Measurement of b jet shapes in proton-proton collisions at $$ \sqrt{s} $$ = 5.02 TeV

We present the first study of charged-hadron production associated with jets originating from b quarks in proton-proton collisions at a center-of-mass energy of 5.02 TeV. The data sample used in this study was collected with the CMS detector at the CERN LHC and corresponds to an integrated luminosity of 27.4 pb−1. To characterize the jet substructure, the differential jet shapes, defined as the normalized transverse momentum distribution of charged hadrons as a function of angular distance from the jet axis, are measured for b jets. In addition to the jet shapes, the per-jet yields of charged particles associated with b jets are also quantified, again as a function of the angular distance with respect to the jet axis. Extracted jet shape and particle yield distributions for b jets are compared with results for inclusive jets, as well as with the predictions from the pythia and herwig++ event generators.

Power corrections to event shapes using Eikonal dressed gluon exponentiation

Event shapes are classical tools for the determination of the strong coupling and for the study of hadronization effects in electron-positron annihilation. In the context of analytical studies, hadronization corrections take the form of power-suppressed contributions to the cross section, which can be extracted from the perturbative ambiguity of Borel-resummed distributions. We propose a simplified version of the well-established method of Dressed Gluon Exponentiation (DGE), which we call Eikonal DGE (EDGE), which determines all dominant power corrections to event shapes by means of strikingly elementary calculations. We believe our method can be generalized to hadronic event shapes and jet shapes of relevance for LHC physics.

Impinging Performance of High-Pressure Water Jets Emitting from Different Nozzle Orifice Shapes

The impinging pressure of a water jet is a key factor in engineering applications, and the jet shape has a great influence on this pressure. In this paper, five different nozzle shapes were designed, and impacting tests were conducted based on a self-designed experimental platform using a PVDF piezoelectric film sensor and a high-speed camera to record the impacting data. Additionally, the computational fluid dynamics (CFD) method was also applied to study the velocity distribution. The results show that the pressure profiles of different water jet shapes impacting onto a solid surface present a consistent pattern, namely, an initial transient and enormous peak pressure and then a longer and smaller stagnation pressure. Although the stagnation pressure in this paper is not sufficiently obvious, the peak pressures of the five water jet shapes are much different from one another. Under the same inlet pressure, the peak pressure of the circular water jet is the largest, and those of the square, triangular, cross-shaped, and elliptical water jets decrease in turn. The flowing regimes captured by the high-speed camera together with the CFD simulation results indicate that the discrepancy in the peak pressure may be a combined action of the liquid velocities and jet head shapes.

Axial flow development characteristics of circular and triangular supersonic jets in the presence of an annular coflow at large separation distance

Experimental studies were conducted to assess the effect of an annular coflow which surrounded a supersonic core jet in a coaxial jet system. Two different core jet shapes were employed which were circular and equilateral triangular. The core jets were maintained at two different total pressures, i.e. 360 and 550 kPa which corresponded to overexpansion conditions. The effect of coflow which surrounded core jet at a distance larger than the core jet diameter was such that the supersonic core length of the core jet was reduced in contrast to the elongation which was reported by earlier researchers for closer distances between the two jets. The Schlieren images of the coaxial jet system had shown that the region between the jet boundary of core jet and inner boundary of the annular coflow had a strong interaction with core jet which was characterised by a wave system and vortices. This region caused a reduction in supersonic core length and weakening of shock structure in the core jet. These findings have been corroborated by total pressure measurements along the core jet centreline. For the same operational conditions, the coflow caused reduction in supersonic core length more for triangular core jet when compared to that for circular core jet.

Recent results on hard probes with ALICE and STAR

This paper reviews recent experimental results on hard probes in heavy-ion collisions from the ALICE and STAR Collaboration. These studies include various observables characterizing jet properties like nuclear modification factors, recoil jet yields, di-jet and photon-jet energy imbalance, and the observables characterizing jet properties like jet fragmentation function and jet shapes; and measurements of high-pT charged hadrons from jet fragmentation and triggered particle correlations will be highlighted.