# Quark Matter 2017

5-11 February 2017
Hyatt Regency Chicago
America/Chicago timezone

## Neutron skin at the LHC

Not scheduled
2h 30m
Hyatt Regency Chicago

#### Hyatt Regency Chicago

151 East Wacker Drive Chicago, Illinois, USA, 60601
Board: K02
Poster

### Speaker

Dr Ilkka Helenius (Tübingen University)

### Description

High-energy nuclear collisions are often classified in terms of centrality. Theoretically, the centrality binning is determined by Glauber models which take the nuclear density as an input. The nuclear density is traditionally parametrized by the Woods-Saxon form and is taken to be the same for protons and neutrons. However, according to the theoretical expectations and experimental measurements as well, the tail of neutron density extends farther than that of the the protons. This results in growth of the neutron-to-proton ratio at the edges of nuclei - a phenomenon referred to as neutron-skin effect. In high-energy nuclear collisions this relative increase of neutrons at the edges will have an influence on the centrality dependence of high-$p_{\rm T}$ electroweak observables.

In this talk we present NLO pQCD predictions for the centrality dependence of inclusive high-$p_{\rm T}$ photon production in Pb+Pb collisions at the LHC taking into account the neutron-skin effect and spatially dependent nuclear PDFs, EPS09s [Helenius, Paukkunen, Eskola, arXiv:1606.09044]. In addition, we consider the ratio between positively and negatively charged hadrons as well as W production [Paukkunen, PLB 745 (2015) 73]. The advantage of these latter observables is that the nuclear modifications of the PDFs largely cancel out allowing for a cleaner study of the neutron-skin effect. According to our predictions, the neutron-skin effect can lead to modifications up to 20% in the most peripheral collisions and could thereby serve as a partial benchmark for the experimental centrality measures. In the future, the neutron skin should play a role in the centrality studies at the planned electron-ion colliders EIC and LHeC.

Preferred Track Electromagnetic Probes Not applicable

### Primary author

Dr Ilkka Helenius (Tübingen University)