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Register a new userComparative analysis of $omega p$, $phi p$, and $J/psi p$ scattering lengths from A2, CLAS, and GlueX threshold measurements
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The high accuracy $phi $-meson photoproduction data from the CLAS experiment in Hall~B of Jefferson Laboratory allow us to determine the near-threshold total cross section of the $gamma ptophi p$ reaction and use it for evaluating the $phi p$ scattering length $alpha_{phi p}$. These data result in an absolute value of $|alpha_{phi p}| = (0.063pm 0.010)$~fm, which is smaller than the typical hadron size. A comparative analysis of $alpha_{phi p}$ with the previously determined scattering lengths for $omega p$ and $J/psi p$ from the A2 and GlueX experiments is performed.
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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 $alpha_{J/psi p}$ is provided within the vector meson dominance model. It results in $|alpha_{J/psi p}| = (3.08pm 0.55 ({rm stat.}) pm 0.45 ({rm syst.}))$~mfm.
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Lubomir Pentchev (Thomas Jefferson National Accelerator Facility
, n Newport News
, Virginia
2020
The $J/psi$-$p$ scattering length, $alpha_{J/psi p}$, can be extracted from the $J/psi$ photoproduction cross section near threshold using the Vector Meson Dominance (VMD) model to relate the reaction $gamma p to J/psi p$ to $J/psi p to J/psi p$. Such estimates based on experimental data result in values for $|alpha_{J/psi p}|$, which are much lower than most of the theoretical predictions. In this work, we study the relations between the different results, depending on the use of the total or the differential cross sections, and the method of extrapolating the data to threshold in the case of a low-statistics data sample, such as the near threshold $J/psi$ photoproduction dataset. We estimate a range for $|alpha_{J/psi p}|$ of $0.003$ to $0.025$~fm as extracted from experimental data within the VMD model and discuss possible reasons for such lower values compared to the theoretical results.
The observed enhancement of $pbar p$-production near the threshold in radiative decays of $J/psi$ and $e^+e^-$-annihilations can be explained with final state interactions among the produced $Nbar N$ system, where the enhancement is essentially determined by $Nbar N$ elastic scattering amplitudes. We propose to use an effective theory for interactions in a $Nbar N$ system near its threshold. The effective theory is similar to the well-known one for interactions in a $NN$ system but with distinctions. It is interesting to note that in the effective theory some corrections to scattering amplitudes at tree-level can systematically be summed into a simple form. These corrections are from rescattering processes. With these corrected amplitudes we are able to describe the enhancement near the threshold in radiative decays of $J/psi$ and $e^+e^-$-annihilations, and the $pbar p$ elastic scattering near the threshold.
The production mechanism of quarkonia states in hadronic collisions is still to be understood by the scientific community. In high-multiplicity $p+p$ collisions, Underlying Event (UE) observables are of major interest. The Multi-Parton Interactions (MPI) is a UE observable, where several interactions occur at the partonic level in a single $p+p$ event. This leads to dependence of particle production on event multiplicity. If the MPI occurs in a harder scale, there will be a correlation between the yield of quarkonia and total charged particle multiplicity. The ALICE experiment at the Large Hadron Collider (LHC) in $p+p$ collisions at $sqrt{s}$ = 7 and 13 TeV has observed an approximate linear increase of relative $J/psi$ yield ($frac{dN_{J/psi}/dy}{<dN_{J/psi}/dy>}$) with relative charged particle multiplicity density ($frac{dN_{ch}/dy}{<dN_{ch}/dy>}$). In our present work we have performed a comprehensive study of the production of charmonia as a function of charged particle multiplicity in $p+p$ collisions at LHC energies using pQCD-inspired multiparton interaction model, PYTHIA8 tune 4C, with and without Color Reconnection (CR) scheme. A detail multiplicity and energy dependent study is performed to understand the effects of MPI on $J/psi$ production. The ratio of $psi(2S)$ to $J/psi$ is also studied as a function of charged particle multiplicity at LHC energies.
The decay $J/psi rightarrow omega p bar{p}$ has been studied, using $225.3times 10^{6}$ $J/psi$ events accumulated at BESIII. No significant enhancement near the $pbar{p}$ invariant-mass threshold (denoted as $X(pbar{p})$) is observed. The upper limit of the branching fraction $mathcal{B}(J/psi rightarrow omega X(pbar{p}) rightarrow omega p bar{p})$ is determined to be $3.9times10^{-6}$ at the 95% confidence level. The branching fraction of $J/psi rightarrow omega p bar{p}$ is measured to be $mathcal{B}(J/psi rightarrow omega p bar{p}) =(9.0 pm 0.2 (text{stat.})pm 0.9 (text{syst.})) times 10^{-4}$.
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