18 research outputs found
Low-energy resonances in the 18O (p,Î¥) 19F reaction
Background: Shell hydrogen burning during the asymptotic giant branch (AGB) phase through the oxygen
isotopes has been indicated as a key process that is needed to understand the observed 18O/16O relative abundance
in presolar grains and in stellar atmospheres. This ratio is strongly influenced by the relative strengths of the
reactions 18O(p,\u3b1) 15N and 18O(p,\u3b3 ) 19F in low-mass AGB stars. While the former channel has been the focus
of a large number of measurements, the (p,\u3b3 ) reaction path has only recently received some attention and its
stellar reaction rate over a wide temperature range rests on only one measurement.
Purpose: Our aim is the direct measurement of states in 19F as populated through the reaction 18O(p,\u3b3 ) 19F
to better determine their influence on the astrophysical reaction rate, and more generally to improve the
understanding of the nuclear structure of 19F.
Method: Branchings and resonance strengths were measured in the proton energy range Elab
p = 150\u2013400 keV,
using a high-purity germanium detector inside a massive lead shield. The measurement took place in the ultralow-
background environment of the Laboratory for Underground Nuclear Astrophysics (LUNA) experiment at
the Gran Sasso National Laboratory, leading to a highly increased sensitivity.
Results: The uncertainty of the \u3b3 branchings and strengths was improved for all four resonances in the studied
energy range; many new transitions were observed in the case of the 334 keV resonance, and individual \u3b3 decays
of the 215 keV resonance were measured for the first time. In addition a number of transitions to intermediate
states that decay through \u3b1 emission were identified. The strengths of the observed resonances are generally in
agreement with literature values.
Conclusions: Our measurements substantially confirm previous determinations of the relevant resonance
strengths. Therefore the 18O(p,\u3b3 ) 19F reaction rate does not change with respect to the reaction rate reported
in the compilations commonly adopted in the extant computations of red-giant branch and AGB stellar models.
Nevertheless, our measurements definitely exclude a nonstandard scenario for the fluorine nucleosynthesis and
a nuclear physics solution for the 18O depletion observed in Group 2 oxygen-rich stardust grains
Elliptic flow of identified hadrons in Pb-Pb collisions at 1asNN = 2.76 TeV
The elliptic flow coefficient (v2) of identified particles in Pb-Pb collisions at 1asNN = 2.76 TeV was measured with the ALICE detector at the Large Hadron Collider (LHC). The results were obtained with the Scalar Product method, a two-particle corre- lation technique, using a pseudo-rapidity gap of | 06\u3b7| > 0.9 between the identified hadron under study and the reference particles. The v2 is reported for \u3c0\ub1, K\ub1, K0S, p+p, \u3c6, \u39b+\u39b, \u39e 12+\u39e+ and \u3a9 12+\u3a9+ in several collision centralities. In the low transverse momentum (pT) region, pT 3 GeV/c
Centrality dependence of inclusive J/\u3c8 production in p-Pb collisions at 1asNN = 5.02 TeV
We present a measurement of inclusive J/\u3c8 production in p-Pb collisions at 1asNN = 5.02TeV as a function of the centrality of the collision, as estimated from the energy deposited in the Zero Degree Calorimeters. The measurement is performed with the ALICE detector down to zero transverse momentum, pT, in the backward ( 124.46 < ycms < 122.96) and forward (2.03 < ycms < 3.53) rapidity intervals in the dimuon decay channel and in the mid-rapidity region ( 121.37 < ycms < 0.43) in the dielectron decay channel. The backward and forward rapidity intervals correspond to the Pb-going and p-going direction, respectively. The pT-differential J/\u3c8 production cross section at backward and forward rapidity is measured for several centrality classes, together with the corresponding average pT and pT2 values. The nuclear modification factor is presented as a function of centrality for the three rapidity intervals, and as a function of pT for several centrality classes at backward and forward rapidity. At mid- and forward rapidity, the J/\u3c8 yield is suppressed up to 40% compared to that in pp interactions scaled by the number of binary collisions. The degree of suppression increases towards central p-Pb collisions at forward rapidity, and with decreasing pT of the J/\u3c8. At backward rapidity, the nuclear modification factor is compatible with unity within the total uncertainties, with an increasing trend from peripheral to central p-Pb collisions
Centrality dependence of high-pT D meson suppression in Pb-Pb collisions at 1asNN = 2.76 TeV
The nuclear modification factor, RAA, of the prompt charmed mesons D0, D+ and D 17+, and their antiparticles, was measured with the ALICE detector in Pb-Pb collisions at a centre-of-mass energy 1asNN = 2.76 TeV in two transverse momentum intervals, 5 < pT < 8GeV/c and 8 < pT < 16GeV/c, and in six collision centrality classes. The RAA shows a maximum suppression of a factor of 5\u20136 in the 10% most central collisions. The suppression and its centrality dependence are compatible within uncertainties with those of charged pions. A comparison with the RAA of non-prompt J/\u3c8 from B meson decays, measured by the CMS Collaboration, hints at a larger suppression of D mesons in the most central collisions
Decay of Er156 compound nucleus
Charged particles and high energy \u3b3 rays from the decay of the 156Er compound nucleus populated at Ex=47 MeV excitation energy by the 12C+144Sm and 64Ni+92Zr reactions have been measured to study possible nonstatistical or entrance channel effects. The experimental spectra and published evaporation residue and neutron data are compared with statistical model calculations. The comparison shows that the statistical model with standard parametrization of level density and yrast lines describes reasonably well the bulk of experimental observables but not the shape of neutron spectra if account is taken of the enhancement factor for E2 transitions. The discrepancies between experimental data and model calculations are discussed
Direct Capture Cross Section and the Ep = 71 and 105 keV Resonances in the 22Ne(p,\u3b3)23Na Reaction
The 22Ne(p,\u3b3)23Na reaction, part of the neon-sodium cycle of hydrogen burning, may explain the
observed anticorrelation between sodium and oxygen abundances in globular cluster stars. Its rate is
controlled by a number of low-energy resonances and a slowly varying nonresonant component. Three new
resonances at Ep = 156.2, 189.5, and 259.7 keV have recently been observed and confirmed. However,
significant uncertainty on the reaction rate remains due to the nonresonant process and to two suggested
resonances at Ep = 71 and 105 keV. Here, new 22Ne(p,\u3b3)23Na data with high statistics and low
background are reported. Stringent upper limits of 6
7 10 1211 and 7
7 10 1211 eV (90% confidence level),
respectively, are placed on the two suggested resonances. In addition, the off-resonant S factor has been
measured at unprecedented low energy, constraining the contributions from a subthreshold resonance and
the direct capture process. As a result, at a temperature of 0.1 GK the error bar of the 22Ne(p,\u3b3)23Na rate is
now reduced by 3 orders of magnitud
Hypernuclear weak decay studies with FINUDA
37reservedmixedM. Agnello;L. Benussi;M. Bertani;H.C. Bhang;G. Bonomi;E. Botta;M. Bregant;T. Bressani;S. Bufalino;L. Busso;D. Calvo;P. Camerini;B. Dalena;F. De Mori;G. DʼErasmo;F.L. Fabbri;A. Feliciello;A. Filippi;E.M. Fiore;H. Fujioka;P. Gianotti;N. Grion;V. Lucherini;S. Marcello;N. Mirfakhrai;F. Moia;P. Montagna;O. Morra;T. Nagae;H. Outa;A. Pantaleo;V. Paticchio;S. Piano;R. Rui;G. Simonetti;R. Wheadon;A. ZenoniM., Agnello; L., Benussi; M., Bertani; H. C., Bhang; Bonomi, Germano; E., Botta; M., Bregant; T., Bressani; S., Bufalino; L., Busso; D., Calvo; P., Camerini; B., Dalena; F., De Mori; G., Dʼerasmo; F. L., Fabbri; A., Feliciello; A., Filippi; E. M., Fiore; H., Fujioka; P., Gianotti; N., Grion; V., Lucherini; S., Marcello; N., Mirfakhrai; F., Moia; P., Montagna; O., Morra; T., Nagae; H., Outa; A., Pantaleo; V., Paticchio; S., Piano; R., Rui; G., Simonetti; R., Wheadon; Zenoni, Ald
The FINUDA experiment at DAPHNE
The forthcoming FINUDA experiment at DANE is presented
Performance of PSI, CURB-65, and SCAP scores in predicting the outcome of patients with community-acquired and healthcare-associated pneumonia
The objective was to compare three score systems, pneumonia severity index (PSI), the Confusion-Urea-Respiratory Rate-Blood pressure-65 (CURB-65), and severe community-acquired pneumonia (SCAP), for prediction of the outcomes in a cohort of patients with community-acquired (CAP) and healthcare-associated pneumonia (HCAP). Large multi-center, prospective, observational study was conducted in 55 hospitals. HCAP patients were included in the high classes of CURB-65, PSI and SCAP scores have a mortality rate higher than that of CAP patients. HCAP patients included in the low class of the three severity rules have a significantly higher incidence of adverse events, including development of septic shock, transfer into an ICU, and death (p < 0.01). At multivariate Cox regression analysis, inclusion in the severe classes of PSI, CURB-65, or SCAP scores and receipt of an empirical therapy not adherent to international guidelines prove to be risk factors independently associated with poor outcome. PSI, CURB-65, and SCAP score have a good performance in patients with CAP but are less useful in patients with HCAP, especially in patients classified in the low-risk classes
J/\u3c8 Elliptic Flow in Pb-Pb Collisions at sqrt[s_{NN}]=2.76\u2009\u2009TeV
We report on the first measurement of inclusive J/\u3c8 elliptic flow v2 in heavy-ion collisions at the LHC. The measurement is performed with the ALICE detector in Pb-Pb collisions at 1asNN=2.76 TeV in the rapidity range 2,5<y<4,0. The dependence of the J=c v2 on the collision centrality and on the J/\u3c8 transverse momentum is studied in the range 0 64pT 64 10 GeV/c. For semicentral Pb-Pb collisions at 1asNN=2.76 TeV, an indication of nonzero v2 is observed with a largest measured value of v2=0.116 \ub1 0.046 (stat) \ub1 0:029 (syst) for J/\u3c8 in the transverse momentum range 2 64 pT 64 4 GeV/c. The elliptic flow measurement complements the previously reported ALICE results on the inclusive J/\u3c8 nuclear modification factor and favors the scenario of a significant fraction of J/\u3c8 production from charm quarks in a deconfined partonic phase