Olena Karacheban

At the Large Hadron Collider (LHC), absolute luminosity calibrations obtained by the van der Meer (vdM) method are affected by the mutual electromagnetic interaction of the two beams. The colliding bunches experience relative orbit shifts, as well as optical distortions akin to the dynamic-$\beta$ effect, that both depend on the transverse beam separation and must therefore be corrected for when deriving the absolute luminosity scale. In the vdM regime, the beam-beam parameter is small enough that the orbit shift can be calculated analytically. The dynamic-$\beta$ corrections to the luminometer calibrations, however, had until the end of Run 2 been estimated in the linear approximation only. In this report, the influence of beam-beam effects on the vdM-based luminosity scale is quantified, together with the associated systematic uncertainties, by means of simulations that fully take into account the non-linearity of the beam-beam force, as well as the resulting non-Gaussian distortions of the transverse beam distributions. Two independent multiparticle simulations, one limited to the weak-strong approximation and one that models strong-strong effects in a self-consistent manner, are found in excellent agreement; both predict a percent-level shift of the absolute pp-luminosity values with respect to those assumed until recently in the physics publications of the LHC experiments. These results also provide guidance regarding further studies aimed at reducing the beam-beam-related systematic uncertainty on beam-beam corrections to absolute luminosity calibrations by the van der Meer method.

The high-luminosity upgrade of the LHC brings unprecedented requirements for real-time and precision bunch-by-bunch online luminosity measurement and beam-induced background monitoring. A key component of the CMS Beam Radiation, Instrumentation and Luminosity system is a stand-alone luminometer, the Fast Beam Condition Monitor (FBCM), which is fully independent from the CMS central trigger and data acquisition services and able to operate at all times with a triggerless readout. FBCM utilizes a dedicated front-end application-specific integrated circuit (ASIC) to amplify the signals from CO$_2$-cooled silicon-pad sensors with a timing resolution of a few nanoseconds, which enables the measurement of the beam-induced background. FBCM uses a modular design with two half-disks of twelve modules at each end of CMS, with four service modules placed close to the outer edge to reduce radiation-induced aging. The electronics system design adapts several components from the CMS Tracker for power, control and read-out functionalities. The dedicated FBCM23 ASIC contains six channels and adjustable shaping time to optimize the noise with regards to sensor leakage current. Each ASIC channel outputs a single binary high-speed asynchronous signal carrying time-of-arrival and time-over-threshold information. The chip output signal is digitized, encoded and sent via a radiation-hard gigabit transceiver and an optical link to the back-end electronics for analysis. This paper reports on the updated design of the FBCM detector and the ongoing testing program.

Abstract The high-luminosity upgrade of the LHC brings unprecedented requirements for real-time and precision bunch-by-bunch online luminosity measurement and beam-induced background monitoring. A key component of the CMS Beam Radiation, Instrumentation and Luminosity system is a stand-alone luminometer, the Fast Beam Condition Monitor (FBCM), which is fully independent from the CMS central trigger and data acquisition services and able to operate at all times with a triggerless readout. FBCM utilizes a dedicated front-end application-specific integrated circuit (ASIC) to amplify the signals from CO 2 -cooled silicon-pad sensors with a timing resolution of a few nanoseconds, which enables the measurement of the beam-induced background. FBCM uses a modular design with two half-disks of twelve modules at each end of CMS, with four service modules placed close to the outer edge to reduce radiation-induced aging. The electronics system design adapts several components from the CMS Tracker for power, control and read-out functionalities. The dedicated FBCM23 ASIC contains six channels and adjustable shaping time to optimize the noise with regards to sensor leakage current. Each ASIC channel outputs a single binary high-speed asynchronous signal carrying time-of-arrival and time-over-threshold information. The chip output signal is digitized, encoded, and sent via a radiation-hard gigabit transceiver and an optical link to the back-end electronics for analysis. This paper reports on the updated design of the FBCM detector and the ongoing testing program.

A prototype of a luminometer, designed for a future $$e^+e^-$$ collider detector, and consisting at present of a four-plane module, was tested in the CERN PS accelerator T9 beam. The objective of this beam test was to demonstrate a multi-plane tungsten/silicon operation, to study the development of the electromagnetic shower and to compare it with MC simulations. The Molière radius has been determined to be 24.0 ± 0.6 (stat.) ± 1.5 (syst.) mm using a parametrization of the shower shape. Very good agreement was found between data and a detailed Geant4 simulation.

A new design of a detector plane of sub-millimetre thickness for an electromagnetic sampling calorimeter is presented. It is intended to be used in the luminometers LumiCal and BeamCal in future linear e $$^{+}$$ e $$^{-}$$ collider experiments. The detector planes were produced utilising novel connectivity scheme technologies. They were installed in a compact prototype of the calorimeter and tested at DESY with an electron beam of energy 1–5 GeV. The performance of a prototype of a compact LumiCal comprising eight detector planes was studied. The effective Molière radius at 5 GeV was determined to be (8.1 ± 0.1 (stat) ± 0.3 (syst)) mm, a value well reproduced by the Monte Carlo (MC) simulation (8.4 ± 0.1) mm. The dependence of the effective Molière radius on the electron energy in the range 1–5 GeV was also studied. Good agreement was obtained between data and MC simulation.

These two data sets provide the coefficients of the parameterisation of the (L/L₀)_Opt luminosity-bias factor as a function of the normalized nominal separation, for horizontal and vertical vdM scans, respectively. The data sets are part of a paper with title "Impact of Beam-Beam Effects on Absolute Luminosity Calibrations at the CERN Large Hadron Collider" and are referred thereby as Table 10 and Table 11.

Extremely radiation hard sensors are needed in particle physics experiments to instrument the region near the beam pipe. Examples are beam halo and beam loss monitors at the Large Hadron Collider, FLASH or XFEL. Currently artificial diamond sensors are widely used. In this paper single crystal sapphire sensors are considered as a promising alternative. Industrially grown sapphire wafers are available in large sizes, are of low cost and, like diamond sensors, can be operated without cooling. Here we present results of an irradiation study done with sapphire sensors in a high intensity low energy electron beam. Then, a multichannel direction-sensitive sapphire detector stack is described. It comprises 8 sapphire plates of 1 cm2 size and 525 μ m thickness, metallized on both sides, and apposed to form a stack. Each second metal layer is supplied with a bias voltage, and the layers in between are connected to charge-sensitive preamplifiers. The performance of the detector was studied in a 5 GeV electron beam. The charge collection efficiency measured as a function of the bias voltage rises with the voltage, reaching about 10% at 095 V. The signal size obtained from electrons crossing the stack at this voltage is about 02200 e, where e is the unit charge.

The CMS Beam Radiation Instrumentation and Luminosity (BRIL) project is composed of several systems providing the experiment protection from adverse beam conditions while also measuring the online luminosity and beam background. Although the readout bandwidth of the Fast Beam Conditions Monitoring system (BCM1F—one of the faster monitoring systems of the CMS BRIL), was sufficient for the initial LHC conditions, the foreseen enhancement of the beams parameters after the LHC Long Shutdown-1 (LS1) imposed the upgrade of the system. This paper presents the new BCM1F, which is designed to provide real-time fast diagnosis of beam conditions and instantaneous luminosity with readout able to resolve the 25 ns bunch structure.

The CMS beam and radiation monitoring subsystem BCM1F during LHC Run I consisted of 8 individual diamond sensors situated around the beam pipe within the tracker detector volume, for the purpose of fast monitoring of beam background and collision products. Effort is ongoing to develop the use of BCM1F as an online bunch-by-bunch luminosity monitor. BCM1F will be running whenever there is beam in LHC, and its data acquisition is independent from the data acquisition of the CMS detector, hence it delivers luminosity even when CMS is not taking data. To prepare for the expected increase in the LHC luminosity and the change from 50 ns to 25 ns bunch separation, several changes to the system are required, including a higher number of sensors and upgraded electronics. In particular, a new real-time digitizer with large memory was developed and is being integrated into a multi-subsystem framework for luminosity measurement. Current results from Run II preparation will be shown, including results from the January 2014 test beam. Presented at TIPP2014 3rd International Conference on Technology and Instrumentation in Particle Physics, Upgraded Fast Beam Conditions Monitor for CMS online luminosity measurement Jessica Lynn Leonard*, Maria Hempel†, Hans Henschel, Olena Karacheban, Wolfgang Lange, Wolfgang Lohmann†, Roberval Walsh DESY Zeuthen, Germany E-mail:jessica.lynn.leonard@desy.de, maria.hempel@desy.de, hans.henschel@desy.de, olena.karacheban@desy.de, wolfgang.lange@desy.de, wolfgang.lohmann@desy.de, roberval.walsh@desy.de Anne Dabrowski, Vladimir Ryjov CERN Geneva, Switzerland E-mail: anne.evelyn.dabrowski@cern.ch, vladimir.ryjov@cern.ch David Stickland Princeton University Princeton, New Jersey, USA E-mail: david.peter.stickland@cern.ch The CMS beam and radiation monitoring subsystem BCM1F during LHC Run I consisted of 8 individual diamond sensors situated around the beam pipe within the tracker detector volume, for the purpose of fast monitoring of beam background and collision products. Effort is ongoing to develop the use of BCM1F as an online bunch-by-bunch luminosity monitor. BCM1F will be running whenever there is beam in LHC, and its data acquisition is independent from the data acquisition of the CMS detector, hence it delivers luminosity even when CMS is not taking data. To prepare for the expected increase in the LHC luminosity and the change from 50 ns to 25 ns bunch separation, several changes to the system are required, including a higher number of sensors and upgraded electronics. In particular, a new real-time digitizer with large memory was developed and is being integrated into a multi-subsystem framework for luminosity measurement. Current results from Run II preparation will be discussed, including results from the January 2014 test beam. Technology and Instrumentation in Particle Physics 2014 2-6 June, 2014 Amsterdam, the Netherlands * Speaker † Also at Brandenburg Technical University, Cottbus, Germany  Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it BCM1F for CMS online luminosity Jessica Lynn Leonard 1. Overview of BCM1F The CMS Fast Beam Condition Monitor (BCM1F)[1] provides bunch-by-bunch information on the flux of beam halo and collision products passing through the inner CMS detector[2]. The system was originally designed to monitor the condition of the beam to ensure low enough tracker occupancy for data-taking. However, BCM1F's purpose has evolved to include fast measurement of luminosity in order to function as an online luminometer.

The absolute luminosity calibration for LHC experiments is derived from dedicated beam separation scans, known as van der Meer (vdM) scans. However, vdM scans are performed with special beam optics, wide beams, and fewer, well-separated bunches to reduce potential systematic effects, and only once per year per collision mode. In order to use the calibration obtained from a vdM scan under physics data-taking conditions with more bunches and significantly higher instantaneous luminosity, an additional measurement of the stability and linearity of the luminometers is required. Potential nonlinear effects are important especially during Run 2 (2015 -- 2018), where pileup during physics data taking reached up to about 50 and above. Short vdM-type (``emittance'') scans were thus performed regularly in CMS since 2017 in the x and y planes in 7 -- 9 beam separation steps at the beginning and end of each fill. They allowed for powerful performance diagnostics of the luminosity subdetectors in CMS throughout the year. In addition, for the subdetectors that publish luminosity measurements online (BCM1F, HF, and PLT) and read out at 40 MHz, emittance scans allow studying effects on a per bunch crossing level, correcting for beam-beam effects per bunch, and separating effects due to sequential bunches (``bunch trains''), as well as monitoring beam evolution during the fill. Analysis techniques and the great potential of emittance scans in Run 3 are illustrated.

The Beam Radiation Instrumentation and Luminosity Project of the CMS experiment, consists of several beam monitoring systems. One system, the upgraded Fast Beams Condition Monitor, is based on 24 single crystal CVD diamonds with a double-pad sensor metallization and a custom designed readout. Signals for real-time monitoring are transmitted to the counting room, where they are received and processed by new back-end electronics designed to extract information on LHC collision, beam induced background and activation products. The Slow Control Driver is designed for the front-end electronics configuration and control. The system architecture and the upgrade status will be presented.

These two data sets provide the coefficients of the parameterisation of the (L/L₀)_Opt luminosity-bias factor as a function of the normalized nominal separation, for horizontal and vertical vdM scans, respectively. The data sets are part of a paper with title "Impact of Beam-Beam Effects on Absolute Luminosity Calibrations at the CERN Large Hadron Collider" and are referred thereby as Table 10 and Table 11.

CMS features three luminosity subdetectors capable of providing real-time ("online") luminosity on a bunch-by-bunch level independently of the main CMS data acquisition system: the Fast Beam Conditions Monitor (BCM1F), the Hadron Forward (HF) calorimeter, and the Pixel Luminosity Telescope (PLT). These luminometers have operated since the beginning of Run 2 (2015 - 2018) at the LHC. In order to obtain an accurate luminosity measurement, we use van der Meer (vdM) scans to provide the absolute calibration, whereas corrections for effects such as efficiency loss due to radiation damage, nonlinear effects at high instantaneous luminosity, or effects due to the bunch train structure of the beams, are measured and subsequently applied. The calibration of the online luminosity subdetectors, the applied corrections, and comparisons with offline measurements using the pixel cluster counting (PCC) method, the radiation monitoring system (RAMSES) and muon system Drift Tubes (DT) are covered.

The Fast Beam Conditions Monitor, BCM1F, in the Compact Muon Solenoid, CMS, experiment was operated since 2008 and delivered invaluable information on the machine induced background in the inner part of the CMS detector supporting a safe operation of the inner tracker and high quality data. Due to the shortening of the time between two bunch crossings from 50 ns to 25 ns and higher expected luminosity at the Large Hadron Collider, LHC, in 2015, BCM1F needed an upgrade to higher bandwidth. In addition, BCM1F is used as an on-line luminometer operated independently of CMS. To match these requirements, the number of single crystal diamond sensors was enhanced from 8 to 24. Each sensor is subdivided into two pads, leading to 48 readout channels. Dedicated fast front-end ASICs were developed in 130 nm technology, and the back-end electronics is completely upgraded. An assembled prototype BCM1F detector comprising sensors, a fast front-end ASIC and optical analog readout was studied in a 5 GeV electron beam at the DESY-II accelerator. Results on the performance are given.

Emittance scans are short van der Meer type scans performed at the beginning and at the end of LHC fills. The beams are scanned across each other in x and y planes. CMS has analyzed these scans to understand long-term trends in CMS luminosity detectors. The CMS Beam Radiation, Instrumentation and Luminosity (BRIL) project provides to LHC three independent online luminosity measurements from the Pixel Luminosity Telescope (PLT), the Fast Beam Condition Monitor (BCM1F) and the Forward Hadronic 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.

The luminosity is a key parameter of each collider experiment for determining its physics potential in terms of normalizing its event statistics. The precise measurement of the luminosity is of crucial importance, since the uncertainty of the luminosity translates directly to the uncertainty of cross section measurement.

RHU modules, described in Sect. 4.5.2, are used for online BCM1F rate measurements. Although it is expected that each channel measures almost the same hit rate, in practice the rates differ significantly. This is due to conditions like larger noise in a few channels requiring a higher discriminator threshold, differences in the sensor efficiency due to progressive radiation damage or a reduced bias voltage. In the future these inefficiencies will be corrected for, but at the moment they are accounted for by normalizing the rates to an average of all channels.

This book offers a cutting-edge technology for beam instrumentation and luminosity measurement, presents a unique diamond-based luminometer performance description, highlights the sources of the systematic errors, and proposes alternative detector material to lower costs of the experiment

There are numerous detectors which have been developed for applications in collider physics and particle physics in general. For applications with extremely high radiation doses novel detector technologies need to be developed. Solid state detectors, in comparison to gaseous or liquid detectors, have a smaller size and better fulfill the requirements for instrumentation near the beam pipe. Examples of solid state detectors applications are beam halo and beam loss monitors at the Large Hadron Collider, FLASH or XFEL [1–7]. Currently silicon and artificial diamond sensors are widely used. Diamond sensors are expensive and of small size, silicon requires cooling which is not beneficial in the limited space available for instrumentation close to the beam pipe.

The BCM1F [1, 2] is designed for bunch-by-bunch luminosity and machine induced background measurements. It is a part of the CMS BRIL Project. In 2014 it was upgraded and currently is based on 24 single crystal CVD (scCVD) diamond sensors.

The LHC [1], is a 27 km long circular particle accelerator and collider, installed in the tunnel previously occupied by LEP [2] at CERN [3], Geneva, Switzerland. It is the largest accelerator system in the world, designed for proton-proton collisions with a maximum of 7 TeV energy per beam.

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 webpages 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.

The LHC Run II started successfully in the beginning of 2015. The CMS experiment came back to operation with three online luminometers: the Fast Beam Conditions Monitor and the Hadron Forward calorimeter, upgraded during the LHC long technical stop, and the newly installed Pixel Luminosity Telescope. From the beginning of operation all the luminometers provided reliable feedback to the LHC.

The era of colliders in particle physics started in the 1960-ties and has developed from MeV to TeV energies. It increased our knowledge and understanding of physics laws in the subnuclear domain at distance scales of about $$10^{-18}$$ m. There are two families of colliders: linear colliders, where particles are accelerated in opposite directions and brought to collision at one interaction point, and circular colliders, where two particle beams are accelerated in opposite directions in a ring-shaped accelerator, stored and collided in particular “interaction points”. The interaction point is surrounded by dedicated particle detectors comprised of several subdetectors using a range of technologies. The information recorded from all subdetectors is used for the measurement of energies and momenta of almost all particles created in a collision.