844 research outputs found
Measurement of beauty-hadron decay electrons in Pb--Pb collisions at sqrt(s_NN) = 2.76 TeV with ALICE
The ALICE Collaboration at the LHC studies heavy-ion collisions to
investigate the properties of the Quark-Gluon Plasma (QGP). Heavy quarks (charm
and beauty) are effective probes for this purpose. Both their energy loss in
the medium as well as their possible thermalization yield information about the
medium properties. Experimentally, the reconstruction of hadrons with charm
valence quarks is possible. For hadrons with beauty valence quarks a promising
strategy is the measurement of their decay electrons. To separate these from
the background electrons (mainly from charm hadron decays, photon conversions
or light-meson decays) the large decay length of beauty hadrons can be
utilized. It leads to a relatively large typical impact parameter of the decay
electrons. By comparing the impact parameter distribution of the signal
electrons with those from the background sources, the signal can be
statistically separated from the background. For this purpose a maximum
likelihood fit is employed using impact parameter distribution templates from
simulations. The resulting nuclear modification factor for electrons from
beauty-hadron decays shows a sizeable suppression for p_T > 3 GeV, albeit still
with large uncertainties.Comment: 4 pages, 4 figures, proceedings for the Hot Quarks 2014 workshop, Las
Negras, Cabo de Gata Natural Park, Andalusia, Spai
Separation of the Charm and Beauty Production in p--Pb and Pb--Pb Collisions with ALICE
Measurements of heavy (charm and beauty) quarks provide useful insights into
the properties of the quark--gluon plasma. The good particle identification
capabilities of ALICE make a measurement based on the electrons from
semi-leptonic decays of heavy-flavour hadrons feasible. This approach makes use
of the large branching ratios () of heavy--flavour hadrons
into electrons. Separation of the contribution from beauty-hadron decay
electrons was achieved by utilizing the large decay length of the associated
hadrons, making the investigation of beauty quarks in the medium possible. By
comparing measurements in p--Pb and Pb--Pb collisions, it is possible to
disentangle effects of cold nuclear matter from those of the hot and dense
medium. The results show a strong change in the transverse momentum
distribution of electrons from beauty-hadron decays in central Pb--Pb
collisions with respect to the proton--proton case. No significant change from
proton--proton collisions can be seen in the p--Pb case, suggesting that the
modification is a final state effect
Electrons from beauty-hadron decays in central Pb-Pb collisions at âs NN = 2.76 TeV
Heavy quarks (charm and beauty) are an important probe for the characterization of the quark-gluon plasma (QGP), a state of color deconfined, hadronic matter. Experimentally, the QGP is produced in ultrarelativistic heavy-ion collisions, where heavy quarks are automatically generated and interact with the produced medium. Within this work, the properties of the beauty quarks in the medium are measured via the semileptonic decays of the associated hadrons. The measurement is based on the particle identification and tracking capabilities of the ALICE detector at the LHC. The separation of eletrons from beauty-hadron decays from the abundant background electrons is achieved using fits of the impact parameter distribution based on templates from Monte Carlo simulations. This approach makes use of the comparatively large decay length of the beauty hadrons (). The large particle multiplicities in central Pb--Pb collisions at \PbPbEnergy~ create a particularly challenging environment for the measurement. The determined nuclear modification factor hints at values above unity for low transverse momenta of the electrons. In this region, the beauty quarks may participate in the collective motion of the medium. The nuclear modification factor decreases towards larger \pt, where an energy loss of the partons in the medium is expected. The measured range of 1.3<\pt<8~\GeVc also represents a region where contributions from both radiative and collisional interactions with the medium can contribute and is thus particularly interesting for the understanding of the interaction of heavy quarks with the medium
Krise des FlĂ€chentarifvertrages und IntegrationsfĂ€higkeit von ArbeitgeberverbĂ€nden: empirische Untersuchungen am Beispiel zweier mittelstĂ€ndischer baden-wĂŒrttembergischer Branchen
"Ausgehend von den in der Literatur diskutierten Erosionstendenzen der deutschen Tarifpolitik und IntegrationsschwĂ€chen der ArbeitgeberverbĂ€nde, untersucht der Beitrag die Funktionsdefizite und LösungsansĂ€tze der VerbĂ€nde der mittelstĂ€ndisch geprĂ€gten baden-wĂŒrttembergischen Steine- & Erden- (ISTE) und SĂ€ge- & Holzindustrie (VSH). Mit Hilfe von leitfadengestĂŒtzten Interviews mit den relevanten EntscheidungstrĂ€gern beider Branchen konnte analysiert werden, dass neben einer schwierigen ökonomischen Situation v.a. die heterogenen Interessen der Mitglieder fĂŒr die schwindende Bindekraft der ArbeitgeberverbĂ€nde ursĂ€chlich sind. Beide untersuchten VerbĂ€nde versuchen durch inhaltlich-tarifpolitische wie ordnungspolitische Reformen ihre IntegrationsfĂ€higkeit zu erhöhen, können aber nur in begrenztem Umfang der steigenden stillen Tarifflucht Einhalt gebieten." (Autorenreferat)"Starting from the literature on the erosion of the German industrial relations system and the weaknesses of the employers' associations, this paper investigates the difficulties faced, and attempted solutions adopted, by employer associations in two sectors in Baden-WĂŒrttemberg: quarrying (ISTE) and the manufacture of wood products (VSH). Both are characterized by small and medium sized firms. Based on interviews with experts from both sectors, the author found out that, apart from difficult economic conditions, the commitment to the employers' associations is especially diminished by the heterogeneity of members' interests. Both employer associations have tried to reform the contents of bargaining policy and to reorganize their structure to enhance their capacity of integration. Despite their efforts, there is an increasing number of firms that are critical of the collective agreements." (author's abstract
Transverse dynamics of charmed hadrons in ultra-relativistic nuclear collisions
Transverse momentum spectra and anisotropic flow distributions
are studied for charmonia and charmed hadrons produced in Pb-Pb collisions and
measured with the ALICE detector at the CERN Large Hadron Collider (LHC). The
investigations are performed within the framework of the Statistical
Hadronization Model with the transverse dynamics evaluated using predictions
from relativistic viscous hydrodynamics as implemented in the computer codes
MUSIC and FluiduM. With this essentially parameter-free approach good agreement
is obtained for spectra in the range GeV/c. The
observed wide distribution in of anisotropic flow coefficients
and for charmonia is also well reproduced, while their magnitude is
generally somewhat over predicted. This finding may be connected to a
difference in spatial distribution between light and charmed hadrons due to a
different diffusion of light and heavy quarks in the hot fireball
Magnetotransport in heterostructures of transition metal dichalcogenides and graphene
We use a van der Waals pickup technique to fabricate different heterostructures containing WSe2(WS2) and graphene. The heterostructures were structured by plasma etching, contacted by one-dimensional edge contacts, and a top gate was deposited. For graphene/WSe2/SiO2 samples we observe mobilities of similar to 12 000 cm(2) V-1 s(-1). Magnetic-field-dependent resistance measurements on these samples show a peak in the conductivity at low magnetic fields. This dip is attributed to the weak antilocalization (WAL) effect, stemming from spin-orbit coupling. Samples where graphene is encapsulated between WSe2(WS2) and hexagonal boron nitride show a much higher mobility of up to similar to 120 000 cm(2) V-1 s(-1). However, in these samples noWAL peak can be observed. We attribute this to a transition from the diffusive to the quasiballistic regime. At low magnetic fields a resistance peak appears, which we ascribe to a size effect due to boundary scattering. Shubnikov-de Haas oscillations in fully encapsulated samples show all integer filling factors due to complete lifting of the spin and valley degeneracies
Multiplicity dependence of jet-like two-particle correlations in p-Pb collisions at = 5.02 TeV
Two-particle angular correlations between unidentified charged trigger and
associated particles are measured by the ALICE detector in p-Pb collisions at a
nucleon-nucleon centre-of-mass energy of 5.02 TeV. The transverse-momentum
range 0.7 5.0 GeV/ is examined,
to include correlations induced by jets originating from low
momen\-tum-transfer scatterings (minijets). The correlations expressed as
associated yield per trigger particle are obtained in the pseudorapidity range
. The near-side long-range pseudorapidity correlations observed in
high-multiplicity p-Pb collisions are subtracted from both near-side
short-range and away-side correlations in order to remove the non-jet-like
components. The yields in the jet-like peaks are found to be invariant with
event multiplicity with the exception of events with low multiplicity. This
invariance is consistent with the particles being produced via the incoherent
fragmentation of multiple parton--parton scatterings, while the yield related
to the previously observed ridge structures is not jet-related. The number of
uncorrelated sources of particle production is found to increase linearly with
multiplicity, suggesting no saturation of the number of multi-parton
interactions even in the highest multiplicity p-Pb collisions. Further, the
number scales in the intermediate multiplicity region with the number of binary
nucleon-nucleon collisions estimated with a Glauber Monte-Carlo simulation.Comment: 23 pages, 6 captioned figures, 1 table, authors from page 17,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/161
Multi-particle azimuthal correlations in p-Pb and Pb-Pb collisions at the CERN Large Hadron Collider
Measurements of multi-particle azimuthal correlations (cumulants) for charged
particles in p-Pb and Pb-Pb collisions are presented. They help address the
question of whether there is evidence for global, flow-like, azimuthal
correlations in the p-Pb system. Comparisons are made to measurements from the
larger Pb-Pb system, where such evidence is established. In particular, the
second harmonic two-particle cumulants are found to decrease with multiplicity,
characteristic of a dominance of few-particle correlations in p-Pb collisions.
However, when a gap is placed to suppress such correlations,
the two-particle cumulants begin to rise at high-multiplicity, indicating the
presence of global azimuthal correlations. The Pb-Pb values are higher than the
p-Pb values at similar multiplicities. In both systems, the second harmonic
four-particle cumulants exhibit a transition from positive to negative values
when the multiplicity increases. The negative values allow for a measurement of
to be made, which is found to be higher in Pb-Pb collisions at
similar multiplicities. The second harmonic six-particle cumulants are also
found to be higher in Pb-Pb collisions. In Pb-Pb collisions, we generally find
which is indicative of a Bessel-Gaussian
function for the distribution. For very high-multiplicity Pb-Pb
collisions, we observe that the four- and six-particle cumulants become
consistent with 0. Finally, third harmonic two-particle cumulants in p-Pb and
Pb-Pb are measured. These are found to be similar for overlapping
multiplicities, when a gap is placed.Comment: 25 pages, 11 captioned figures, 3 tables, authors from page 20,
published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/87
Computational approaches to understanding reaction outcomes of organic processes in ionic liquids
This review considers how various computational methods have been applied to explain the changes in reaction outcome on moving from a molecular to an ionic liquid solvent. Initially, different conceptual approaches to modelling ionic liquids are discussed, followed by a consideration of the limitations and constraints of these approaches. A series of case studies demonstrating the utility of computational approaches to explain processes in ionic liquids are considered; some of these address the solubility of species in ionic liquids while others examine classes of reaction where the outcome in ionic liquids can be explained through the application of computational approaches. Overall, the utility of computational methods to explain, and potentially predict, the effect of ionic liquids on reaction outcome is demonstrated
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