A. Bingül

A straw proportional counter is the basic element of the ATLAS Transition Radiation Tracker (TRT). Its detailed properties as well as the main properties of a few TRT operating gas mixtures are described. Particular attention is paid to straw tube performance in high radiation conditions and to its operational stability.

The ATLAS (A Toroidal LHC ApparatuS) Inner Detector provides charged particle tracking in the centre of the ATLAS experiment at the Large Hadron Collider (LHC). The Inner Detector consists of three subdetectors: the Pixel Detector, the Semiconductor Tracker (SCT), and the Transition Radiation Tracker (TRT). This paper summarizes the tests that were carried out at the final stage of SCT+TRT integration prior to their installation in ATLAS. The combined operation and performance of the SCT and TRT barrel and endcap detectors was investigated through a series of noise tests, and by recording the tracks of cosmic rays. This was a crucial test of hardware and software of the combined tracker detector systems. The results of noise and cross-talk tests on the SCT and TRT in their final assembled configuration, using final readout and supply hardware and software, are reported. The reconstruction and analysis of the recorded cosmic tracks allowed testing of the offline analysis chain and verification of basic tracker performance parameters, such as efficiency and spatial resolution, in combined operation before installation.

The ATLAS TRT barrel is a tracking drift chamber using 52,544 individual tubular drift tubes. It is one part of the ATLAS Inner Detector, which consists of three sub-systems: the pixel detector spanning the radius range 4 to 20 cm, the semiconductor tracker (SCT) from 30 to 52 cm, and the transition radiation tracker (TRT) from 56 to 108 cm. The TRT barrel covers the central pseudo-rapidity region |η|< 1, and the TRT while endcaps cover the forward and backward eta regions. These TRT systems provide a combination of continuous tracking with many measurements in individual drift tubes (or straws) and of electron identification based on transition radiation from fibers or foils interleaved between the straws themselves. This paper describes the recently-completed construction of the TRT Barrel detector, including the quality control procedures used in the fabrication of the detector.

The ATLAS TRT end-cap is a tracking drift chamber using 245,760 individual tubular drift tubes. It is a part of the TRT tracker which consist of the barrel and two end-caps. The TRT end-caps cover the forward and backward pseudo-rapidity region 1.0 < |η| < 2.0, while the TRT barrel central η region |η| < 1.0. The TRT system provides a combination of continuous tracking with many measurements in individual drift tubes (or straws) and of electron identification based on transition radiation from fibers or foils interleaved between the straws themselves. Along with other two sub-system, namely the Pixel detector and Semi Conductor Tracker (SCT), the TRT constitutes the ATLAS Inner Detector. This paper describes the recently completed and installed TRT end-cap detectors, their design, assembly, integration and the acceptance tests applied during the construction.

The reconstruction of photon conversions is importantin order to improve the reconstruction efficiency of the physics measurements involving photons. However, there are significant number of conversions in which only one of the two tracks emitted electrons is reconstructed in the detector due to very asymmetric energy sharing between the electron-positron pair. The momentum determination of the parent photon can be improved by estimating the missing energy in such conversions. In this study, we propose a simple statistical method that can be used to determine the mean value of the missing energy. By using simulated minimum bias events at LHC conditions and a toy detector simulation, the performance of the method is tested for several decay channels commonly used in particle physics analyses. A considerable improvement in the mass reconstruction precision is obtained when reconstructing particles decaying to photons whose energies are less than 20 GeV.

In this study, a procedure for designing a free-form lens for long-range LED illumination is presented. The geometrical form of the proposed lens is obtained by minimizing optical path lengths of the rays emitted from a point-like light source. Optical ray tracing simulations of two different LEDs and the free-form lens are performed by using Zemax OpticStudio. In addition, the prototype of the free-form lens is manufactured by the plastic injection molding method using PMMA material. Nine of the lenses are used to build an LED projector in the form of a 3x3 lens matrix. The optical measurements of the projector are compared with the results predicted in the simulations. It is found that the beam divergence of the projector is less than 10 degrees when using suitable LEDs in visible and near infrared regions.

The ATLAS inner detector consists of three sub-systems: the pixel detector spanning the radius range 4cm-20cm, the semiconductor tracker at radii from 30 to 52 cm, and the transition radiation tracker (TRT), tracking from 56 to 107 cm. The TRT provides a combination of continuous tracking with many projective measurements based on individual drift tubes (or straws) and of electron identification based on transition radiation from fibres or foils interleaved between the straws themselves. This paper describes the on and off detector electronics for the TRT as well as the TRT portion of the data acquisition (DAQ) system.

We present the optical design of a compact telephoto objective that can be accommodated on 6U-sized CubeSats for Earth observation. The design consists of spherical lenses made of space-compatible materials and operates in the visible region. The objective has F/5.5 diffraction-limited performance over the 2.58-degree full field of view and is optimized for panchromatic imaging in the visible spectrum. The tolerance analysis of the optical design is performed to generate error budgets related to optical manufacturing and alignment. The results show that a design achieves the targeted MTF budget.

The ATLAS Transition Radiation Tracker (TRT) is the outermost of the three subsystems of the ATLAS Inner Detector at the Large Hadron Collider at CERN. It consists of almost 300000 thin-wall drift tubes (straws) providing on average 30 two-dimensional space points with 0.12-0.15 mm resolution for charged particle tracks with |η| < 2 and pT > 0.5 GeV/c. Along with continuous tracking, it provides particle identification capability through the detection of transition radiation X-ray photons generated by high velocity particles in the many polymer fibers or films that fill the spaces between the straws. Custom-built analog and digital electronics is optimized to operate as luminosity increases to the LHC design. In this talk, a review of the commissioning and first and current operational experience of the TRT detector and its performance at LHC will be presented. Emphasis will be given to performance studies based on the reconstruction and analysis of LHC collisions. A comparison of the TRT response and the particle identification in pp and Pb-Pb collisions will be presented. The results are also compared with the expected performance.

The ATLAS (one of two general purpose detectors at the LHC) Transition Radiation Tracker (TRT) is the outermost of the three tracking subsystems of the ATLAS Inner Detector. It is a large straw-based detector and contains about 350,000 electronics channels. The performance of the TRT as tracking and particularly particle identification detector strongly depends on stability of the operation parameters with most important parameter being the gas gain which must be kept constant across the detector volume. The gas gain in the straws can vary significantly with atmospheric pressure, temperature, and gas mixture composition changes. This paper presents a concept of the gas gain stabilisation in the TRT and describes in detail the Gas Gain Stabilisation System (GGSS) integrated into the Detector Control System (DCS). Operation stability of the GGSS during Run-1 is demonstrated.

Non-iterative methods for the mass constraint of decays such as π0→γγ are developed as an alternative to relatively complex and slow iterative methods. Constraints involving only the refit of the decay pair energies are presented in the form of a direct quadratic solution and an empirical solution. The empirical solution is then expanded to three-dimensions where the opening angle of the decay pair is also refitted. The performance of these methods is compared to that of traditional iterative chi-square methods.

When selecting signals from two-photon invariant mass spectra the signal significance can be optimised by selecting signal candidates from a narrow mass window around the signal peak. However, such tight cuts can lead to large systematic errors. In this study systematic errors due to inaccuracies in the Monte Carlo simulation of the peak width are studied for three selection methods. It is shown that in the presence of such inaccuracies a wider selection window is required to reduce systematic errors. The Ranking selection method is found to be much less sensitive to systematic errors of this type.

The selection of neutral pions with a high purity while maintaining also a high efficiency can be important in the formation of statistically significant mass spectra in the reconstruction of short-lived particles such as the omega meson (ω→π+π−π0). In this study a Ranking method, where pions are ranked according to a pion estimator, is described and detailed results from a Monte-Carlo study are presented. The results show that the Ranking method, when applied to high multiplicity events, yields significant improvements in the purity of selected pion candidates and facilitates the relaxation of standard cuts thereby avoiding some systematic uncertainties.

Abstract The inclusive production rate of the ρ ± ( 770 ) vector meson in hadronic Z decays is measured with the ALEPH detector at the LEP collider. A total of 3.2 million hadronic events are selected from data recorded between 1991 and 1995. Decays of ρ ± → π 0 + π ± are reconstructed for x E > 0.05 and x p > 0.05 where x p = p ρ / p beam and x E = E ρ / E beam . The average ρ ± multiplicity per hadronic event is evaluated to be N ( ρ ± ) = 2.59 ± 0.03 ± 0.15 ± 0.04 where the first error is statistical and the second systematic. The third error is from the uncertainty in the extrapolation to x p = x E = 0 . The rates and differential cross-section are compared with Monte Carlo model predictions and OPAL measurements. Residual Bose–Einstein correlations are found to be an important component in the analysis.

To overcome the mass constraint problem of particle decays, a non-iterative method is developed as an alternative to relatively complicated and slow iterative methods. The new method can be applied to any two-body decay or a many-body decay which can be reduced to a two-body decay having well known daughter masses. By using a toy detector simulation and ALEPH full simulation data, the performance of the new method is compared with the traditional iterative chi-square method for several decay types. No significant difference is obtained between the two methods in terms of improvement in momentum resolution. However, the non-iterative method is found to be much faster than the chi-square method.

In particle physics, uncertainties in the reconstructed momentum of parent particles are introduced due to detector resolution. Traditionally, the momentum resolution of the parent particle is improved by minimizing a non-linear chi-square function via iterative methods. In this study, it is shown that the same chi-square minimization procedure results in a set of linear equations which can be solved non-iteratively in the center of mass frame of the parent particle. By using ALEPH full simulation data, the performance of the new method is compared with relatively slower iterative method for several decay channels. No significant difference between them is obtained in terms of improvement in momentum resolution. However, the new approach is found to be simple to implement and faster than that of traditional iterative method.

The inclusive production of the charged vector meson ρ±(770) in hadronic Z decays is measured with the ALEPH detector at the LEP collider. Decays of ρ± → π0 + π± are reconstructed for x > 0.05 where x = Eρ/Ebeam. The results are compared with Monte Carlo model predictions and OPAL measurements. Bose‐Einstein effects are found to be important in extracting ρ±(770) from two pion invariant mass spectra.

The selection of $\eta$ mesons with a high efficiency and a high purity can be important in the formation of statistically significant invariant mass spectra in the reconstruction of short-lived particles such as $\eta' \rightarrow \pi^{+} \pi^{-} \eta$. In this study, a cut-based standard method and a Ranking method to reduce combinatorial background in the reconstruction of $\eta \rightarrow \gamma \gamma$ decays in high multiplicity hadronic events are presented. By using recorded ALEPH data and fully simulated events, the performances of the methods are compared. Results show that the Ranking method yields significant improvements in the purity of the selected $\eta$ meson relative to the standard method.

With increasing requirements from particle physics for effective multi-variate discrimination techniques, a number of alternative probability density estimate (PDE) methods have appeared in recent years. These relatively advanced methods attempt to form effective PDEs in the presence of low statistics where a simple histogramming method does not perform well. In this paper a multi-variate histogrammed PDE method is presented. The method incorporates a simple Laplace smoothing procedure and χ2-triggered optimisation that results in the automatic selection of near-optimal binning and greatly improved PDE performance at low statistics. The performance of the smoothed histogrammed PDE is compared to a theoretically ideal PDE, and to results from a kernel PDE and a neural network.