Luminosity Spectrum Reconstruction at Linear Colliders

A good knowledge of the luminosity spectrum is mandatory for many measurements at future e+e- colliders. As the beam-parameters determining the luminosity spectrum cannot be measured precisely, the luminosity spectrum has to be measured through a gauge process with the detector. The measured distributions, used to reconstruct the spectrum, depend on Initial State Radiation, cross-section, and Final State Radiation. To extract the basic luminosity spectrum, a parametric model of the luminosity spectrum is created, in this case the spectrum at the 3 TeV Compact Linear Collider (CLIC). The model is used within a reweighting technique to extract the luminosity spectrum from measured Bhabha event observables, taking all relevant effects into account. The centre-of-mass energy spectrum is reconstructed within 5% over the full validity range of the model. The reconstructed spectrum does not result in a significant bias or systematic uncertainty in the exemplary physics benchmark process of smuon pair production.Comment: Version accepted by EPJC. Minor change

Effect of splinting scan bodies on the trueness of complete-arch digital implant scans with 5 different intraoral scanners

Statement of problem: The absence of fixed reference points can affect the trueness of complete-arch intraoral digital implant scans. The effect of splinting intraoral scan bodies (ISBs) or the inclusion of artificial landmarks (AL) on the trueness of complete-arch digital implant scans is still unclear. Purpose: The purpose of this study was to analyze the effect of splinting ISBs or the inclusion of AL on the trueness of complete-arch digital implant scans with 5 intraoral scanners (IOSs). Material and methods: Six tissue-level dental implants (Straumann Tissue Level) were placed in an edentulous patient, and the correspondent definitive cast was digitized with a desktop scanner (IScan4D LS3i) to obtain the reference digital cast. Digital scans (n=10) were performed with 5 IOSs: TRIOS 4, Virtuo Vivo, Medit i700, iTero Element 5D, and Cerec Primescan. Three different scanning techniques were evaluated: conventional (cIOSs), splinted (sIOSs), and AL (AL-IOSs). The scan data obtained were imported into a metrology software program and superimposed to the reference digital cast by using a best-fit algorithm. The overall deviations of the positions of the ISBs were evaluated by using the root-mean-square (RMS) error (α=.05). Results: The mean ±standard deviation trueness values for the cIOSs, sIOSs, and AL-IOSs groups were 48 ±8 µm, 53 ±7 µm, and 49 ±11 µm, respectively, with no statistically significant differences (P=.06). Significant differences were found for the IOSs used with each technique (P<.001). Primescan (27 ±4 µm cIOSs; 28 ±3 µm sIOSs; 31 ±3 µm AL-IOSs) showed significantly higher trueness than iTero 5D (47 ±5 µm cIOSs; 47 ±4 µm sIOSs; 50 ±6 µm AL-IOSs) (P=.002) and TRIOS 4 (93 ±18 µm cIOSs; 76 ±18 µm sIOSs; 107 ±13 µm AL-IOSs) (P=.001) for all techniques. In addition, no significant differences were found between the techniques by using iTero 5D or Primescan (P=.348 and P=.059, respectively). Conclusions: The cIOSs, sIOSs, and AL-IOSs techniques showed similar trueness. The IOS used influenced the trueness of complete-arch digital implant scans.info:eu-repo/semantics/acceptedVersio

Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign

Abstract: In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 109 M ⊙. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87’s spectrum. We can exclude that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded

CLIC: Status and Plan

The Compact Linear Collider (CLIC) is a high energy electron–positron collider with a maximal centre-of-mass energy of 3 TeV. In order to achieve high luminosity small bunches with high intensity are necessary. These lead to strong beam-beam forces, which create a challenging background environment. The accelerator concept and the detectors designed for CLIC are presented. Results from detector benchmark studies presented in the CLIC conceptual design report are summarised

Radiation and Background Levels in a CLIC Detector due to Beam-Beam Effects: Optimisation of Detector Geometries and Technologies

The high charge density---due to small beam sizes---and the high energy of the proposed CLIC concept for a linear electron--positron collider with a centre-of-mass energy of up to 3~TeV lead to the production of a large number of particles through beam-beam interactions at the interaction point during every bunch crossing (BX). A large fraction of these particles safely leaves the detector. A still significant amount of energy will be deposited in the forward region nonetheless, which will produce secondary particles able to cause background in the detector. Furthermore, some particles will be created with large polar angles and directly cause background in the tracking detectors and calorimeters. The main sources of background in the detector, either directly or indirectly, are the incoherent $mathrm{e}^{+}mathrm{e}^{-}$ pairs and the particles from $gammagamma ightarrow$ hadron events. The background and radiation levels in the detector have to be estimated, to study if a detector is feasible, that can handle the CLIC background conditions. Based on full detector simulations of incoherent $mathrm{e}^{+}mathrm{e}^{-}$ pairs with the Geant4 based Mokka program, the detector geometry of a CLIC detector is optimised to minimise the background in the vertex detector. Following the optimisation of the geometry, the background and radiation levels for incoherent pairs and $gammagamma ightarrow$ hadron events are estimated. The possibility of identifying high energy electron showers with the most forward calorimeter, the BeamCal, is investigated. During the optimisation of the detector layout, the hit density from backscattering particles in the innermost vertex layer is reduced from $14cdot10^{-3}$ hits per square millimetre and bunch crossing to $0.5cdot10^{-3}~mathrm{Hits/mm}^{2}mathrm{/BX}$. The total hit density from incoherent pairs is found to be $6cdot10^{-3}~mathrm{Hits/mm}^{2}mathrm{/BX}$, with an additional $0.7cdot10^{-3}~mathrm{Hits/mm}^{2}mathrm{/BX}$ from $gammagamma ightarrow$ hadron events. Including safety and cluster factors, an occupancy of 2% for $20 imes20~mumathrm{m}^{2}$ pixel sensors in the innermost vertex layer is estimated, which will require fast time-stamping of hits, but no multi-hit capable readout system. A total ionising dose of 50~$mathrm{Gy}/mathrm{yr}$ and an equivalent neutron flux of $1.5cdot10^{10}~mathrm{n}_{mathrm{eq}}/mathrm{cm}^{2}/mathrm{yr}$ are found for the innermost vertex layer, which will require moderately radiation tolerant sensors. The occupancy at the inner radii of the hadronic calorimeter endcap, due to neutrons produced by showers in the BeamCal, is found to be too large, and either smaller pad sizes, or an improved shielding are necessary to reduce the occupancy to acceptable levels. It is possible to identify electron showers on top of the incoherent pair background in the BeamCal, and the identification efficiency is found to be beneficial to reject background events for the search of particles from beyond the Standard Model