62237714
Partial wave analysis using graphics processing units
Partial wave analysis is an important tool for determining resonance properties in hadron spectroscopy. For large data samples however, the un-binned likelihood fits employed are computationally very expensive. At the Beijing Spectrometer (BES) III experiment, an increase in statistics compared to earlier experiments of up to two orders of magnitude is expected. In order to allow for a timely analysis of these datasets, additional computing power with short turnover times has to be made available. It turns out that graphics processing units (GPUs) originally developed for 3D computer games have an architecture of massively parallel single instruction multiple data floating point units that is almost ideally suited for the algorithms employed in partial wave analysis. We have implemented a framework for tensor manipulation and partial wave fits called GPUPWA. The user writes a program in pure C++ whilst the GPUPWA classes handle computations on the GPU, memory transfers, caching and other technical details. In conjunction with a recent graphics processor, the framework provides a speed-up of the partial wave fit by more than two orders of magnitude compared to legacy FORTRAN code.
122573727
Results from the Beijing Spectrometer III
The new BES III detector at BEPCII collected 106 million ψ and about 226 million J/ψ events in 2009. Results based on these samples are reported, including branching ratios for χXcJ → π0π0,ηη, 4π0, γyV and VV, where V is a ρ, ω, or Φ as well as first measurements of the branching ratios for ψ → γ0hc and hc → γηc and measurements of the mass and width of the hc. Results in hadron spectroscopy include the confirmation of the pp threshold enhancement in J/ψ→γpp and confirmation of the X(1835) in J/ψ→γηπ+π−
18175820
Measurement and QCD analysis of the diffractive deep-inelastic scattering cross section at HERA
A detailed analysis is presented of the diffractive deep-inelastic scattering process ep→eXY, where Y is a proton or a low mass proton excitation carrying a fraction 1-xIP>0.95 of the incident proton longitudinal momentum and the squared four-momentum transfer at the proton vertex satisfies |t|<1 GeV2. Using data taken by the H1 experiment, the cross section is measured for photon virtualities in the range 3.5≤Q2≤1600 GeV2, triple differentially in xIP, Q2 and β=x/xIP, where x is the Bjorken scaling variable. At low xIP, the data are consistent with a factorisable xIP dependence, which can be described by the exchange of an effective pomeron trajectory with intercept αIP(0)=1.118±0.008(exp.)+0.029-0.010(model). Diffractive parton distribution functions and their uncertainties are determined from a next-to-leading order DGLAP QCD analysis of the Q2 and β dependences of the cross section. The resulting gluon distribution carries an integrated fraction of around 70% of the exchanged momentum in the Q2 range studied. Total and differential cross sections are also measured for the diffractive charged current process e+p→ν̄eXY and are found to be well described by predictions based on the diffractive parton distributions. The ratio of the diffractive to the inclusive neutral current ep cross sections is studied. Over most of the kinematic range, this ratio shows no significant dependence on Q2 at fixed xIP and x or on x at fixed Q2 and β.
62672040
Partial wave analysis at BES III harnessing the power of GPUs
Partial wave analysis (PWA) is a core tool for determining resonance properties in hadron spectroscopy. The unbinned likelihood fits employed are however computationally very expensive especially in view of the very large data samples being collected at the Beijing Spectrometer (BES) III experiment and expected from future experiments such as Glue‐X and PANDA. Using the power of massively parallel floating point calculations on graphics processing units (GPUs), we have managed to speed up PWA by more than two orders of magnitude compared to legacy implementations. The resulting software framework allows for the fast creation and running of PWA code. Modern hardware and software thus solve the PWA speed problems—many questions concerning fit methods and especially the reliability of fit results however remain open.
120101281
The Mu3e Experiment
Abstract The Mu3e experiment is designed to search for charged lepton flavour violation in the process μ + → e + e − e + with a branching ratio sensitivity of 10 − 16 . This requires a detector capable of coping with rates of up to 2 ⋅ 10 9 muons/s whilst being able to reduce backgrounds from accidental coincidences and the process μ + → e + e − e + ν ¯ μ ν e to below the 10 − 16 level. The use of 50 μ m thin high-voltage monolithic active pixel sensors in conjunction with an innovative tracking concept provide the momentum and position resolution necessary, whilst the timing resolution is provided by a combination of scintillating fibres and tiles. The recently approved Mu3e experiment will be located at the Paul Scherrer Institute in Switzerland and is currently preparing for detector construction.
119113295
Measurement of isolated photon production in deep-inelastic scattering at HERA
The production of isolated photons in deep-inelastic scattering ep→eγX is measured with the H1 detector at HERA. The measurement is performed in the kinematic range of negative four-momentum transfer squared 4<Q2<150 GeV2 and a mass of the hadronic system WX>50 GeV. The analysis is based on a total integrated luminosity of 227 pb-1. The production cross section of isolated photons with a transverse energy in the range 3<ETγ<10 GeV and pseudorapidity range -1.2<ηγ<1.8 is measured as a function of ETγ, ηγ and Q2. Isolated photon cross sections are also measured for events with no jets or at least one hadronic jet. The measurements are compared with predictions from Monte Carlo generators modelling the photon radiation from the quark and the electron lines, as well as with calculations at leading and next to leading order in the strong coupling. The predictions significantly underestimate the measured cross sections.
123334423
Study of semiinclusive production of eta-prime mesons in B decays
119228788
Search for resonances decaying into top-quark pairs using fully hadronic decays in pp collisions with ATLAS at $ \sqrt{s}=7 $ TeV
A bstractA search for resonances produced in 7 TeV proton-proton collisions and decaying into top-quark pairs is described. In this Letter events where the top-quark decay produces two massive jets with large transverse momenta recorded with the ATLAS detector at the Large Hadron Collider are considered. Two techniques that rely on jet substructure are used to separate top-quark jets from those arising from light quarks and gluons. In addition, each massive jet is required to have evidence of an associated bottom-quark decay. The data are consistent with the Standard Model, and limits can be set on the production cross section times branching fraction of a Z′ boson and a Kaluza-Klein gluon resonance. These limits exclude, at the 95% credibility level, Z′ bosons with masses 0.70-1.00 TeV as well as 1.28-1.32 TeV and Kaluza-Klein gluons with masses 0.70-1.62 TeV.
118733497
Search for an excess of events with an identical flavour lepton pair and significant missing transverse momentum in $\sqrt{s}=7$ TeV proton–proton collisions with the ATLAS detector
Results are presented of a search for particles decaying into final states with significant missing transverse momentum and exactly two identical flavour leptons (e, μ) of opposite charge in $\sqrt{s}=7$ TeV collisions at the Large Hadron Collider. This channel is particularly sensitive to supersymmetric particle cascade decays producing flavour correlated lepton pairs. Flavour uncorrelated backgrounds are subtracted using a sample of opposite flavour lepton pair events. Observation of an excess beyond Standard Model expectations following this subtraction procedure would offer one of the best routes to measuring the masses of supersymmetric particles. In a data sample corresponding to an integrated luminosity of 35 pb−1 no such excess is observed. Model-independent limits are set on the contribution to these final states from supersymmetry and are used to exclude regions of a phenomenological supersymmetric parameter space.