Looking for single top quarks in D0 data

The search for the electroweak production of top quarks is entering an exciting time: with the ever increasing luminosity furnished by the Tevatron ppbar Collider at Fermilab and sophisticated analysis techniques we are now able to approach the expected standard model production cross section for this new mode of production. Using 370pb-1 of D0 data and likelihoods as discriminants to extract the signal from the large backgrounds, we set upper limits on the standard model production cross section in the s-channel of 5.0 pb and in the t-channel of 4.4 pb, at 95% confidence level.Comment: 5 pages, 3 figures. Contributed to the proceedings of the 34th International Meeting on Fundamental Physics. El Escorial, Spain, April 200

Evidence for single top quark production at D0

The results of the first analysis to show evidence for production of single top quarks are presented. Using 0.9 fb-1 of data collected with the D0 detector at the Fermilab Tevatron, the analysis is performed in the electron+jets and muon+jets decay modes, taking special care in modeling the large backgrounds, applying a new powerful b-quark tagging algorithm and using three multivariate techniques to extract the small signal in the data. The combined measured production cross section is 4.8 +- 1.3 pb. The probability to measure a cross section at this value or higher in the absence of a signal is 0.027%, corresponding to a 3.5 standard deviation significance.Comment: 6 pages, 4 figures. Presented at 42nd Rencontres de Moriond on Electroweak Interactions and Unified Theories, La Thuile, Italy, 10-17 Mar 200

Single top quark production at the Tevatron

The observation of single top quark production by the CDF and D0 collaborations is one of the flagship measurements of the Run II of the Tevatron. The Tevatron combined single top quark cross section is measured to be: $\sigma(tb+X,~tqb+X)=2.8^{+0.6}_{-0.5}$~pb for a top quark mass of 170~GeV. This result is in agreement with the standard model production of a single top quark together with a jet in \ppbar collisions at $\sqrt{s}$=1.96~TeV and allows to measure the CKM matrix element $|V_{tb}|$ without assumptions about the number of quark families. Other analyses involving tau leptons have been performed, and several properties, like the top quark width or the polarization have been measured.Comment: Presented at 45th Rencontres de Moriond: QCD and High Energy Interactions, La Thuile, Aosta Valley, Italy, 13-20 Mar 201

Searches for gauge mediated supersymmetry breaking at ALEPH with centre-of-mass energies up to 209 GeV

A total of 628 pb-1 of data collected with the ALEPH detector at centre-of-mass energies from 189 to 209 GeV is analysed in the search for gauge mediated supersymmetry breaking (GMSB) topologies. In this framework, a novel search for six-lepton final states when the stau is the next-to-lightest supersymmetric particle (NLSP) and has negligible lifetime is performed. Other possible signatures at LEP are studied and the ALEPH final results described for two acoplanar photons, non-pointing single photons, acoplanar leptons, large impact parameter leptons, detached slepton decay vertices, heavy stable charged sleptons and multi-leptons plus missing energy final states. No evidence is found for new phenomena, and lower limits on the masses of the relevant supersymmetric particles are derived. A scan of a minimal GMSB parameter space is performed and lower limits are set for the NLSP mass at 54 GeV and for the mass scale parameter Lambda at 10 TeV, independent of the NLSP lifetime. Including the results from the neutral Higgs boson searches, a NLSP mass limit of 77 GeV is obtained and values of Lambda up to 16 TeV are excluded.Comment: PhD thesis Royal Holloway University of London, September 2002 111 pages, with 55 figures and 22 table

MITP Colours in Darkness workshop summary report

This report summarises the talks and discussions that took place over the course of the MITP Youngst@rs Colours in Darkness workshop 2023. All talks can be found at https://indico.mitp.uni-mainz.de/event/377/

Differential cross section measurements for the production of a W boson in association with jets in proton–proton collisions at √s = 7 TeV

Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb[superscript −1]. The measured cross sections are compared to predictions from Monte Carlo generators, MadGraph + pythia and sherpa, and to next-to-leading-order calculations from BlackHat + sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the pT distributions of the leading jets at high pT values, the distributions of the HT at high-HT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio

Impacts of the Tropical Pacific/Indian Oceans on the Seasonal Cycle of the West African Monsoon

The current consensus is that drought has developed in the Sahel during the second half of the twentieth century as a result of remote effects of oceanic anomalies amplified by local land–atmosphere interactions. This paper focuses on the impacts of oceanic anomalies upon West African climate and specifically aims to identify those from SST anomalies in the Pacific/Indian Oceans during spring and summer seasons, when they were significant. Idealized sensitivity experiments are performed with four atmospheric general circulation models (AGCMs). The prescribed SST patterns used in the AGCMs are based on the leading mode of covariability between SST anomalies over the Pacific/Indian Oceans and summer rainfall over West Africa. The results show that such oceanic anomalies in the Pacific/Indian Ocean lead to a northward shift of an anomalous dry belt from the Gulf of Guinea to the Sahel as the season advances. In the Sahel, the magnitude of rainfall anomalies is comparable to that obtained by other authors using SST anomalies confined to the proximity of the Atlantic Ocean. The mechanism connecting the Pacific/Indian SST anomalies with West African rainfall has a strong seasonal cycle. In spring (May and June), anomalous subsidence develops over both the Maritime Continent and the equatorial Atlantic in response to the enhanced equatorial heating. Precipitation increases over continental West Africa in association with stronger zonal convergence of moisture. In addition, precipitation decreases over the Gulf of Guinea. During the monsoon peak (July and August), the SST anomalies move westward over the equatorial Pacific and the two regions where subsidence occurred earlier in the seasons merge over West Africa. The monsoon weakens and rainfall decreases over the Sahel, especially in August.Peer reviewe

Measurements of the pp → ZZ production cross section and the Z → 4ℓ branching fraction, and constraints on anomalous triple gauge couplings at √s = 13 TeV

Four-lepton production in proton-proton collisions, pp -> (Z/gamma*)(Z/gamma*) -> 4l, where l = e or mu, is studied at a center-of-mass energy of 13 TeV with the CMS detector at the LHC. The data sample corresponds to an integrated luminosity of 35.9 fb(-1). The ZZ production cross section, sigma(pp -> ZZ) = 17.2 +/- 0.5 (stat) +/- 0.7 (syst) +/- 0.4 (theo) +/- 0.4 (lumi) pb, measured using events with two opposite-sign, same-flavor lepton pairs produced in the mass region 60 4l) = 4.83(-0.22)(+0.23) (stat)(-0.29)(+0.32) (syst) +/- 0.08 (theo) +/- 0.12(lumi) x 10(-6) for events with a four-lepton invariant mass in the range 80 4GeV for all opposite-sign, same-flavor lepton pairs. The results agree with standard model predictions. The invariant mass distribution of the four-lepton system is used to set limits on anomalous ZZZ and ZZ. couplings at 95% confidence level: -0.0012 < f(4)(Z) < 0.0010, -0.0010 < f(5)(Z) < 0.0013, -0.0012 < f(4)(gamma) < 0.0013, -0.0012 < f(5)(gamma) < 0.0013