On-line luminosity measurements at LEP

At each LEP interaction point, the luminosity is measured on-line by small angle Bhabha monitors. These monitors are optimized to observe in all bunches relative luminosity changes in a few seconds. The description of the detectors is given, together with the method used to calculate the luminosity after background correction. Optimization of the LEP performances was done with beam separation scans using the luminosity measurements. Those scans also provide a unique measurement of the vertical beam size at the interaction point

Plans for High Beta Optics in the LHC

ISBN 978-3-95450-115-1 - http://accelconf.web.cern.ch/AccelConf/IPAC2012/papers/moppc007.pdfInternational audienceBased on what has been learned with the first high β* = 90 m operation in 2011, we describe the potential and practical scenarios for reaching very high β* in the LHC in 2012 and beyond. Very high β* optics require dedicated running time and conditions in the LHC. We describe a plan which is optimized to maximize the physics potential in a minimum of dedicated running time

90 m β * optics for ATLAS/ALFA

http://accelconf.web.cern.ch/AccelConf/IPAC2011/papers/tupz002.pdfInternational audienceWe describe a high β∗ optics developed for the ATLAS detector at the LHC interaction point IP1. Roman Pots have been installed 240 m left and right of IP1 to allow to measure the absolute luminosity and the total elastic cross section for ATLAS with ALFA (Absolute Luminosity for ATLAS). Ultimately, it is planned to perform these mea- surements at a very high β∗ of 2625 m. Here we describe a new, intermediate β∗ = 90 m optics, which has been opti- mized for compatibility with the present LHC running con- ditions. We describe the main features and the expected performance of this optics for ALFA

Length Measurement of High-brightness Electron Beam thanks to the 3-Phase Method

ISBN 978-3-95450-132-8International audienceThe goal of 3-phase method is to determine the length of an electron beam without dedicated diagnostics by varying the measurement conditions of its energy spread, through a change in the RF phase of an accelerating structure. The originality here comes from the fact that it is applied on high-brightness electron beams of few MeV generated by RF photo-injectors. It allows testing the accuracy of 3-phase method, since the length to reconstruct is known as being that of the laser pulse generating the beam. It requires establishing the longitudinal transfer matrix of a RF photo-injector, which is difficult since the electron velocity vary from 0 to relativistic during its path*. The 3-phase method in RF photo-injector has been simulated by ASTRA and PARMELA codes, validating the principle of the method. First measurement has been done on PHIL accelerator at LAL, showing a good agreement with the expected length. I will then show results obtained at PITZ with a standing wave booster and a comparison with those coming from a Cerenkov detector. Finally, measurements at higher energy performed on the SOLEIL LINAC with travelling wave accelerating structures will be exposed

Tracking and Tolerances Study for the ATLAS High Beta Optics

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Overall Optics Solutions for Very High Beta in Atlas

accelconf.web.cern.ch/accelconf/e08/papers/wepp004.pdfInternational audienceAn insertion optics with a beta-star of at least 2600 m has been requested by the ATLAS experiment at the LHC. This is very far from the standard LHC physics optics and implies a significant reduction in the phase advance from this insertion corresponding to about half a unit in tune. We describe several alternatives how this could be integrated in overall LHC optics solutions with the possibility to inject, ramp and un-squeeze to the required very high beta

Overall Optics Solutions for very high Beta in ATLAS

An insertion optics with a $\beta$* of at least 2600m has been requested by the ATLAS experiment at the LHC. This is very far from the standard LHC physics optics and implies a significant reduction in the phase advance from this insertion corresponding to about half a unit in tune. We describe several alternatives how this could be integrated in overall LHC optics solutions with the possibility to inject, ramp and un-squeeze to the required very high-$\beta$*

Determination of the forward slope in p pp~p and pˉ p\bar p~p elastic scattering up to LHC energy

In the analysis of experimental data on $p p$ (or $\bar p p$) elastic differential cross section it is customary to define an average forward slope $b$ in the form $\exp{(-b|t|)}$, where $t$ is the momentum transfer. Taking as working example the results of experiments at Tevatron and SPS, we will show with the help of the impact picture approach, that this simplifying assumption hides interesting information on the complex non-flip scattering amplitude, and that the slope $b$ is not a constant. We investigate the variation of this slope parameter, including a model-independent way to extract this information from an accurate measurement of the elastic differential cross section. An extension of our results to the LHC energy domain is presented in view of future experiments.Comment: 12 pages, 6 figures, to appear in EPJ

Evaluation of demarcation line after epithelium-off iontophoresis corneal collagen cross-linking for progressive keratoconus

The aim of the study was to visualize and evaluate the characteristics and depth of the demarcation line with anterior segment optical coherence tomography (AS-OCT) after epithelium-off iontophoresis corneal collagen cross-linking (epi-off I-CXL). In this prospective, consecutive, single center study 18 eyes of 18 patients with keratoconus were involved. One month after epi-off I-CXL, all the patients underwent an AS-OCT scan to search for a demarcation line and its characteristics. The corneal stromal demarcation line was identified in all the eyes. Mean depth of the corneal stromal demarcation line was 261.8 ± 46.7 μm (range: 184 to 362 μm), at 56.7 ± 12% corneal depth. In conclusion, epi-off I-CXL determines a demarcation line that can be visualized with AS-OCT, which seems clearly distinguishable and similar to that created in standard CXL

MAROC: Multi-Anode ReadOut Chip for MaPMTs

International audienceFor the ATLAS luminometer, made of Roman pots, a complete readout ASIC has been designed in 0.35 SiGe technology. It is used to readout 64 channels multi anode photomultipliers and supplies 64 trigger outputs and a multiplexed charge. Since its delivery in November 2005, the MAROC chip has been tested at LAL. Despite a substrate coupling effect which affects the performance when all channels are used in high gain, the chip has shown nice global behavior and it has been used during beam tests at CERN in October 2006