Jet fragmentation in pp and PbPb collisions at a centre-of-mass energy of 2.76 TeV per nucleon pair was studied using data collected with the CMS detector at the LHC. Fragmentation functions are constructed using charged-particle tracks with transverse momenta p T > 4 GeV/c for dijet events with a leading jet of p T > 100 GeV/c. The fragmentation functions in PbPb events are compared to those in pp data as a function of collision centrality, as well as dijet-p T imbalance. Special emphasis is placed on the most central PbPb events including dijets with unbalanced momentum, indicative of energy loss of the hard scattered parent partons. The fragmentation patterns for both the leading and subleading jets in PbPb collisions agree with those seen in pp data at 2.76 TeV. The results provide evidence that, despite the large parton energy loss observed in PbPb collisions, the partition of the remaining momentum within the jet cone into high-p T particles is not strongly modified in comparison to that observed for jets in vacuum.

Context. Molecular filaments and hubs have received special attention recently thanks to new studies showing their key role in star formation. While the (column) density and velocity structures of both filaments and hubs have been carefully studied, their magnetic field (B-field) properties have yet to be characterized. Consequently, the role of B-fields in the formation and evolution of hub-filament systems is not well constrained. Aims. We aim to understand the role of the B-field and its interplay with turbulence and gravity in the dynamical evolution of the NGC 6334 filament network that harbours cluster-forming hubs and high-mass star formation. Methods. We present new observations of the dust polarized emission at 850 μm toward the 2 pc × 10 pc map of NGC 6334 at a spatial resolution of 0.09 pc obtained with the James Clerk Maxwell Telescope (JCMT) as part of the B-field In STar-forming Region Observations (BISTRO) survey. We study the distribution and dispersion of the polarized intensity (PI), the polarization fraction (PF), and the plane-of-the-sky B-field angle (χB_POS) toward the whole region, along the 10 pc-long ridge and along the sub-filaments connected to the ridge and the hubs. We derived the power spectra of the intensity and χBPOS along the ridge crest and compared them with the results obtained from simulated filaments. Results. The observations span ~3 orders of magnitude in Stokes I and PI and ~2 orders of magnitude in PF (from ~0.2 to ~ 20%). A large scatter in PI and PF is observed for a given value of I. Our analyses show a complex B-field structure when observed over the whole region (~ 10 pc); however, at smaller scales (~1 pc), χBPOS varies coherently along the crests of the filament network. The observed power spectrum of χBPOS can be well represented with a power law function with a slope of − 1.33 ± 0.23, which is ~20% shallower than that of I. We find that this result is compatible with the properties of simulated filaments and may indicate the physical processes at play in the formation and evolution of star-forming filaments. Along the sub-filaments, χBPOS rotates frombeing mostly perpendicular or randomly oriented with respect to the crests to mostly parallel as the sub-filaments merge with the ridge and hubs. This variation of the B-field structure along the sub-filaments may be tracing local velocity flows of infalling matter in the ridge and hubs. Our analysis also suggests a variation in the energy balance along the crests of these sub-filaments, from magnetically critical or supercritical at their far ends to magnetically subcritical near the ridge and hubs. We also detect an increase in PF toward the high-column density (NH2 ≳ 1023 cm−2) star cluster-forming hubs. These latter large PF values may be explained by the increase in grain alignment efficiency due to stellar radiation from the newborn stars, combined with an ordered B-field structure. Conclusions. These observational results reveal for the first time the characteristics of the small-scale (down to ~ 0.1 pc) B-field structure of a 10 pc-long hub-filament system. Our analyses show variations in the polarization properties along the sub-filaments that may be tracing the evolution of their physical properties during their interaction with the ridge and hubs. We also detect an impact of feedback from young high-mass stars on the local B-field structure and the polarization properties, which could put constraints on possible models for dust grain alignment and provide important hints as to the interplay between the star formation activity and interstellar B-fields.

Measurements of fragmentation functions for jets associated with an isolated photon are presented for the first time in pp and PbPb collisions. The analysis uses data collected with the CMS detector at the CERN LHC at a nucleon-nucleon center-ofmass energy of 5.02 TeV. Fragmentation functions are obtained for jets with p jet T > 30 GeV/c in events containing an isolated photon with p γ T > 60 GeV/c, using charged tracks with transverse momentum p trk T > 1 GeV/c in a cone around the jet axis. The association with an isolated photon constrains the initial p T and azimuthal angle of the parton whose shower produced the jet. For central PbPb collisions, modifications of the jet fragmentation functions are observed when compared to those measured in pp collisions, while no significant differences are found in the 50% most peripheral collisions. Jets in central PbPb events show an excess (depletion) of low (high) p T particles, with a transition around 3 GeV/c. This measurement shows for the first time the in-medium shower modifications of partons (quark dominated) with well defined initial kinematics. It constitutes a new well-controlled reference for testing theoretical models of the parton passage through the QGP. the pseudorapidity coverage up to |η| = 5.2. In the case of PbPb events, the HF signals are used to determine the degree of overlap ("centrality") of the two colliding Pb nuclei [21] and the event-by-event azimuthal angle of maximum particle density ("event plane") [35]. A more detailed description of the CMS detector can be found in Ref. [36].The event samples are selected online with a dedicated photon trigger requiring one photon with p γ T > 40 GeV/c [29], and are subjected to offline requirements to remove non-collision events [29,37]. For jets and photons, the reconstruction algorithms, analysis selections, and corrections for the energy scale and resolution are the same as in Ref. [29]. For the analysis of PbPb collisions, the event centrality is defined as the fraction of the total inelastic hadronic cross section, starting at 0% for the most central collisions, and is evaluated as percentiles of the distribution of the energy deposited in the HF calorimeters [21]. Results are presented in four centrality intervals, ranging from a central 0-10% (i.e., the 10% of the events having the largest overlap area of the two nuclei [38]), to a peripheral 50-100% (the one closest to a pp-like environment) intervals.The photon candidates are restricted to the barrel region of the ECAL, |η γ | < 1.44, and are required to have p γ T > 60 GeV/c. Electron contamination and anomalous signals caused by the interaction of heavily ionizing particles with the silicon avalanche photodiodes used for the ECAL readout are removed [39]. Background from ECAL showers induced by hadrons are rejected using the ratio of HCAL over ECAL energy inside a cone of radius ∆R = √ (∆η) 2 + (∆φ) 2 = 0.15 around the photon candidate [39,40]. Background contributions from fragmentation and decay photons are rejected by imposing isolation ...

The latest generation of Galactic-plane surveys is enhancing our ability to study the effects of galactic environment upon the process of star formation. We present the first data from CO Heterodyne Inner Milky Way Plane Survey 2 (CHIMPS2). CHIMPS2 is a survey that will observe the Inner Galaxy, the Central Molecular Zone (CMZ), and a section of the Outer Galaxy in 12CO, 13CO, and C18O (J = 3 → 2) emission with the Heterodyne Array Receiver Program on the James Clerk Maxwell Telescope (JCMT). The first CHIMPS2 data presented here are a first look towards the CMZ in 12CO J = 3→2 and cover −3○ ≤ ℓ ≤ 5○ and ∣${b}$∣ ≤ 0${_{.}^{\circ}}$5 with angular resolution of 15 arcsec, velocity resolution of 1 km s−1, and rms $\Delta \, T_A ^\ast =$ 0.58 K at these resolutions. Such high-resolution observations of the CMZ will be a valuable data set for future studies, whilst complementing the existing Galactic Plane surveys, such as SEDIGISM, the ${Herschel}$ infrared Galactic Plane Survey, and ATLASGAL. In this paper, we discuss the survey plan, the current observations and data, as well as presenting position-position maps of the region. The position-velocity maps detect foreground spiral arms in both absorption and emission.