Session G14: Hadronic Physics

On Demand

Inclusive electron scattering yields from a hydrogen target at a beam energy of 10.6 GeV have been measured with the CLAS12 spectrometer at Jefferson Laboratory. These data cover a wide kinematic area in invariant mass of the final hadrons W up to 3 GeV and four- momentum transfer Q$^{\mathrm{2}}$ from 1 to 10 GeV$^{\mathrm{2}}$. These will be used to measure inclusive cross sections in the range of W\textless 3.0 GeV in Q$^{\mathrm{2}}$ bins of \textless 0.3 GeV$^{\mathrm{2}}$. Knowledge on the W-evolution of the inclusive cross sections is of particular importance in order to gain insight into the parton distributions in the resonance region and their evolution over a wide range of Q$^{\mathrm{2}}$. The CLAS results on nucleon resonance electrocouplings for the first time allow us to evaluate the s-channel resonance contributions in inclusive electron scattering observables for Q$^{\mathrm{2}}$\textless 6.0 GeV$^{\mathrm{2}}$, offering new prospects for the exploration of the parton distributions in the resonance region and for studies of quark-hadron duality. The current status of this analysis will be shown and the longer-term plans will be discussed.   

Not Participating

The unique scientific capabilities for studies of the transverse spatial and momentum structure of the nucleon offered by the HallC Jlab science program as enabled by the two-arm combination of a high-resolution neutral-particle spectrometer (NPS) and a magnetic spectrometer (HMS). It makes possible to validate QCD factorization, a cornerstone of 3D transverse momentum imaging, by measurements of the basic semi-inclusive neutral-pion cross section. In order to extract the real part of the Compton form factor without any assumptions NPS enables precision measurements of the deeply-virtual Compton scattering cross section at different beam energies. NPS intending to push the energy scale of real Compton scattering, the process of choice to explore factorization in a whole class of wide-angle processes and its extension to neutral pion photo-production, by measurements using the combination of high precision calorimetry. I will discuss the status of the instrumentation and the experimental program enabled by the NPS, as well as new science ideas.   

On Demand

The quality of the recent GlueX J/psi photoproduction data from~Hall D at Jefferson Laboratory and the proximity of the data to the energy threshold, gives access to a variety of interesting physics aspects. As an~example, an estimation of the J/psi-nucleon scattering length \textbar J/psip\textbar is~ provided within the vector meson dominance model. It results in~\textbar J/psp\textbar $=$ (3.08~$+$- 0.55(stat:)~$+$- 0.42(syst:)) mfm which is much smaller~than a typical size of a hadron.   

On Demand

The Jefferson Lab experiment E12-16-007 ($J/\psi-007)$ ran in February 2019 and made a measurement of the elastic $J/\psi$ photo-production cross section as a function of proton momentum transfer variable $t$ and photon energy $E_{\gamma}$ in the region where all charm pentaquark states reported by the LHCb collaboration were discovered. The experiment has been performed using a bremsstrahlung beam generated by a 10.6 GeV incident electron beam traversing a copper radiator upstream of a hydrogen target in Hall C. The two high momentum spectrometers of Hall C, HMS and SHMS have been used to detect the $e^{+} e^{-}$ di-lepton $J/\psi$ decay pair in coincidence. In combination with the high incident photon flux, the optimized spectrometer settings provided the preferred kinematics where the s-channel resonant pentaquarks signals, if they exist, should strongly dominate over those of the regular $t$-channel $J/\psi$ production. We shall present results from the $J/\psi-007$ experiment and either confirm or refute the true resonant nature of these states.   

On Demand

The proposed K-Long Facility at JLab, which uses the GlueX detectors, will provide high statistics data in the sector of strange and multi-strange hadrons. Within the KLF it is proposed to produce a $\text{K}_\text{L}$-beam via the photoproduction of $\phi$ by untagged photons off an additional Be-target. Using this high intensity beam, facilitates the access to strangeness and its production on a liquid hydrogen and deuterium targets in the GlueX spectrometer. Finally the existing spectrometer is used to reconstruct final state particles. In this talk, we will report on the ongoing Monte Carlo simulations on hyperon production using the reaction $\text{K}_\text{L}p\to\Sigma^{+}(1670)\to\Lambda\pi^{+}$ as an example. We will focus on the differentiation of kaon induced reactions in contrast to background reactions.   

Equation of State of Two-Flavor Chiral Perturbation Theory at Next-to-Leading-Order

We study the properties of finite isospin quantum chromodynamics (QCD) using chiral perturbation theory ($\chi$PT), which is the low-energy effective theory of QCD valid at scales much smaller than the typical hadronic scale, $\sim4\pi f_{\pi}$, where $f_{\pi}$ is the pion decay constant. For isospin chemical potentials larger (in magnitude) than the pion mass ($m_{\pi}$), it is known that pions condense in the vacuum. The system has been studied extensively at tree-level. We extend this study of the pion-condensed phase to include leading order quantum fluctuations and show how to correctly construct the one-loop effective potential. Using the effective potential, we compute the pressure, isospin density, equation of state and the chiral and pion condensates. We compare our results with those from recent lattice calculations in $2+1$ flavor QCD with physical quark masses. We find that the agreement of tree level $\chi$PT with the lattice is good and improves through the inclusion of loop effects in $\chi$PT.   

On Demand

In this presentation, we will look at double inclusive gluon production, via glasma graphs, in high energy collisions. Specifically, we will see how a bias that modifies the spectral shape of the gluon distributions affects the transverse momentum spectrum and azimuthal correlations. That is, we consider reweighted functional averages over the stochastic ensemble of small-x gluons. Such bias could, for example, be due to the selection of configurations with a greater number of gluons or higher mean transverse momentum squared. We find that fairly simple modification of the gluon distributions can have interesting effects on the azimuthal correlations.   

On Demand

A study of events where the two leading jets are separated by a large pseudorapidity interval void of particle activity, known as jet-gap-jet events, is presented. The jets have transverse momentum $p_T >$ 40 GeV and pseudorapidity 1.4 $< | η_{jet} | <$ 4.7, and opposite-signed pseudorapidities $η_{jet1} · η_{jet2} <$ 0. The analysis is based on an inclusive dijet data sample collected by the CMS experiment in pp collisions during the low-luminosity run in 2015 at $\sqrt(s) =$ 13 TeV with an integrated luminosity of 0.66 pb$^{−1}$ . The fraction of jet-gap-jet events is presented as a function of the pseudorapidity difference between the leading two jets, the transverse momentum of the subleading jet, and the azimuthal angle separation between the leading two jets. The results are compared to perturbative quantum chromodynamics predictions based on the Balitsky-Fadin-Kuraev-Lipatov framework. The study also presents the first experimental observation of jet-gap-jet events with a leading proton.