prime -> eta_c pi pi is simply related to the well studied decay psi^prime -> J/psi pi pi and can thus be used for absolute normalization of other decay modes of the eta_c^prime. The total rate of the discussed decay should be approximately three to four times the corresponding rate for the psi^prime$ resonance making the channel with charged pions the most probable exclusive decay mode of the eta_c^prime with the branching ratio in the range 5-10 %.
As a test of the color-singlet mechanism of the nonrelativistic QCD (NRQCD) factorization approach, we consider the exclusive two-quarkonium productions in electron-positron annihilation e+ e- -> eta_c + gamma and e+ e- -> J/psi + J/psi at B factories. The cross sections are computed to the next-to-leading order in alpha_s and are resummed to all orders in half the relative velocity v of the charm quark in each meson rest frame. The available theoretical prediction of the cross section for e+ e- -> J/psi + eta_c at the same level of theoretical accuracies is consistent with the available exper…
The $η$-$η^\prime$ pseudoscalar mixing angle and the gluonium content of the $η^\prime$ meson are deduced from an updated phenomenological analysis of $V\to Pγ$ and $J/ψ\to VP$ decays. In absence of gluonium, the value of the mixing angle in the quark-flavour basis is found to be $ϕ_P=(41.5\pm 1.2)^\circ$ from $V\to Pγ$ and $ϕ_P=(40.5\pm 2.4)^\circ$ from $J/ψ\to VP$. In presence of gluonium, the values for the mixing angle and the gluonic content of the $η^\prime$ wave function are $ϕ_P=(41.4\pm 1.3)^\circ$ and $Z^2_{η^\prime}=0.04\pm 0.09$ from $V\to Pγ$ and $ϕ_P=(44.5\pm 4.3)^\circ$ and $Z^2…
It is shown that the study of the ω-ρinterference pattern in the J/psi -> (rho+omega)eta -> pi+pi-eta decay provides evidence for the large (nearly 90 degrees) relative phase between the isovector one-photon and three-gluon decay amplitudes.
Taking into account the new data on the full width of D^{\ast\pm}(2010) and the mass difference of the charged and neutral beauty mesons B^\pm, B^0,\bar B^0, the branching ratios of the decays psi(3770), Upsilon(10580) to pi^+pi^-, K bar K, rho(omega)pi, rho(omega)eta, rho(omega)eta^prime, K^ast bar K+ c.c, rho^+ rho^-, and K^ast bar K^ast are re-evaluated in the model in which the Okubo-Zweig-Iizuka rule is violated due to the real intermediate state D\bar D in case of psi(3770) and B\bar B in case of Upsilon(10580). The inclusive annihilation of psi(3770) and Upsilon(10580) into light hadron…
We show results from calculations in full lattice QCD of the mass, leptonic width and radiative decay rate to eta_c of the J/psi meson. These provide few % tests of QCD. Another (1.5%) test comes from comparison of time-moments of the vector charmonium correlator with results derived from the experimental values of R(e+e- to hadrons) in the charm region.
We present a new calculation, in the nonrelativistic QCD (NRQCD) factorization formalism, of the relativistic corrections to the double-charmonium cross section sigma[e+ e- -> J/psi+eta_c] at the energy of the Belle and BABAR experiments. In comparison with previous work, our calculation contains several refinements. These include the use of the improved results for the nonperturbative NRQCD matrix elements, the resummation of a class of relativistic corrections, the use of the vector-meson-dominance method to calculate the fragmentation contribution to the pure QED amplitude, the inclusion of…
We propose that the radiative decay process, η_b\to J/ψγ, may serve as a clean searching mode for η_b in hadron collision facilities. By a perturbative QCD calculation, we estimate the corresponding branching ratio to be of order 10^{-7}. Though very suppressed, this radiative decay channel in fact has larger branching ratio than the hadronic decay process η_b\to J/ψJ/ψ, which was previously hoped to be a viable mode for ferreting out η_b in Tevatron Run 2. The discovery potential of η_b through this channel seems promising in the forthcoming LHC experiments and maybe even in Tevatron Run 2, t…
We investigate the masses of the lowest c\bar{c} states, the J/psi and eta_c, in nuclear matter using QCD sum rules. Up to dimension four, the differences between the operator product expansions in vacuum and in medium arise from the density-dependent change in the gluon condensate and from a new contribution proportional to the nucleon expectation value of the twist-2 gluon operator. Both terms together give an attractive shift of about 5-10 MeV to the J/psi and eta_c masses in nuclear matter.
The transverse mass spectra of Omega, J/psi and psi' in Pb+Pb collisions at 158 AGeV are studied within a hydrodynamical model of the quark gluon plasma expansion and hadronization. The model reproduces the existing data with the common hadronization parameters: temperature T=T_H = 170 MeV and average collective transverse velocity v_T = 0.2.
We present the results of recent work on the central exclusive production of meson pairs. We concentrate on the case of flavour-singlet pseudoscalar mesons eta, eta' and show that the central exclusive process, as modelled using a recent novel application of the 'hard exclusive' perturbative formalism, is potentially highly sensitive to the size of the gluon content of these states. We also discuss the exclusive production of meson pairs in the lower mass region, and present the first results of the new Dime Monte Carlo.
The eta(1760) may be significantly produced in J/Psi radiative decay. We deduce from experimental data that its branching ratio to two gluons is bounded, 0.4 +- 0.3 < BR(eta(1760) -> gg) < 0.9 +- 0.3, consistent with gluonic admixture. Moreover, the expectation that there should be an isoscalar analogue of the gluonic (hybrid) meson candidate pi(1800) is argued to reinforce hybrid admixture in eta(1760). Two-gluon coupling of hybrids is estimated in a spectator model to be considerably larger than that of quarkonium. In addition, the two-photon coupling of eta(1760) is estimated to be 1.4 +- 0…
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.
Exclusive J/psi production, gamma* p -> J/psi p, offers a unique opportunity to determine the gluon density of the proton in the small x domain. We use the available HERA data to determine the gluon distribution in the region 10^{-4} <~ x <~ 10^{-2} and 2 <~ Q^2 <~ 10 GeV^2, where the uncertainty on the gluon extracted from the global parton analyses is large. The gluon density is found to be approximately flat at the lower scale; it is compared with those of recent global analyses.
It is argued that the search of the J/psi --> f0(980)omega and J/psi --> a0(980)rho decays and the more precise definition of B(J/psi --> f0(980)phi) are the urgent purposes in the J/ψspectroscopy. It is shown that the study of the omega-rho0 interference pattern in the J/psi --> (ρ^0+ω)eta --> pi+pi-eta decay provides evidence for the large (nearly pi/2) relative phase between the isovector one-photon and three-gluon decay amplitudes .
We investigate the origin of the double logarithms of Q^2/m_c^2 that appear in the calculation of the cross section for e+e- -> J/psi + eta_c at next-to-leading order in alpha_s. We find that, diagram-by-diagram, the double logarithms are accounted for by Sudakov double logarithms and endpoint double logarithms. The Sudakov double logarithms cancel in the sum over all diagrams, but the endpoint double logarithms do not. We reinterpret the endpoint double logarithms in terms of a leading region of loop integration in which a spectator fermion line becomes soft. This reinterpretation may simplif…
Our approach to low-x deep inelastic scattering based on the ell-perp factorization of perturbative QCD (the color-dipole picture) yields parameter-free absolute predictions for J/Psi production. The connection of J/Psi production to the low-x saturation scale and to the gluon structure function is clarified.
A phenomenological analysis of radiative $V\to Pγ$ and $P\to Vγ$ decays is performed with the purpose of determining the gluonic content of the $η$ and $η^\prime$ wave functions. Our results show that within our model there is no evidence for a gluonium contribution in the $η$, $Z_η^2=0.00\pm 0.12$, or the $η^\prime$, $Z_{η^\prime}^2=0.04\pm 0.09$. In terms of a mixing angle description this corresponds to $ϕ_P=(41.4\pm 1.3)^\circ$ and $|ϕ_{η^\prime G}|=(12\pm 13)^\circ$. In addition, the $η$-$η^\prime$ mixing angle is found to be $ϕ_P=(41.5\pm 1.2)^\circ$ if we don't allow for a gluonium comp…
We consider a contribution to J/psi hadroproduction in which the meson production is mediated by three-gluon partonic state, with two gluons coming from the target and one gluon from the projectile. This mechanism involves double gluon density and thus it enters at a non-leading twist, but it is enhanced at large energies due to large double gluon density at small x. The three-gluon contribution to J/psi hadroproduction is calculated within perturbative QCD in the k_T factorization framework, and it is found to provide a significant correction to the standard leading twist cross-section at the…
Next-to-Leading-Order(NLO) QCD corrections to J/jpsi plus eta_c production in e+e- annihilation at sqrt{s}=10.6 GeV is calculated in this paper, and an analytic result is obtained. By choosing proper physical parameters, a K factor (ratio of NLO to LO) of about 2, which is in agreement with the result in Ref.\cite{Zhang:2005ch}, is obtained. Our results show that the Next-Next-to-Leading-Order(NNLO) corrections might be quite large. The plot of the K-factor vs the center-of-mass energy sqrt{s} shows that it is more difficult to obtain a convergent result from the perturbative QCD without resum…
Presented here is a study of the large p_T J/psi production in hard diffractive process by the pomeron exchange at the Fermilab Tevatron. We find that this process (p\bar p \to p+J/psi+X) can be used to probe the gluon content of the pomeron and to measure the gluon fraction of the pomeron. And the diffractive direct J/psi production can also provide another crucial test for the color-octet fragmentation mechanism. Using the renormalised pomeron flux factor D\approx 1/9, the single diffractive J/psi production cross section at large p_T (\geq 8GeV) is found to be of order of 0.01 nb, and the r…
We investigate photo-production of vector mesons J/Psi and Psi(2s), based on both HERA and LHC data, using 2 fits of unintegrated gluon distributions. The latter are subject to non-linear Balitsky-Kovchegov evolution (Kutak-Sapeta gluon; KS) and linear next-to-leading order Balitsky-Kuraev-Fadin-Lipatov evolution (Hentschinski-Sabio Vera-Salas; HSS gluon) respectively. Apart from extending previous studies to the case of radially excited charmonium Psi(2s), we further use an improved set of charmonium wave functions and provide an estimate of the uncertainties associated with the HSS gluon. Wh…
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…
New, more precise data on diffractive J/psi photoproduction and on exclusive J/psi production in the process pp -> p + J/psi + p at the LHC allow a better constraint on the low-x gluon distribution in the domain of relatively low scales Q^2 ~ 2-6 GeV^2. We account for the `skewed' effect and for the real part of the amplitude, as well as for the absorptive corrections in the case of the exclusive process pp -> p + J/psi + p. The predictions for exclusive J/psi production at \sqrt{s}=8 and 14 TeV and for exclusive Upsilon(1S) production at 7, 8 and 14 TeV are also given. We present results at l…
Motivated by recent interest in soft $J/Ψ$ production in B decays, we investigate ${B}^0 \to J/ΨD^{(\star)}$ and $η_c D^{(\star)}$ decays in perturbative QCD. We find that, within that framework, these decays are calculable since the heavy $c\bar{c}$ pair in the final states is created by a hard gluon. The branching ratios are estimated to be around $10^{-7}\sim 10^{-8}$, too small to be consistent with the data, suggesting that other mechanism(s) contribute to the observed excess of soft $J/Ψ$ in ${B}^0 \to J/Ψ+ X$ decays. The possibility of the production of a hybrid $s{\bar d}g$ meson with …
The modifications induced in the calculation of the cross section of the diffractive process gamma gamma -> J/Psi J/Psi when the gluon propagator is changed are analyzed. Instead of the usual perturbative gluon propagator, alternative forms obtained using non-perturbative methods like Dyson-Schwinger equations are used to consider in a more consistent way the contributions of the infrared region. The result shows a reduction in the differential cross-section for low momentum transfer once compared with the perturbative result, to be confirmed with future experimental results from TESLA.
Using a nonrelativistic potential model, we calculate the cross section for the leading-order gluon dissociation of J/psi by including the full gluon wave function. We find that the resulting cross section as a function of gluon energy is reduced by about a factor of three at its maximum value compared to that calculated in the dipole approximation that is usually adopted in theoretical studies. The effect of the reduced cross section on the J/psi dissociation width at finite temperature is also discussed.
We review the search for the quark-gluon plasma using the signal of the suppression of J/psi production in high-energy heavy-ion collisions. Recent observations of anomalous J/psi suppression in high-energy Pb-Pb collisions observed by the NA50 Collaboration are examined and compared with earlier results from pA and nucleus-nucleus collisions with heavy ions of smaller mass numbers. The anomalous suppression of J/psi production in Pb-Pb collisions can be explained as due to the occurrence of a new phase of strong J/psi absorption, which sets in when the number of nucleon-nucleon collisions at …
The NA50 Collaboration has recently observed a strong suppression of J/Psi production in Pb-Pb collisions at 158 Gev/n. We show that this recent observation finds a quantitative explanation in a model which relates the suppression mechanism to the local energy density, whose value is higher in Pb-Pb collisions than in any other system studied previously. The sensitivity of the phenomenon to small changes in the energy density could be suggestive of quark-gluon plasma formation.
We review the theory and phenomenology of the axial U(1) problem with emphasis on the role of gluonic degrees of freedom in eta and eta' production processes, especially the low-energy pN -> pN eta and pN -> pN eta' reactions.
We critically reexamine the formalism for treating the leading-twist contributions from the two-gluon Fock components occurring in hard processes that involve eta and eta' mesons and establish a consistent set of conventions for the definition of the gluon distribution amplitudes, the anomalous dimensions as well as the projector of a two-gluon state onto an eta or eta' state. We calculate the eta, eta'--photon transition form factor to order alpha_s and show the cancellation of the collinear and UV singularities explicitly. An estimate of the lowest Gegenbauer coefficients of the gluon and qu…
Diffractive production of J/Psi particles by virtual photons on a proton target is studied with a view towards understanding two important corrections to the leading order result. First, the effect of Fermi motion of the heavy quarks is studied by performing a systematic expansion in the relative velocity, and a simple correction factor is derived. This is considerably less than estimated previously. Second, since the kinematics necessarily requires that non-zero momentum be transferred to the proton, off-forward gluon distributions are probed by the scattering process. To estimate the importa…
I briefly review the formalism for treating the leading-twist two-gluon states appearing in processes which involve eta and eta' mesons. The constraints on the size of the lowest order Gegenbauer coefficients of the two-gluon distribution amplitude are obtained from the fit to the eta and eta' transition form factor data. The results are applied to chi -> eta eta (eta' eta') decays and deeply virtual electroproduction of eta and eta' mesons.
It is reported on a leading-twist analysis of the eta - photon and eta' - photon transition form factors. The analysis allows for an estimate of the lowest Gegenbauer coefficients of the quark and gluon distribution amplitudes.
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 estimate the survival probability of $J/ψ$ in relativistic heavy-ion collisions, using both short-distance QCD and nuclear absorption mechanism. The suppression is found to be almost 100 percent for a thermally equilibrating quark-gluon plasma. The measurement of such a huge suppression of $J/ψ$ may suggest the existence of a deconfined partonic medium, possibly a thermalised quark-gluon plasma, at RHIC.
We study the scattering lengths of charmonia (J/psi and eta_c) with light hadrons (pi, rho and N) by the quenched lattice QCD simulations on 24x24x24x48, 32x32x32x48 and 48x48x48x48 lattices with the lattice spacing a = 0.068 fm. The scattering length is extracted by using the Luscher's phase-shift formula together with the measurement of the energy shift Delta E of two hadrons on the lattice. We find that there exist attractive interactions in all channels, J/psi(eta_c)-pi, J/psi(eta_c)-rho and J/psi(eta_c)-N: The s-wave J/psi-pi (eta_c-pi) scattering length is determined as 0.0119+-0.0039 fm…
