Observation and studies of jet quenching in PbPb collisions at √sNN = 2.76 TeV

Jet production in PbPb collisions at a nucleon-nucleon center-of-mass energy of 2.76 TeV was studied with the Compact Muon Solenoid (CMS) detector at the LHC, using a data sample corresponding to an integrated luminosity of 6.7 μb^(−1). Jets are reconstructed using the energy deposited in the CMS calorimeters and studied as a function of collision centrality. With increasing collision centrality, a striking imbalance in dijet transverse momentum is observed, consistent with jet quenching. The observed effect extends from the lower cutoff used in this study (jet pT = 120 GeV/c) up to the statistical limit of the available data sample (jet pT ≈ 210 GeV/c). Correlations of charged particle tracks with jets indicate that the momentum imbalance is accompanied by a softening of the fragmentation pattern of the second most energetic, away-side jet. The dijet momentum balance is recovered when integrating low transverse momentum particles distributed over a wide angular range relative to the direction of the away-side jet

A Survey of Bottlenose Dolphins (Tursiops truncatus) in the Shannon Estuary

The bottlenose dolphin Tursiops truncatus is a ubiquitous species found throughout the temperate and tropical oceans of the world. The bottlenose dolphin population that occurs in the Shannon is one of only six known resident European populations. Since 1994, a small dolphin watching industry has been operating in the estuary, with plans for expansion. The objectives of this were to a) assess the degree of residency of bottlenose dolphins in the Shannon; b) estimate the population size and assess the production of calves; c) examine the social structure of the population; d) study habitat use and e) examine the effects of boats on dolphin behaviour. Boat-based surveys and photo-identification techniques were used to derive a population estimate and to examine distribution and movements of individually identifiable dolphins over a two-year period. Land-based scan samples were used to examine behavioural activity and interactions of dolphins with all categories of boat traffic. Trips on dolphin watching boats examined whether these boats were interacting with the same individual dolphins on a trip, daily or weekly basis. Dolphins were recorded in all months of the year but with a seasonal peak between May and September. Many of the identifiable dolphins were resighted throughout the study indicating a high degree of residency. Using photo-identification and mark-recapture analyses, the population estimate for the Shannon is 113 dolphins (CV 0.14, 95% C.I. 94 - 161). The presence of neonatal calves only from July – September indicates that there is a marked breeding season for this population and that the area is important as a nursery area. Group sizes ranged from singletons to groups of 32 animals and while dolphins were seen throughout the study area, groups were frequently encountered in the narrow water at Kilcredaun and in the mouth of the estuary. A second area of concentrated sightings was identified further up-river around Moneypoint and Tarbert/Killimer. This group comprised a smaller number of individuals, and the re-encounter rate of these individuals in the same area suggests a degree of habitat partitioning. These dolphins may be more vulnerable to dolphin watching activities than the more diffuse numbers in the outer estuary. The influence of tidal cycle was recorded at Kilcredaun and at Killimer/Tarbert with a distinct peak in sightings in the four-hour period before low tide. The frequency distribution of association indices shows that there are few "strong" associations between individuals and supports the notion of a fluid and gregarious social structure. Dolphin watching boats were involved in 61.8% of all interactions with dolphin groups, higher than any other category of boat. At present, two operators make approximately 200 dolphin watching trips annually, carrying a total of 2,400 passengers per year. The operators are highly successful in locating dolphins (97%) and the tour boats rarely come into contact with each other on the water and generally search in different areas and watch different groups. The potential for land-based dolphin watching was examined and possible sites identified. The information from this study provides a basis from which sound conservation management strategies can be developed, in order to properly conserve the species and its habitat, to develop a sustainable dolphin watching industry and to develop/monitor other coastal zone industries such as oil and gas exploration and shipping development within the Shannon.Funder: Marine Institut

Search for resonances in the dilepton mass distribution in pp collisions at √s = 7 TeV

A search for narrow resonances at high mass in the dimuon and dielectron channels has been performed by the CMS experiment at the CERN LHC, using pp collision data recorded at √s=7 TeV. The event samples correspond to integrated luminosities of 40 pb^(−1) in the dimuon channel and 35 pb^(−1) in the dielectron channel. Heavy dilepton resonances are predicted in theoretical models with extra gauge bosons (Z′) or as Kaluza-Klein graviton excitations (G_(KK)) in the Randall-Sundrum model. Upper limits on the inclusive cross section of Z′(G_(KK)) → ℓ^+ ℓ^− relative to Z → ℓ^+ ℓ^− are presented. These limits exclude at 95% confidence level a Z′ with standard-model-like couplings below 1140GeV, the superstring-inspired Z'_ψ below 887 GeV, and, for values of the coupling parameter kM_(Pl) of 0.05 (0.1), Kaluza-Klein gravitons below 855 (1079) GeV

Measurement of W^+W^− production and search for the Higgs boson in pp collisions at √s = 7 TeV

A measurement of W^+W^− production in pp collisions at √s = 7 TeV and a search for the Higgs boson are reported. The W^+W^− candidates are selected in events with two leptons, either electrons or muons. The measurement is performed using LHC data recorded with the CMS detector, corresponding to an integrated luminosity of 36 pb^(−1). The pp → W^+W^− cross section is measured to be 41.1±15.3 (stat)±5.8(syst)±4.5(lumi)pb consistent with the standard model prediction. Limits on WWγ and WWZ anomalous triple gauge couplings are set. The search for the standard model Higgs boson in the W^+W^− decay mode does not reveal any evidence of excess above backgrounds. Limits are set on the production of the Higgs boson in the context of the standard model and in the presence of a sequential fourth family of fermions with high masses. In the latter context, a Higgs boson with mass between 144 and 207 GeV/c^2 is ruled out at 95% confidence level

Search for Three-Jet Resonances in pp Collisions at √s = 7 TeV

A search for three-jet hadronic resonance production in pp collisions at a center-of-mass energy of 7 TeV has been conducted by the CMS Collaboration at the LHC, using a data sample corresponding to an integrated luminosity of 35 pb^(-1). Events with high jet multiplicity and a large scalar sum of jet transverse momenta are analyzed using a signature-based approach. The number of expected standard model background events is found to be in good agreement with the observed events. Limits on the cross section times branching ratio are set in a model of gluino pair production with an R-parity-violating decay to three quarks, and the data rule out such particles within the mass range of 200 to 280 GeV/c^2

Search for physics beyond the standard model using multilepton signatures in pp collisions at √s=7 TeV

A search for physics beyond the standard model in events with at least three leptons and any number of jets is presented. The data sample corresponds to 35 pb^(−1) of integrated luminosity in pp collisions at √s=7 TeV collected by the CMS experiment at the LHC. A number of exclusive multileptonic channels are investigated and standard model backgrounds are suppressed by requiring sufficient missing transverse energy, invariant mass inconsistent with that of the Z boson, or high jet activity. Control samples in data are used to ascertain the robustness of background evaluation techniques and to minimise the reliance on simulation. The observations are consistent with background expectations. These results constrain previously unexplored regions of supersymmetric parameter space