Benchmarking the Particle Background in the LHC Experiments

The experiments for the Large Hadron Collider LHC at CERN have to work for 15 years in the presence of a very high particle background of photons in the energy range from 100\,keV to 10\,MeV and neutrons in the range from thermal energies ($\approx 0.025\,$eV) to 20\,MeV. \\ The background is so high that it becomes a major design criterion for the ATLAS ex\-peri\-ment, a general purpose experiment at LHC that will be operational in the year 2005. The exact level of this background is poorly known. At present an uncertainty factor of five has to be assumed to which the limited knowledge of the shower processes in the absorber material and the ensueing neutron and photon production is estimated to contribute with a factor 2.5. \\ So far, the background has been assessed only through extensive Monte Carlo evaluation with the particle transport code FLUKA. The lack of relevant measurements, which were not done up to now, are to a large extent responsible for this uncertainty. Hence it is essential to benchmark the background predictions with measurements in order to reduce the uncertainties resulting from the shower processes. This work describes in detail the benchmarking measurements and analysis of these backgrounds in an experimental arrangement that approaches rather closely the layout and shielding in the ATLAS detector. The absolute yield and energy of the particles ema\-nating from the final stages of the hadronic shower were measured using a Bi$_4$Ge$_3$O$_{12}$ detector. \\ In this study particular care was taken to guard against spurious effects, which could mask the measurements of the photon background. Typically we expect to measure a photon per $10^4$ incident hadrons which is equivalent to a reduction factor in energy of $\approx 10^8$. At first, calibration measurements with well known radioactive sources were carried out in order to evaluate the response to photons and neutrons of the used detector. The photon results show excellent agreement with the simulations, while the neutrons show some FLUKA specific discrepancies that are however well understood. The actual benchmarking task comprised measurements with different beam intensities and momenta, different positions and absorber thicknesses in order to reduce systematic effects and assess residual activities from other sources. \\ The careful analysis of the measurements including a detailed evaluation of the systematic uncertainties provides a good understanding of all effects due to residual activities, dead-time corrections and other rate effects of the set-up. Comparing the measurements with detailed FLUKA simulations shows that under all different measurement conditions the agreement is on the 20\,\% level. These studies also give answer to the nature of the particles emanating from the absorber. \\ Finally a method to obtain the measured photon rates and energies from the total measured and simulated numbers was developed. The comparison of the measurements with the FLUKA calculations can hence be used to reduce the uncertainties resulting from the shower processes, so that the background simulations can predict the ATLAS background with higher reliability

The Eckert number phenomenon: experimental investigations on the heat transfer from a moving wall in the case of a rotating cylinder

The Eckert number phenomenon was investigated theoretically by Geropp in 1969 and describes a reversal in heat transfer from a moving wall at an Eckert number Ec ≈ 1. In this report the Eckert number phenomenon is confirmed experimentally for the first time. For that purpose the heat transfer from a heated, vertically rotating cylinder in a crossflow was investigated. In order to perform the experiments in a range where the predicted phenomenon occurs, extreme rotational speeds were necessary. A heating concept had to be developed which allowed an input of heating power independent of the speed and which therefore had to be contact-free. The results show, among other things, that the temperature difference between the wall and the surrounding fluid has a significant effect on the predicted reversal of heat transfer at the wall. Moreover, maximum heat transfer occurs at an Eckert number Ec ≈ 0.3, which is of great importance for the cooling of hot surfaces in a gas-flow

CERN Neutrinos to Gran Sasso (CNGS): First Beam

The CNGS, CERN Neutrinos to Gran Sasso project, aims at directly detecting muon-neutrino to tau-neutrino oscillations. An intense muon-neutrino beam (10 to the 17 muon neutrinos)is generated at CERN per day and directed towards the Gran Sasso National Laboratory, LNGS, in Italy, 732 km away from CERN. In LNGS large and complex detectors will allow to detect, in particular, the rare tau-neutrinos created by âoscillation' from muon-neutrinos on their way between CERN and LNGS. On average around three tau-neutrino events are predicted per year in each of the ~2000 ton detectors. The construction of the CNGS beam facility started in September 2000, and the first neutrino beam has been produced in July 2006. In the presently approved physics programme, it is foreseen to run the facility for five years

Proton Beam Defocusing as a Result of Self-Modulation in Plasma

The AWAKE experiment will use a \SI{400}{GeV/c} proton beam with a longitudinal bunch length of $\sigma_z = 12\,\rm{cm}$ to create and sustain GV/m plasma wakefields over 10 meters . A 12 cm long bunch can only drive strong wakefields in a plasma with $n_{pe} = 7 \times 10^{14}\,\rm{electrons/cm}^3$ after the self-modulation instability (SMI) developed and microbunches formed, spaced at the plasma wavelength. The fields present during SMI focus and defocus the protons in the transverse plane \cite{SMI}. We show that by inserting two imaging screens downstream the plasma, we can measure the maximum defocusing angle of the defocused protons for plasma densities above $n_{pe} = 5 \times 10^{14}\,\rm{electrons/cm}^{-3}$. Measuring maximum defocusing angles around 1 mrad indirectly proves that SMI developed successfully and that GV/m plasma wakefields were created. In this paper we present numerical studies on how and when the wakefields defocus protons in plasma, the expected measurement results of the two screen diagnostics and the physics we can deduce from it.Comment: 3 pages, 2 figures, Conference Proceedings of NAPAC 201

The Two-Screen Measurement Setup to Indirectly Measure Proton Beam Self-Modulation in AWAKE

The goal of the first phase of the AWAKE \cite{AWAKE1,AWAKE2} experiment at CERN is to measure the self-modulation \cite{SMI} of the $\sigma_z = 12\,\rm{cm}$ long SPS proton bunch into microbunches after traversing $10\,\rm{m}$ of plasma with a plasma density of $n_{pe}=7\times10^{14}\,\rm{electrons/cm}^3$. The two screen measurement setup \cite{Turner2016} is a proton beam diagnostic that can indirectly prove the successful development of the self-modulation of the proton beam by imaging protons that got defocused by the transverse plasma wakefields after passing through the plasma, at two locations downstream the end of the plasma. This article describes the design and realization of the two screen measurement setup integrated in the AWAKE experiment. We discuss the performance and background response of the system based on measurements performed with an unmodulated Gaussian SPS proton bunch during the AWAKE beam commissioning in September and October 2016. We show that the system is fully commissioned and adapted to eventually image the full profile of a self-modulated SPS proton bunch in a single shot measurement during the first phase of the AWAKE experiment.Comment: 5 pages 8 figure

Infinite-Dimensional Programmable Quantum Processors

A universal programmable quantum processor uses program quantum states to apply an arbitrary quantum channel to an input state. We generalize the concept of a finite-dimensional programmable quantum processor to infinite dimension assuming an energy constraint on the input and output of the target quantum channels. By proving reductions to and from finite-dimensional processors, we obtain upper and lower bounds on the program dimension required to approximately implement energy-limited quantum channels. In particular, we consider the implementation of Gaussian channels. Due to their practical relevance, we investigate the resource requirements for gauge-covariant Gaussian channels. Additionally, we give upper and lower bounds on the program dimension of a processor implementing all Gaussian unitary channels. These lower bounds rely on a direct information-theoretic argument, based on the generalization from finite to infinite dimension of a certain replication lemma for unitaries.Comment: 38 pages, 2 figures, published versio

Polycrystalline CdTe Detectors: A Luminosity Monitor for the LHC

The luminosity at the four interaction points of the Large Hadron Collider must be continuously monitored in order to provide an adequate tool for the control and optimization of the collision parameters and the beam optics. At both sides of the interaction points absorbers are installed to protect the super-conducting accelerator elements from quenches causes by the deposited energy of collision products. The luminosity detectors will be installed in the copper core of these absorbers to measure the electromagnetic and hadronic showers caused by neutral particles that are produced at the proton-proton collision in the interaction points. The detectors have to withstand extreme radiation levels (10^8 Gy/yr at the design luminosity) and their long-term operation has to be assured without requiring humain intervention. In addition the demand for bunch-by-bunch luminosity measurements, i.e. 40MHz detection speed, puts severe constraints on the detectors. Polycrystalline CdTe detectors have a high potential to fulfill the requirements and are considered as LHC luminosity monitors. In this paper the interaction region is shown and the characteristics of the CdTe detectors are presented

Using System Dynamics Models to Understand and Improve Application Landscape Design

Application landscape design has become a key challenge for enterprises. For further exploration of related enterprise architecture benefits establishing shared mental models among all application landscape designers is required, i.e. architectural thinking. Thus, to complement existing approaches by modeling human behavior and decision effects which form implicit application landscape evolution principles, we propose the use of System Dynamics. We derive five guidelines from literature for developing a corresponding method. To exemplify the approach, a concrete causal loop diagram on the topic of technological standardization is presented. A subsequent evaluation based on expert interviews demonstrates the model content validity as well as the modeling method\u27s suitability to foster communication among different communities of practice

Indirect Self-Modulation Instability Measurement Concept for the AWAKE Proton Beam

AWAKE, the Advanced Proton-Driven Plasma Wakefield Acceleration Experiment, is a proof-of-principle R&D experiment at CERN using a 400 GeV/c proton beam from the CERN SPS (longitudinal beam size sigma_z = 12 cm) which will be sent into a 10 m long plasma section with a nominal density of approx. 7x10^14 atoms/cm3 (plasma wavelength lambda_p = 1.2mm). In this paper we show that by measuring the time integrated transverse profile of the proton bunch at two locations downstream of the AWAKE plasma, information about the occurrence of the self-modulation instability (SMI) can be inferred. In particular we show that measuring defocused protons with an angle of 1 mrad corresponds to having electric fields in the order of GV/m and fully developed self-modulation of the proton bunch. Additionally, by measuring the defocused beam edge of the self-modulated bunch, information about the growth rate of the instability can be extracted. If hosing instability occurs, it could be detected by measuring a non-uniform defocused beam shape with changing radius. Using a 1 mm thick Chromox scintillation screen for imaging of the self-modulated proton bunch, an edge resolution of 0.6 mm and hence a SMI saturation point resolution of 1.2 m can be achieved.Comment: 4 pages, 4 figures, EAAC conference proceeding