Homage to Jacques Séguinot 1932–2020 Ekelöf, Tord
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
November 2023, 2023-11-00, Letnik:
1056
Journal Article
Interfacial processes are involved in many areas of chemistry, physics and biochemistry, but following the structural changes of surfaces and thin films at relevant timescales remains challenging. ...Time-of flight neutron reflectometry can determine changes in surface composition and film thickness, but the speed of these measurements is typically limited by the neutron flux over the range of wavelengths available at existing instrumentation. This necessarily means that, even using the time-of-flight method, measurements over several angles of incidence are required to cover the full Q-range important for structural determination. The very high intensity of the ESS pulsed source makes such configuration changes very inefficient, as the measurements can potentially be recorded in seconds or even milliseconds. Here, we present a conceptual design and some preliminary results from a new type of fast beam shutter system that will allow efficient measurement of broad angular ranges at sub-second timescales. The shutter system is conceptually also potentially useful for a fast aperture application on the ZOOM instrument at the ISIS Target station 2. By using two perpendicular shutters with slits cut into them, it is possible to create a square aperture within the beam as the neutron pulse passes. We believe that the flexibility demonstrated will mean that this system has the potential to be generally useful in many neutron instrumentation applications.
A EC-supported conceptual design study ESSSB has been carried out during the years 2018-2022 of how the 5 MW linear proton accelerator of the European Spallation Source, currently under construction ...in Lund, Sweden, can be used to generate a world-uniquely intense neutrino Super Beam for precision measurement of the leptonic CP violating phase CP. Support for a continuation of this study 2023-2026 has recently been granted by EC. The uniquely high power of the ESS proton linac will allow for the neutrino oscillation measurements to be made at the second oscillation maximum, rather than at the first maximum where other experiments measure, and thereby for a more precise measurement to be made of CP. This paper describes the results of the conceptual design of ESSSB lay-out, infrastructure and components as well as of the evaluation of the physics performance for leptonic CP violation discovery and, in particular, for the precision in the measurement if the CP violation phase CP as well as the plans for the continuation of the work, which will include design studies of a Low energy nuSTORM and an Low Energy Monitored Neutrino Beam.
The future of ESS is bright Schweika, Werner; Lindroos, Mats; Zanini, Luca ...
EPJ Web of conferences,
2023, Letnik:
286
Journal Article
Recenzirano
Odprti dostop
The European Spallation Source ESS has still a huge upgrade potential by using an accelerator ring structure for proton pulse compression that can change the long pulse to a medium pulse structure. ...Therefore, we consider the performance of a medium pulse structure on the existing ESS target, moderator and neutron instrumentation. A medium proton pulse will enhance the neutron peak brightness of thermal and cold neutrons by about one order of magnitude and even up to two orders of magnitude at shortest wavelengths used at ESS, largely increasing the performance of the ESS instruments for neutron scattering. The arguments for a medium pulse length are that it is best adapted to the resolution requirements of the ESS instruments, the coupled moderator, the typical long instruments; furthermore, that it seems feasible to realise a medium pulse length by advanced, slow extraction from an accelerator ring, and feasible for the rotating tungsten target to take the high-power load. We discuss the implications of a medium proton pulse length and its specific choice for the instrument resolution, and for moderator and target. The proposed upgrade is stimulated by the new project ESSnuSB for a neutrino super beam at ESS and motivated by the synergy effect of using a common pulse compressor ring. The upgrade will be a most economical and efficient path for the ESS to a next higher level from an already world leading long-pulse source, transforming with a medium pulse structure into an even much more powerful, future next generation neutron source.
The ESSνSB project Cederkall, Joakim; Christiansen, Peter; Park, Joochun ...
Pos : proceedings of science,
2020, Letnik:
EPS-HEP2019
Journal Article, Conference Proceeding
Recenzirano
Odprti dostop
The ESSνSB project aims to produce a neutrino beam of unique intensity for a long-baseline oscillation measurement of CP-violation in the leptonic sector. The project, supported within the H2020 ...framework programme of the European Union, is currently in a conceptual design study phase, and work is ongoing within the project to develop viable solutions for the upgrade of the linear accelerator of the European Spallation Source (ESS), for the associated ring accumulator and the high-power target stations, as well as to establish solutions for the near and far detectors. The unique strength of the project lies in the capability to produce a neutrino beam that is intense enough to place the far detector at the second oscillation maximum. Such a placement will reduce the sensitivity of the experiment to systematic errors, which, due to the recently established value of the neutrino mixing angle θ13, is now known to limit the measurement precision at the first oscillation maximum. In this paper we outline the basic components of the project and discuss the status of the ongoing conceptual design study.
Cross-sections for the production of a Z boson in association with two photons are measured in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data used correspond to an integrated ...luminosity of 139 fb(-1) recorded by the ATLAS experiment during Run 2 of the LHC. The measurements use the electron and muon decay channels of the Z boson, and a fiducial phase-space region where the photons are not radiated from the leptons. The integrated Z(-> ll)gamma gamma cross-section is measured with a precision of 12% and differential cross-sections are measured as a function of six kinematic variables of the Z gamma gamma system. The data are compared with predictions from MC event generators which are accurate to up to next-to-leading order in QCD. The cross-section measurements are used to set limits on the coupling strengths of dimension-8 operators in the framework of an effective field theory.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
This letter documents a search for flavour-changing neutral currents (FCNCs), which are strongly sup-pressed in the Standard Model, in events with a photon and a top quark with the ATLAS detector. ...The analysis uses data collected in pp collisions at & RADIC;s =13 TeV during Run 2 of the LHC, corresponding to an integrated luminosity of 139 fb-1. Both FCNC top-quark production and decay are considered. The final state consists of a charged lepton, missing transverse momentum, a b-tagged jet, one high-momentum photon and possibly additional jets. A multiclass deep neural network is used to classify events either as signal in one of the two categories, FCNC production or decay, or as background. No significant ex-cess of events over the background prediction is observed and 95% CL upper limits are placed on the strength of left-and right-handed FCNC interactions. The 95% CL bounds on the branching fractions for the FCNC top-quark decays, estimated (expected) from both top-quark production and decay, are B(t & RARR; u & gamma; ) < 0.85 (0.88+0.37 -0.25) x 10-5 and B(t & RARR; c & gamma; ) < 4.2 (3.40+1.35-0.95) x 10-5 for a left-handed tq & gamma; cou-pling, and B(t & RARR; u & gamma; ) < 1.2 (1.20+0.50 -0.33) x10-5 and B(t & RARR; c & gamma; ) < 4.5 (3.70+1.47 -1.03) x10-5 for a right-handed coupling. & COPY; 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons .org /licenses /by /4 .0/). Funded by SCOAP3.
This Letter reports the observation of WZ gamma production and a measurement of its cross section using 140.1 +/- 1.2 fb(-1) of proton-proton collision data recorded at a center-of-mass energy of 13 ...TeV by the bosons decaying leptonically, pp -> WZ gamma -> l'(perpendicular to)nu l(+) l(-)gamma (l(')(+) = e, mu), is measured in a fiducial phasespace region defined such that the leptons and the photon have high transverse momentum and the photon is isolated. The cross section is found to be 2.01 +/- 0.30(stat) +/- 0.16(syst) fb. The corresponding standard model predicted cross section calculated at next-to-leading order in perturbative quantum chromodynamics and at leading order in the electroweak coupling constant is 1.50 +/- 0.06 fb. The observed significance of the WZ gamma signal is 6.3 sigma, compared with an expected significance of 5.0 sigma.
The 𝐶𝑃 properties of the coupling between the Higgs boson and the top quark are investigated using 139 fb −1 of proton–proton collision data recorded by the ATLAS experiment at the LHC at a ...centre-of-mass energy of √𝑠 = 13 TeV. The 𝐶𝑃 structure of the top quark–Higgs boson Yukawa coupling is probed in events with a Higgs boson decaying into a pair of 𝑏-quarks and produced in association with either a pair of top quarks, 𝑡̄𝑡𝐻,or a single top quark, 𝑡𝐻. Events containing one or two electrons or muons are used for the measurement. Multivariate techniques are used to select regions enriched in 𝑡̄𝑡𝐻 and 𝑡𝐻 events, where dedicated 𝐶𝑃 -sensitive observables are exploited. In an extension of the Standard Model (SM) with a 𝐶𝑃 -odd admixture in the top–Higgs Yukawa coupling, the mixing angle between 𝐶𝑃 -even and 𝐶𝑃 -odd couplings is measured to be 𝛼 = 11 ◦+52 ◦−73◦ , compatible with the SM prediction corresponding to 𝛼 = 0.
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