Intercalibration of the barrel electromagnetic calorimeter of the CMS experiment at start-up

Calibration of the relative response of the individual channels of the barrel electromagnetic calorimeter of the CMS detector was accomplished, before installation, with cosmic ray muons and test beams. One fourth of the calorimeter was exposed to a beam of high energy electrons and the relative calibration of the channels, the intercalibration, was found to be reproducible to a precision of about 0.3%. Additionally, data were collected with cosmic rays for the entire ECAL barrel during the commissioning phase. By comparing the intercalibration constants obtained with the electron beam data with those from the cosmic ray data, it is demonstrated that the latter provide an intercalibration precision of 1.5% over most of the barrel ECAL. The best intercalibration precision is expected to come from the analysis of events collected in situ during the LHC operation. Using data collected with both electrons and pion beams, several aspects of the intercalibration procedures based on electrons or neutral pions were investigated

Chemical composition of atmospheric particulate matter soluble fraction and meteorological variables in São Paulo state, Brazil Composição química da fração solúvel do material particulado atmosférico e variáveis meteorológicas no estado de São Paulo, Brasil

The objective of this work was to characterize and compare the chemical composition of the PM10 soluble fraction in relation to meteorological variables such as wind direction and air masses backward trajectories. The PM10 was collected during winter of 1999 in two contrasting sites: the São Paulo city and the State Park of Serra do Mar (Cunha) inside the Atlantic Forest Reserve. The aqueous extracts of PM10 were analyzed by Ion Chromatography for major ions (Na+, K+, Mg2+, Ca2+, NH4+, Cl-, NO3-, SO4(2-)) and by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) for trace elements (Al, Mn, Fe, Pb, Zn, etc.). In São Paulo, the dominant chemical species were SO4(2-), NO3-, NH4+, Zn, Fe, Al, Ba, Cu, Pb, Mn and Ni while in Cunha, Na+, K+, Cl-, SO4(2-), Zn and Ni were dominant. The chemical composition related to the wind direction during sampling reflected short-range influence due to soil occupation and anthropic activities.<br>Este trabalho teve como objetivo a caracterização e a comparação da composição química da fração solúvel do PM10, com variáveis meteorológicas, tais como, direção do vento e trajetórias de massas de ar. O PM10 foi coletado durante o inverno de 1999 em dois locais contrastantes: na cidade de São Paulo e no Parque Estadual da Serra do Mar (Cunha), Reserva de Mata Atlântica. Os extratos aquosos do PM10 foram analisados por Cromatografia de Íons para quantificação dos íons maiores (Na+, K+, Mg2+, Ca2+, NH4+, Cl-, NO3-, SO4(2-)) e por ICP-MS para quantificação dos elementos traço (Al, Mn, Fe, Pb, Zn, etc.). As espécies químicas que predominaram foram SO4(2-), NO3-, NH4+, Zn, Fe, Al, Ba, Cu, Pb, Mn e Ni em São Paulo, e Na+, K+, Cl-, SO4(2-), Zn e Ni em Cunha. A composição química relacionada com a direção do vento que prevaleceu durante a amostragem, refletiu um transporte de curta escala influenciado pela ocupação do solo e as atividades antrópicas

Search for a very light Higgs boson in Z decays

A search has been made for a very light Higgs boson in the processes e+e- → e+e-H and e+e- →μ+μ-H using data collected by ALEPH at the LEP e+e- collider at centre of mass energies close to the Z peak. The mass range between 0 and 57 MeV is unambigously excluded at the 95% confidence level. If we combine this with our previously published analysis, the complete range from 0 to 24 GeV is excluded at 95% CL. The search is extended to light Higgs bosons of the minimal supersymmetric standard model, with the result that all possibilities of coupling are excluded for Higgs masses below 3 GeV

Determination of the leptonic branching ratios of the Z

The ratios of the numbers of Z bosons decaying to e+e−, μ+μ− and τ+τ− pairs to the number decaying to hadrons have been measured. The branching ratios and partial widths for each channel were determined and found to be equal, consistent with lepton universality. The mean leptonic branching ratio was found to be 0.0321 ± 0.0013 and the leptonic partial width to be 85.4 ± 5.3 MeV. The partial widths for hadronic decays and for invisible decays were deduced to be 1833 ± 116 MeV and 569 ± 92 MeV, respectively. The number of light neutrino types, assuming only the standard model value for the ratio , was found to be 3.35 ± 0.41

Search for neutralino production in Z decays

Limits on Z decay branching ratios into neutralinos are reported. They were obtained from searches for monojets, acoplanar jets, acoplanar lepton pairs, single photons and acoplanar photon pairs as signaturs for the reactions e+e- → χχ′ and e+e- → χχ′, where χ is the lightest neutralino and χ′ any heavier one. The data sample used for these searches corresponds to about 23 000 events of Z decay into multihadrons, collected at LEP by the ALEPH detector for centre of mass energies at and near the Z peak. The results obtained are used to restrict the parameter space of the minimal supersymmetric standard model

A precise determination of the number of families with light neutrinos and of the Z boson partial widths

More extensive and precise results are reported on the parameters of Z decay. On the basis of 20 000 Z decays collected with the ALEPH detector at LEP we find Mz=91.182±0.026 (exp.) ±0.030 (beam) GeV, Γz=2.541±0.056 GeV and σhad0=41.4±0.8 nb. The partial widths for the hadronic and leptonic channels are Γhad=1804±44 MeV, Γe+e−=82.1±3.4 MeV, Γμ+μ−=87.9±6.0 MeV and Γτ+τ−=86.1±5.6 MeV, in good agreement with the standard model. On the basis of the average leptonic width Γℓ+ℓ−=83.9±2.2 MeV, the effective weak mixing angle is found to be sin2θw(Mz)=0.231±0.008. Usin g the partial widths calculated in the standard model, the number of light neutrino families is Nν=3.01±0.15 (exp.)±0.05 (theor.)

Search for excited neutrinos in Z decay

Excited neutrinos decaying into a neutrino and a photon are searched for in the ALEPH detector at LEP. No evidence is found for Z decay into v̄v∗ or v̄∗v∗ final states. Upper limits are derived on excited neutrino couplings up to excited neutrino masses close to the Z mass. Lower limits on the v∗ mass, independent of the v∗ decay modes, are deduced from the total Z width

Search for excited leptons in Z0 decay

We have looked for evidence of excited lepton production in Z0 decay observed in the ALEPH detector at LEP. We find no ℓℓγγ events and set new limits at 95% CL on ℓ∗ masses at 44.6, 44.6 and 41.2 GeV/c2 for respectively. Observed events in the ℓℓγ channels are consistent with radiative effects and we set limits for the first time on the coupling for ℓ∗ masses in the range up to 86 GeV/c2