120 research outputs found

    Time based readout of a silicon photomultiplier (SiPM) for Time Of Flight Positron Emission Tomography (TOF-PET)

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    Time of flight (TOF) measurements in positron emission tomography (PET) are very challenging in terms of timing performance, and should achieve ideally less than 100ps FWHM precision. We present a time-based differential technique to read out SiPMs that has less than 25ps rms electronic jitter. The novel readout is a fast front end circuit (NINO) based on a first stage differential current mode amplifier with 20input resistance. Therefore the amplifier inputs are connected differentially to the SiPM’s anode and cathode ports. The leading edge of the output signal provides the time information, while the trailing edge provides the energy information. Based on a Monte Carlo photon-generation model, SPICE simulations were run with a 3x3mm2 SiPM-model, read out with a differential current amplifier. The results of these simulations are presented here and compared with experimental data obtained with a 3x3x15mm3 LSO crystal coupled to a SiPM. The measured time coincidence precision is interpreted by the combined Monte Carlo/ SPICE simulation, as well as by Poisson statistics

    Study of Charm Fragmentation into D^{*\pm} Mesons in Deep-Inelastic Scattering at HERA

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    The process of charm quark fragmentation is studied using D±D^{*\pm} meson production in deep-inelastic scattering as measured by the H1 detector at HERA. Two different regions of phase space are investigated defined by the presence or absence of a jet containing the D±D^{*\pm} meson in the event. The parameters of fragmentation functions are extracted for QCD models based on leading order matrix elements and DGLAP or CCFM evolution of partons together with string fragmentation and particle decays. Additionally, they are determined for a next-to-leading order QCD calculation in the fixed flavour number scheme using the independent fragmentation of charm quarks to D±D^{*\pm} mesons.Comment: 33 pages, submitted to EPJ

    Jet production in ep collisions at high Q(2) and determination of alpha(s)

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    The production of jets is studied in deep-inelastic e(+/-) p scattering at large negative four momentum transfer squared 150 LT Q(2) LT 15000 GeV2 using HERA data taken in 1999-2007, corresponding to an integrated luminosity of 395 pb(-1). Inclusive jet, 2-jet and 3-jet cross sections, normalised to the neutral current deep-inelastic scattering cross sections, are measured as functions of Q(2), jet transverse momentum and proton momentum fraction. The measurements are well described by perturbative QCD calculations at next-to-leading order corrected for hadronisation effects. The strong coupling as determined from these measurement

    The lender of last resort and liquidity provision: How much of a departure is the sub-prime crisis?

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    The traditional role of the lender of last resort (LOLR) is to avoid unnecessary bank failures that could threaten systemic stability, while ensuring that there are suitable safeguards for central bank balance sheets and that moral hazard is minimised. The sub-prime crisis has shown that traditional models of bank liquidity risk and of LOLR require revision, as was already apparent to a lesser extent in the Russia/LTCM episode. Funding risk now interacts with market liquidity risk, to create difficult challenges for central banks. Even in the relatively non-systemic period up to September 2008, the LOLR had to adapt radically, for example, in terms of lending to investment banks, taking lower quality collateral and lending for longer maturities. Central banks have also been challenged by difficulties in maintaining confidentiality of support and by the interaction of these problems with low levels of deposit insurance. Since September 2008, although action has mostly been in line with traditional approaches for systemic crises, there have been some further adaptations in line with the systemic nature of the crisis, notably by the Federal Reserve acting as market maker or investor of last resort in illiquid securities markets

    Entwicklung eines TOF Positron Emissions Tomographie Systems mit MPPC Auslese

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    Anwendung neuartiger Silizium-Photo-Detektoren in der Positron Emissions Tomographie

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