Spin asymmetries in electron-jet production at the future electron ion collider

We study all the possible spin asymmetries that can arise in back-to-back electron-jet production, ep → e + jet + X, as well as the associated jet fragmentation process, ep → e+jet(h)+X, in electron-proton collisions. We derive the factorization formalism for these spin asymmetries and perform the corresponding phenomenology for the kinematics relevant to the future electron ion collider. In the case of unpolarized electron-proton scattering, we also give predictions for azimuthal asymmetries for the HERA experiment. This demonstrates that electron-jet production is an outstanding process for probing unpolarized and polarized transverse momentum dependent parton distribution functions and fragmentation functions.

Quenching effects in the cumulative jet spectrum

The steeply falling jet spectrum induces a bias on the medium modifications of jet observables in heavy-ion collisions. To explore this effect, we develop a novel analytic framework to study the quenched jet spectrum and its cumulative. We include many energy-loss-related effects, such as soft and hard medium induced emissions, broadening, elastic scattering, jet fragmentation, cone size dependence, and coherence effects. We show that different observables, based on the jet spectrum, are connected, e.g., the nuclear modification, spectrum shift, and the quantile procedure. We present the first predictions for the nuclear modification factor and the quantile procedure with cone size dependence. As a concrete example, we compare dijet and boson+jet events to unfold the spectrum bias effects, and improve quark-, and gluon-jet classification using arguments based on the cumulative. Besides pointing out its flexibility, finally, we apply our framework to other energy loss models such as the hybrid weak/strong-coupling approach.

Jet fragmentation transverse momentum distributions in pp and p-Pb collisions at $$ \sqrt{s} $$, $$ \sqrt{s_{\mathrm{NN}}} $$ = 5.02 TeV

Jet fragmentation transverse momentum (jT) distributions are measured in proton-proton (pp) and proton-lead (p-Pb) collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5.02 TeV with the ALICE experiment at the LHC. Jets are reconstructed with the ALICE tracking detectors and electromagnetic calorimeter using the anti-kT algorithm with resolution parameter R = 0.4 in the pseudorapidity range |η| < 0.25. The jT values are calculated for charged particles inside a fixed cone with a radius R = 0.4 around the reconstructed jet axis. The measured jT distributions are compared with a variety of parton-shower models. Herwig and Pythia 8 based models describe the data well for the higher jT region, while they underestimate the lower jT region. The jT distributions are further characterised by fitting them with a function composed of an inverse gamma function for higher jT values (called the “wide component”), related to the perturbative component of the fragmentation process, and with a Gaussian for lower jT values (called the “narrow component”), predominantly connected to the hadronisation process. The width of the Gaussian has only a weak dependence on jet transverse momentum, while that of the inverse gamma function increases with increasing jet transverse momentum. For the narrow component, the measured trends are successfully described by all models except for Herwig. For the wide component, Herwig and PYTHIA 8 based models slightly underestimate the data for the higher jet transverse momentum region. These measurements set constraints on models of jet fragmentation and hadronisation.

QGP modification to single inclusive jets in a calibrated transport model

We study inclusive jet suppression and modifications in the quark-gluon plasma (QGP) with a transport-based model. The model includes vacuum-like parton shower evolution at high-virtuality, a linearized transport for jet-medium interactions, and a simple ansatz for the jet-induced hydrodynamic response of the medium. Model parameters are calibrated to nuclear modification factors for inclusive hadron $$ {R}_{AA}^h $$ R AA h and single inclusive jets $$ {R}_{AA}^j $$ R AA j with cone size R = 0.4 in 0–10% central Au-Au and Pb-Pb collisions measured at the RHIC and LHC. The calibrated model consistently describes the cone-size dependent $$ {R}_{AA}^j $$ R AA j (R), modifications to inclusive jet fragmentation functions and jet shape. We discuss the origin of these modifications by analyzing the medium-induced jet energy flow in this model and elucidate the interplay of hard parton evolution and jet-induced medium response. In particular, we demonstrate that the excess of soft hadrons at pT∼ 2 GeV/c in jet fragmentation function and jet shape at large $$ r=\sqrt{\Delta {\eta}^2+\Delta {\phi}^2} $$ r = Δ η 2 + Δ ϕ 2 are consequences of both soft medium-induced gluon radiation and jet-induced medium excitation.