First results on angular distributions of thermal dileptons in nuclear collisions
NA60 Collaboration, R. Arnaldi, K. Banicz, K. Borer, J. Castor, B. Chaurand, W. Chen, C. Cicalo, A. Colla, P. Cortese, S. Damjanovic, A. David, A. de Falco, A. … 展开作者
NA60 Collaboration, R. Arnaldi, K. Banicz, K. Borer, J. Castor, B. Chaurand, W. Chen, C. Cicalo, A. Colla, P. Cortese, S. Damjanovic, A. David, A. de Falco, A. Devaux, L. Ducroux, H. En'yo, J. Fargeix, A. Ferretti, M. Floris, A. Foerster, P. Force, N. Guettet, A. Guichard, H. Gulkanian, J. M. Heuser, M. Keil, L. Kluberg, Z. Li, C. Lourenco, J. Lozano, F. Manso, P. Martins, A. Masoni, A. Neves, H. Ohnishi, C. Oppedisano, P. Parracho, P. Pillot, T. Poghosyan, G. Puddu, E. Radermacher, P. Ramalhete, P. Rosinsky, E. Scomparin, J. Seixas, S. Serci, R. Shahoyan, P. Sonderegger, H. J. Specht, R. Tieulent, G. Usai, R. Veenhof, H. K. Woehri
CERN SPS的NA 60实验研究了158 A GeV In-In碰撞中双μ子的产生。在0.2<M<2.6 GeV的完整质量区域中发现的强过量对高于已知源，先前被解释为热辐射。现在我们给出有关角分布的第一个结果。在Collins-Soper参考系中，结构函数参数λ、μ和ν均为零，在极角和方位角上的投影分布是均匀的。没有任何极化是一致的解释多余的双μ子作为热辐射从一个随机系统。
英文摘要：
The NA60 experiment at the CERN SPS has studied dimuon production in 158A GeV In-In collisions. The strong excess of pairs above the known sources found in the complete mass region 0.2<M<2.6 GeV has previously been interpreted as thermal radiation. We now present first results on the associated angular distributions. Using the Collins-Soper reference frame, the structure function parameters λ, μand νare measured to be zero, and the projected distributions in polar and azimuth angles are found to be uniform. The absence of any polarization is consistent with the interpretation of the excess dimuons as thermal radiation from a randomized system.
We review the current understanding of time-like virtual photon emission from QCD matter. The phenomenology of dilepton emission is discussed and basic theoretical concepts are introduced. The experimental findings are presented, grouped into production of lepton pairs in elementary processes, production off cold nuclear matter and emission from heavy-ion collisions. The review emphasizes the role of dilepton emission as tool for studying exotic phases of QCD matter. Open questions and a route to probe the QCD phase diagram with dileptons are outlined.
It is shown that production of low-mass $e^+e^-$-pairs in ultraperipheral nuclear collisions is enhanced due to the Sommerfeld-Gamow-Sakharov (SGS) factor. This effect is especially strong near the threshold of creation of unbound $e^+e^-$-pairs with low masses in the two-photon fusion. Coulomb attraction of the non-relativistic components of such pairs may lead to the increased intensity of 511 keV photons. It can be recorded at the NICA collider and has some astrophysical implications. The analogous effect can be observed at LHC in dilepton production.
An intermediate baryon system formation and the angular distributions of the slow particles emitted in hadron-nuclear and nuclear-nuclear interactions at high energies
We use the microscopic GiBUU transport model to calculate dilepton ($e^+e^-$) production in heavy-ion collisions at SIS18 energies focusing on the effect of collisional broadening of the $ρ$-meson. The collisional width of the $ρ$-meson at finite temperature and baryon density in nuclear matter is calculated on the basis of the collision integral of the GiBUU model. A systematic comparison with HADES data on dilepton production in heavy-ion collisions is performed. The collisional broadening of the $ρ$ improves the agreement between theory and experiment for the dilepton invariant-mass distrib…
Observation of $t\bar{t}$ production in the lepton+jets and dilepton channels in $p$+Pb collisions at $\sqrt{s_\mathrm{NN}}=8.16$ TeV with the ATLAS detector
