https://web2.ph.utexas.edu/~cmarkert/matsui.pdf

$J/\psi$ Suppression by Quark-Gluon Plasma Formation

Semihard processes in QCD

A golden age for heavy-quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of related experimental activity. The early years of this period were chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in 2004, which presented a comprehensive review of the status of the field at that time and provided specific recommendations for further progress. However, the broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles could only be partially anticipated. Since the release of the YR, the BESII program concluded only to give birth to BESIII; the B-factories and CLEO-c flourished; quarkonium production and polarization measurements at HERA and the Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the deconfinement regime. All these experiments leave legacies of quality, precision, and unsolved mysteries for quarkonium physics, and therefore beg for continuing investigations at BESIII, the LHC, RHIC, FAIR, the Super Flavor and/or Tau-Charm factories, JLab, the ILC, and beyond. The list of newly found conventional states expanded to include h(c)(1P), chi(c2)(2P), B-c(+), and eta(b)(1S). In addition, the unexpected and still-fascinating X(3872) has been joined by more than a dozen other charmonium- and bottomonium-like "XYZ" states that appear to lie outside the quark model. Many of these still need experimental confirmation. The plethora of new states unleashed a flood of theoretical investigations into new forms of matter such as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the spectroscopy, decays, production, and in-medium behavior of c (c) over bar, b (b) over bar, and b (c) over bar bound states have been shown to validate some theoretical approaches to QCD and highlight lack of quantitative success for others. Lattice QCD has grown from a tool with computational possibilities to an industrial-strength effort now dependent more on insight and innovation than pure computational power. New effective field theories for the description of quarkonium in different regimes have been developed and brought to a high degree of sophistication, thus enabling precise and solid theoretical predictions. Many expected decays and transitions have either been measured with precision or for the first time, but the confusing patterns of decays, both above and below open-flavor thresholds, endure and have deepened. The intriguing details of quarkonium suppression in heavy-ion collisions that have emerged from RHIC have elevated the importance of separating hot- and cold-nuclear-matter effects in quark-gluon plasma studies. This review systematically addresses all these matters and concludes by prioritizing directions for ongoing and future efforts.

/pdf/heavy-quarkonium-progress-puzzles-and-opportunities-2tru0l8jyp.pdf

Heavy quarkonium: progress, puzzles, and opportunities

The Two photon particle production mechanism. Physical problems. Applications. Equivalent photon approximation

Asymptotic behaviour of exclusive processes in QCD

$\frac{J}{\ensuremath{\psi}}$ photoproduction has been measured from beryllium and tantalum targets by observing the yield of single muons at a transverse momentum of 1.65 GeV/c with a bremsstrahlung beam of ${E}_{0}=20$ GeV. The results have been interpreted in terms of a nuclearoptics model to yield the $\ensuremath{\psi}$-nucleon total cross section. The result is ${\ensuremath{\sigma}}_{\ensuremath{\psi}N}=3.5\ifmmode\pm\else\textpm\fi{}0.8$ mb.

A Measurement of the a-Dependence of psi Photoproduction

Exclusive photoproduction cross sections have been measured for the processes $\ensuremath{\gamma}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}n$, $\ensuremath{\gamma}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}p$, $\ensuremath{\gamma}p\ensuremath{\rightarrow}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\Delta}}^{++}$, $\ensuremath{\gamma}p\ensuremath{\rightarrow}{\ensuremath{\rho}}^{0}p$, $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}\ensuremath{\Lambda}$, and $\ensuremath{\gamma}p\ensuremath{\rightarrow}{K}^{+}{\ensuremath{\Sigma}}^{0}$ at large $t$ and $u$ values at several energies for each process between 4 and 7.5 GeV. These measurements taken together with past data taken at small values of $t$ and $u$ provide complete angular distributions. The data show the usual small $t$ and $u$ peaks and a central region in which the cross section decreases approximately as ${s}^{\ensuremath{-}7}$. The results are discussed within the context of parton or constituent models.

Measurements of exclusive photoproduction processes at large values of t and u from 4 to 7.5 GeV

The differential cross sections for the elastic scattering of ..pi../sup +/, ..pi../sup -/, K/sup +/, K/sup -/, p, and p-bar on protons have been measured in the t interval -0.04 to -0.75 GeV/sup 2/ at five momenta: 50, 70, 100, 140, and 175 GeV/c. The t distributions have been parametrized by the quadratic exponential form dsigma/dt = A exp( B abs. value(t) + C abs. value(t)/sup 2/ and the energy dependence has been described in terms of a single-pole Regge model. The pp and K/sup +/p diffraction peaks are found to shrink with ..cap alpha..' approx. 0.20 and approx. 0.15 GeV/sup -2/, respectively. The p-barp diffraction peak is antishrinking while ..pi../sup +/- and K/sup -/p are relatively energy-independent. Total elastic cross sections are calculated by integrating the differential cross sections. The rapid decline in sigma/sub el/ observed at low energies has stopped and all six reactions approach relatively constant values of sigma/sub el/. The ratio of sigma/sub el//sigma/sub tot/ approaches a constant value for all six reactions by 100 GeV, consistent with the predictions of the geometric-scaling hypothesis. This ratio is approx. 0.18 for pp and p-barp, and approx. 0.12--0.14 for ..pi../sup +/- and K/sup +/-. A crossover is observedmore » between K/sup +/p and K/sup -/p scattering at abs. value t approx =0.19 GeV/sup 2/, and between pp and p-barp at abs. value t approx=0.11 GeV/sup 2/. Inversion of the cross sections into impact-parameter space shows that protons are quite transparent to mesons even in head-on collisions. The probability for a meson to pass through a proton head-on without interaction inelastically is approx. 20%, while it is only approx. 6% for an incident proton or antiproton. Finally, the results are compared with various quark-model predictions.« less

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pi+- p, K+- p, p p and anti-p p Elastic Scattering from 50-GeV/c to 175-GeV/c

/pdf/high-energy-photoproduction-of-charged-pions-at-backward-4tq17tk4d3.pdf

High-energy photoproduction of charged pions at backward angles.

/pdf/neutral-boson-photoproduction-on-hydrogen-at-high-energies-2h05z1j54b.pdf

D. Gustavson

Papers

A Measurement of the a-Dependence of psi Photoproduction

Measurements of exclusive photoproduction processes at large values of t and u from 4 to 7.5 GeV

pi+- p, K+- p, p p and anti-p p Elastic Scattering from 50-GeV/c to 175-GeV/c

High-energy photoproduction of charged pions at backward angles.

Neutral Boson Photoproduction on Hydrogen at High-Energies