Abstract

Abstract

APS/DNP / Gluon saturation search using $\gamma$+hadron correlations in LHCb

Gluon saturation at small Byorken-$x$ has been in the minds of particle and nuclear physicists for decades. This state can explain several observations in nuclear collisions such as particle collectivity and depleted yields of particle coming from soft gluons. Previous DIS results from HERA show a fast increase of gluons as their fractional momentum decreases. The size of gluons is inversely proportional to the $Q^2$ scale of the process. Therefore, small-$x$ gluons from small $Q^2$ processes are the ones where we expect to be saturated. The saturation scale $Q^2_S(x)$ is still to be determined experimentally. The LHCb experiment is a forward spectrometer with vertexing, tracking, $p$, $K$, $pi$, $e$, $\mu$ identification and calorimetry in the region 1.6$< \eta <$ 4.9. LHCb is the only experiment in the world which can probe $x \sim 10^{-6}-10^{-4}$, up to two orders of magnitude smaller than HERA. A direct probe of gluons with access to small-$x$ and $Q^2$ can be performed with $\gamma$+hadron correlation measurements. These correlations can also provide the fraction $x$ of the gluon and the $Q^2$ of the process. This talk is going to report the status of the analysis efforts aimed of finding evidences of gluon saturation and its scale $Q^2_S(x)$ at LHCb. Future improvements in these measurements with additional triggers and a soft particle tracker in LHCb are also going to be discussed.