Forward J/\(\psi\) in ultraperipheral collisions with the ALICE detector during LHC Run 2

Ragoni, Simone (2022). Forward J/\(\psi\) in ultraperipheral collisions with the ALICE detector during LHC Run 2. University of Birmingham. Ph.D.

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Abstract

The ALICE Collaboration has studied coherent J/\(\psi\) photoproduction in Pb–Pb ultraperipheral collisions (UPC) since Run 1. The data sample collected during the LHC Run 2 at forward rapidity, i.e. \(−4 < y < −2.5\), has opened new possibilities. New differential measurements are feasible, and it is then possible to study the properties of coherent J/\(\psi\) . A symmetric collision system such as Pb–Pb has an inherent ambiguity on the sign of the rapidity of the J/\(\psi\) with respect to the ion which is emitting the photon. The analysis of coherent J/\(\psi\) photoproduction in conjuction with neutron emission provides a viable new route to solve this ambiguity, and to probe for nuclear shadowing effects down to a Bjorken-\(x\) of about \(10^{−5}\). The two solutions with the forward rapidity acceptance of the ALICE detector are then sensitive to nuclear shadowing at Bjorken-\(x\) \(\simeq 10^{−2}\) and \(10^{−5}\). In addition, the dataset also allows for the study of the angular distributions of the decay muons of the J/\(\psi\) , thus providing a tool to assess the polarisation of coherently photopro- duced J/\(\psi\). It is found that coherent J/\(\psi\) polarisation is measured to be consistent with transverse polarisation.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):