Search results for "nuclear experiment"
showing 10 items of 7971 documents
Measurement of an Excess in the Yield of J/ψ at Very Low pT in Pb-Pb Collisions at √sNN = 2.76 TeV
2016
We report on the first measurement of an excess in the yield of J=ψ at very low transverse momentum (pT < 0.3 GeV=c) in peripheral hadronic Pb-Pb collisions at √sNN=2.76 TeV, performed by ALICE at the CERN LHC. Remarkably, the measured nuclear modification factor of J=ψ in the rapidity range 2.5 <y< 4 reaches about 7 (2) in the pT range 0–0.3 GeV=c in the 70%–90% (50%–70%) centrality class. The J=ψ production cross section associated with the observed excess is obtained under the hypothesis that coherent photoproduction of J=ψ is the underlying physics mechanism. If confirmed, the observation of J=ψ coherent photoproduction in Pb-Pb collisions at impact parameters smaller than twice the nu…
Simultaneous measurement of β-delayed proton and γ decay of 27P
2016
This is the first study of 27P to measure both the β-delayed proton and β-delayed γ decays. While no new proton groups in the astrophysically interesting energy region of 300–400 keV were observed, a new upper limit on the proton branching of 0.16% was estimated. Several new γ -ray lines were observed, mainly coming from the isobaric analog state in 27Si, which has been assigned a more accurate energy value of 6638(1) keV. peerReviewed
High-spin states beyond the proton drip-line: Quasiparticle alignments in Cs-113
2015
Excited states have been studied in the deformed proton emitter 113Cs. Gamma-ray transitions have been unambiguously assigned to 113Cs by correlation with its characteristic proton decay, using the method of recoil-decay tagging. Two previously identified rotational bands have been observed and extended to tentative spins of 45/2 and 51/2 h¯, with excitation energies over 8 MeV above the lowest state. These are the highest angular momenta and excitation energies observed to date in any nucleus beyond the proton drip-line. Transitions in the bands have been rearranged compared to previous work. A study of aligned angular momenta, in comparison to the predictions of Woods–Saxon cranking calcu…
Characteristics of segmented super clover detector in close geometry decay measurements
2001
Characteristics of the segmented Super Clover germanium detector response in close geometries have been studied. Results obtained with localising hit pattern recognition are compared with results from add-back and individual crystal analysis. The detector has been used at the focal plane of a gas filled recoil separator to detect isomeric gamma-rays from the nuclei produced in the 150Sm(42Ca,4n)188Pb reaction. Coincidence data from the detector was analysed and the level scheme below the 1.2 μ s isomeric state in 188Pb could be deduced. peerReviewed
Centrality Dependence of the Charged-Particle Multiplicity Density at Midrapidity in Pb-Pb Collisions at √sNN = 5.02 TeV
2016
The pseudorapidity density of charged particles, dNch=dη, at midrapidity in Pb-Pb collisions has been measured at a center-of-mass energy per nucleon pair of √sNN=5.02 TeV. For the 5% most central collisions, we measure a value of 1943±54. The rise in dNch=dη as a function of √sNN is steeper than that observed in proton-proton collisions and follows the trend established by measurements at lower energy. The increase of dNch=dη as a function of the average number of participant nucleons, hNparti, calculated in a Glauber model, is compared with the previous measurement at √sNN=2.76 TeV. A constant factor of about 1.2 describes the increase in dNch=dη from √sNN=2,76 to 5.02 TeV for all central…
Azimuthal Anisotropy of Heavy-Flavor Decay Electrons in p-Pb Collisions at √sNN = 5.02 TeV
2019
Angular correlations between heavy-flavor decay electrons and charged particles at midrapidity (|η|<0.8) are measured in p-Pb collisions at √sNN=5.02 TeV. The analysis is carried out for the 0%–20% (high) and 60%–100% (low) multiplicity ranges. The jet contribution in the correlation distribution from high-multiplicity events is removed by subtracting the distribution from low-multiplicity events. An azimuthal modulation remains after removing the jet contribution, similar to previous observations in two-particle angular correlation measurements for light-flavor hadrons. A Fourier decomposition of the modulation results in a positive second-order coefficient (v2) for heavy-flavor decay ele…
Independent isotopic yields in 25 MeV and 50 MeV proton-induced fission of natU
2016
Independent isotopic yields for elements from Zn to La in the 25 MeV proton-induced fission of natUnatU were determined with the JYFLTRAP facility. In addition, isotopic yields for Zn, Ga, Rb, Sr, Zr, Pd and Xe in the 50 MeV proton-induced fission of natUnatU were measured. The deduced isotopic yield distributions are compared with a Rubchenya model, the GEF model with universal parameters and the semi-empirical Wahl model. Of these, the Rubchenya model gives the best overall agreement with the obtained data. Combining the isotopic yield data with mass yield data to obtain the absolute independent yields was attempted. The result depends on the mass yield distribution. peerReviewed
Centrality dependence of the nuclear modification factor of charged pions, kaons, and protons in Pb-Pb collisions at √sNN = 2.76 TeV
2016
Transverse momentum (pT) spectra of pions, kaons, and protons up to pT = 20 GeV/c have been measured in Pb-Pb collisions at √sNN = 2.76 TeV using the ALICE detector for six different centrality classes covering 0%–80%. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at pT ≈ 3 GeV/c in central Pb-Pb collisions that decreases for more peripheral collisions. For pT > 10 GeV/c, the nuclear modification factor is found to be the same for all three particle species in each centrality interval within systematic uncertainties of 10%–20%. This suggests there is no direct interplay between the energy loss in the medium and the particle species composition in the hard core of …
Insight into particle production mechanisms via angular correlations of identified particles in pp collisions at √s = 7 TeV
2017
Two-particle angular correlations were measured in pp collisions at s√=7 TeV for pions, kaons, protons, and lambdas, for all particle/anti-particle combinations in the pair. Data for mesons exhibit an expected peak dominated by effects associated with mini-jets and are well reproduced by general purpose Monte Carlo generators. However, for baryon–baryon and anti-baryon–anti-baryon pairs, where both particles have the same baryon number, a near-side anti-correlation structure is observed instead of a peak. This effect is interpreted in the context of baryon production mechanisms in the fragmentation process. It currently presents a challenge to Monte Carlo models and its origin remains an op…
Nanosecond-Scale Proton Emission from Strongly Oblate-Deformed ^{149}Lu.
2021
Using the fusion-evaporation reaction ^{96}Ru(^{58}Ni,p4n)^{149}Lu and the MARA vacuum-mode recoil separator, a new proton-emitting isotope ^{149}Lu has been identified. The measured decay Q value of 1920(20) keV is the highest measured for a ground-state proton decay, and it naturally leads to the shortest directly measured half-life of 450_{-100}^{+170} ns for a ground-state proton emitter. The decay rate is consistent with l_{p}=5 emission, suggesting a dominant πh_{11/2} component for the wave function of the proton-emitting state. Through nonadiabatic quasiparticle calculations it was concluded that ^{149}Lu is the most oblate deformed proton emitter observed to date.