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Event generator for jet tomography in electron-ion collisions
We develop the first event generator, the electron-heavy-ion-jet-interaction-generator (eHIJING), for the jet tomography study of electron-ion collisions. In this generator, energetic jet partons produced from the initial hard scattering undergo multiple collisions with the nuclear target. The collision rate is proportional to the transverse-momentum-dependent (TMD) gluon density in the nucleus, which is given by a simple model inspired by the physics of gluon saturation. Medium-modified QCD splitting functions within the higher-twist (HT) and generalized higher-twist (GHT) frameworks are utilized to simulate parton showering in the nuclear medium that takes into account the non-Abelian Landau-Pomeranchuck-Midgal interference effect. Employing eHIJING, we revisit hadron production in semi-inclusive deep inelastic scattering (SIDIS) as measured by EMC, HERMES, and recent CLAS experiments. eHIJING with both GT and GHT frameworks gives reasonably good descriptions of these experimental data. Predictions for experiments at the future electron-ion colliders are also provided. It is demonstrated that future measurements of the transverse momentum broadening of single hadron spectra can be used to map out the two-dimensional kinematic (Q 2 , x B ) dependence of the jet transport coefficient $\hat{q}$ in cold nuclear matter.
Update of inclusive cross sections of single and pairs of identified light charged hadrons
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Beam Spin Asymmetry in Semi-Inclusive Electroproduction of Hadron Pairs
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Observation of Azimuth-Dependent Suppression of Hadron Pairs in Electron Scattering off Nuclei
Here, we present the first measurement of dihadron angular correlations in electron-nucleus scattering. The data were taken with the CLAS detector and a 5.0 GeV electron beam incident on deuterium, carbon, iron, and lead targets. Relative to deuterium, the nuclear yields of charged-pion pairs show a strong suppression for azimuthally opposite pairs, no suppression for azimuthally nearby pairs, and an enhancement of pairs with large invariant mass. These effects grow with increased nuclear size. The data are qualitatively described by the GIBUU model, which suggests that hadrons form near the nuclear surface and undergo multiple scattering in nuclei. These results show that angular correlation studies can open a new way to elucidate how hadrons form and interact inside nuclei.
Observation of Enhanced Double Parton Scattering in Proton-Lead Collisions at $\sqrt{s_{NN}}$= 8.16 TeV
A study of prompt charm-hadron pair production in proton-lead collisions at $\sqrt{s_{NN}$ = 8.16 TeV is performed using data corresponding to an integrated luminosity of about 30 nb -1 , collected with the LHCb experiment. Production cross sections for different pairs of charm hadrons are measured and kinematic correlations between the two charm hadrons are investigated. This is the first measurement of associated production of two charm hadrons in proton-lead collisions. The results confirm the predicted enhancement of double parton scattering production in proton-lead collisions compared to the single parton scattering production.
An effective field theory approach to quarkonium at small transverse momentum
In this work we apply effective field theory (EFT) to observables in quarkonium production and decay that are sensitive to soft gluon radiation, in particular measurements that are sensitive to small transverse momentum. Within the EFT framework we study χQ decay to light quarks followed by the fragmentation of those quarks to light hadrons. We derive a factorization theorem that involves transverse momentum distribution (TMD) fragmentation functions and new quarkonium TMD shape functions. We derive renormalization group equations, both in rapidity and virtuality, which are used to evolve the different terms in the factorization theorem to resum large logarithms. This theoretical framework will provide a systematic treatment of quarkonium production and decay processes in TMD sensitive measurements.
Transverse momentum dependent shape function for $J/ψ$ production in SIDIS
It has been shown previously that the transverse momentum dependent (TMD) factorization of heavy quarkonium production requires a TMD shape function. Its perturbative tail can be extracted by matching the cross sections valid at low and high transverse momenta. In this article we compare the order-$α$ s TMD expressions with the order-${α}_{s}^{2}$ collinear ones for $J/ψ$ production in semi-inclusive deep inelastic scattering (SIDIS), employing nonrelativistic QCD in both cases. In contrast to previous studies, we find that the small transverse momentum limit of the collinear expressions contains discontinuities. We demonstrate how to properly deal with them and include their finite contributions to the TMD shape functions. Moreover, we show that soft gluon emission from the low transverse momentum Born diagrams provide the same leading order TMD shape functions as required for the matching. Their revised perturbative tails have a less divergent behavior as compared to the TMD fragmentation functions of light hadrons. Finally, we investigate the universality of TMD shape functions in heavy quarkonium production, identify the need for process dependent factorization and discuss the phenomenological implications.
Transverse single-spin asymmetry of forward 𝜂 mesons in 𝑝 ↑ +𝑝 collisions at √𝑠 =200 GeV
Utilizing the 2012 transversely polarized proton data from the Relativistic Heavy Ion Collider at Brookhaven National Laboratory, the forward 𝜂-meson transverse single-spin asymmetry (𝐴 𝑁 ) was measured for 𝑝 ↑ +𝑝 collisions at √𝑠 =200 GeV as a function of Feynman-x (𝑥 𝐹 ) for 0.2 <|𝑥 𝐹 | <0.8 and transverse momentum (𝑝 𝑇 ) for 1.0 <𝑝 𝑇 <5.0 GeV/𝑐. Large asymmetries at positive 𝑥 𝐹 are observed (⟨𝐴 𝑁 ⟩=0.086±0.019), agreeing well with previous measurements of 𝜋 0 and 𝜂𝐴 𝑁 , but with reach to higher 𝑥 𝐹 and 𝑝 𝑇 . The contribution of initial-state spin-momentum correlations to the asymmetry, as calculated in the collinear twist-3 framework, appears insufficient to describe the data.
Resonances in e + e − annihilation near 2.2 GeV
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Strange quark suppression from a simultaneous Monte Carlo analysis of parton distributions and fragmentation functions
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Precise measurement of the f s / f d ratio of fragmentation fractions and of B s 0 decay branching fractions
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Observation of a near-threshold enhancement in the Λ Λ ¯ mass spectrum from e + e − → ϕ Λ Λ ¯ at s from 3.51 to 4.60 GeV
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Invariant jet mass measurements in p p collisions at s = 200 GeV at RHIC
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QCD analysis of pion fragmentation functions in the xFitter framework
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g T ( x ) contribution to single spin asymmetries in SIDIS
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Parton rescattering and gluon saturation in dijet production at EIC
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