Heavy-flavour spectra in high energy nucleus-nucleus collisions

The propagation of the heavy quarks produced in relativistic nucleus-nucleus collisions at RHIC and LHC is studied within the framework of Langevin dynamics in the background of an expanding deconfined medium described by ideal and viscous hydrodynamics. The transport coefficients entering into the relativistic Langevin equation are evaluated by matching the hard-thermal-loop result for soft collisions with a perturbative QCD calculation for hard scatterings. The heavy-quark spectra thus obtained are employed to compute the differential cross sections, the nuclear modification factors R_AA and the elliptic flow coefficients v_2 of electrons from heavy-flavour decay.Comment: 22 pages, 20 figures; added one reference, corrected typos and a few figure

Heavy quarkonium: progress, puzzles, and opportunities

A golden age for heavy quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of related experimental activity. The early years of this period were chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in 2004, which presented a comprehensive review of the status of the field at that time and provided specific recommendations for further progress. However, the broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles could only be partially anticipated. Since the release of the YR, the BESII program concluded only to give birth to BESIII; the $B$-factories and CLEO-c flourished; quarkonium production and polarization measurements at HERA and the Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the deconfinement regime. All these experiments leave legacies of quality, precision, and unsolved mysteries for quarkonium physics, and therefore beg for continuing investigations. The plethora of newly-found quarkonium-like states unleashed a flood of theoretical investigations into new forms of matter such as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the spectroscopy, decays, production, and in-medium behavior of c\bar{c}, b\bar{b}, and b\bar{c} bound states have been shown to validate some theoretical approaches to QCD and highlight lack of quantitative success for others. The intriguing details of quarkonium suppression in heavy-ion collisions that have emerged from RHIC have elevated the importance of separating hot- and cold-nuclear-matter effects in quark-gluon plasma studies. This review systematically addresses all these matters and concludes by prioritizing directions for ongoing and future efforts.Comment: 182 pages, 112 figures. Editors: N. Brambilla, S. Eidelman, B. K. Heltsley, R. Vogt. Section Coordinators: G. T. Bodwin, E. Eichten, A. D. Frawley, A. B. Meyer, R. E. Mitchell, V. Papadimitriou, P. Petreczky, A. A. Petrov, P. Robbe, A. Vair

Charged-particle distributions in √s=13 TeV pp interactions measured with the ATLAS detector at the LHC

Charged-particle distributions are measured in proton–proton collisions at a centre-of-mass energy of 13 TeV, using a data sample of nearly 9 million events, corresponding to an integrated luminosity of 170 μb−1170 μb−1, recorded by the ATLAS detector during a special Large Hadron Collider fill. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the dependence of the mean transverse momentum on the charged-particle multiplicity are presented. The measurements are performed with charged particles with transverse momentum greater than 500 MeV and absolute pseudorapidity less than 2.5, in events with at least one charged particle satisfying these kinematic requirements. Additional measurements in a reduced phase space with absolute pseudorapidity less than 0.8 are also presented, in order to compare with other experiments. The results are corrected for detector effects, presented as particle-level distributions and are compared to the predictions of various Monte Carlo event generators

Charged-particle distributions at low transverse momentum in √<i>s</i>=13 TeV <i>pp</i> interactions measured with the ATLAS detector at the LHC

Measurements of distributions of charged particles produced in proton-proton collisions with a centre-of-mass energy of 13 TeV are presented. The data were recorded by the ATLAS detector at the LHC and correspond to an integrated luminosity of 151 [Formula: see text]. The particles are required to have a transverse momentum greater than 100 MeV and an absolute pseudorapidity less than 2.5. The charged-particle multiplicity, its dependence on transverse momentum and pseudorapidity and the dependence of the mean transverse momentum on multiplicity are measured in events containing at least two charged particles satisfying the above kinematic criteria. The results are corrected for detector effects and compared to the predictions from several Monte Carlo event generators

Anomalous fracture-extension pressure in granitic rocks

Fracture-extension pressures appreciably higher than the least principal earth-stress were observed in hydraulic fractures formed in a pair of 3 km (9600 ft) deep boreholes drilled near the Valles Caldera in northern New Mexico. Pressurization of open wellbores in rock containing preexisting fractures may open these fractures, instead of creating new fractures at right angles to the least principal stress. The pressure necessary to flow into these fractures may be appreciably higher than the least principal stress. Upon sand-propping one such pre-existing fracture, a lower fracture extension pressure was observed. A second fracture in a parallel well-bore 92 m (300 ft) away, at the same depth of 2 km (6500 ft) exhibited the lower fracture extension pressure without propping, but with about 90/sup 0/ difference in fracture direction. Fractures created through perforations at a depth of 3 km (9600 ft) not only exhibited breakdown pressures upon initial pressurization, but sometimes even higher ''breakdown'' pressures upon repressurization. These phenomena may be of interest in the interpretation of earth stress measurements made by hydraulic fracturing

Preliminary evaluation of the second hot dry rock geothermal energy reservoir: results of phase 1, run segment 4

Results of the preliminary assessment of the second hot dry rock reservoir at the Fenton Hill field site are presented. This second reservoir was created by fracturing a deeper interval of granite rock located at a depth of 2.93 km (9620 ft) in the same wellbore pair used in the creation of the first reservoir; no additional redrilling was required. The new fracture system has a vertical extent of at least 320 m (1050 ft), suggesting that the combined heat-transfer area of the old and new fracture systems is 11 times that of the old system. The virgin rock temperature at the bottom of the deeper interval was 197/sup 0/C (386/sup 0/F). Water at a flow rate of 6 l/s (100 gpm) was circulated through the reservoir for a period of 23 days. Downhole measurements of the water temperature at the reservoir outlet, as well as temperatures inferred from geothermometry, showed that the thermal drawdown of the reservoir was negligible and preliminary estimates indicate that the minimum effective heat-transfer area of the new reservoir is 45,000 m/sup 2/ (480,000 ft/sup 2/), which is six times larger than the first reservoir. The following are presented: operational plan, reservoir geometry and flow paths, flow impedance, geochemistry, heat extraction, dye tracer flow distribution studies, and seismicity. (MHR

Downhole electrical detection of hydraulic fractures in GT-2 and EE-1

Electrical geophysical methods including mise a la masse and self-potential (SP) for determination of hydraulic fracture characteristics were used at the hot dry rock geothermal project. Electrical and induction logs indicated that the resistivity contrast between the granite and 200/sup 0/C water at the 2926-m (9600-ft) depth is a factor of 1000 or more. Thus the water in a hydraulic fracture, formed to connect two adjacent deep holes, is a good conductor compared to the confining granite. Mise a la masse-type measurements were made to help determine the characteristics for hydraulic fractures formed in each of the two geothermal holes GT-2 and EE-1. Once a hydraulic fracture has been formed, mise a la masse effects are obtained both with the fracture pressurized above hydrostatic and when depressurized to hydrostatic. This indicates that once the fracture has been created, enough natural propping exists that a conductive zone persists even when the fracture is deflated. A fracture was formed in a 18-m (60-ft) zone immediately below 1957 m (6420 ft) in EE-1. Later a set of SP logs was run in this zone with no pressure, with pressure building, with pressure decreasing, and again with the fracture depressurized. Results show that during times of change of parameters in hydraulically fractured regions in the hole, natural SP logging helps to determine the position of the fracture. However, after a fracture has come to equilibrium with fluid parameters such as temperature, pressure, salinity, and pH, an effect of the fracture may not be evident. Self-potential logs provide an excellent method for locating the bottom of steel casing that has been set in the hole

Man-made geothermal reservoirs

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