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Register a new userBroadening of Transverse Momentum of Partons Propagating through a Medium
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Broadening of the transverse momentum of a parton propagating through a medium is treated using the color dipole formalism, which has the advantage of being a well developed phenomenology in deep-inelastic scattering and soft processes. Within this approach, nuclear broadening should be treated as color filtering, i.e. absorption of large-size dipoles leading to diminishing (enlarged) transverse separation (momentum). We also present a more intuitive derivation based on the classic scattering theory of Moli`ere. This derivation helps to understand the origin of the dipole cross section, part of which comes from attenuation of the quark, while another part is due to multiple interactions of the quark. It also demonstrates that the lowest-order rescattering term provides an A-dependence very different from the generally accepted A^{1/3} behavior. The effect of broadening increases with energy, and we evaluate it using different phenomenological models for the unintegrated gluon density. Although the process is dominated by soft interactions, the phenomenology we use is tested using hadronic cross section data.
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The quark-gluon plasma produced in heavy-ion collisions is anisotropic throughout its evolution. This anisotropy changes the physics of jet-medium interaction, making it dependent on the momentum direction of the jet. In this paper we analyze transverse momentum broadening of a jet parton interacting with soft gluons in an anisotropic plasma. Our analysis equally applies to momentum broadening of quasiparticles in kinetic theory. We subtract contribution from instability modes in the deep infrared and discuss how our calculation should be complemented in that regime. The resulting anisotropic collision kernel for momentum broadening is qualitatively different from the equilibrium collision kernel and from the isotropic ansatz used in effective kinetic theory. Because of increased medium screening, there is substantially less transverse broadening at low and intermediate momenta.
We utilize the technology of open quantum systems in conjunction with the recently developed effective field theory for forward scattering to address the question of massless jet propagation through a weakly-coupled quark-gluon plasma in thermal equilibrium. We discuss various possible hierarchies of scales that may appear in this problem, by comparing thermal scales of the plasma with relevant scales in the effective field theory. Starting from the Lindblad equation, we derive and solve a master equation for the transverse momentum distribution of a massless quark jet, at leading orders both in the strong coupling and in the power counting of the effective field theory. Markovian approximation is justified in the weak coupling limit. Using the solution to the master equation, we study the transverse momentum broadening of a jet as a function of the plasma temperature and the time of propagation. We discuss the physical origin of infrared sensitivity that arises in the solution and a way to handle it in the effective field theory formulation. We suspect that the final measurement constraint can only cut-off leading infrared singularities and the solution to the Markovian master equation resums a logarithmic series. This work is a stepping stone towards understanding jet quenching and jet substructure observables on both light and heavy quark jets as probes of the quark-gluon plasma.
Heavy ion collisions at high energies can be used as an interesting way to recreate and study the medium of the quark-gluon plasma (QGP). We particularly investigate the jets produced in hard binary collisions and their interactions with a tentative medium. These jets were obtained numerically from the Monte-Carlo simulations of hard collisions using the KATIE-algorithm [1], where parton momenta within the colliding nucleons were describe by means of unintegrated parton distribution functions (uPDF). We evolved these jets within a medium that contains both, transverse kicks (yielding a broadening in momentum transvers to the jet-axis) as well as medium induced radiation within the MINCAS-algorithm [2] following the works of [3,4]. We produce qualitative results for the decorrelation of dijets. In particular, we study deviations from a transverse momentum broadening that follows a Gaussian distribution. [1] A. van Hameren, Comput.Phys.Commun. 224 (2018) 371-380 [2] K. Kutak, W. P{l}aczek, R. Straka, Eur.Phys.J. C79 (2019) no.4, 317 [3] J.-P. Blaizot, F. Dominguez, E. Iancu, Y. Mehtar-Tani, JHEP 1301 (2013) 143 [4] J.-P. Blaizot, F. Dominguez, E. Iancu, Y. Mehtar-Tani, JHEP 1406 (2014) 075
The transverse momentum distributions of various hadrons produced in most central Pb+Pb collisions at LHC energy Root(s_NN) = 2.76 TeV have been studied using our earlier proposed unified statistical thermal freeze-out model. The calculated results are found to be in good agreement with the experimental data measured by the ALICE experiment. The model calculation fits provide the thermal freeze-out conditions in terms of the temperature and collective flow effect parameters for different particle species. Interestingly the model parameter fits reveal a strong collective flow in the system which appears to be a consequence of the increasing particle density at LHC. The model used incorporates a longitudinal as well as transverse hydrodynamic flow. The chemical potential has been assumed to be nearly equal to zero for the bulk of the matter owing to a high degree of nuclear transparency effect at such energies. The contributions from heavier decay resonances are also taken into account in our calculations.
Data for Drell-Yan (DY) processes on nuclei are currently available from fixed target experiments up to the highest energy of $sqrt{s}=40GeV$. The bulk of the data cover the range of short coherence length, where the amplitudes of the DY reaction on different nucleons do not interfere. In this regime, DY processes provide direct information about broadening of the transverse momentum of the projectile parton experiencing initial-state multiple interactions. We revise a previous analysis of data from the E772 experiment and perform a new analysis of broadening including data from the E866 experiment at Fermilab. We conclude that the observed broadening is about twice as large as the one found previously. This helps to settle controversies that arose from a comparison of the original determination of broadening with data from other experiments and reactions.
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