2,404 research outputs found
Study of W± boson in the ALICE muon spectrometer: considerations and analysis using the HLT tool
W± bosons produced in proton-proton collisions can be observed in the ALICE muon spectrometer via their decay into single muons at a transverse momentum, pt ~ Mw/2 40 GeV/c. However the identification of these single muons is complicated by a large amount of muonic background, especially in the low pt region. Therefore, it is necessary to apply precise pt cuts below the region of interest. This can be done by means of the High Level Trigger (HLT). In this paper we present the performance of detecting high pt muons at the HLT level. In order to improve the momentum resolution of the L0 trigger, fast clusterization of the tracking chambers together with L0 trigger matching and fast tracking reconstruction is applied. This will reduce the background in the high pt muon analysis
Studies of the Giant Dipole Resonance in Al, Ca, Fe, Ni and Pb with high energy-resolution inelastic proton scattering under 0
A survey of the fine structure of the Isovector Giant Dipole Resonance
(IVGDR) was performed, using the recently commissioned zero-degree facility of
the K600 magnetic spectrometer at iThemba LABS. Inelastic proton scattering at
an incident energy of 200 MeV was measured on Al, Ca, Fe,
Ni and Pb. A high energy resolution (
40 keV FWHM) could be achieved after utilising faint-beam and
dispersion-matching techniques. Considerable fine structure is observed in the
energy region of the IVGDR and characteristic energy scales are extracted from
the experimental data by means of a wavelet analysis. The comparison with
Quasiparticle-Phonon Model (QPM) calculations provides insight into the
relevance of different giant resonance decay mechanisms. Photoabsorption cross
sections derived from the data assuming dominance of relativistic Coulomb
excitation are in fair agreement with previous work using real photons.Comment: 15 pages, 15 figure
Wavelet signatures of -splitting of the Isoscalar Giant Quadrupole Resonance in deformed nuclei from high-resolution (p,p) scattering off Nd
The phenomenon of fine structure of the Isoscalar Giant Quadrupole Resonance
(ISGQR) has been studied with high energy-resolution proton inelastic
scattering at iThemba LABS in the chain of stable even-mass Nd isotopes
covering the transition from spherical to deformed ground states. A wavelet
analysis of the background-subtracted spectra in the deformed 146,148,150Nd
isotopes reveals characteristic scales in correspondence with scales obtained
from a Skyrme RPA calculation using the SVmas10 parameterization. A semblance
analysis shows that these scales arise from the energy shift between the main
fragments of the K = 0, 1 and K = 2 components.Comment: 7 pages, 6 figure
No evidence of an 11.16 MeV 2+ state in 12C
An experiment using the 11B(3He,d)12C reaction was performed at iThemba LABS
at an incident energy of 44 MeV and analyzed with a high energy-resolution
magnetic spectrometer, to re-investigate states in 12C published in 1971. The
original investigation reported the existence of an 11.16 MeV state in 12C that
displays a 2+ nature. In the present experiment data were acquired at
laboratory angles of 25-, 30- and 35- degrees, to be as close to the c.m.
angles of the original measurements where the clearest signature of such a
state was observed. These new low background measurements revealed no evidence
of the previously reported state at 11.16 MeV in 12C
Binary projectile fragmentation of 12C at an incident energy of 33.3 MeV/nucleon
Direct binary projectile fragmentation is being investigated for the case where a 400 MeV 12C projectile breaks up into an particle and a 8Be fragment in the interaction with a thin 93Nb and 197Au target. While the 8Be fragments were measured at 9 , the correlated particles were detected in an angular range between 16 and 30 on the opposite side of the beam. From the preliminary results presented here one may obtain information on the amount of quasi-elastic fragmentation (both fragments do not suffer any further interactions after they are produced). These experimental results indicate that the quasi-elastic break-up process is the dominant contribution to the measured correlation spectra. As was also observed in earlier work, the most forward quasi-elastically emitted particles have energies exceeding the beam velocity
Fine structure of the isoscalar giant quadrupole resonance in 40Ca due to Landau damping?
The fragmentation of the Isoscalar Giant Quadrupole Resonance (ISGQR) in 40Ca
has been investigated in high energy-resolution experiments using proton
inelastic scattering at E_p = 200 MeV. Fine structure is observed in the region
of the ISGQR and its characteristic energy scales are extracted from the
experimental data by means of a wavelet analysis. The experimental scales are
well described by Random Phase Approximation (RPA) and second-RPA calculations
with an effective interaction derived from a realistic nucleon-nucleon
interaction by the Unitary Correlation Operator Method (UCOM). In these results
characteristic scales are already present at the mean-field level pointing to
their origination in Landau damping, in contrast to the findings in heavier
nuclei and also to SRPA calculations for 40Ca based on phenomenological
effective interactions, where fine structure is explained by the coupling to
two-particle two-hole (2p-2h) states.Comment: Phys. Lett. B, in pres
COVID deaths in South Africa: 99 days since South Africaâs first death
Background. Understanding the pattern of deaths from COVID-19 in South Africa (SA) is critical to identifying individuals at high risk of dying from the disease. The Minister of Health set up a daily reporting mechanism to obtain timeous details of COVID-19 deaths from the provinces to track mortality patterns.Objectives. To provide an epidemiological analysis of the first COVID-19 deaths in SA.Methods. Provincial deaths data from 28 March to 3 July 2020 were cleaned, information on comorbidities was standardised, and data were aggregated into a single data set. Analysis was performed by age, sex, province, date of death and comorbidities.Results. SA reported 3 088 deaths from COVID-19, i.e. an age-standardised death rate of 64.5 (95% confidence interval (CI) 62.3 - 66.8) deaths per million population. Most deaths occurred in Western Cape (65.5%) followed by Eastern Cape (16.8%) and Gauteng (11.3%). The median age of death was 61 years (interquartile range 52 - 71). Males had a 1.5 times higher death rate compared with females. Individuals with two or more comorbidities accounted for 58.6% (95% CI 56.6 - 60.5) of deaths. Hypertension and diabetes were the most common comorbidities reported, and HIV and tuberculosis were more common in individuals aged <50 years.Conclusions. Data collection for COVID-19 deaths in provinces must be standardised. Even though the data had limitations, these findings can be used by the SA government to manage the pandemic and identify individuals who are at high risk of dying from COVID-19
Charge separation relative to the reaction plane in Pb-Pb collisions at TeV
Measurements of charge dependent azimuthal correlations with the ALICE
detector at the LHC are reported for Pb-Pb collisions at TeV. Two- and three-particle charge-dependent azimuthal correlations in
the pseudo-rapidity range are presented as a function of the
collision centrality, particle separation in pseudo-rapidity, and transverse
momentum. A clear signal compatible with a charge-dependent separation relative
to the reaction plane is observed, which shows little or no collision energy
dependence when compared to measurements at RHIC energies. This provides a new
insight for understanding the nature of the charge dependent azimuthal
correlations observed at RHIC and LHC energies.Comment: 12 pages, 3 captioned figures, authors from page 2 to 6, published
version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/286
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
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