# XQCD 2016

1-3 August 2016
Plymouth University
Europe/London timezone
The 14th International workshop on QCD in extreme conditions, Aug. 1-3 2016
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# Contribution Poster

Plymouth University - Portland Square
QCD phase diagram

# The $U_A(1)$ breaking in the chiral limit of two-flavour QCD

## Speakers

• Dr. Bastian BRANDT

## Content

We study the strength of the anomalous breaking of the $U_A(1)$ symmetry in the chiral limit of two-flavour QCD at the transition temperature using the difference of the pseudoscalar and scalar iso-vector screening masses. To this end we use simulations with non-perturbatively $O(a)$-improved Wilson fermions for three different pion masses in the range of 200-550MeV on lattices with a temporal extent of 16 and volumes of $32^3$ to $64^3$. We compare our results to the strong breaking at zero temperature and find that the effect of the breaking in the mass difference is reduced by at least a factor of five. This indicates a weak $U_A(1)$ breaking at the transition temperature and raises the question of its influence on the nature of the chiral transition. It is generally expected that a weaker breaking strenghtens the chiral phase transition.