guest ::
| Home > Publications database > Luminosity measurement at CMS |
| Home > Publications database > Luminosity measurement at CMS |
| Book/Report/Dissertation / PhD Thesis | PUBDB-2017-11439 |
; ;
2017
Verlag Deutsches Elektronen-Synchrotron
This record in other databases:
Please use a persistent id in citations: doi:10.3204/PUBDB-2017-11439
Report No.: DESY-THESIS-2017-043
Abstract: Luminosity is a key quantity of any collider, since it allows for the determination of the absolute cross sections from the observed rates in a detector. Since theHiggs boson discovery in 2012, the highest priority at the Large Hadron Collider (LHC) has been given to an accurate understanding of the electroweak scale anda search for new physics. Precise luminosity measurements in such conditions are of crucial importance, as they determine the precision of any physics cross sectionmeasurement.To increase the production of particles of interest, usually of low cross section, the LHC is running at the highest possible luminosity. After the first Long Shutdown(LS1) the original performance goal for the luminosity of 1 × 1034 cm−2 s−1 was reached with 1011 protons per bunch and a bunch spacing of 25 ns. In suchconditions radiation hard detectors with extremely fast response time are required, especially for instrumentation near the beam.The Compact Muon Solenoid experiment is equipped with three online luminometers, which fulfill the listed requirements: the Fast Beam Conditions Monitor(BCM1F), the Pixel Luminosity Telescope (PLT) and the Forward Hadron calorimeter (HF).The BCM1F was upgraded during LS1 from 8 to 24 diamond sensors and is read out by a dedicated fast ASIC. The back-end comprises a deadtime-less histogrammingunit, with 6.25 ns bin width and analog-to-digital converters with 2 ns sampling time in the VME standard. A microTCA system with better time resolutionis in development.Particles originating from collisions and machine induced background arrive with 12 ns time difference. Because of its excellent time resolution BCM1F measuresseparately both luminosity and machine induced background particles. The performance of the detector in the first running period and radiation damage monitoringof the sensors and electronics chain form the first part of this thesis.Calibration of the luminometers at the LHC is done using van der Meer (VdM) scans. The proton beams are scanned against each other separately in the x andy directions. The effective width of the beams is measured and the visible cross section, the key quantity for the luminosity measurement, is determined. The impact of detector instability, beam-beam effects, correlations of the particle density distributions in the x and y planes, and satellite and ghost bunches are studied indetail and systematic uncertainties are derived. The systematic error on the visible cross section was estimated to be 3.1% in the 50 ns operation period. A comparisonof the VdM scans of 2015 and 2016 completes the second part of the thesis, as well as a comparison of the results delivered by other luminometers.As a contribution to the upgrade of the beam instrumentation for the high luminosity LHC, a novel single crystal sapphire detector was designed, built andstudied in a test-beam. The detector comprises a stack of sapphire plates. The response depends on the direction of the incident particles. The performance of thedetector is described in the third part of the thesis. It is demonstrated that this sapphire detector can be used for the detection of single relativistic particles. Theresults point to the dominant contribution of the electrons to the signal generation in sapphire.
|
The record appears in these collections: |
Book
Luminosity Measurement at the Compact Muon Solenoid Experiment of the LHC
Springer Nature Switzerland : Springer International Publishing, Springer Theses 142 pp. (2018) [10.1007/978-3-319-93139-5] = Dissertation, Brandenburg University of Technology Cottbus-Senftenberg, 2017
Fulltext
BibTeX |
EndNote:
XML,
Text |
RIS
PDF