A measurement of the transverse momentum spectra of jets in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV is reported. Jets are reconstructed from charged particles using the anti-$k_{\rm T}$ jet algorithm with jet resolution parameters $R$ of $0.2$ and $0.3$ in pseudo-rapidity $|\eta|<0.5$. The transverse momentum $p_{\rm T}$ of charged particles is measured down to $0.15$ GeV/$c$ which gives access to the low $p_{\rm T}$ fragments of the jet. Jets found in heavy-ion collisions are corrected event-by-event for average background density and on an inclusive basis (via unfolding) for residual background fluctuations and detector effects. A strong suppression of jet production in central events with respect to peripheral events is observed. The suppression is found to be similar to the suppression of charged hadrons, which suggests that substantial energy is radiated at angles larger than the jet resolution parameter $R=0.3$ considered in the analysis. The fragmentation bias introduced by selecting jets with a high $p_{\rm T}$ leading particle, which rejects jets with a soft fragmentation pattern, has a similar effect on the jet yield for central and peripheral events. The ratio of jet spectra with $R=0.2$ and $R=0.3$ is found to be similar in Pb-Pb and simulated PYTHIA pp events, indicating no strong broadening of the radial jet structure in the reconstructed jets with $R<0.3$.
Average values of the number of participating nucleons (Npart), number of binary collisions (Ncoll), and the nuclear overlap function (TAA) for the centrality intervals used in the jet analysis.
Charged jet spectra using two cone radius parameters R = 0.2 and 0.3 and a leading track selection of pT > 0.15 GeV, for centrality 0-10%. The two systematic uncertainties correspond to the shape uncertainty and the correlated uncertainty.
Charged jet spectra using two cone radius parameters R = 0.2 and 0.3 and a leading track selection of pT > 0.15 GeV, for centrality 10-30%. The two systematic uncertainties correspond to the shape uncertainty and the correlated uncertainty.
Strange baryon and in particular multi-strange baryon production is suggested to be a useful probe in the search for quark gluon plasma formation in heavy ion collisions. We have measured the (Ω − + Ω + ) (Ξ − + Ξ + ) production ratio to be 0.8±0.4 at central rapidity and ϱ T > 1.6 GeV/c.
We have searched for the decay D 0 → μ + μ − among 1.25 × 10 5 μ + μ − pairs produced by 350 GeV/ c π − particles interacting in copper and tungsten targets. Using a high-resolution silicon-microstrip detector followed by a large-acceptance magnetic spectrometer and a muon filter we are able to discriminate between prompt and non-prompt muons and to measure dimuon masses. No candidate compatible with a D 0 → μ + μ − decay has been found, allowing us to set an upper limit on the branching fraction B( D 0 → μ + μ − ) of 7.6 × 10 −6 at the 90% confidence level.
Multi-strange baryon and anti-baryon production is expected to be a useful probe in the search for Quark-Gluon Plasma formation. We present the transverse mass distributions of negative particles, K o s, Λs, Λ s, and Ξ − s produced in sulphurtungsten interactions at 200 GeV/c per nucleon and give the corrected ratios Λ Λ, Ξ − Λ and Ξ − /Λ . We note that our ratio Ξ − / Λ appears large in comparison to that from p p interactions.
The relative production yields and transverse mass spectra for Λ, Λ , Ξ − and Ξ + hyperons in proton-tungsten interactions are presented and compared with the WA85 results from central sulphur-tungsten interactions. A study of the negative particle yield has also been undertaken and the ratio of Λ hyperons to negative particles has been calculated.
Forum