456 research outputs found

    Improving quantum interferometry by using entanglement (to take a decision you'd better use entanglement)

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    We address the use of entanglement to improve the precision of generalized quantum interferometry, i.e. of binary measurements aimed to determine whether or not a perturbation has been applied by a given device. For the most relevant operations in quantum optics, we evaluate the optimal detection strategy and the ultimate bounds to the minimum detectable perturbation. Our results indicate that entanglement-assisted strategies improve the discrimination in comparison with conventional schemes. A concrete setup to approach performances of the optimal strategies is also suggested.Comment: 2 fig

    Influência do aumento da concentração do CO2 atmosfÊrico e da temperatura do ar no desenvolvimento da cultura do cafÊ

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    O clima condiciona fortemente a produtividade agrícola e mesmo alteraçþes moderadas a severas das condiçþes ambientais poderão afetar a produção, levando a perdas económicas e impactos sociais. O previsível aumento da concentração de CO2 atmosfÊrico, associado a alteraçþes nos padrþes de pluviosidade, ao aumento na duração e intensidade da seca, bem como a um aumento generalizado das temperaturas, são realidades cada vez mais presentes em todos os cenårios agrícolas. As interaçþes complexas entre estes diferentes fatores alterarão as respostas das plantas com potencial impacto acrescido na produtividade e qualidade dos produtos finais. O aumento da concentração atmosfÊrica de diferentes gases com efeito de estufa, com destaque para o CO2, tem ocorrido em simultâneo com o aumento da temperatura do ar. Desde o início da revolução industrial no sÊc. XVIII, a concentração de CO2 aumentou de ca. 280 ΟL CO2 L-1, tendo ultrapassado 400 ΟL CO2 L-1 em 2013, sendo previsível que possa atingir valores entre 421 e 936 ΟL CO2 L-1 no final do sÊculo. Adicionalmente, previsþes recentes para este sÊculo apontam para aumentos da temperatura ao nível da superfície do planeta que poderão ir de 0,3-1,7 ºC, atÊ um extremo de 2,6-4,8 ºC. Este eventual aumento de temperatura levarå a alteraçþes dråsticas nos teores de humidade do ar e consequentemente nos regimes de pluviosidade. Estas circunstâncias poderão promover condiçþes de seca mais frequentes e extremas. Contrastando com o impacto negativo da redução da disponibilidade hídrica ou do aumento da temperatura, o aumento do valor de CO2 per se pode ter um papel positivo, pois estimula a produção. A cultura do cafÊ Ê uma das mais importantes culturas de rendimento do mundo, estando presente em mais de 80 países da região tropical e sendo suportada por 2 espÊcies, Coffea arabica L. (cafÊ tipo Aråbica) e Coffea canephora Pierre ex A. Froehner, (cafÊ tipo Robusta). Neste contexto torna-se premente o estudo dos mecanismos (com destaque para os ecofisiológicos) envolvidos na aclimatação das plantas, a um ambiente em permanente mudança. Recentes projeçþes indicam perdas significativas da årea de cultivo de Coffea sp (particularmente de C. arabica), mas estudos recentes mostraram que o aumento dos valores de CO2 na atmosfera têm um efeito claramente mitigador do impacto de temperaturas supra-óptimas, moderando os impactos antes estimados com base em modelos que não têm em linha de conta este efeito benÊfico do CO2. O conhecimento proveniente de estudos multidisciplinares e a obtenção de indicadores ecofisiológicos auxiliarå na seleção de indivíduos mais tolerantes e servirå de ferramentas para o melhoramento de novas plantas com uma maior capacidade de adaptação.info:eu-repo/semantics/publishedVersio

    Search for the standard model Higgs boson decaying into two photons in pp collisions at sqrt(s)=7 TeV

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    A search for a Higgs boson decaying into two photons is described. The analysis is performed using a dataset recorded by the CMS experiment at the LHC from pp collisions at a centre-of-mass energy of 7 TeV, which corresponds to an integrated luminosity of 4.8 inverse femtobarns. Limits are set on the cross section of the standard model Higgs boson decaying to two photons. The expected exclusion limit at 95% confidence level is between 1.4 and 2.4 times the standard model cross section in the mass range between 110 and 150 GeV. The analysis of the data excludes, at 95% confidence level, the standard model Higgs boson decaying into two photons in the mass range 128 to 132 GeV. The largest excess of events above the expected standard model background is observed for a Higgs boson mass hypothesis of 124 GeV with a local significance of 3.1 sigma. The global significance of observing an excess with a local significance greater than 3.1 sigma anywhere in the search range 110-150 GeV is estimated to be 1.8 sigma. More data are required to ascertain the origin of this excess.Comment: Submitted to Physics Letters

    Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV

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    Results are presented from a search for a W' boson using a dataset corresponding to 5.0 inverse femtobarns of integrated luminosity collected during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV. The W' boson is modeled as a heavy W boson, but different scenarios for the couplings to fermions are considered, involving both left-handed and right-handed chiral projections of the fermions, as well as an arbitrary mixture of the two. The search is performed in the decay channel W' to t b, leading to a final state signature with a single lepton (e, mu), missing transverse energy, and jets, at least one of which is tagged as a b-jet. A W' boson that couples to fermions with the same coupling constant as the W, but to the right-handed rather than left-handed chiral projections, is excluded for masses below 1.85 TeV at the 95% confidence level. For the first time using LHC data, constraints on the W' gauge coupling for a set of left- and right-handed coupling combinations have been placed. These results represent a significant improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe

    Measurement of isolated photon production in pp and PbPb collisions at sqrt(sNN) = 2.76 TeV

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    Isolated photon production is measured in proton-proton and lead-lead collisions at nucleon-nucleon centre-of-mass energies of 2.76 TeV in the pseudorapidity range |eta|<1.44 and transverse energies ET between 20 and 80 GeV with the CMS detector at the LHC. The measured ET spectra are found to be in good agreement with next-to-leading-order perturbative QCD predictions. The ratio of PbPb to pp isolated photon ET-differential yields, scaled by the number of incoherent nucleon-nucleon collisions, is consistent with unity for all PbPb reaction centralities.Comment: Submitted to Physics Letters

    Measurement of the Lambda(b) cross section and the anti-Lambda(b) to Lambda(b) ratio with Lambda(b) to J/Psi Lambda decays in pp collisions at sqrt(s) = 7 TeV

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    The Lambda(b) differential production cross section and the cross section ratio anti-Lambda(b)/Lambda(b) are measured as functions of transverse momentum pt(Lambda(b)) and rapidity abs(y(Lambda(b))) in pp collisions at sqrt(s) = 7 TeV using data collected by the CMS experiment at the LHC. The measurements are based on Lambda(b) decays reconstructed in the exclusive final state J/Psi Lambda, with the subsequent decays J/Psi to an opposite-sign muon pair and Lambda to proton pion, using a data sample corresponding to an integrated luminosity of 1.9 inverse femtobarns. The product of the cross section times the branching ratio for Lambda(b) to J/Psi Lambda versus pt(Lambda(b)) falls faster than that of b mesons. The measured value of the cross section times the branching ratio for pt(Lambda(b)) > 10 GeV and abs(y(Lambda(b))) < 2.0 is 1.06 +/- 0.06 +/- 0.12 nb, and the integrated cross section ratio for anti-Lambda(b)/Lambda(b) is 1.02 +/- 0.07 +/- 0.09, where the uncertainties are statistical and systematic, respectively.Comment: Submitted to Physics Letters
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