Single-beam Data Research Articles

Readiness of the ATLAS Tile Calorimeter for LHC collisions

The Tile hadronic calorimeter of the ATLAS detector has undergone extensive testing in the experimental hall since its installation in late 2005. The readout, control and calibration systems have been fully operational since 2007 and the detector successfully collected data from the LHC single beams in 2008 and first collisions in 2009. This paper gives an overview of the Tile Calorimeter performance as measured using random triggers, calibration data, data from cosmic ray muons and single beam data. The detector operation status, noise characteristics and performance of the calibration systems are presented, as well as the validation of the timing and energy calibration carried out with minimum ionising cosmic ray muons data. The calibration systems' precision is well below the design of 1%. The determination of the global energy scale was performed with an uncertainty of 4%.

SU‐GG‐T‐306: Can Single Dataset in Treatment Planning System Represent Several Beam‐Matched Accelerators?

Purpose: Beam matched accelerators can provide the flexibility within the radiotherapy department. Furthermore, the accelerators could be represented by single beam data set in the treatment planning system (TPS). The aim of this study was to evaluate the match between dosimetrical characteristics of Elekta accelerators. Method and Materials: The data from three accelerators was used in analysis. Three photon and six electron beams were matched according to the vendor specification. The first accelerator data served as reference. Subset of commissioning measurements for second and third accelerators was performed. The comparison was done in absolute terms, i.e. that PDDs and profiles were used with corresponding accelerator output factors. Results: The average difference between the sets of open field PDDs was −0.7%, −0.1% and −0.1% for 6, 10 and 15MV, respectively. Difference up to −2.2% was observed for 60° motorized wedge PDDs. Aligned profiles showed good agreement, with differences generally less than 1% at dmax and 10 cm for field sizes up to 30×30 cm2. For 40×40 cm2 diagonal profiles at dmax the maximum differences of 2.4% was observed. The difference of up to 4.5% between output factors for small fields have been observed which may result in larger discrepancies in IMRT fields. Conclusion: Beam match for photon beams showed a satisfactory agreement for open fields and support the use of a single data set for TPS. However, vendor's beam matching criteria is not strict enough and better beam matching could be achieved if instead of single value the subset of dosimetrical data is used together with corresponding output factors for both open and wedged fields. Although, scanned data for electron beams showed good agreement larger differences (up to 5%) in electron cone output factors does not support the use of a single dataset in TPS.

Geodetic constraints from multi-beam laser altimeter crossovers

The round-trip travel time measurements made by spacecraft laser altimeters are primarily used to construct topographic maps of the target body. The accuracy of the calculated bounce point locations of the laser pulses depends on the quality of the spacecraft trajectory reconstruction. The trajectory constraints from Doppler and range radio tracking data can be supplemented by altimetric “crossovers”, to greatly improve the reconstruction of the spacecraft trajectory. Crossovers have been used successfully in the past (e.g., Mars Orbiter Laser Altimeter on Mars Global Surveyor), but only with single-beam altimeters. The same algorithms can be used with a multi-beam laser altimeter, but we present a method using the unique cross-track topographic information present in the multi-beam data. Those crossovers are especially adapted to shallow (small angle) intersections, as the overlapping area is large, reducing the inherent ambiguities of single-beam data in that situation. We call those “swath crossovers”. They prove particularly useful in the case of polar-orbiting spacecraft over slowly rotating bodies, because all the non-polar crossovers have small intersection angles. To demonstrate this method, we perform a simplified simulation based on the Lunar Reconnaissance Orbiter (LRO) and its five-beam Lunar Orbiter Laser Altimeter. We show that swath crossovers over one lunar month can independently, from geometry alone, recover the imposed orbital perturbations with great accuracy (5 m horizontal, < 1 m vertical, about one order of magnitude smaller than the imposed perturbations). We also present new types of constraints that can be derived from the swath crossovers, and designed to be used in a precision orbit determination setup. In future work, we will use such multi-beam altimetric constraints with data from LRO.

Muon identification procedure for the ATLAS detector at the LHC using Muonboy reconstruction package and tests of its performance using cosmic rays and single beam data

ATLAS is one of the four experiments at the Large Hadron Collider (LHC) at CERN. This experiment has been designed to study a large range of physics including searches for previously unobserved phenomena such as the Higgs Boson and super-symmetry. The ATLAS Muon Spectrometer (MS) is optimized to measure final state muons in a large momentum range, from a few GeV up to TeV. Its momentum resolution varies from (2-3%) at 10-100 GeV/c to 11% at 1 TeV, taking into account the high level background environment, the inhomogeneous magnetic field, and the large size of the apparatus (24 m diameter by 44 m length). A robust muon identification and high momentum measurement accuracy is crucial to fully exploit the physics potential of the LHC.The basic principles of the muon reconstruction packages Muonboy, STACO, MuTag are discussed in this paper. Details of the modifications done in order to adapt the pattern recognition to the cosmic-ray configuration as well as its performance with the recent cosmic-rays and single beam data are presented.

ATLAS tile calorimeter data preparation for LHC first beam data taking and commissioning data

The Tile Calorimeter (TileCal) is the barrel hadronic calorimeter of the ATLAS experiment presently in an advanced state of commissioning with cosmic and single beam data at the LHC collider.The complexity of the detector, the number of electronics channels and the high rate of acquired events requires a systematic strategy of the System Preparation for the Data Taking. This is done through a precise calibration of the detector, prompt update of the Database reconstruction constants, validation of the Data Processing and assessment of quality of the data both with calibration signals as well as data obtained with cosmic muons and the first LHC beam.This article will present the developed strategies and tools to calibrate the calorimeter and to monitor the variations of the extracted calibration constants as a function of time; the present plan and future upgrades to deploy and update the detector constants used in reconstruction; the techniques employed to validate the reconstruction software; the set of tools of the present TileCal data quality system and its integration in ATLAS online and offline frameworks

Data Quality Monitoring Display for ATLAS experiment at the LHC

The start of collisions at the LHC brings a new era of particle physics and much improved potential to observe signatures of new physics. Some of these may be evident already from the very beginning of collisions. It's essential at this point in the experiment to be prepared to quickly and efficiently determine the quality of the incoming data. Easy visualization of data for the shift crew and experts is one of the key factors in the data quality assessment process. This paper describes the design and implementation of the Data Quality Monitoring Display and discusses experience from its usage and performance during ATLAS commissioning with cosmic ray and single beam data.

Performance of the ATLAS liquid argon calorimeter with cosmic muons and single LHC beam data

The Liquid Argon (LAr) calorimeter is a key detector in the ATLAS (A Toroidal LHC ApparatuS) experiment at the Large Hadron Collider (LHC), designed to provide precision measurements of electrons, photons, jets and missing transverse energy. Cosmic muon data has been recorded by the LAr calorimeter at various stages of commissioning, with the first single LHC beam data being recorded in September 2008. We present here the LAr calorimeter performance studies based on cosmic muons and LHC beam data. In 2008, ∼99% of the LAr readout channels were fully operational. The high energy deposits in the calorimeter readout cells have been used to validate the signal shape reconstruction from calibration predictions at a level better than ∼2%. The measured timing alignment agrees with expectations at the 2ns level. The non-uniformity of the barrel electromagnetic (EM) calorimeter has been estimated less than 2% thanks to cosmic muons.

Identification and filtering of uncharacteristic noise in the CMShadron calorimeter

Commissioning studies of the CMS hadron calorimeter have identified sporadic uncharacteristic noise and a small number of malfunctioning calorimeter channels. Algorithms have been developed to identify and address these problems in the data. The methods have been tested on cosmic ray muon data, calorimeter noise data, and single beam data collected with CMS in 2008. The noise rejection algorithms can be applied to LHC collision data at the trigger level or in the offline analysis. The application of the algorithms at the trigger level is shown to remove 90% of noise events with fake missing transverse energy above 100 GeV, which is sufficient for the CMS physics trigger operation.

Readiness of the ATLAS detector: Performance with the first beam and cosmic data

During 2008 the ATLAS experiment went through an intense period of preparation to have the detector fully commissioned for the first beam period. In about 30 h of beam time available to ATLAS in 2008 the systems went through a rapid setup sequence, from successfully recording the first bunch ever reaching ATLAS, to setting up the timing of the trigger system synchronous to the incoming single beams. The so-called splash events were recorded, where the beam was stopped on a collimator 140 m upstream of ATLAS, showering the experiment with millions of particles per beam shot. These events were found to be extremely useful for timing setup. After the stop of the beam operation, the experiment went through an extensive cosmic ray data taking campaign, recording more than 500 million cosmic ray events. These events have been used to make significant progress on the calibration and alignment of the detector. This paper describes the commissioning programme and the results obtained from both the single beam data and the cosmic data recorded in 2008.

Analysis of Multibeam Data for Neutron Reflectivity

We offer mathematical proof that multiple-beam neutron reflectivity, corresponding to simultaneous collection of data at multiple angles (wavevector transfers) does not perform better, errorwise for counting noise, than single-beam data collection for the same total number of reflected neutrons-and may perform much worse, depending on the beam modulation strategy used. The basic idea is that the nominal statistical benefit of summing data at, say, N different wavevector transfers is undone by needing to collect N differently modulated (i.e., weighted) sums in order to extract the reflectivities. To our knowledge, a general proof of this behavior for arbitrary strategies has been lacking. The formal result can be summarized by saying that the best nondiagonal matrix modulation strategies are orthogonal (unitary) matrices, or constant multiples thereof, and that these can do no better than diagonal--i.e., single-beam--strategies.

An uncertainty model for deep ocean single beam and multibeam echo sounder data

Comparing single beam and multibeam echo sounder data where surveys overlap we find that: 95% of multibeam measurements are repeatable to within 0.47% of depth; older single beam data can be at least as accurate as multibeam; single beam and multibeam profiles show excellent agreement at full-wavelengths longer than 4 km; archival sounding errors are not Gaussian; 95% of archival soundings in the northwest Atlantic are accurate to within 1.6% of depth; the 95th percentile error is about five times greater in pre-1969 data than in post-1968 data; many of the largest errors are located over large seafloor slopes, where small navigation errors can lead to large depth errors. Our uncertainty model has the form σ 2 = a 2 + (bz)2 + (cs)2, where 2σ is approximately the 95th percentile error, z is the depth, s is the slope, and a, b, c are constants we determine separately for pre-1969 and post-1968 data.

Measurements of Urea and Glucose in Aqueous Solutions with Dual-Beam Near-Infrared Fourier Transform Spectroscopy

This study investigates the use of a dual-beam, optical null, FT-IR spectrometer to measure trace organic components in aqueous solutions in the combination band region 5000–4000 cm−1. The spectrometer may be used for both single- and dual-beam measurements, thereby facilitating comparison of these two modes of operation. The concentrations of aqueous solutions of urea and glucose in the ranges 0–40 mg/dL and 0–250 mg/dL, respectively, were determined by principal component regression using both modes. The dual-beam technique eliminated instrumental variations present in the single-beam measurements that must be taken into account when quantifying trace components from single-beam spectra. The data obtained with the dual-beam technique resulted in more stable calibration models based on principal component regression. These calibration models need fewer factors and yield lower prediction errors than those based on traditional single-beam data.

Comparison of target strength distributions and fish densities obtained with split and single beam echo sounders

We compared results from analysis of split-beam and single-beam acoustic surveys using two data sets, one from the Baltic Sea (both systems at 70 kHz) and one from Lake Erie (70 kHz single beam, 70 and 120 kHz split beam). First, we show that there is a bias towards smaller targets associated with implementation of a commonly used algorithm for deconvolving target strength distributions from single beam data (modified Craig–Forbes). This bias is 0.8 dB for a circular transducer. Differences in water column fish density estimates were not large although the single beam analysis consistently resulted in lower fish densities (85–95% of split beam densities). Target strength distributions obtained by split and single beam methods were very similar for the Baltic Sea data resulting in almost identical overall average TS. This was also true for epilimnetic targets strength distributions in Lake Erie. However, hypolimnetic target strength distributions still yielded smaller target strengths with single than with the two split beam units. The split beam analysis yielded target strength distributions with a wider dynamic range and more detail than the single beam analysis. Nevertheless, the traditional single beam analysis gave results for larger targets (over −56 dB) that were comparable to the information gained from the split beam units.

Verification of Single Beam Treatment Planning Using a Ferrous Dosimeter Gel and MRI (FeMRI)

A method for analysing and comparing treatment planning system (TPS) data and ferrous dosimeter gel measurements evaluated with MRI (FeMRI) was developed, including image processing to final absorbed dose images. Measurements were analysed according to this method and FeMRI data were thereby compared with the TPS-calculated dose distribution. For photons, differences between FeMRI- and TPS dose data were mainly within +/- 2%. Minor shortcomings found in both the FeMRI system and the TPS are explained and discussed. For electron beams, there was an overall good agreement. It was found that the TPS underestimates the lateral scattering dose outside the primary beam, but the reported dose difference corresponds to a small spatial deviation (less than 2 mm). It is important to consider this single beam data comparison when the method is extended to more complicated situations, for example when using several beams.

Fuzzy Optimal Associative Memory for Background Prediction of Near-Infrared Spectra

A fuzzy optimal associative memory (FOAM) has been devised for background correction of near-infrared spectra. The FOAM yields improved predicted background scans for calculation of near-IR absorbance spectra of glucose in plasma matrices from single-beam data. The FOAM is an enhanced optimal associative memory (OAM) that uses a fuzzy function for encoding the spectra. The FOAM can predict a matching reference spectrum for a near-IR absorbance spectrum with low glucose absorbances by using second-derivative spectra. Glucose concentrations were predicted from calibration models furnished by partial least-squares (PLS). The FOAM stored reference spectra obtained from either water/phosphate buffer or plasma/glucose solutions. Both of these associative memories were evaluated. The standard error of prediction (SEP) for glucose concentration from an optimal PLS calibration model based on FOAM-corrected spectra was 0.60 mM for the water/phosphate buffer spectra. For FOAM-corrected spectra from plasma/glucose reference spectra, the SEP was 0.68 mM. The SEP of conventionally corrected double-beam second-derivative spectra was 0.81 mM. FOAM-corrected spectra generally furnish improved calibration models.

Physiographic features on the northern Gulf of Mexico continental slope

The continental slope of the northern Gulf of Mexico is diapirically controlled and is comprised of coalescing salt sheets, salt withdrawal basins, salt ridges, salt tongues and sills, and submarine canyons. Bathymetric information from single-beam data has resulted in several published maps. Many of the map areas have been remapped, using multibeam surveys, by the US National Ocean Service, and names have been given to the major physiographic features. The multibeam program was discontinued before complete coverage of the slope was accomplished. We provide charts of the remaining areas with names of features that have been accepted by the US Board of Geographic Names.

In-situ target strength measurements of Antarctic zooplankton

In situ measurements of target strength were made of krill (Euphausiasuperba) and salps (Salpathompsoni) at 120 and 200 kHz. Concurrently, a 2-m Isaacs-Kidd underwater trawl was used to sample the zooplankton population; animal length, wet weight, and maturity stages were recorded. These data were combined to derive empirical models of TS versus length for both species. The individual target strength measurements were collected at 120 kHz with a split-beam echosounder and a single-target detection algorithm. Because the two transducers were essentially colocated, range bin and off-axis angles from the 120-kHz detections were used to extract the corresponding target strength from the 200-kHz single-beam data. Backscattering strengths of salps are shown to be higher at 200 than 120 kHz. Utilizing these scattering characteristics, signal separation methods are explored that would be useful in acoustic surveys of krill distribution and abundance. Data were collected as part of the United States Antarctic Marine Living Resources Program, near Elephant Island, Antarctica, during the Austral summer of 1994. [Work of D. A. Demer was supported by the Hertz Foundation.]

Predicting bathymetry from Geosat-ERM and shipborne profiles in the South Atlantic Ocean

Portions of two Geosat-ERM altimeter tracks and corresponding suborbital shipboard gravity and bathymetry profiles in the South Atlantic Ocean were analyzed: one across the Walvis Ridge (about 1100 km long) and the other in the Brazil Basin (about 2300 km long). Together, these profiles sample those types of sea-floor topography which dominate the gravity signature at wavelengths of 20 to 300 km. The Walvis Ridge is a massive aseismic ridge and the Brazil Basin profile crosses both an old seamount (emplaced at the time the crust was young) and a very young mid-plate volcano. Both profiles cross fracture zones. After the gravity and bathymetry profiles were split into subprofiles, various cross-spectral characteristics could be determined by FFT techniques. Analysis showed that observed admittance is not well constrained by either an Airy-type or flexural compensation models across the Walvis Ridge, but those over the Brazil Basin can be readily explained by an Airy-type model with a mean crustal thickness of about 20 km. A theoretical filter was then designed, based on a priori geological knowledge, and used to predict bathymetry from the high-passed gravity/geoid anomalies. Not surprisingly, the predicted bathymetry shows more detailed and correct short-wavelength (20–300 km) features than those predicted from the historical data base, as represented e.g., by the DBDB5 gridded bathymetric model. For areas where historical shipboard bathymetry measurements are widely spaced (longer than about 10 km for single-beam data) but where some regional geologic information is available (such as the relative ages of mid-plate volcanoes and crust), bathymetry predicted from altimetric data can be used to upgrade regional bathymetrie data bases, on which regional geologic/geophysical understanding depends.