Abstract
The ATLAS luminosity monitor, LUCID (LUminosity Cherenkov Integrating Detector), had to be upgraded for the second run of the LHC accelerator that started in spring 2015. The increased energy of the proton beams and the higher luminosity required a redesign of LUCID to cope with the more demanding conditions. The novelty of the LUCID-2 detector is that it uses the thin quartz windows of photomultipliers as Cherenkov medium and a small amounts of radioactive 207Bi sources deposited on to these windows to monitor the gain stability of the photomultipliers. The result is a fast and accurate luminosity determination that can be kept stable during many months of data taking. LUCID-2 can also measure the luminosity accurately online for each of the up to 2808 colliding bunch pairs in the LHC . These bunch pairs are separated by only 25 ns and new electronics has been built that can count not only the number of pulses above threshold but also integrate the pulses.
Highlights
A new luminosity detector for the ATLAS experiment [1] has been designed in 2013, installed in 2014 and commissioned in 2015
The inelastic proton collisions are generated with Phojet 1.12 [8], the ATLAS detector response is modeled with GEANT3/GCALOR [9], with the exception of the LUCID detector which is modeled with GEANT4 [7]
In LUCID-1, the Edro Programmable Mezzanine Cards (EPMC), equipped with Altera Cyclone II FPGAs, received hits as LVDS signals generated by custom Constant Fraction Discriminator (CFD) VME boards located in the same electronics room as the LUMAT boards
Summary
This section is devoted to the Monte Carlo simulations used to upgrade the design of the LUCID detector from Run 1 to Run 2. The threshold determines the detector event efficiency ( ) and some of the systematic effects, as it will be discussed later in the text. The pulse-height spectra below threshold is empty and the probability to detect an event (P) can be expressed as a function of the average number of collisions per bunch crossing (μ):. One can see that the probability to have an event becomes close to one when the product μ is too large. This is called zero-starvation and imposes a limit on.
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