First results on angular distributions of thermal dileptons in nuclear collisions.
نویسندگان
چکیده
The NA60 experiment at the CERN Super Proton Synchrotron 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 lambda, mu, and nu are 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.
منابع مشابه
Modeling Magnetic Field in Heavy ion Collisions Using Two Different Nuclear Charge Density Distributions
By studying the properties of matter during heavy-ion collisions, a better understanding of the Quark-Gluon plasma is possible. One of the main areas of this study is the calculation of the magnetic field, particularly how the values of conductivity affects this field and how the field strength changes with proper time. In matching the theoretical calculations with results obtained in lab, two diffe...
متن کاملIntermediate mass dileptons in relativistic nuclear collisions
We consider the production of lepton pairs with intermediate masses, in relativistic nuclear collisions. Thermal sources are briefly discussed, as well as a newer production mechanism which involves jet-plasma interactions. Estimates for high pT lepton pairs are provided.
متن کاملDileptons and Direct Photons at SPS
The study of dilepton and direct photon emission was one of the main topics of the experimental program at the SPS devoted to the search of signals for QGP formation. Three generations of experiments, Helios-3, NA38/NA50, CERES and NA60 measured e+e− or μ+μ− production in various colliding systems and at different energies. While lepton pair production in p-A collisions was found to be reasonab...
متن کاملExclusive photoproduction of lepton pairs at LHC
Exclusive photoproduction of dileptons, γp → `+`− p, will be measured in ultraperipheral collisions at LHC. The mechanism where the lepton pair comes from a heavy timelike photon radiated from a quark interferes with the pure QED process γγ → `+`−. As an analog of deeply virtual Compton scattering, this timelike Compton scattering is a way to study generalized parton distributions in the nucleo...
متن کاملThermal Dileptons as a Possible Source of the Soft Dilepton Enhancement Measured in A-a Collisions at Sps Energies
The production of soft dileptons in a thermal mesonic medium is discussed in the context of recent CERN experimental data reported by the CERES Collaboration. We do not intend to give a general and critical review, but instead concentrate mainly on our approach, however, incorporating many of the recent attempts in the literature. We calculate the contributions to the dilepton yield arising fro...
متن کاملذخیره در منابع من
با ذخیره ی این منبع در منابع من، دسترسی به آن را برای استفاده های بعدی آسان تر کنید
عنوان ژورنال:
- Physical review letters
دوره 102 22 شماره
صفحات -
تاریخ انتشار 2009