Photon pair distributions and event-mixing at low invariant mass

Neutral meson cross-section and direct photon HBT measurements in high energy pp, pA, and AA collisions rely on either subtracting or dividing out the background underlying the $M_mathrm{inv}$ or $Q_mathrm{inv}$ distributions. In this paper we investigate the photon pair distributions for simulated proton-proton collisions at $sqrt{s}=13~$TeV, and show that the correlated part of the background in $M_mathrm{inv}$ gets poorly described by the conventional event-mixing method implemented in experimental analyses. We show that it fails to describe the background as it gives a qualitatively different shape especially at invariant masses around the $pi^{0}$ and $eta$ meson mass. We show that this is caused by the correlations originating from parton fragmentation, and discuss a new method that attempts to describe the correlated part of the combinatorial background by only pairing photons when the parton ancestors are close in $eta$ and $varphi$.

Producing fully-charm structures in the $J/psi$-pair invariant mass spectrum

Very recently, the LHCb Collaboration reported the observation of several enhancements in the invariant mass spectrum of a $J/psi$ pair between 6.2 and 7.4 GeV. In this work, we propose the dynamical mechanism to mimic the experimental data of a di-$J/psi$ mass spectrum given by LHCb, which is based on the reactions, where all the possible combinations of a double charmonium directly produced by a proton-proton collision are transferred into a final state $J/psi J/psi$. We find that the LHCb experimental data can be well reproduced. We further extend our framework to study a di-$Upsilon(1S)$ system, and give the line shape of a differential cross section of a partner process in a $bbar{b}$ system on the invariant mass of $Upsilon(1S)Upsilon(1S)$, which shows that there should exist possible enhancements near $m_{Upsilon(1S)Upsilon(1S)}=$19.0, 19.3, 19.7 GeV in the $Upsilon(1S)$-pair invariant mass spectrum. These predictions can be tested in LHCb and CMS, which can be as a potential research issue in near future.

Photoproduction of a large invariant mass $gamma rho$ pair at small momentum transfer

The collinear factorization framework allows to describe the exclusive photoproduction of a $gamma,rho$ pair in the generalized Bjorken regime in terms of a perturbatively calculable coefficient function and universal generalized parton distributions. The kinematics are defined by a large invariant mass of the $gamma rho$ pair and a small transverse momentum of the final nucleon. We calculate the scattering amplitude at leading order in $alpha_s$ and the differential cross sections for the process where the $rho-$meson is either longitudinally or transversely polarized, in the kinematics of the near future Jlab experiments. Our estimate of the cross section demonstrates that this process is measurable at JLab 12-GeV.

An analysis of gamma-ray data collected at traffic intersections in Northern Virginia

Gamma-ray spectral data were collected from sensors mounted to traffic signals around Northern Virginia. The data were collected over a span of approximately fifteen months. A subset of the data were analyzed manually and subsequently used to train machine-learning models to facilitate the evaluation of the remaining 50k anomalous events identified in the dataset. We describe the analysis approach used here and discuss the results in terms of radioisotope classes and frequency patterns over day-of-week and time-of-day spans. Data from this work has been archived and is available for future and ongoing research applications.

Accessing Generalized Parton Distributions in Exclusive Photoproduction of a $gamma rho$ Pair with a Large Invariant Mass

We propose and study the photoproduction of a $gamma,rho$ pair with a large invariant mass and a small transverse momentum of the final nucleon, as a way to access generalized parton distributions. In the kinematics of JLab 12-GeV, we demonstrate the feasibility of this measurement.