Charged-particle production was studied in proton-proton collisions collected at the LHC with the ALICE detector at centre-of-mass energies 0.9 TeV and 2.36 TeV in the pseudorapidity range |{eta}| < ...1.4. In the central region (|{eta}| < 0.5), at 0.9 TeV, we measure charged-particle pseudorapidity density d N{sub ch}/d{eta} = 3.02 {+-} 0.01(stat.){sub -0.05}{sup +0.08}(syst.) for inelastic interactions, and d N{sub ch}/d{eta} = 3.58 {+-} 0.01(stat.){sub -0.12}{sup +0.12}(syst.) for non-single-diffractive interactions. At 2.36 TeV, we find d N{sub ch}/d{eta} = 3.77 {+-} 0.01(stat.){sub -0.12}{sup +0.25}(syst.) for inelastic, and d N{sub ch}/d{eta} = 4.43 {+-} 0.01(stat.){sub -0.12}{sup +0.37}(syst.) for non-single-diffractive collisions. The relative increase in charged-particle multiplicity from the lower to higher energy is 24.7% {+-} 0.5%(stat.){sub -2.8}{sup +5.7}%(syst.) for inelastic and 23.7% {+-} 0.5%(stat.){sub -1.1}{sup +4.6}%(syst.) for non-single-diffractive interactions. This increase is consistent with that reported by the CMS collaboration for non-single-diffractive events and larger than that found by a number of commonly used models. The multiplicity distribution was measured in different pseudorapidity intervals and studied in terms of KNO variables at both energies. The results are compared to proton-antiproton data and to model predictions.
Dual-energy mammographic imaging experimental tests have been performed using a compact dichromatic imaging system based on a conventional x-ray tube, a mosaic crystal, and a 384-strip silicon ...detector equipped with full-custom electronics with single photon counting capability. For simulating mammal tissue, a three-component phantom, made of Plexiglass, polyethylene, and water, has been used. Images have been collected with three different pairs of x-ray energies:
16
–
32
keV
,
18
–
36
keV
, and
20
–
40
keV
. A Monte Carlo simulation of the experiment has also been carried out using the MCNP-4C transport code. The Alvarez-Macovski algorithm has been applied both to experimental and simulated data to remove the contrast between two of the phantom materials so as to enhance the visibility of the third one.
The
J
/
ψ
azimuthal distribution relative to the reaction plane has been measured by the NA50 experiment in Pb-Pb collisions at 158 GeV/nucleon. Various physical mechanisms related to charmonium ...dissociation in the medium created in the heavy ion collision are expected to introduce an anisotropy in the azimuthal distribution of the observed
J
/
ψ
mesons at SPS energies. Hence, the measurement of
J
/
ψ
elliptic anisotropy, quantified by the Fourier coefficient
v
2
of the
J
/
ψ
azimuthal distribution relative to the reaction plane, is an important tool to constrain theoretical models aimed at explaining the anomalous
J
/
ψ
suppression observed in Pb-Pb collisions. We present the measured
J
/
ψ
yields in different bins of azimuthal angle relative to the reaction plane, as well as the resulting values of the Fourier coefficient
v
2
as a function of the collision centrality and of the
J
/
ψ
transverse momentum. The reaction plane has been estimated from the azimuthal distribution of the neutral transverse energy detected in an electromagnetic calorimeter. The analysis has been performed on a data sample of about 100 000 events, distributed in five centrality or
p
T
sub-samples. The extracted
v
2
values are significantly larger than zero for non-central collisions and are seen to increase with
p
T
.
Charmonium production in p–A collisions is a unique tool for the study of the interaction of bound cc states in nuclear matter. It can provide details on the basic features of the resonance formation ...mechanism and, in particular, on its non-perturbative aspects. In this Letter, we present an experimental study of charmonia and Drell–Yan production in proton–nucleus collisions at 450 GeV/c. The results are analyzed in the framework of the Glauber model and lead to the values of the nuclear absorption cross-section σabspA for J/ψ and ψ′. Then, we compare the J/ψ absorption in proton–nucleus and sulphur–uranium interactions, using NA38 data. We obtain that, for the J/ψ, σabspA and σabsSU are compatible, showing that no sizeable additional suppression mechanism is present in S–U collisions, and confirming that the anomalous J/ψ suppression only sets in for Pb–Pb interactions.
The calibration and performance of the Silicon Drift Detector of the ALICE experiment during the 2008 cosmic ray run will be presented. In particular the procedures to monitor the running parameters ...(baselines, noise, drift speed) are detailed. Other relevant parameters (SOP delay, time-zero, charge calibration) were also determined.
The J/ $\psi$ normal nuclear absorption Borges, G.
European Physical Journal C: Particles and Fields,
08/2005, Letnik:
43, Številka:
1-4
Journal Article, Conference Proceeding
Recenzirano
We present a new determination of the ratio of cross-sections (J/$\psi$)/DY as expected for nucleus-nucleus reactions if J/$\psi$ would only be normally absorbed by nuclear matter. This anticipated ...behaviour is based on proton-nucleus data exclusively, and compared, as a function of centrality, with updated S-U results from experiment NA38 and with the most Pb-Pb results from experiment NA50.
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