112091395
Power Distribution in a CMS Tracker for the SLHC
An upgraded tracker for CMS will need a new architecture for powering to keep the power dissipated in the power cables to acceptable levels. Inductor topologies to reduce the stray magnetic field are discussed together with measurements of the magnetic field produced by prototype inductors. A transformer based DC-DC converter has the potential to produce a high stepdown ratio whilst producing a low stray field and retaining high efficiency. The relative merits of buck configuration and transformer based DC-DC converters are discussed.
53579013
Observability of Higgs produced with top quarks and decaying to bottom quarks
The decay, H → bb, is dominant for a Standard Model Higgs boson in the mass range just above the exclusion limit of 114.4 GeV/c 2 reported by the LEP experiments. Unfortunately, an overwhelming abundance of b¯ b events arising from more mundane sources, together with the lack of precision inherent in the reconstruction of the Higgs mass, renders this decay modeaprioriundetectable in the case of direct Higgs production at the LHC. It is therefore of no small interest to investigate whether H → bb can be observed in those cases where the Higgs is produced in association with other massive particles. In this note, the results of a study of Higgs bosons produced in association with top quarks and decaying via H → bb are presented. The study was performed as realistically as possible by employing a full and detailed Monte Carlo simulation of the CMS detector followed by the application of trigger and reconstruction algorithms that were developed for use with real data. Important systematic effects resulting from such sources as the uncertainties in the jet energy scale and the estimated rates for correctly tagging b jets or mistagging non-b jets have been taken into account. The impact of large theoretical uncertainties in the cross sections for t tp lusN jets processes due to an absence of next-to-leading order calculations is also considered.
119530771
Acceleration in the linear non-scaling fixed-field alternating-gradient accelerator EMMA
In a fixed-field alternating-gradient (FFAG) accelerator, eliminating pulsed magnet operation permits rapid acceleration to synchrotron energies, but with a much higher beam-pulse repetition rate. Conceived in the 1950s, FFAGs are enjoying renewed interest, fuelled by the need to rapidly accelerate unstable muons for future high-energy physics colliders. Until now a ‘scaling’ principle has been applied to avoid beam blow-up and loss. Removing this restriction produces a new breed of FFAG, a non-scaling variant, allowing powerful advances in machine characteristics. We report on the first non-scaling FFAG, in which orbits are compacted to within 10 mm in radius over an electron momentum range of 12–18 MeV/c. In this strictly linear-gradient FFAG, unstable beam regions are crossed, but acceleration via a novel serpentine channel is so rapid that no significant beam disruption is observed. This result has significant implications for future particle accelerators, particularly muon and high-intensity proton accelerators.
17120432
Measurement of the Top Quark Mass using Quantities with Minimal Dependence on the Jet Energy Scale
We present three measurements of the top quark mass in the lepton plus jets channel with 1.9fb 1 of data using quantities with minimal dependence on the jet energy scale in the lepton plus jets channel at CDF. One measurement uses the mean transverse decay length of b-tagged jets (L2d) to determine the top mass, another uses the transverse momentum of the lepton (LepPt) to determine the top mass, and a third measurement uses both variables simultaneously. Using the L2d variable we measure a top mass of (176.7 +10.0 8.9 (stat)± 3.4(syst)) GeV/c 2 , using the LepPt variable we measure a top mass of (173.5 +8.9 9.1 (stat)± 4.2(syst)) GeV/c 2 , and doing the combined measurement using both variables we arrive at a top mass result of (175.3 ± 6.2(stat) ± 3.0(syst)) GeV/c2. Since some of the systematic uncertainties are statistically limited, these results are expected to improve significantly if more data is added at the Tevatron in the future, or if the measurement is done at the LHC.
125438498
Top quark mass measurements
The top quark, with its extraordinarily large mass (nearly that of a gold atom), plays a significant role in the phenomenology of EWSB in the Standard Model. In particular, the top quark mass when combined with the W mass constrains the mass of the as yet unobserved Higgs boson. Thus, a precise determination of the mass of the top quark is a principal goal of the CDF and D0 experiments. With the data collected thus far in Runs 1 and 2 of the Tevatron, CDF and D0 have measured the top quark mass in both the lepton+jets and dilepton decay channels using a variety of complementary experimental techniques. The author presents an overview of the most recent of the measurements.
11057739
Initial experience with the CDF layer 00 silicon detector
We report on initial experience with the CDF Layer 00 Detector. Layer 00 is an innovative, low-mass, silicon detector installed in CDF during the upgrade for Run 2A of the Tevatron. Noise pickup present during operation at CDF is discussed. An event-by-event pedestal correction implemented by CDF is presented. This off-line solution prevents L00 from being used in the current incarnation of the on-line displaced track trigger. Preliminary performance of Layer 00 is described.
117958796
H− Source Developments at CERN
Future CERN programmes for LHC and ISOLDE require increasing the beam intensity and brightness from the Proton Synchotron Booster (PSB). This could be achieved by injection from a higher energy H− linac. A new injector will require a high performance, high reliability, negative hydrogen ion source. This paper will present the requirements for such a source together with the first results for a prototype microwave driven source.
119634910
Energy-density fluctuations in de Sitter space
Abstract Quantum fluctuations in de Sitter space or in the de Sitter phase of an inflationary universe give rise to a spectrum of classical energy-density perturbations which is scale invariant. The analysis presented in this letter is based on a consistent expansion in powers of ħ, and on the functional Schrodinger approach to quantum field theory in de Sitter space. The result holds for a large class of initial states of the quantum field, including the Bunch-Davies vacuum.
122487779
Minimal Dynamical Electroweak Symmetry Breaking
109966470
DESIGN, CONSTRUCTION AND OPERATION OF THE NEW CERN SC RF SYSTEM
A fast cycling RF-system giving high energy-gain per revolution was required to overcome the intensity limitations set by space-charge in the CERN SC. All other frequency modulation methods being discarded for power reasons, a high Q system tuned by a rotary capacitor was chosen.
19481064
Pulsed ECR source in afterglow operation at CERN
A pulsed 14 GHz ECR4 source, adapted to operate in the afterglow mode, was delivered by GANIL to CERN in the framework of the Heavy Ion Facility Project. After four months of operation to commission the facility, it completed its first operational run of nine weeks at the end of 1994, providing lead ions to nuclear physics and ion cooling experiments. A very stable beam, with a useful length of over 1 ms, of 80 eμA of Pb27+ was provided by the source over this period. The operational problems experienced during the commissioning and operation, and the investigations to improve performance for the next experimental physics run are presented.