Tuesday, November 24, 2020, 11:00 am — Videoconference / Virtual Event (see link below)
Abstract: The production of soft photons in small systems was extensively studied in fixed-target experiments at beam momenta ranging from 10.5 to 450 GeV/c.
Most experiments reported an excess of soft photons compared with the expectation from hadron decays that could not be explained by initial- and final-state bremsstrahlung. The emergence of a photon excess in a transverse momentum (pT) range far below 0.2 GeV/c was dubbed the soft-photon puzzle.
At the Intersecting Storage Rings (ISR) at CERN, also an excess of dielectrons had been measured at low invariant mass and small pair pT_ee in pp collisions at sqrt(s) = 63 GeV. In ALICE the reconstruction efficiency of low-pT electrons can be increased by reducing the magnetic field of the central barrel solenoid.
This allows a better electron background rejection and simultaneously enables the investigation of a kinematic domain at low dielectron invariant mass m_ee and pair transverse momentum pT_ee similar to that of the ISR experiment, which was previously inaccessible at the LHC.
In this talk, a measurement of dielectron production in proton-proton (pp) collisions at sqrt(s) = 13 TeV, recorded with the ALICE detector at the CERN LHC, will be presented. The data set was taken with a reduced magnetic solenoid field of 0.2 T. The cross section for dielectron production is studied as a function of mee, pT_ee, and event multiplicity dNch/deta. Comparison of the measured dielectron yield to the hadronic decay cocktail at 0.15
Hosted by: Takao Sakaguchi
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