Luminosity Monitor Research Articles

Luminosity monitoring in ATLAS with MPX detectors

The ATLAS-MPX detectors are based on the Medipix2 silicon devices designed by CERN for the detection of multiple types of radiation. Sixteen such detectors were successfully operated in the ATLAS detector at the LHC and collected data independently of the ATLAS data-recording chain from 2008 to 2013. Each ATLAS-MPX detector provides separate measurements of the bunch-integrated LHC luminosity. An internal consistency for luminosity monitoring of about 2% was demonstrated. In addition, the MPX devices close to the beam are sensitive enough to provide relative-luminosity measurements during van der Meer calibration scans, in a low-luminosity regime that lies below the sensitivity of the ATLAS calorimeter-based bunch-integrating luminometers. Preliminary results from these luminosity studies are presented for 2012 data taken at √s = 8 TeV proton-proton collisions.

Dual-stage ignition of boron particle agglomerates

The ignition characteristics of boron particle agglomerates prepared by drying 2–3mm water slurry droplets of crystalline or amorphous boron powders were investigated by introducing suspended agglomerates into a flow of high temperature oxidizing gases (oxygen/nitrogen/water vapor) obtained by a combination of combustion and electrical heating. Monitoring of the agglomerate luminosity, spectra, and temperature revealed a dual-stage ignition process. The first stage ignition was observed at flow temperatures as low as 715K and was followed by agglomerate quenching if the oxygen concentration in the flow was below some critical value. As the oxygen concentration of the flow was increased beyond this critical value, the second stage ignition leading to full-fledge combustion was observed. The ignition characteristics of boron particle agglomerates were theoretically investigated by developing a numerical model that considers the oxygen concentration gradient inside the agglomerate in order to simulate the ignition process. The model results accurately captured the qualitative behavior of the first stage ignition and quenching as well as the dual-stage ignition processes. The model identified the closure of pores in the agglomerate due to the build-up of the boron oxide layer, which effectively seals off the large interior surface area of the agglomerate from the oxidizer, as being the mechanism responsible for the two-stage ignition phenomenon. The critical flow conditions in terms of flow temperature and ambient oxygen concentration for the second stage ignition were determined by this model. The experimental result for the critical ambient oxygen concentration for the second stage ignition in dry flow was determined to be 70%, which is fairly close to the model prediction of 79%.

The MICE luminosity monitor

The MICE experiment will provide the first measurement of ionisation cooling, a technique suitable for reducing the transverse emittance of a tertiary muon beam in a future neutrino factory accelerator facility. MICE is presently in the final stages of commissioning its beam line. The MICE luminosity monitor has proved an invaluable tool throughout this process, providing independent measurements of particle rate from the MICE target, normalisation for beam line detectors and verification of simulation codes.

Production status of the JLAB Hall-A GEM and Si [formula omitted] Tracker

We developed and tested a new charged particle tracking system, able to operate in high luminosity experiments, which will be installed at Jefferson Laboratory HallA (VA, USA) for optimally exploit the new 12GeV energy electron beam available at the end of 2013. The tracker is made of six GEM (Gas Electron Multiplier) large chambers and two 10×20cm2 planes of SIlicon microstrip Detectors (SIDs). Each GEM chamber is composed by three 40×50cm2 GEM modules, with two-dimensional strip readout, with expected spatial resolution of about 70μm. The same dedicated acquisition system will be used for both detectors (GEM & SID) for a grand total of more than 50,000 channels. The readout electronics is divided into two parts: the front-end cards (based on the existing APV25 chip), hosted on the detectors periphery and the digitizer, a multi purpose VME-64x/VXS board located far from the high radiation environment. The very same electronics has been adopted by the Olympus experiment (DESY, Hamburg, D) to read out the six GEM chambers of its luminosity monitor. The developed detectors and electronics are now ready for the production, which will last for the next 2 years.

Development of detector and physics analysis tools for PANDA experiments at FAIR

The PANDA collaboration at FAIR facility will address a rich variety of physics programs for studies of strong interaction and perturbative QCD. In India, initiatives have been taken up for the design and construction of some components of the PANDA detector. A silicon photo multiplier based scintillation detector is being planned to be built in India in collaboration with GSI, Darmstadt. Simulation studies and R&D work are being carried out in designing this detector which can provide a fast trigger signal for the PANDA experiments. The other component of the PANDA detector which the Indian group is interested to develop is luminosity monitor detector(LMD). Currently two possible solutions are being considered for LMD: (i)a double sided silicon micro strip detector and (ii) radiation hard Gallium Nitride(GaN)/Diamond sensors with a pitch of 50 μm. Simulations are being carried out. The analysis tools of vertex and kinematic fitting have been developed within the software framework of Pandaroot. The vertex fitting for the primary and secondary vertex based on kinematic constraints have been implemented for the full decay tree reconstruction. Simulation studies have been performed using a few benchmark channels to evaluate the performance of these methods.

Beam delivery system tuning and luminosity monitoring in the Compact Linear Collider

Emittance preservation in the beam delivery system (BDS) is one of the major challenges in the Compact Linear Collider (CLIC). The fast detuning of the final focus optics requires an on-line tuning procedure in order to keep luminosity close to the maximum. In this paper we discuss different tuning techniques to mitigate the displacement of magnets in the CLIC BDS and in particular in the final focus system. Some of them require a fast luminosity measurement. Here we study the possibility to use beam-beam background processes at CLIC 3 TeV c.m. energy as a fast luminosity signal. In particular, the hadron multiplicity in the detector region is investigated.

NNLO massive corrections to Bhabha scattering and theoretical precision of BabaYaga@NLO

We provide an exact calculation of next-to-next-to-leading order (NNLO) massive corrections to Bhabha scattering in QED, relevant for precision luminosity monitoring at meson factories. Using realistic reference event selections, exact numerical results for leptonic and hadronic corrections are given and compared with the corresponding approximate predictions of the event generator BabaYaga@NLO. It is shown that the NNLO massive corrections are necessary for luminosity measurements with per mille precision. At the same time they are found to be well accounted for in the generator at an accuracy level below the one per mille. An update of the total theoretical precision of BabaYaga@NLO is presented and possible directions for a further error reduction are sketched.

Radiation Damage Studies and Operation of the DØ Luminosity Monitor

The D0 Luminosity Monitor (LM) employs scintillating wedges with photomultiplier tube readout to detect particles from inelastic collisions in p interactions at the Fermilab Tevatron Collider. The Luminosity Monitor provides a real-time measurement of the relative luminosity during data-taking, and, with the determination of the effective inelastic cross section, it also provides an absolute measurement of the luminosity delivered to the D0 Experiment, which is later used for normalization of D0 physics results. In the course of normal Tevatron operations these scintillators accrue significant radiation damage. Operating parameters are monitored and adjusted to compensate for this degradation, and the scintillators are periodically replaced to facilitate stable performance. Results from radiation damage studies to the scintillator as well as the stability of the luminosity measurement will be presented.

The DØ Luminosity Monitor Operations and Performance

Abstract The D0 Luminosity Monitor (LM) plays a crucial role in D0 physics analyses by providing the normalization for many cross section measurements. The detector consists of two sets of 24 scintillator wedges read out with photomultiplier tubes. The detector is located in the forward regions surrounding the beam pipe, covering a pseudo-rapidity range of 2.7

The Online Luminosity Calculator of ATLAS

Online luminosity monitoring at the LHC is important for optimizing the luminosity at the experimental insertions and vital for good data taking of the LHC experiments. It is an important diagnostic tool, in particular for the normalization of trigger rates and data samples. The ATLAS experiment has several sub-detectors, which can be used for relative luminosity measurements. In order to collect all data from the variety of different sources and to process them centrally, the software application "Online Luminosity Calculator" has been developed.

NNLO leptonic and hadronic corrections to Bhabha scattering and luminosity monitoring at meson factories

Virtual fermionic N_f = 1 and N_f = 2 contributions to Bhabha scattering are combined with realistic real corrections at next-to-next-to-leading order in QED. The virtual corrections are determined by the package bha_nnlo_hf, and real corrections with the Monte Carlo generators Bhagen-1Ph, Helac-Phegas and Ekhara. Numerical results are discussed at the energies of and with realistic cuts used at the Phi factory DAFNE, at the B factories PEP-II and KEK, and at the charm/tau factory BEPC II. We compare these complete calculations with the approximate ones realized in the generator BabaYaga@NLO used at meson factories to evaluate their luminosities. For realistic reference event selections we find agreement for the NNLO leptonic and hadronic corrections within 0.07% or better and conclude that they are well accounted for in the generator by comparison with the present experimental accuracy.

A Cherenkov Detector for Monitoring ATLAS Luminosity

LUCID is the luminosity monitor of the LHC accelerator for the ATLAS experiment. Thanks to an intrinsically fast response and to its custom readout electronics, LUCID estimates the number of interactions per LHC bunch crossing and provides an interaction trigger to the experiment. The performance of LUCID is evaluated in the full luminosity range of LHC (up to 10 34 cm −1 s −1 ) by means of a PYTHIA simulation of inelastic pp collisions at s = 7 TeV and a full GEANT4 simulation of the detector.

Luminosity monitoring and calibration of BLM

The BEPCII Luminosity Monitor (BLM) monitors relative luminosity per bunch. The counting rates of gamma photons, which are proportional to the luminosities from the BLM at the center of mass system energy of the ψ (3770) resonance, are obtained with a statistical error of 0.01% and a systematic error of 4.1%. Absolute luminosities are also determined by the BESIII End-cap Electro-Magnetic Calorimeter (EEMC) using Bhabha events with a statistical error of 2.3% and a systematic error of 3.5%. The calibration constant between the luminosities obtained with the EEMC and the counting rates of the BLM are found to be 0.84±0.03 (×1026 cm−2·count−1). With the calibration constant, the counting rates of the BLM can be scaled up to absolute luminosities.

An LHCb general-purpose acquisition board for beam and background monitoring at the LHC

In this paper we will present an LHCb custom-made acquisition board which was developed for a continuous beam and background monitoring during LHC operations at CERN. The paper describes both the conceptual design and its performance, and concludes with results from the first period of beam operations at the LHC.The main purpose of the acquisition board is to process signals from a pair of beam pickups to continuously monitor the intensity of each bunch, and to monitor the phase of the arrival time of each proton bunch with respect to the LHC bunch clock. The extreme versatility of the board also allowed the LHCb experiment to build a high-speed and high-sensitivity readout system for a fast background monitor based on a pair of plastic scintillators.The board has demonstrated very good performance and proved to be conceptually valid during the first months of operations at the LHC. Connected to the beam pickups, it provides the LHCb experiment with a real-time measurement of the total intensity of each beam and of the arrival time of each beam at the LHCb Interaction Point. It also monitors the LHC filling scheme and the beam current per bunch at a continuous rate of 40 MHz, and assures a proper global timing of LHCb. The continuous readout of the scintillators at bunch clock speed provides the LHCb experiment with high-resolution information about the beam halo and fast losses during both injection and circulating beam. It has also provided valuable information to the LHC during machine commissioning with beam. Recent results also shows that it could contribute as a luminosity monitor independent from the LHCb experiment readout system.Beam, background and luminosity measurements are continuously fed back to the LHC in the data exchange framework between the experiments and the LHC machine aimed at improving efficiently the experimental conditions real-time.

Studies of mono-crystalline CVD diamond pixel detectors

Abstract The Pixel Luminosity Telescope (PLT) is a dedicated luminosity monitor, presently under construction, for the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC). It measures the particle flux in several three layered pixel diamond detectors that are aligned precisely with respect to each other and the beam direction. At a lower rate it also performs particle track position measurements. The PLT's mono-crystalline CVD diamonds are bump-bonded to the same readout chip used in the silicon pixel system in CMS. Mono-crystalline diamond detectors have many attributes that make them desirable for use in charged particle tracking in radiation hostile environments such as the LHC. In order to further characterize the applicability of diamond technology to charged particle tracking we performed several tests with particle beams that included a measurement of the intrinsic spatial resolution with a high resolution beam telescope.

Results from a beam test of a prototype PLT diamond pixel telescope

We describe results from a beam test of a telescope consisting of three planes of single-crystal, diamond pixel detectors. This telescope is a prototype for a small-angle luminosity monitor, the Pixel Luminosity Telescope (PLT), for CMS. We recorded the pixel addresses and pulse heights of all pixels over threshold as well as the fast-or signals from all three telescope planes. We present results on the telescope performance including occupancies, pulse heights, fast-or efficiencies and particle tracking. These results show that the PLT design meets all required specifications.

Simulation study of real-time monitor for BEPC-II luminosity

A fast and real time luminosity monitor system will be used in the BEPC-II (Beijing Electron Positron Collider, China). Photons generated in radiative Bhabha scattering at the interaction point are transformed into charged particles, and then the luminosity of each bunch pair is measured through collecting the Cherenkov light produced by charged particles in fused silica. The whole process happening in the detector is simulated. The physics acceptance and detection threshold with the monitor accuracy of 1% are set based on the simulation spectra of photoelectron yield calibrated by e− beam data.

A fast luminosity monitor for BEPCII

The fast luminosity monitor counting the γ photons above a given energy threshold emitted from radiative Bhabha scattering has been operated in the BEPCII to measure the relative luminosity bunch by bunch for the first time and used successfully in beam tuning of BEPCII. In the relative mode the monitor is able to deliver the relative luminosities with an accuracy of 0.8%. By steering the electron beam while observing the counting rate changes of the monitor the horizontal and vertical sizes of the bunch spots can be estimated as: sxe+ = sxe– = 0.356 mm, sye+ = sye– = 0.011 mm.

The ATLAS luminosity monitor

The main luminosity monitor of the ATLAS experiment consists of an array of Cherenkov counters. The intrinsically fast response of the detector and its readout electronics makes it ideal for measuring the number of interactions per LHC bunch crossing, and for providing an interaction trigger to the ATLAS experiment. The detector already took some data during the first beam interactions produced by the LHC. An original method to derive the detector response with an analytical approach is presented here.

Combination of electroweak and QCD corrections to single W production at the Fermilab Tevatron and the CERN LHC

Precision studies of the production of a high-transverse momentum lepton in association with missing energy at hadron colliders require that electroweak and QCD higher-order contributions are simultaneously taken into account in theoretical predictions and data analysis. Here we present a detailed phenomenological study of the impact of electroweak and strong contributions, as well as of their combination, to all the observables relevant for the various facets of the $p\smartpap \to {\rm lepton} + X$ physics programme at hadron colliders, including luminosity monitoring and Parton Distribution Functions constraint, $W$ precision physics and search for new physics signals. We provide a theoretical recipe to carefully combine electroweak and strong corrections, that are mandatory in view of the challenging experimental accuracy already reached at the Fermilab Tevatron and aimed at the CERN LHC, and discuss the uncertainty inherent the combination. We conclude that the theoretical accuracy of our calculation can be conservatively estimated to be about 2% for standard event selections at the Tevatron and the LHC, and about 5% in the very high $W$ transverse mass/lepton transverse momentum tails. We also provide arguments for a more aggressive error estimate (about 1% and 3%, respectively) and conclude that in order to attain a one per cent accuracy: 1) exact mixed ${\cal O}(\alpha \alpha_s)$ corrections should be computed in addition to the already available NNLO QCD contributions and two-loop electroweak Sudakov logarithms; 2) QCD and electroweak corrections should be coherently included into a single event generator.