Recent studies on high-multiplicity events in small collision systems(proton-proton and proton-lead)have drawn considerable research interest toward the possibility of the formation of partonic medium in such systems.One of the important consequences of the formation of dense partonic medium is the quenching of high-momentum final-state particles,resulting in several experimental observations such as suppression in nuclear modification factor RAA,modification of jet shape observableρ(r)and jet fragmentation(z^(ch))distributions,etc.In this work,we studyρ(r)and z^(ch)for inclusive charged-particle jets in proton-proton(pp)collisions at√s=13 TeV using the PYTHIA 8 Monash 2013 Monte Carlo simulation.We show that the color reconnection(CR)and multiparton interaction(MPI)mechanisms in PYTHIA 8 can lead to an increased rate of jet production.We also find that the mechanisms of MPI and CR and change in the gluonic contribution in high-multiplicity events result in significant modification ofρ(r)and z^(ch)compared to those in minimum bias events for 10and gluonic contribution with the amount of modification inρ(r):the larger the number of MPIs and/or gluonic contribution,the larger the amount of modification ofρ(r).
A recent satellite observation has revealed the presence of energy conversion in the separatrix region(SR)of magnetotail reconnection,driven by perpendicular components.We investigated this phenomenon by means of particle-in-cell simulations in two-dimensional(2D)and three-dimensional(3D)systems.Our result indicates that in the 2D simulation,energy conversion in the SR is dominated by parallel components,with the main influencing factor being the parallel electric field,which is not consistent with the observation.However,a case that is similar to the observation is found in the 3D simulation,suggesting that the observation result may be attributed to the 3D characteristics.Our findings provide a potential explanation for the satellite observation.
Magnetic reconnection processes and their impact on planetary magnetospheric dynamics exhibit significant differences due to differences in upstream solar wind conditions and internal planetary environments.Current understanding of reconnection phenomena at Mercury is rooted in the MESSENGER mission.However,direct detection of reconnection remains rare.Here,we aim to assess the limitations of MESSENGER in detecting reconnection in Mercury’s space and to discuss key issues of reconnection that will be addressed by BepiColombo,including the dynamics of magnetic flux ropes,particle acceleration,density asymmetric reconnection,IMF-driven near-tail structures,and potential modes of magnetospheric convection.
Based on current sheet flapping motion on 27 August 2018 in the dusk flank magnetotail,as recorded by instruments aboard Magnetospheric Multiscale(MMS)spacecraft,we present the first study of guide field reconnection observed in the flux rope embedded in kink-like flapping current sheets near the dusk-side flank of the magnetotail.Unlike more common magnetotail reconnections,which are symmetric,these asymmetric small-scale(λ_(i)~650 km)reconnections were found in the highly twisted current sheet when the direction normal to the sheet changes from the Z direction into the Y direction.The unique feature of this unusual reconnection is that the reconnection jets are along the Z direction-different from outflow in the X direction,which is the more usual situation.This vertical reconnection jet is parallel or antiparallel to the up-and-down motion of the tail’s current sheet.The normalized reconnection rate R is estimated to be~0.1.Our results indicate that such asymmetric reconnections can significantly enlarge current sheet flapping,with large oscillation amplitudes.This letter presents direct evidence of guide field reconnection in a highly twisted current sheet,characterized by enlarged current sheet flapping as a consequence of the reconnection outflow.
