Luminosity measurements at CMS

The topic of this thesis are the methods used for luminosity measurements at the CMS experiment, focusing on calibration of luminometers using Simon van der Meer's method and using so-called "emittance scans" in various studies.\\ The thesis starts with a brief introduction to the Large Hadron Collider (LHC), the Compact Muon Solenoid (CMS) experiment and their purpose. The concept of luminosity fixed target and colliding beams experiments is discussed. The different luminosity detectors at CMS are described. The Van der Meer (VdM) scan method is described accompanied by a modern theoretical derivation assuming Gaussian beams and a brief outline of the various corrections and systematic uncertainties applied post-calibration. An extensive report on the software framework used in VdM analysis at CMS is done - for both the previously used (although optimized) core version and its automated wrapper.\\ The final chapter discusses the use of "emittance scans" - short VdM-like scans at the beginning and end of every fill - for luminosity calibration. A novel, self-contained (non-reliant on comparison to other detectors) method for non-linearity estimation using those scans is discussed, as well as their further use for long term stability monitoring

Summer student report - Upgrade work for the Fast Beam Condition Monitor at CMS

Report on summer student internship at CERN. Describes work done towards the replacement of the Fast Beam Conditions Monitor (BCM1F) - activities related to the test beam conducted by the BRIL (Background Radiation Instrumentation and Luminosity) experiment in July 2016, analog opto-hybrids testing and XDAQ development for the uTCA readout system currently under development

CMS emittance scans for luminosity calibration in 2017

Emittance scans are short van der Meer type scans performed at the beginning and at the end of LHC fills. The beams are scanned against each other in X and Y planes in 7 displacement steps. These scans are used for LHC diagnostics and since 2017 for a cross check of the CMS luminosity calibration. An XY pair of scans takes around 3 minutes. The BRIL project provides to LHC three independent online luminosity measurement from the Pixel Luminosity Telescope (PLT), the Fast Beam Condition Monitor (BCM1F) and the Forward calorimeter (HF). The excellent performance of the BRIL detector front-ends, fast back-end electronics and CMS XDAQ based data processing and publication allow the use of emittance scans for linearity and stability studies of the luminometers. Emittance scans became a powerful tool and dramatically improved the understanding of the luminosity measurement during the year. Since each luminometer is independently calibrated in every scan the measurements are independent and ratios of luminometers can directly be used as a final validation for 2017 data. Two independent analyses of emittance scans are launched a Python-based offline framework and an online XDAQ-based application. Results are published on the monitoring web-pages in real-time for the XDAQ-based analysis and typically within 15 minutes for the Python-based framework, which has however the advantage of being rerunnable

Emittance scans for CMS luminosity calibration

Emittance scans are short van der Meer type scans performed at the beginning and at the end of LHC fills. The beams are scanned against each other in X and Y planes in 9 displacement steps and are used for LHC diagnostics and since 2017 for CMS luminosity calibration cross check. An XY pair of scans takes less than 4 minutes elapsed time. BRIL project provides to LHC three independent online luminosity measurement from PLT, BCM1F and HF. The excellent performance of BRIL detectors, fast back-end electronics and CMS XDAQ based data processing and publication allow the use of emittance scans for linearity and stability studies of the luminometers. Emittance scans became a powerful tool and dramatically improved understanding of luminosity measurement during the year. Since each luminometer is independently calibrated in every scan the measurements are independent and ratios of luminometers can strictly be used as a final validation. Two independent analyses of emittance scans are launched: offline python based framework and online XDAQ based application. Results are published on the monitoring web-pages in real-time for the XDAQ based analysis and within typically 15 minutes for the python based framework, which has however the advantage of being rerunnable

Emittance scans for CMS luminosity calibration

Emittance scans are short van der Meer type scans performed at the beginning and at the end of LHC fills. The beams are scanned against each other in X and Y planes in 9 displacement steps and are used for LHC diagnostics and since 2017 for CMS luminosity calibration cross check. An XY pair of scans takes less than 4 minutes elapsed time. BRIL project provides to LHC three independent online luminosity measurement from PLT, BCM1F and HF. The excellent performance of BRIL detectors, fast back-end electronics and CMS XDAQ based data processing and publication allow the use of emittance scans for linearity and stability studies of the luminometers. Emittance scans became a powerful tool and dramatically improved understanding of luminosity measurement during the year. Since each luminometer is independently calibrated in every scan the measurements are independent and ratios of luminometers can strictly be used as a final validation. Two independent analyses of emittance scans are launched: offline python based framework and online XDAQ based application. Results are published on the monitoring web-pages in real-time for the XDAQ based analysis and within typically 15 minutes for the python based framework, which has however the advantage of being rerunnable

Precision luminosity measurement in proton-proton collisions at root S=13 TeV in 2015 and 2016 at CMS

The measurement of the luminosity recorded by the CMS detector installed at LHC interaction point 5, using proton-proton collisions at root S = 13 TeV in 2015 and 2016, is reported. The absolute luminosity scale is measured for individual bunch crossings using beam-separation scans (the van der Meer method), with a relative precision of 1.3 and 1.0% in 2015 and 2016, respectively. The dominant sources of uncertainty are related to residual differences between the measured beam positions and the ones provided by the operational settings of the LHC magnets, the factorizability of the proton bunch spatial density functions in the coordinates transverse to the beam direction, and the modeling of the effect of electromagnetic interactions among protons in the colliding bunches. When applying the van der Meer calibration to the entire run periods, the integrated luminosities when CMS was fully operational are 2.27 and 36.3 fb(-1) in 2015 and 2016, with a relative precision of 1.6 and 1.2%, respectively. These are among the most precise luminosity measurements at bunched-beam hadron colliders.Peer reviewe

The Pixel Luminosity Telescope: a detector for luminosity measurement at CMS using silicon pixel sensors

International audienceThe Pixel Luminosity Telescope is a silicon pixel detector dedicated to luminosity measurement at the CMS experiment at the LHC. It is located approximately 1.75 m from the interaction point and arranged into 16 “telescopes”, with eight telescopes installed around the beam pipe at either end of the detector and each telescope composed of three individual silicon sensor planes. The per-bunch instantaneous luminosity is measured by counting events where all three planes in the telescope register a hit, using a special readout at the full LHC bunch-crossing rate of 40 MHz. The full pixel information is read out at a lower rate and can be used to determine calibrations, corrections, and systematic uncertainties for the online and offline measurements. This paper details the commissioning, operational history, and performance of the detector during Run 2 (2015–18) of the LHC, as well as preparations for Run 3, which will begin in 2022