Paul Scherrer Institute

About: Paul Scherrer Institute is a facility organization based out in Villigen, Switzerland. It is known for research contribution in the topics: Neutron & Large Hadron Collider. The organization has 9248 authors who have published 23984 publications receiving 890129 citations. The organization is also known as: PSI.

Final results of Borexino Phase-I on low-energy solar neutrino spectroscopy

Abstract: Borexino has been running since May 2007 at the Laboratori Nazionali del Gran Sasso laboratory in Italy with the primary goal of detecting solar neutrinos. The detector, a large, unsegmented liquid scintillator calorimeter characterized by unprecedented low levels of intrinsic radioactivity, is optimized for the study of the lower energy part of the spectrum. During Phase-I (2007–2010), Borexino first detected and then precisely measured the flux of the Be 7 solar neutrinos, ruled out any significant day-night asymmetry of their interaction rate, made the first direct observation of the pep neutrinos, and set the tightest upper limit on the flux of solar neutrinos produced in the CNO cycle (carbon, nitrogen, oxigen) where carbon, nitrogen, and oxygen serve as catalysts in the fusion process. In this paper we discuss the signal signature and provide a comprehensive description of the backgrounds, quantify their event rates, describe the methods for their identification, selection, or subtraction, and describe data analysis. Key features are an extensive in situ calibration program using radioactive sources, the detailed modeling of the detector response, the ability to define an innermost fiducial volume with extremely low background via software cuts, and the excellent pulse-shape discrimination capability of the scintillator that allows particle identification. We report a measurement of the annual modulation of the Be 7 neutrino interaction rate. The period, the amplitude, and the phase of the observed modulation are consistent with the solar origin of these events, and the absence of their annual modulation is rejected with higher than 99% C.L. The physics implications of Phase-I results in the context of the neutrino oscillation physics and solar models are presented.

Activation of the human brain by monetary reward

Abstract: WITH the purpose of studying neural activation associated with reward processing in humans, we measured regional cerebral blood flow in 10 right-handed healthy subjects performing a delayed go-no go task in two different reinforcement conditions. Correct responses were either rewarded by money or a simple 'ok' reinforcer. Behaviour rewarded by money, as compared with the 'ok' reinforcement, was most significantly associated with activation of dorsolateral and orbital frontal cortex and also involved the midbrain and thalamus. These results may reflect the processing of reward information, although arousal effects cannot be completely excluded. It is suggested that the observed foci are implicated in the assessment of consequences in goal-directed behaviour which agrees with research in non-human primates.

Enhanced light absorption by mixed source black and brown carbon particles in UK winter

Abstract: Black carbon (BC) and light-absorbing organic carbon (brown carbon, BrC) play key roles in warming the atmosphere, but the magnitude of their effects remains highly uncertain. Theoretical modelling and laboratory experiments demonstrate that coatings on BC can enhance BC’s light absorption, therefore many climate models simply assume enhanced BC absorption by a factor of ∼1.5. However, recent field observations show negligible absorption enhancement, implying models may overestimate BC’s warming. Here we report direct evidence of substantial field-measured BC absorption enhancement, with the magnitude strongly depending on BC coating amount. Increases in BC coating result from a combination of changing sources and photochemical aging processes. When the influence of BrC is accounted for, observationally constrained model calculations of the BC absorption enhancement can be reconciled with the observations. We conclude that the influence of coatings on BC absorption should be treated as a source and regionally specific parameter in climate models. Uncertainties in the absorptive properties of black and brown carbon particles limit our understanding of their warming potential. Following an extensive field campaign, Liuet al. report that the magnitude of warming is dependent on particle coatings, which vary due to source and photochemical aging.

Combined explanations of (g -2 )μ ,e and implications for a large muon EDM

Abstract: With the long-standing tension between experiment and standard-model (SM) prediction in the anomalous magnetic moment of the muon, ${a}_{\ensuremath{\mu}}=(g\ensuremath{-}2{)}_{\ensuremath{\mu}}/2$, at the level of $3--4\ensuremath{\sigma}$, it is natural to ask if there could be a sizable effect in the electric dipole moment (EDM) ${d}_{\ensuremath{\mu}}$ as well. In this context it has often been argued that in UV complete models the electron EDM, which is very precisely measured, excludes a large effect in ${d}_{\ensuremath{\mu}}$. However, the recently observed $2.5\ensuremath{\sigma}$ tension in ${a}_{e}=(g\ensuremath{-}2{)}_{e}/2$, if confirmed, requires that the muon and electron sectors effectively decouple to avoid constraints from $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}$. We briefly discuss UV complete models that possess such a decoupling, which can be enforced by an Abelian flavor symmetry ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$. We show that, in such scenarios, there is no reason to expect a correlation between the electron and muon EDM, so that the latter can be sizable. New limits on ${d}_{\ensuremath{\mu}}$ improved by up to two orders of magnitude are expected from the upcoming $(g\ensuremath{-}2{)}_{\ensuremath{\mu}}$ experiments at Fermilab and J-PARC. Beyond, a proposed dedicated muon EDM experiment at PSI could further advance the limit. In this way, future improved measurements of ${a}_{e}$, ${a}_{\ensuremath{\mu}}$, as well as the fine-structure constant $\ensuremath{\alpha}$ are not only set to provide exciting precision tests of the SM, but, in combination with EDMs, to reveal crucial insights into the flavor structure of physics beyond the SM.