87 research outputs found
Target mass number dependence of subthreshold antiproton production in proton-, deuteron- and alpha-particle-induced reactions
Data from KEK on subthreshold \bar{\mrm{p}} as well as on and
\mrm{K}^\pm production in proton-, deuteron- and -induced reactions
at energies between 2.0 and 12.0 A GeV for C, Cu and Pb targets are described
within a unified approach. We use a model which considers a nuclear reaction as
an incoherent sum over collisions of varying numbers of projectile and target
nucleons. It samples complete events and thus allows for the simultaneous
consideration of all final particles including the decay products of the
nuclear residues. The enormous enhancement of the \bar{\mrm{p}} cross
section, as well as the moderate increase of meson production in deuteron and
induced compared to proton-induced reactions, is well reproduced for
all target nuclei. In our approach, the observed enhancement near the
production threshold is mainly due to the contributions from the interactions
of few-nucleon clusters by simultaneously considering fragmentation processes
of the nuclear residues. The ability of the model to reproduce the target mass
dependence may be considered as a further proof of the validity of the cluster
concept.Comment: 9 pages, 4 figure
A Search for Photons with Energies Above 2X10(17) eV Using Hybrid Data from the Low-Energy Extensions of the Pierre Auger Observatory
Ultra-high-energy photons with energies exceeding 10(17) eV offer a wealth of connections to different aspects of cosmic-ray astrophysics as well as to gamma-ray and neutrino astronomy. The recent observations of photons with energies in the 10(15) eV range further motivate searches for even higher-energy photons. In this paper, we present a search for photons with energies exceeding 2 x 10(17) eV using about 5.5 yr of hybrid data from the low-energy extensions of the Pierre Auger Observatory. The upper limits on the integral photon flux derived here are the most stringent ones to date in the energy region between 10(17) and 10(18) eV
Inclusive and multiplicity dependent production of electrons from heavy-flavour hadron decays in pp and p-Pb collisions
Measurements of the production of electrons from heavy-flavour hadron decays in pp collisions at root s = 13 TeV at midrapidity with the ALICE detector are presented down to a transverse momentum (p(T)) of 0.2 GeV/c and up to p(T) = 35 GeV/c, which is the largest momentum range probed for inclusive electron measurements in ALICE. In p-Pb collisions, the production cross section and the nuclear modification factor of electrons from heavy-flavour hadron decays are measured in the p(T) range 0.5 < p(T) < 26 GeV/c at root s(NN) = 8.16 TeV. The nuclear modification factor is found to be consistent with unity within the statistical and systematic uncertainties. In both collision systems, first measurements of the yields of electrons from heavy-flavour hadron decays in different multiplicity intervals normalised to the multiplicity-integrated yield (self-normalised yield) at midrapidity are reported as a function of the self-normalised charged-particle multiplicity estimated at midrapidity. The self-normalised yields in pp and p-Pb collisions grow faster than linear with the self-normalised multiplicity. A strong p(T) dependence is observed in pp collisions, where the yield of high-p(T) electrons increases faster as a function of multiplicity than the one of low-p(T) electrons. The measurement in p-Pb collisions shows no p(T) dependence within uncertainties. The self-normalised yields in pp and p-Pb collisions are compared with measurements of other heavy-flavour, light-flavour, and strange particles, and with Monte Carlo simulations
Measurement of the non-prompt D-meson fraction as a function of multiplicity in proton-proton collisions at = 13 TeV
The fractions of non-prompt (i.e. originating from beauty-hadron decays) D0
and D+ mesons with respect to the inclusive yield are measured as a function of the
charged-particle multiplicity in proton-proton collisions at a centre-of-mass energy of √s =
13 TeV with the ALICE detector at the LHC. The results are reported in intervals of
transverse momentum (pT) and integrated in the range 1 < pT < 24 GeV/c. The fraction
of non-prompt D0 and D+ mesons is found to increase slightly as a function of pT in
all the measured multiplicity intervals, while no significant dependence on the charged-
particle multiplicity is observed. In order to investigate the production and hadronisation
mechanisms of charm and beauty quarks, the results are compared to PYTHIA 8 as well
as EPOS 3 and EPOS 4 Monte Carlo simulations, and to calculations based on the colour
glass condensate including three-pomeron fusion
Angular distributions in the decay B -> K*l(+)l(-)
We use a sample of 384 million BBbar events collected with the Babar detector at the PEP-II e+e- collider to study angular distributions in the rare decays B -> K* l+l-, where l+l- is either e+e- or mu+mu-. For low dilepton invariant masses, m(l+l-)3.2$ GeV/c^2, we measure AFB=0.76 (+0.52,-0.32) +/- 0.07 FL=0.71 (+0.20,-0.22) +/- 0.04.We are grateful for the excellent luminosity and machine
conditions provided by our PEP-II colleagues, and
for the substantial dedicated effort from the computing
organizations that support BABAR. The collaborating
institutions wish to thank SLAC for its support and
kind hospitality. This work is supported by DOE and
NSF (USA), NSERC (Canada), CEA and CNRS-IN2P3
(France), BMBF and DFG (Germany), INFN (Italy),
FOM (The Netherlands), NFR (Norway), MES (Russia),
MEC (Spain), and STFC (United Kingdom). Individuals
have received support from the Marie Curie EIF (European
Union) and the A. P. Sloan Foundation.Peer reviewe
EuFeAs under high pressure: an antiferromagnetic bulk superconductor
We report the ac magnetic susceptibility and resistivity
measurements of EuFeAs under high pressure . By observing nearly
100% superconducting shielding and zero resistivity at = 28 kbar, we
establish that -induced superconductivity occurs at ~30 K in
EuFeAs. shows an anomalous nearly linear temperature dependence
from room temperature down to at the same . indicates that
an antiferromagnetic order of Eu moments with ~20 K persists
in the superconducting phase. The temperature dependence of the upper critical
field is also determined.Comment: To appear in J. Phys. Soc. Jpn., Vol. 78 No.
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