Speaker
Description
This work aims to shed light on the puzzle of small systems, which came about after the measurement of a non-zero high-p$_\perp$ v$_2$ in high multiplicity pA and pp collisions but the persistent absence of jet quenching in those systems. This was done using the JEWEL event generator with a brick-like medium definition mimicking a small collision system. We concentrate on two observables: R$_{AA}$, which measures the energy loss of jets, and v$_2$ of high p$_\perp$ hadrons, which quantifies the azimuthal anisotropy of produced particles. We obtain the results for those two observables as a function of number of scatterings (N$_{scat}$) in the brick-like medium, this way, our conclusions are largely independent of any assumptions about the medium evolution and expansion.
What we have found is that the observables do not depend only on the number of interactions but also on the screening mass ($m_D$), which controls how much energy and momentum are transferred at each interaction, and on how far in the parton shower evolution the interactions happen. In fact, we saw that R$_{AA}$ and v$_2$ scale with $m_D^2 \cdot N_{scat}$. The results also strongly indicate that more interactions (and thus more energy/momentum transfer) are required to create a visible v$_2$ signal than an R$_{AA}$ one. This means that, if we can see v$_2$, in principle, we should also be able to observe an R$_{AA}$ in those systems. These results are discussed in our recent paper [1].
[1] C. Le Roux, J. G. Milhano and K. Zapp. "Modification of jets travelling through a brick-like medium": arXiv:2412.14983
