Heavy Vector Mesons Research Articles

Coherent photon-hadron interactions inpAcollisions: Small-xphysics after HERA

In this letter we study the photoproduction of heavy quarks and vector mesons in the coherent proton-nucleus (pA) interactions for RHIC and LHC energies and analyze if these processes can be used to determine the QCD dynamics at high energies. The integrated cross section and rapidity distribution are estimated using the Color Glass Condensate (CGC) formalism. A comparison with the linear dynamics predictions is also presented. Our results indicate that the nonlinear dynamics can be proven in those reactions, which are well suited for studing saturation effects.

Coherent vector meson photoproduction from deuterium at intermediate energies

We analyze the cross section for vector meson photoproduction off a deuteron for the intermediate range of photon energies starting at a few giga-electron-volts above the threshold and higher. We reproduce the steps in the derivation of the conventional nonrelativistic Glauber expression based on an effective diagrammatic method while making corrections for Fermi motion and intermediate-energy kinematic effects. We show that, for intermediate-energy vector meson production, the usual Glauber factorization breaks down, and we derive corrections to the usual Glauber method to linear order in longitudinal nucleon momentum. The purpose of our analysis is to establish methods for probing interesting physics in the production mechanism for \ensuremath{\phi} mesons and heavier vector mesons. We demonstrate how neglecting the breakdown of Glauber factorization can lead to errors in measurements of basic cross sections extracted from nuclear data.

Decay constants of heavy vector mesons in relativistic Bethe–Salpeter method

In a previous Letter, we computed the decay constants of heavy pseudoscalar mesons in the framework of relativistic (instantaneous) Bethe–Salpeter method (full 0− Salpeter equation), in this Letter, we solve the full 1− Salpeter equation and compute the leptonic decay constants of heavy–heavy and heavy–light vector mesons. The theoretical estimate of mass spectra of these heavy–heavy and heavy–light vector mesons are also presented. Our results for the decay constants and mass spectra include the complete relativistic contributions. We find FDs∗≈375±24, FD∗≈340±23(D∗0,D∗±), FBs∗≈272±20, FB∗≈238±18(B∗0,B∗±), FBc∗≈418±24, FJ/Ψ≈459±28, FΨ(2S)≈364±24, Fϒ≈498±20 and Fϒ(2S)≈366± 27 MeV.

PQChPT with staggered sea and valence Ginsparg–Wilson quarks: vector meson masses

We consider partially quenched, mixed chiral perturbation theory with staggered sea and Ginsparg–Wilson valence quarks in order to extract a chiral-continuum extrapolation expression for the vector meson mass up to order , at one-loop level. Based on general principles, we accomplish the task without explicitly constructing a sophisticated, heavy vector meson chiral Lagrangian.

The vector probe in heavy-ion reactions

We review essential elements in using the JP = 1− channel as a probe for hot and dense matter as produced in (ultra-) relativistic collisions of heavy nuclei. The uniqueness of the vector channel resides in the fact that it directly couples to photons, both real and virtual (dileptons), enabling the study of thermal radiation and in-medium effects on both light (ρ, ω, ϕ) and heavy (Ψ, ϒ) vector mesons. We emphasize the importance of inter-relations between photons and dileptons, and characterize relevant energy/mass regimes through connections to QGP emission and chiral symmetry restoration. On the basis of a critical analysis of our current understanding of data from fixed-target energies, we identify open key questions to be addressed.

The ALICE dimuon spectrometer

The ALICE forward muon spectrometer has been designed to measure the complete spectrum of heavy quark vector mesons via their muonic decays in pp, proton–nucleus (pA) and nucleus–nucleus (A–A) collisions. Here we present the main design criteria, an overview of the spectrometer and the status and plans of the project.

Exclusive photoproduction of a heavy vector meson in QCD

The process of exclusive heavy vector meson photoproduction, gamma p -> V p, is studied in the framework of QCD factorization. The mass of the produced meson, V = Upsilon or J/Psi, provides a hard scale for the process. We demonstrate, that in the heavy quark limit and at the one-loop order in perturbation theory, the amplitude factorizes in a convolution of a perturbatively calculable hard-scattering amplitude with the generalized parton densities and the nonrelativistic QCD matrix element <O_1>_V. We evaluate the hard scattering amplitude at one-loop order and compare the data with theoretical predictions using an available model for generalized parton distributions.

A Fast Track Trigger for the H1 collaboration

A new Fast Track Trigger was built for the H1 Experiment at the electron–proton collider HERA. This trigger allows the full three-dimensional reconstruction of all charged tracks measured in the central drift chamber within 25 μs. Particles are reconstructed down to 100 MeV in a high track multiplicity environment with a momentum resolution of better than 3% for 1 GeV tracks. This new device is thus ideally suited to trigger on exclusive final states by identifying particle resonances in e.g. open heavy quark or vector meson production. The trigger makes use of highly parallel track reconstruction algorithms implemented in modern electronics by exploiting high density FPGAs with embedded content addressable memory functionalities for track linking and Floating Point DSPs for track fitting. First results from the commissioning of the frontend system are presented.

Electron-positron pairs as a probe for hadrons in dense matter

In this paper the latest results from the analysis of e + e −-pairs emitted in Pb + Au collisions at 40 AGeV/c and a combined analysis of all data available at 158 AGeV/c are presented. The enhancement of low-mass e + e −-pairs (m ee > 0.2 GeV/c 2) with respect to the expected yield from hadron decays first reported at 158 AGeV/c is also found at 40 AGeV/c and is even larger there. Comparing to various theoretical models based on π + π − annihilation, the data can only be reproduced, if the properties of the intermediate p in the hot and dense medium are modified. Hadron data taken at the same beam energies sheds light on the dynamical evolution of the fireball and addresses the question whether the medium modification is linked to baryon density rather than temperature. In the future e + e −-pairs emitted in heavy-ion collisions will be measured at the LHC with the ALICE Transition Radiation Detector (TRD). Here, special emphasis will be put on the production of heavy vector mesons (J/ψ, ϒ).

Understanding DsJ(2317)

We analyze the hadronic and radiative decay modes of the recently observed DsJ(2317) meson, in the hypothesis that it can be identified with the scalar sℓP=12+ state of cs̄ spectrum (Ds0). The method is based on heavy quark symmetries and vector meson dominance ansatz. We find that the hadronic isospin violating mode Ds0→Dsπ0 is enhanced with respect to the radiative mode Ds0→Ds∗γ. The estimated width of the meson is Γ(Ds0)≃7 keV.

Reduced fermi-motion effect by kinematical corrections in diffractive leptoproduction of heavy quarkonium

The diffractive leptoproductions of heavy vector mesons J/ Ψ and Ψ′ off a nucleon are studied with perturbative QCD, focusing on effects of the Fermi motion due to relative transverse momentum k τ between c and c inside the vector meson. Those effects are calculated under the constraint to ensure the S-wave c c states in the vector meson light-cone wave functions. We find that proper treatment of that constraint moderates the strong suppression of the diffractive production cross sections due to the previous improper one, demonstrating key roles of the Fermi-motion effects when confronting with experimenting data of the Ψ′ production as well as J/ Ψ production from HERA.

Diffractive heavy vector meson production from the BFKL equation

Diffractive heavy vector meson photoproduction accompanied by proton dissociation is studied for arbitrary momentum transfer. The process is described by the non-forward BFKL equation, for which a complete analytical solution is found, giving the scattering amplitude. The impact of non-leading corrections to the BFKL equation is also analysed. Results are compared to the HERA data on J/psi production.

Spin structure function g 1 (x, Q) and the DHGHY integral I(Q) at low Q: predictions from the GVMD model

Theoretical predictions for polarized nucleon structure function $g_1(x,Q^2)$ at low $Q^2$ are obtained in the framework of the Generalized Vector Meson Dominance model. Contributions from both light and heavy vector mesons are evaluated. In the photoproduction limit the first moment of $g_1$ is related to the static properties of nucleon via the Drell-Hearn-Gerasimov-Hosoda-Yamamoto sum rule. This property is employed to fix the magnitude of the light vector meson contribution to $g_1$, using the recent measurements in the region of baryonic resonances. Results are compared to the data on $g_1(x,Q^2)$. Finally, the DHGHY moment function $I(Q^2)$ is calculated, and our theoretical predictions are confronted with the recent preliminary data obtained at the Jefferson Laboratory.

Exclusive production of heavy flavours in the pp system near meson thresholds

We investigate the production of heavy vector mesons with ss̄, cc̄ and bb̄ contents. Starting from a factorization of the full transition amplitude into a hard production amplitude and soft initial and final state interactions, we employ the exchange of three gluons or an instanton 4q qq̄ interaction for the production mechanism. The structure of the mesons produced and the interacting protons are formulated as constituent qq̄ or quark–scalar diquark systems in a covariant relativistic quark model. As an upper limit, we find a typical suppression of the total threshold charm and bottom cross section relative to ϕ(1020) production by typically two and five orders of magnitude, respectively; the proper inclusion of effects from Lorentz contraction and the deformation of the interacting proton turns out to be of significant importance.

Determination of the strong g-coupling and of the μ B * B γ - strength from two-photon decays of heavy vector mesons

We describe a calculation of the two-photon decays of heavy vector-mesons, B * → Bγγ and D * → Dγγ, by using the “heavy meson chiral Lagrangian”. The decay amplitudes are expressed in terms of the strong coupling g of the Lagrangian at various powers and the strength of the anomalous magnetic dipole μ B * B γ (respectively μ D * D γ). In the charm case we are able to express the branching ratio Γ( D *0 → D 0γγ)/Γ( D *0) as a function of g only and we expect it to be in the 10 −6 − 10 −5 range, depending on the value of g. The determination of μ B *0 B 0γ , μ B *+ B+ γ requires a more involved analysis, including the consideration of bremsstrahlung radiation for the B *+ → B +γγ case.

Diffractive production of vector mesons at HERA

Selected recent results on diffractive vector-meson production from the H1 and ZEUS experiments at the HERA ep collider are reviewed and compared with the predictions of the vector-meson dominance model and of perturbative QCD. The helicity structure and energy dependence are studied for production of light and heavy vector mesons across a range of the photon virtuality Q 2 and the squared four-momentum transfer t. The cross section for elastic photoproduction of Ψ is also presented.

Meson Synchrotron Emission from Central Engines of Gamma-Ray Bursts with Strong Magnetic Fields.

Gamma-ray bursts (GRBs) are presumed to be powered by the still unknown central engines with timescales in the range from 1 ms to approximately a few seconds. We propose that the GRB central engines would be a viable site for strong meson synchrotron emission if they were compact astrophysical objects, such as neutron stars or rotating black holes with extremely strong magnetic fields (H approximately 1012-1017 G), and if protons or heavy nuclei were accelerated to ultrarelativistic energies on the order of approximately 1012-1022 eV. We show that the charged scalar mesons like pi+/- and heavy vector mesons like rho, which have several decay modes onto pi+/-, could be emitted, with a high intensity that is a thousand times larger than photons, through strong couplings to ultrarelativistic nucleons. These meson synchrotron emission processes eventually produce a burst of very high energy cosmic neutrinos with 1012 eV</=Enu. These neutrinos are to be detected during the early-time duration of short GRBs.

Diffractive heavy vector meson production at HERA

Selected recent results from the HERA experiment H1 on diffractive J ψ and ψ(2 S) electroproduction in ep collisions are reviewed [1]. The topics covered are J ψ cross sections as a function of the hadronic centre of mass energy W and of the four-momentum transfer Q 2. The corrected φtφ distribution for J ψ mesons together with the extraction of the elastic slope parameter b is shown as well as a study of the helicity structure through decay angular distributions. Finally, the Q 2 dependence of the cross section ration of ψ(2 S) to J ψ will be presented.

Photoproduction of heavy vector mesons at HERA – a test field for diffraction

Exclusive diffractive photoproduction of heavy vector mesons (V=\(\phi, J/\psi\), and \(\Upsilon\)) at HERA is studied in a model employing a dipole Pomeron exchange (P) with an inelastic \(\gamma PV\) vertex. The model is fitted to the data on \({\mathrm{d}\sigma/\mathrm{d}t}\), B, and \(\sigma_{\mathrmel}\) for \(Q^2=0\) and beyond the threshold region. The elastic cross sections for both \(\phi\) and \(J/\psi\) photoproduction show a moderate increase within the HERA energy region. The flattening of the slope B(s) (indicating little or no shrinkage) for \(J/\psi\) is not correlated with the slope of the Pomeron trajectory. Estimates for \(\Upsilon\) photoproduction at HERA are given.

RADIATIVE DECAY OF HEAVY MESONS IN A RELATIVISTIC QUARK MODEL

Radiative decays of heavy vector mesons are considered in the lowest order in a field-theoretic quark model of composite hadrons. The translationally invariant hadron states required in such a calculation are described by constituent quark field operators satisfying equal time algebra and harmonic oscillator wave functions. The constituent quark field operators are Lorentz-boosted through a spin rotation to describe hadrons in motion. The model, like its earlier success in describing different hadronic phenomena, in the present investigation without any free parameters also obtains the radiative decay widths and transition moments in reasonable agreement with other theoretical calculations as well as experimental measurements.