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Register a new userE-by-e jet suppression, anisotropy, medium response and hard-soft tomography
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Authors
Yayun He
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The Linear Boltzmann Transport (LBT) model for jet propagation and interaction in quark-gluon plasma (QGP) has been used to study jet quenching in high-energy heavy-lion collisions. The suppression of single inclusive jet production, medium modification of $gamma$-jet correlation, jet profiles and fragmentation functions as observed in experiments at Large Hadron Collider (LHC) can be described well by LBT in which jet-induced medium response is shown to play an essential role. In event-by-event simulations of jet quenching within LBT, jet azimuthal anisotropies are found to correlate linearly with the anisotropic flows of bulk hadrons from the underlying hydrodynamic events.
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An $omega$-meson in motion with respect to a nuclear medium can couple to a $sigma$-meson through a particle-hole excitation. This coupling is large. We investigate its consequences for the width of $omega$-mesons in matter and for the s-wave annihilation of pions into lepton pairs which can take place in relativistic heavy ion collisions. We find that the two pion decay of $omega$-mesons, resulting from the $omega-sigma$ transition and the subsequent $2pi$ decay of the $sigma$-meson, leads to a substantial broadening of $omega$-mesons in matter and possibly to an observable effect in experiments measuring the $e^+e^-$ decay of vector mesons produced in nuclei and in relativistic heavy-ion collisions. The inverse process, the s-wave annihilation of pions into $omega$-mesons decaying into $e^+e^-$ pairs, has in general a much smaller cross section than the corresponding p-wave annihilation through $rho$-mesons and is expected to contribute rather little to the total $e^+e^-$ pair production in relativistic heavy ion collisions.
The transverse electron scattering response function of 3He is studied in the quasi-elastic peak region for momentum transfers between 500 and 700 MeV/c. A conventional description of the process leads to results at a substantial variation with experiment. To improve the results, the present calculation is done in a reference frame (the ANB or Active Nucleon Breit frame) which diminishes the influence of relativistic effects on nuclear states. The laboratory frame response function is then obtained via a kinematics transformation. In addition, a one-body nuclear current operator is employed that includes all leading order relativistic corrections. Multipoles of this operator are listed. It is shown that the use of the ANB frame leads to a sizable shift of the quasi-elastic peak to lower energy and, contrary to the relativistic current, also to an increase of the peak height. The additionally considered meson exchange current contribution is quite small in the peak region. In comparison with experiment one finds an excellent agreement of the peak positions. The peak height agrees well with experiment for the lowest considered momentum transfer (500 MeV/c), but tends to be too high for higher momentum transfer (10% at 700 MeV/c).
The transverse electron scattering response function of 3He was recently studied by us in the quasi-elastic peak region for momentum transfers q between 500 and 700 MeV/c. Those results, obtained using the Active Nucleon Breit frame (ANB), are here supplemented by calculations in the laboratory, Breit and ANB frames using the two-fragment model discussed in our earlier work on the frame dependence of the the longitudinal response function R_L(q,omega). We find relatively frame independent results and good agreement with experiment especially for the lower momentum transfers. This agreement occurs when we neglect an omega-dependent piece of the one-body current relativistic correction. An inclusion of this term leads however to a rather pronounced frame dependence at q=700 MeV/c. A discussion of this term is given here. This report also includes a correction to our previous ANB results for R_T(q,omega).
The influence of short-range correlations (SRC) on the triple-coincidence (e,e$$pp) reactions is studied. The non-relativistic model uses a mean-field potential to account for the distortions that the escaping particles undergo. Apart from the SRC, that are implemented through a Jastrow ansatz with a realistic correlation function, we incorporate the contribution from pion exchange and intermediate $Delta _{33}$ currents. The (e,e$$pp) cross sections are predicted to exhibit a sizeable sensitivity to the SRC. The contribution from the two-nucleon breakup channel to the semi-exclusive $^{12}$C(e,e$$p) cross section is calculated in the kinematics of a recent NIKHEF-K experiment. In the semi-exclusive channel, a selective sensitivity in terms of the missing energy and momentum to the SRC is found.
The heavy ion total cross section for continuum e+ e- pair production has been calculated to all orders in Z alpha. The formula resulting from an exact solution of the semiclassical Dirac equation in the ultrarelativistic limit is evaluated numerically. An energy dependent spatial cutoff of the heavy ion potential is utilized, leading to an exact formula agreeing with the known perturbative formula in the ultrarelativistic, perturbative limit. Cross sections and sample momentum distributions are evaluated for heavy ion beams at SPS, RHIC, and LHC energies. e+ e- pair production probabilities are found to be reduced from perturbation theory with increasing charge of the colliding heavy ions and for all energy and momentum regions investigated.
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