Dependence of semi-inclusive jet and high-$p_{T}$ charged particle production on event activity at high backward-rapidity in $\sqrt{s_\mathrm{NN}}$ = 200 GeV $p$+Au collisions at STAR

About

Observations of flow-like signals in small-system collisions, $pp$ and $p$/$d$+A, have led to a resurgence of interest and measurements, the results of which have perhaps permanently challenged the naive picture of initial geometry and subsequent early-time dynamics for these systems. In the wake of this renewed interest, jet and high-$p_\mathrm{T}$ particle measurements in small systems are proving similarly fruitful and challenging. While no clear signal of jet quenching has been observed, inclusive measurements at both LHC and RHIC energies of $p$/$d$+A collisions show jet spectra enhancement/suppression at high Bjorken-$x$ when binned by event activity (EA) at high backward-rapidity (the A-going direction). In this talk we present the first semi-inclusive small-system jet spectra measurements at RHIC energies. The results show significant suppression of the jet spectra normalized per trigger in high-EA relative to low-EA collisions. PYTHIA 8 simulations verify that the modification of these spectra is not the result of trivial autocorrelations. Surprisingly, these simulations do show a qualitatively similar modification and studies to understand the cause will be presented. Finally, we present charged particle correlations with EA at high backward-rapidity, which hint at energy conservation or fluctuating proton effects..

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