Very recently, the
ferroelectric photovoltaic property of bismuth ferrite (BiFeO3, BFO) has attracted much attention. However, the physical
mechanisms for its anomalous photovoltaic effect and switchable photovoltaic
effect are still largely unclear. Herein, a novel design was proposed
to realize a high photovoltaic output in BiFeO3 films by
manipulating its oxygen vacancy concentration through the alteration
of the Bi content. Subsequent results and analysis manifested that
the highest photovoltaic output was achieved in Bi1.05FeO3 films, differing 1000 times from that of Bi0.95FeO3 films. Simultaneously, the origin of photovoltaic
effect in all BiFeO3 films was suggested as the bulk photovoltaic
mechanism instead of the Schottky effect. Moreover, oxygen vacancy
migration should be the dominant factor determining the switchable
photovoltaic effect rather than the ferroelectric polarization. A
switchable Schottky-to-Ohmic interfacial contact model was proposed
to illustrate the observed switchable photovoltaic or diodelike effect.
Therefore, the present work may open a new way to realize the high
power output and controllable photovoltaic switching behavior for
the photovoltaic applications of BiFeO3 compounds.
Measurement of the top quark mass in the tt → lepton+jets channel from √ s = 8 TeV ATLAS data and combination with previous resultsThe ATLAS CollaborationThe top quark mass is measured using a template method in the tt → lepton + jets channel (lepton is e or µ) using ATLAS data recorded in 2012 at the LHC. The data were taken at a proton-proton centre-of-mass energy of √ s = 8 TeV and correspond to an integrated luminosity of 20.2 fb −1 . The tt → lepton + jets channel is characterized by the presence of a charged lepton, a neutrino and four jets, two of which originate from bottom quarks (b). Exploiting a three-dimensional template technique, the top quark mass is determined together with a global jet energy scale factor and a relative b-to-light-jet energy scale factor. The mass of the top quark is measured to be m top = 172.08 ± 0.39 (stat) ± 0.82 (syst) GeV. A combination with previous ATLAS m top measurements gives m top = 172.69 ± 0.25 (stat) ± 0.41 (syst) GeV.The ATLAS experiment [20] at the LHC is a multipurpose particle detector with a forward-backward symmetric cylindrical geometry and a near 4π coverage in the solid angle.1 It consists of an inner tracking detector surrounded by a thin superconducting solenoid providing a 2 T axial magnetic field, electromagnetic and hadronic calorimeters, and a muon spectrometer. The inner tracking detector covers the pseudorapidity range |η| < 2.5. It consists of silicon pixel, silicon microstrip, and transition radiation tracking detectors. Lead/liquid-argon (LAr) sampling calorimeters provide electromagnetic (EM) energy measurements with high granularity. A hadronic (steel/scintillator-tile) calorimeter covers the central pseudorapidity range (|η| < 1.7). The endcap and forward regions are instrumented with LAr calorimeters for both the EM and hadronic energy measurements up to |η| = 4.9. The muon spectrometer surrounds the calorimeters and is based on three large air-core toroid superconducting magnets with eight coils each. Its bending power is 2.0 to 7.5 T m. It includes a system of precision tracking chambers and fast detectors for triggering.A three-level trigger system was used to select events. The first-level trigger is implemented in hardware and used a subset of the detector information to reduce the accepted rate to at most 75 kHz. This is followed by two software-based trigger levels that together reduced the accepted event rate to 400 Hz on average depending on the data-taking conditions during 2012.
Data and simulation samplesThe analysis is based on pp collision data recorded by the ATLAS detector in 2012 at a centre-of-mass energy of √ s = 8 TeV. The integrated luminosity is 20.2 fb −1 with an uncertainty of 1.9% [21]. The modelling of top quark pair (tt) and single-top-quark signal events, as well as most background processes, relies on MC simulations. For the simulation of tt and single-top-quark events, the P -B v1 [22-1 ATLAS uses a right-handed coordinate system with its origin at the nominal interaction point (IP) in the centre of the detector...
Abstract:The electroweak production and subsequent decay of single top quarks in the t-channel is determined by the properties of the Wtb vertex, which can be described by the complex parameters of an effective Lagrangian. An analysis of a triple-differential decay rate in t-channel production is used to simultaneously determine five generalised helicity fractions and phases, as well as the polarisation of the produced top quark. The complex parameters are then constrained. This analysis is based on 20.2 fb −1 of protonproton collision data at a centre-of-mass energy of 8 TeV collected with the ATLAS detector at the LHC. The fraction of decays containing transversely polarised W bosons is measured to be f 1 = 0.30 ± 0.05. The phase between amplitudes for transversely and longitudinally polarised W bosons recoiling against left-handed b-quarks is measured to be δ − = 0.002π +0.016π +0.017π , giving no indication of CP violation. The fractions of longitudinal or transverse W bosons accompanied by right-handed b-quarks are also constrained. Based on these measurements, limits are placed at 95% CL on the ratio of the complex coupling parameters Re [g R /V L ∈ [−0.12, 0.17] and Im [g R /V L ∈ [−0.07, 0.06]. Constraints are also placed on the ratios |V R /V L | and |g L /V L |. In addition, the polarisation of single top quarks in the t-channel is constrained to be P > 0.72 (95% CL). None of the above measurements make assumptions about the value of any of the other parameters or couplings and all of them are in agreement with the Standard Model.
Keywords: Electroweak interaction, Hadron-Hadron scattering (experiments), Top physicsArXiv ePrint: 1707.05393Open Access, Copyright CERN, for the benefit of the ATLAS Collaboration. Article funded by SCOAP 3 .https://doi.org/10.1007/JHEP12(2017)017 JHEP12(2017)017 The ATLAS collaboration 43
IntroductionThe top quark is the heaviest known fundamental particle, making the measurement of its production and decay kinematic properties an important probe of physical processes beyond the Standard Model (SM). Within the SM, the top quark decays predominantly through the electroweak interaction to an on-shell W boson and a b-quark. Due to its large mass [1], its lifetime O(10 −25 s) is smaller than its hadronisation time-scale O(10 −24 s), allowing this quark to be studied as a free quark. Since the top-quark lifetime is also shorter than the depolarisation timescale O(10 −21 s) [2] and the W boson is produced onshell in the top-quark decay, the top-quark spin information is directly transferred to its decay products. Comparing angular measurements of the decay products of polarised top quarks with precise SM predictions provides a unique way to study the non-SM couplings in the Wtb vertex [3]. The normalised triple-differential cross-section (to be defined in section 2) is the joint probability distribution in all three of the angles determining the -1 -
JHEP12(2017)017kinematics of the decay t → W b from a polarised initial state. Its analysis is the most complete investigation of ...
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