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I review the present status in the theoretical and phenomenological understanding of hadron properties in strongly interacting matter. The topics covered are the EMC effect, nucleon structure functions in cold nuclear matter, spectral properties of light vector mesons in hot and cold nuclear matter, and in-medium properties of heavy flavored hadrons.
In an experiment currently being performed at the Institute for High Energy Physics, Serpukhov, Russia, a beam of charged kaons is directed on a copper target. In the electromagnetic field of the target nuclei, two reactions occur: K{sup +}γ → K{sup +}π{sup 0} and K{sup +}γ → K{sup 0}π{sup +}. A peculiar distinction between these two reactions is that there is a chiral anomaly contribution in the former reaction, but not in the latter. This contribution can be directly seen through comparison of the cross sections of these reactions near the threshold. In Ref. [1] expressions for these cross sections are derived taking into account the anomaly and the contribution of the lightest vector mesons. In this talk an overview of the derivation is provided and cross sections numerical values near the threshold are presented.
We append a simple Pomeron pole amplitude by t and Q{sup 2}, MV dependencies inspired by geometrical ideas. The experimentally transition from soft to hard dynamics is realized by the introduction of a two-component Pomeron with different Q{sup 2} and M{sub V}-dependent residues. A unified description of deeply virtual Compton scattering (DVCS), of exclusive electroproduction of all vector mesons as well as of elastic pp scattering is suggested.
We apply the BLM scale setting procedure directly to amplitudes (cross sections) of several semihard processes. It is shown that, due to the presence of β{sub 0}-terms in the NLA results for the impact factors, the obtained optimal renormalization scale is not universal, but depends both on the energy and on the process in question. We illustrate this general conclusion considering the following semihard processes: (i) inclusive production of two forward high-p{sub T} jets separated by large interval in rapidity (Mueller-Navelet jets); (ii) high-energy behavior of the total cross section for highly virtual photons; (iii) forward amplitude of the production of two light vector mesons in the collision of two virtual photons.
We present new results on the decay patterns of scalar and tensor glueballs in the top-down holographic Witten-Sakai-Sugimoto model. This model, which has only one free dimensionless parameter, gives semi-quantitative predictions for the vector meson spectrum, their decay widths, and also a gluon condensate in agreement with SVZ sum rules. The holographic predictions for scalar glueball decay rates are compared with experimental data for the widely discussed gluon candidates f{sub 0}(1500) and f{sub 0}(1710)
We compare the predictions of two saturation models for production of vector mesons and of photons in electron-ion collisions. The models considered are the b-CGC and the rcBK. The calculations were made in the kinematical range of the LHeC and of the future eRHIC.
This paper reports on a search for lepton flavor violating decays of a {tau} lepton to a lighter-mass charged lepton and an {omega} vector meson. The data sample corresponds to an integrated luminosity of 384 fb{sup -1} recorded by the BaBar experiment at the SLAC PEP-II asymmetric-energy B Factory. No evidence for a signal is found and the upper limits on the branching ratios are determined to be B({tau}{sup {+-}} {yields} e{sup {+-}}{omega}) < 1.1 x 10{sup -7} and B({tau}{sup {+-}} {yields} {mu}{sup {+-}}{omega}) < 1.0 x 10{sup -7} at 90% confidence level.
Color transparency (CT) phenomena in elastic electroproduction of vector mesons off nuclei are usually infected by the onset of coherence length (CL) effects. However, at low energies corresponding to the CLAS experiment at Jefferson Lab (JLab), one can study practically the net CT effects, since CL is much shorter than the nuclear radius. We investigate various manifestations of CT effects using rigorous quantum mechanical approach based on the path integral technique. We include also the effects of {rho} meson decay inside the nucleus leading to a rise of the nuclear suppression towards small values of Q{sup 2}. Motivated by the last CLAS data we predict the A, Q{sup 2} and l{sub c} dependence of nuclear transparency for {rho}{sup 0} mesons produced incoherently off nuclei. We also perform predictions for expected signal of CT corresponding to the planned JLab upgrade to 12 GeV electron beam.
In this work, we calculate the CP-averaged branching ratios and the polarization fractions of the charmless hadronic B{sub c}{yields}A{sub 2}A{sub 3} decays within the framework of perturbative QCD (pQCD) approach, where A is either a light {sup 3}P{sub 1} or {sup 1}P{sub 1} axial-vector meson. These 32 decay modes can occur through the annihilation topology only. Based on the perturbative calculations and phenomenological analysis, we find the following results: (a) the branching ratios of the considered 32 B{sub c}{yields}A{sub 2}A{sub 3} decays are in the range of 10{sup -5} to 10{sup -8}; (b) B{sub c}{yields}a{sub 1}b{sub 1}, K{sub 1}{sup 0}K{sub 1}{sup +} and some other decays have sizable branching ratios and can be measured at the LHC experiments; (c) the branching ratios of B{sub c}{yields}A{sub 2}({sup 1}P{sub 1})A{sub 3}({sup 1}P{sub 1}) decays are generally much larger than those of B{sub c}{yields}A{sub 2}({sup 3}P{sub 1})A{sub 3}({sup 3}P{sub 1}) decays with a factor around (10{approx}100); (d) the branching ratios of B{sub c}{yields}K{sub 1}{sup 0}K{sub 1}{sup +} decays are sensitive to the value of {theta}{sub K}, which will be tested by the running LHC and forthcoming SuperB experiments; (e) the large longitudinal polarization contributions govern most considered decays and play the dominant role.
In the last 15 years collaborations world-wide have contributed to the discovery of many exotic candidate states, such as those made from two quarks and two antiquarks. With these discoveries there has been renewed interest in spectroscopy and in particular, searches for other such particles. Thomas Jefferson National Accelerator Facility is home to the GlueX experiment which uses a 12 GeV electron beam incident on a diamond radiator to produce a linearly polarized, coherent Bremsstrahlung photon beam. The primary goal of GlueX is to search for so-called exotic hybrid mesons (comprised of a quark, an anti quark, and a gluon) by first mapping out the conventional spectrum of mesons starting with the often poorly understood excited vector mesons. Photoproduction at these energies is relatively unexplored and the use of a polarized beam allows GlueX to discriminate between various production mechanisms which may aid in the identification of exotic hybrid mesons. Successfully commissioned in 2015, GlueX has recently completed data taking for its first phase (GlueX-I) which represents orders of magnitude more statistics than previous photoproduction experiments. In this talk we will present an overview of the spectroscopy being performed at Jefferson Lab with a focus on GlueX.
We report measurements of production cross sections for 𝜌 + , 𝜌 0 , 𝜔, 𝐾* + , 𝐾* 0 , 𝜙, 𝜂, 𝐾$^0_𝑆$, 𝑓 0 (980), 𝐷 + , 𝐷 0 , 𝐷$^+_𝑠$, 𝐷* + , 𝐷* 0 , and 𝐷*$^+_𝑠$ in 𝑒 + 𝑒 − collisions at a center-of-mass energy near 10.58 GeV. The data were recorded by the Belle experiment, consisting of 571 fb −1 at 10.58 GeV and 74 fb −1 at 10.52 GeV. Production cross sections are extracted as a function of the fractional hadron momentum 𝑥 𝑝 . The measurements are compared to pythia Monte Carlo generator predictions with various fragmentation settings, including those that have increased fragmentation into vector mesons over pseudoscalar mesons. The cross sections measured for light hadrons are consistent with no additional increase of vector over pseudoscalar mesons. The charmed-meson cross sections are compared to earlier measurements—when available—including older Belle results, which they supersede. They are in agreement before application of an improved initial-state radiation correction procedure that causes slight changes in their 𝑥 𝑝 shapes.
The GlueX experiment is housed in the newest experimental hall at the Thomas Jefferson National Accelerator Facility in Newport News, Virginia. It was successfully commissioned in 2015 and is in its third year of data taking. GlueX uses a 12 GeV electron beam incident on a diamond radiator, producing a linearly polarized, coherent Bremsstrahlung photon beam. The ultimate goal of GlueX is to search for exotic hybrid mesons (e.g. $q\bar{q}g$), with either exotic or conventional quantum numbers, whose existence, or lack thereof, would allow for the exploration of the gluon-gluon coupling present in QCD through the manifestation of hadrons with gluonic degrees of freedom. Photo-production at these energies is fairly unexplored and the linear beam polarization allows GlueX to discriminate between various production mechanisms which may be an effective way to identify such exotic hybrid mesons. In addition to exotic mesons, GlueX will also be poised to map out the conventional meson spectrum and to study the spectrum of excited vector mesons, which are often poorly understood. Here in these proceedings, we will present an overview of the GlueX experiment, its goals, current physics results, and future plans.
The GlueX experiment is housed in the newest experimental hall at the Thomas Jefferson National Accelerator Facility in Newport News, Virginia. It was successfully commissioned in 2015 and is in its third year of data taking. GlueX uses a 12 GeV electron beam incident on a diamond radiator, producing a linearly polarized, coherent Bremsstrahlung photon beam. The ultimate goal of GlueX is to search for exotic hybrid mesons (e.g. $q\bar{q}g$), with either exotic or conventional quantum numbers, whose existence, or lack thereof, would allow for the exploration of the gluon-gluon coupling present in QCD through the manifestation of hadrons with gluonic degrees of freedom. Photo-production at these energies is fairly unexplored and the linear beam polarization allows GlueX to discriminate between various production mechanisms which may be an effective way to identify such exotic hybrid mesons. In addition to exotic mesons, GlueX will also be poised to map out the conventional meson spectrum and to study the spectrum of excited vector mesons, which are often poorly understood. Here in these proceedings, we will present an overview of the GlueX experiment, its goals, current physics results, and future plans.
Here, we study the equation of state of hot and dense hadronic matter using an extended chiral mean field (CMF) model framework where the addition is the inclusion of interactions of thermally excited mesons. This is implemented by calculating the in-medium masses of pseudoscalar and vector mesons, obtained through the explicit chiral symmetry-breaking and vector-interaction terms in the Lagrangian, respectively, prior to applying the mean-field approximation. As a result, the in-medium meson contributions generate a feedback term to the CMF’s equations of motion, which then modifies the equation of state. With this improvement, we quantify the effect on the equation of state of strongly interacting matter through comparisons with state-of-the-art lattice QCD results and other hadronic models like the hadron resonance gas model. We find that the results of the updated hadronic CMF model with an improved meson description (mCMF) provide a better agreement with lattice-QCD data for thermodynamic state variables across a wide range of temperatures and baryon chemical potentials.
Jefferson Lab's experiment E04-005, the largest integrated luminosity real photon CLAS experiment to date, provided a large sample of leptonic data; allowing for studies of the rho - omega interference in the dileptonic decay channel, as well as charge radius and comparative branching ratio studies of the eta and eta' through the Dalitz decay channel. An experimental study of the rho - omega provides valuable input for theoretical models and calculations in addition to establishing a comparative basis for medium modification studies of vector mesons off of heavier targets. The total statistics collected for the eta dalitz exceed the world's published statistics by an order of magnitude, while the eta' Daltiz decay is observed and measured for the first time.
We extend our previous work on the spin alignment of the ϕ vector meson in the hadronic phase of the quark gluon plasma, by including effects of nucleon scatterings. The emission rates are calculated in a realistic hydrodynamic background simulated with the code FLUIDuM , for different beam energies. We find that all the effects taken into account cannot explain the out-of-plane spin alignment of the ϕ meson observed experimentally.
With the availability of new high-statistics and wide-angle measurements for several exclusive non-πN meson photoproduction channels from Jefferson Lab, we examine the fundamental scaling law of 90° scattering in QCD that was originally derived in the high-energy perturbative limit. The data show scaling to be prominently visible even in the medium-energy domain of 2.5 GeV ≲√s≲2.84 GeV, where √s is the center-of-mass energy. While constituent quark exchange suffices for pseudoscalar mesons, additional gluon exchanges from higher Fock states of the hadronic wave functions appear be needed for vector-meson production. Finally, the case of the Φ(1020), where two-gluon exchanges are known to dominate, is especially illuminating.