Abstract
We examine the spectrum of bremsstrahlung photons that results from the stopping of the initial net charge distributions in ultrarelativistic nucleus-nucleus collisions at the CERN Large Hadron Collier (LHC). This effect has escaped detection so far since it becomes sizable only at very low transverse momentum and at sufficiently forward rapidity. We argue that it may be within reach of the next-generation LHC heavy-ion detector ALICE-3 that is currently under study, and we comment on the physics motivation for measuring it.
Highlights
In ultrarelativistic nucleus-nucleus collisions, bremsstrahlung of soft photons at forward rapidity traces the deceleration of incoming charges and is insensitive to the subsequent dynamical evolution
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Photon emission around central mid-rapidity is expected to be sensitive to the internal structure of the charge distribution, while soft photon emission at forward rapidity is expected to be described by the classical formulation recalled here
Summary
In ultrarelativistic nucleus-nucleus collisions, bremsstrahlung of soft photons at forward rapidity traces the deceleration of incoming charges and is insensitive to the subsequent dynamical evolution. In the late 1990s, calculations of classical electromagnetic bremsstrahlung indicated that the expected effects are measurable in an experimentally accessible kinematic regime and that they could allow one to distinguish between different stopping scenarios [4,5,6]. This prompted studies for a dedicated forward detector at the BNL Relativistic Heavy Ion Collider (RHIC) [4] which, was not realized.
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