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Lattice Design for the LHEC Recirculating Linac

Description: In this paper, we present a lattice design for the Large Hadron Electron Collider (LHeC) recirculating linac. The recirculating linac consists of one roughly 3-km long linac hosting superconducting RF (SRF) accelerating cavities, two arcs and one transfer line for the recirculation. In two passes through a pulsed SRF linac the electron beam can get a maximum energy of 140 GeV. Alternatively, in the Energy Recovery Linac (ERL) option the beam passes through a CW linac four times (two passes for acceleration and two for deceleration) for a maximum energy of 60 GeV.
Date: May 20, 2011
Creator: Sun, Yipeng; /CERN; Eide, Anders; /CERN; Zimmermann, Frank; /CERN et al.
Partner: UNT Libraries Government Documents Department

First Beam Measurements with the LHC Synchrotron Light Monitors

Description: The continuous monitoring of the transverse sizes of the beams in the Large Hadron Collider (LHC) relies on the use of synchrotron radiation and intensified video cameras. Depending on the beam energy, different synchrotron light sources must be used. A dedicated superconducting undulator has been built for low beam energies (450 GeV to 1.5 TeV), while edge and centre radiation from a beam-separation dipole magnet are used respectively for intermediate and high energies (up to 7 TeV). The emitted visible photons are collected using a retractable mirror, which sends the light into an optical system adapted for acquisition using intensified CCD cameras. This paper presents the design of the imaging system, and compares the expected light intensity with measurements and the calculated spatial resolution with a cross calibration performed with the wire scanners. Upgrades and future plans are also discussed.
Date: July 13, 2012
Creator: Lefevre, Thibaut; /CERN; Bravin, Enrico; /CERN; Burtin, Gerard; /CERN et al.
Partner: UNT Libraries Government Documents Department

First Operation of the Abort Gap Monitor for LHC

Description: The Large Hadron Collider (LHC) beam-dump system relies on extraction kickers that need 3 microseconds to rise to their nominal field. Since particles transiting the kickers during the rise will not be dumped properly, the proton population in this interval must always remain below quench and damage limits. A specific monitor to measure the particle population of this gap has been designed based on the detection of synchrotron radiation using a gated photomultiplier. Since the quench and damage limits change with the beam energy, the acceptable population in the abort gap and the settings of the monitor must adapt accordingly. This paper presents the design of the monitor, the calibration procedure and the detector performance with beam.
Date: July 6, 2012
Creator: Lefevre, Thibaut; /CERN; Bart Pedersen, Stephane; /CERN; Boccardi, Andrea; /CERN et al.
Partner: UNT Libraries Government Documents Department

Design for a Longitudinal Density Monitor for the LHC

Description: Synchrotron radiation is currently used on the LHC for beam imaging and for monitoring the proton population in the 3 microsecond abort gap. In addition to these existing detectors, a study has been initiated to provide longitudinal density profiles of the LHC beams with a high dynamic range and a 50ps time resolution. This would allow for the precise measurement both of the bunch shape and the number of particles in the bunch tail or drifting into ghost bunches. A solution is proposed based on counting synchrotron light photons with two fast avalanche photo-diodes (APD) operated in Geiger mode. One is free-running but heavily attenuated and can be used to measure the core of the bunch. The other is much more sensitive, for measurement of the bunch tails, but must be gated off during the passage of the bunch to prevent the detector from being swamped. An algorithm is then applied to combine the two measurements and correct for the detector dead-time, afterpulsing and pile-up effects. Initial results from laboratory testing of this system are described here.
Date: July 13, 2012
Creator: Jeff, Adam; /CERN; Bart Pedersen, Stephane; /CERN; Boccardi, Andrea; /CERN et al.
Partner: UNT Libraries Government Documents Department

Designs for a Linac-Ring LHeC

Description: We consider three scenarios for the recirculating electron linear accelerator (RLA) of a linac-ring type electron-proton collider based on the LHC (LHeC): (i) a pulsed linac with a final beam energy of 60 GeV ['p-60'], (ii) a higher luminosity configuration with two cw linacs and energy-recovery (ERL) also at 60 GeV ['erl'], and (iii) a high energy option using a pulsed linac with 140-GeV final energy ['p-140']. We discuss parameters, synchrotron radiation, footprints, and performance for the three scenarios.
Date: June 21, 2012
Creator: Zimmermann, Frank; /CERN; Bruning, Oliver; /CERN; Ciapala, Edmond; /CERN et al.
Partner: UNT Libraries Government Documents Department

A 12 GHz RF Power Source for the CLIC Study

Description: The CLIC RF frequency has been changed in 2008 from the initial 30 GHz to the European X-band 11.9942 GHz permitting beam independent power production using klystrons for CLIC accelerating structure testing. A design and fabrication contract for five klystrons at that frequency has been signed by different parties with SLAC. France (IRFU, CEA Saclay) is contributing a solid state modulator purchased in industry and specific 12 GHz RF network components to the CLIC study. RF pulses over 120 MW peak at 230 ns length will be obtained by using a novel SLED-I type pulse compression scheme designed and fabricated by IAP, Nizhny Novgorod, Russia. The X-band power test stand is being installed in the CLIC Test Facility CTF3 for independent structure and component testing in a bunker, but allowing, in a later stage, for powering RF components in the CTF3 beam lines. The design of the facility, results from commissioning of the RF power source and the expected performance of the Test Facility are reported.
Date: July 3, 2012
Creator: Schirm, Karl; /CERN; Curt, Stephane; /CERN; Dobert, Steffen; /CERN et al.
Partner: UNT Libraries Government Documents Department

Production of a Z boson and two jets with one heavy-quark tag

Description: We present a next-to-leading-order calculation of the production of a Z boson with two jets, one or more of which contains a heavy quark (Q = c, b). We show that the cross section with only one heavy-quark jet is larger than that with two heavy-quark jets at both the Fermilab Tevatron and the CERN LHC. These processes are the dominant irreducible backgrounds to a Higgs boson produced in association with a Z boson, followed by h {yields} b{bar b}. Our calculation makes use of a heavy-quark distribution function, which resums collinear logarithms and makes the next-to-leading-order calculation tractable.
Date: October 1, 2005
Creator: Campbell, J.; /CERN; Ellis, R.K.; /Fermilab, /CERN; Maltoni, F.; U., /CERN /Louvain et al.
Partner: UNT Libraries Government Documents Department

Commissioning of the LHC Low Level RF System Remote Configuration Tools

Description: The LHC Low Level RF system (LLRF) is a complex multi-loop system used to regulate the superconductive cavity gap voltage as well as to reduce the impedance presented by RF stations to the beam. The RF system can have a profound impact on the stability of the beam; a mis-configured RF system has the potential of causing longitudinal instabilities, beam diffusion and beam loss. To configure the RF station for operation, a set of parameters in the LLRF multi-loop system have to be defined. Initial system commissioning as well as ongoing operation requires a consistent method of computer based remote measurement and model-based design of each RF station feedback system. This paper describes the suite of Matlab tools used for configuring the LHC RF system during the start up in Nov2009-Feb2010. We present a brief overview of the tool, examples of commissioning results, and basics of the model-based design algorithms. This work complements our previous presentation, where the algorithms and methodology followed in the tools were described.
Date: August 26, 2010
Creator: Van Winkle, Daniel; /SLAC; Fox, John; /SLAC; Mastorides, Themis; /SLAC et al.
Partner: UNT Libraries Government Documents Department

Status of SM Calculations of b to s Transitions

Description: We report recent progress in SM calculations of b {yields} s transitions. We discuss the first NNLL prediction of the {bar B} {yields} X{sub s}{gamma} branching ratio, including important additional subtleties due to non-perturbative corrections and logarithmically-enhanced cut effects, and also recent results on the inclusive mode {bar B} {yields} X{sub s}{ell}{sup +}{ell}{sup -}. Moreover, new results on the corresponding exclusive modes are reviewed. Finally, we comment on the present status of the so-called B {yields} K{pi} puzzle in hadronic b {yields} s transitions.
Date: April 4, 2007
Creator: Hurth, Tobias & /SLAC, /CERN
Partner: UNT Libraries Government Documents Department

Radiation Transport Calculations and Simulations

Description: This article is an introduction to the Monte Carlo method as used in particle transport. After a description at an elementary level of the mathematical basis of the method, the Boltzmann equation and its physical meaning are presented, followed by Monte Carlo integration and random sampling, and by a general description of the main aspects and components of a typical Monte Carlo particle transport code. In particular, the most common biasing techniques are described, as well as the concepts of estimator and detector. After a discussion of the different types of errors, the issue of Quality Assurance is briefly considered.
Date: June 30, 2011
Creator: Fasso, Alberto; /SLAC; Ferrari, A. & /CERN
Partner: UNT Libraries Government Documents Department

Scattering Amplitudes: The Most Perfect Microscopic Structures in the Universe

Description: This article gives an overview of many of the recent developments in understanding the structure of relativistic scattering amplitudes in gauge theories ranging from QCD to N = 4 super-Yang-Mills theory, as well as (super)gravity. I also provide a pedagogical introduction to some of the basic tools used to organize and illuminate the color and kinematic structure of amplitudes. This article is an invited review introducing a special issue of Journal of Physics A devoted to 'Scattering Amplitudes in Gauge Theories'.
Date: November 4, 2011
Creator: Dixon, Lance J. & /SLAC, /CERN
Partner: UNT Libraries Government Documents Department

New Physics Search in Flavour Physics

Description: With the running B, kaon and neutrino physics experiments, flavour physics takes centre stage within today's particle physics. We discuss the opportunities offered by these experiments in our search for new physics beyond the SM and discuss their complementarity to collider physics. We focus on rare B and kaon decays, highlighting specific observables in an exemplary mode. We also comment on the so-called B {yields} {pi}{pi} and B {yields} K{pi} puzzles. Moreover, we briefly discuss the restrictive role of long-distance strong interactions and some new tools such as QCD factorization and SCET to handle them.
Date: January 4, 2006
Creator: Hurth, Tobias & /SLAC, /CERN
Partner: UNT Libraries Government Documents Department

Some interesting min-bias distributions for early LHC runs

Description: A few observable distributions in min-bias (inelastic, non-diffractive) events which could be well constrained with early LHC data are presented, with some comments on their significance for placing constraints on theoretical models. The effects of fiducial cuts (p{perpendicular} > 0.5 GeV, |{eta}| < 2.5) and extrapolation from the Tevatron are illustrated.
Date: December 1, 2007
Creator: Skands, P.Z. & /Fermilab, /CERN
Partner: UNT Libraries Government Documents Department

C++ and data

Description: High performance computing with a large code base and C++ has proved to be a good combination. But when it comes to storing data, C++ is a problematic choice: it offers no support for serialization, type definitions are amazingly complex to parse, and the dependency analysis (what does object A need to be stored?) is incredibly difficult. Nevertheless, the LHC data consists of C++ objects that are serialized with help from ROOT's reflection database and interpreter CINT. The fact that we can do it on that scale, and the performance with which we do it makes this approach unique and stirs interest even outside HEP. I will show how CINT collects and stores information about C++ types, what the current major challenges are (dictionary size), and what CINT and ROOT have done and plan to do about it.
Date: January 1, 2008
Creator: Naumann, Axel; /CERN; Canal, Philippe & /Fermilab
Partner: UNT Libraries Government Documents Department

The role of interpreters in high performance computing

Description: Compiled code is fast, interpreted code is slow. There is not much we can do about it, and it's the reason why interpreters use in high performance computing is usually restricted to job submission. We show where interpreters make sense even in the context of analysis code, and what aspects have to be taken into account to make this combination a success.
Date: January 1, 2008
Creator: Naumann, Axel; /CERN; Canal, Philippe & /Fermilab
Partner: UNT Libraries Government Documents Department

New Physics Search in the LHCb Era

Description: The authors present theoretical and experimental preparations for an indirect search for new physics (NP) using the rare decay {bar B}{sub d} {yields} {bar K}*{sup 0}{mu}{sup +}{mu}{sup -}. They design new observables with very small theoretical uncertainties and good experimental resolution.
Date: June 11, 2010
Creator: Hurth, Tobias; /SLAC, /CERN & ,
Partner: UNT Libraries Government Documents Department

Geometry Description Markup Language for Physics Simulation And Analysis Applications.

Description: The Geometry Description Markup Language (GDML) is a specialized XML-based language designed as an application-independent persistent format for describing the geometries of detectors associated with physics measurements. It serves to implement ''geometry trees'' which correspond to the hierarchy of volumes a detector geometry can be composed of, and to allow to identify the position of individual solids, as well as to describe the materials they are made of. Being pure XML, GDML can be universally used, and in particular it can be considered as the format for interchanging geometries among different applications. In this paper we will present the current status of the development of GDML. After having discussed the contents of the latest GDML schema, which is the basic definition of the format, we will concentrate on the GDML processors. We will present the latest implementation of the GDML ''writers'' as well as ''readers'' for either Geant4 [2], [3] or ROOT [4], [10].
Date: January 23, 2007
Creator: Chytracek, R.; /CERN; McCormick, J.; /SLAC; Pokorski, W.; /CERN et al.
Partner: UNT Libraries Government Documents Department

Advances in X-Band TW Accelerator Structures Operating in the 100 MV/M Regime

Description: A CERN-SLAC-KEK collaboration on high gradient X-band accelerator structure development for CLIC has been ongoing for three years. The major outcome has been the demonstration of stable 100 MV/m gradient operation of a number of CLIC prototype structures. These structures were fabricated using the technology developed from 1994 to 2004 for the GLC/NLC linear collider initiative. One of the goals has been to refine the essential parameters and fabrication procedures needed to realize such a high gradient routinely. Another goal has been to develop structures with stronger dipole mode damping than those for GLC/NLC. The latter requires that the surface temperature rise during the pulse be higher, which may increase the breakdown rate. One structure with heavy damping has been RF processed and another is nearly finished. The breakdown rates of these structures were found to be higher by two orders of magnitude compared to those with equivalent acceleration mode parameters but without the damping features. This paper presents these results together with some of the earlier results from non-damped structures.
Date: July 5, 2012
Creator: Higo, Toshiyasu; /KEK, Tsukuba; Higashi, Yasuo; /KEK, Tsukuba; Matsumoto, Shuji; /KEK, Tsukuba et al.
Partner: UNT Libraries Government Documents Department

Commissioning of the cryogenics of the LHC long straight sections

Description: The LHC is made of eight circular arcs interspaced with eight Long Straight Sections (LSS). Most powering interfaces to the LHC are located in these sections where the particle beams are focused and shaped for collision, cleaning and acceleration. The LSSs are constituted of several unique cryogenic devices and systems like electrical feed-boxes, standalone superconducting magnets, superconducting links, RF cavities and final focusing superconducting magnets. This paper presents the cryogenic commissioning and the main results obtained during the first operation of the LHC Long Straight Sections.
Date: January 1, 2010
Creator: Perin, A.; Casas-Cubillos, J.; Claudet, S.; /CERN; Darve, C.; /Fermilab et al.
Partner: UNT Libraries Government Documents Department

Optimization of the CLIC Baseline Collimation System

Description: Important efforts have recently been dedicated to the improvement of the design of the baseline collimation system of the Compact Linear Collider (CLIC). Different aspects of the design have been optimized: the transverse collimation depths have been recalculated in order to reduce the collimator wakefield effects while maintaining a good efficiency in cleaning the undesired beam halo; the geometric design of the spoilers have also been reviewed to minimize wakefields; in addition, the optics design have been polished to improve the collimation efficiency. This paper describes the current status of the CLIC collimation system after this optimization.
Date: July 6, 2012
Creator: Resta-Lopez, Javier; /Oxford U., JAI; Angal-Kalinin, Deepa; /Daresbury; Fernandez-Hernando, Juan; /Daresbury et al.
Partner: UNT Libraries Government Documents Department

LHC Beam Diffusion Dependence on RF Noise: Models And Measurements

Description: Radio Frequency (RF) accelerating system noise and non-idealities can have detrimental impact on the LHC performance through longitudinal motion and longitudinal emittance growth. A theoretical formalism has been developed to relate the beam and RF loop dynamics with the bunch length growth [1]. Measurements were conducted at LHC to validate the formalism, determine the performance limiting RF components, and provide the foundation for beam diffusion estimates for higher energies and intensities. A brief summary of these results is presented in this work. During a long store, the relation between the energy lost to synchrotron radiation and the noise injected to the beam by the RF accelerating voltage determines the growth of the bunch energy spread and longitudinal emittance. Since the proton synchrotron radiation in the LHC is very low, the beam diffusion is extremely sensitive to RF perturbations. The theoretical formalism presented in [1], suggests that the noise experienced by the beam depends on the cavity phase noise power spectrum, filtered by the beam transfer function, and aliased due to the periodic sampling of the accelerating voltage signal V{sub c}. Additionally, the dependence of the RF accelerating cavity noise spectrum on the Low Level RF (LLRF) configurations has been predicted using time-domain simulations and models [2]. In this work, initial measurements at the LHC supporting the above theoretical formalism and simulation predictions are presented.
Date: September 14, 2010
Creator: Mastorides, T.; /SLAC; Rivetta, C.; /SLAC; Fox, J.D.; /SLAC et al.
Partner: UNT Libraries Government Documents Department

Energy deposited in the high luminosity inner triplets of the LHC by collision debris

Description: The 14 TeV center of mass proton-proton collisions in the LHC produce not only debris interesting for physics but also showers of particles ending up in the accelerator equipment, in particular in the superconducting magnet coils. Evaluations of this contribution to the heat, that has to be transported by the cryogenic system, have been made to guarantee that the energy deposition in the superconducting magnets does not exceed limits for magnet quenching and the capacity of the cryogenic system. The models of the LHC base-line are detailed and include description of, for energy deposition, essential elements like beam-pipes and corrector magnets. The evaluations made using the Monte-Carlo code FLUKA are compared to previous studies using MARS. For the consolidation of the calculations, a dedicated comparative study of these two codes was performed for a reduced setup.
Date: June 1, 2008
Creator: Wildner, E.; /CERN; Broggi, F.; /INFN, Milan; Cerutti, F.; Ferrari, A. et al.
Partner: UNT Libraries Government Documents Department