The GANDALF 6U-VME64x/VXS module has been developed for the digitization and real time analysis of detector signals. To perform different applications such as analog-to-digital or time-to-digital ...conversions, coincidence matrix formation, fast pattern recognition and trigger generation, this module comes with exchangeable analog and digital mezzanine cards. Based on this platform, we present a 128-channel TDC which is implemented in a single Xilinx Virtex-5 FPGA using a shifted clock sampling method. In contrast to common TDC concepts, the input signal is sampled by 16 equidistant phase-shifted clocks. A particular challenge of the design is the minimum skew routing of the input signals to the sampling flip-flops. We present measurement results for the differential nonlinearity and the time resolution of the TDC readout system.
The GANDALF 6U-VME64x/VXS module has been developed to cope with a variety of readout tasks in nuclear physics experiments and is operated at the COMPASS-II experiment at CERN. Based on this module, ...a 128-channel Time-to-Digital Converter with a time resolution of 93 ps has been implemented successfully in a Xilinx Virtex-5 FPGA using a shifted clock sampling algorithm. Beyond that, the design was extended by adding scaler channels for simultaneous rate measurements.
State-of-the-art experiments in nuclear and high-energy physics typically operate with high-luminosity beams which leads to high event rates and large amounts of data from the detectors. The ...background-induced occupancy of the detector channels can be quite high; therefore it is important to have sophisticated trigger subsystems which process the data in realtime to generate trigger objects for the global trigger decision. In this work we present a FPGA based low-latency trigger processor for the COMPASS-II experiment.
The production of vector mesons in deep inelastic scattering is an
interesting yet scarsely explored channel to study the transverse spin
structure of the nucleon and the related phenomena. The ...COMPASS collaboration
has performed the first measurement of the Collins and Sivers asymmetries for
inclusively produced $\rho^0$ mesons. The analysis is based on the data set
collected in deep inelastic scattering in $2010$ using a $160\,\,\rm{GeV}/c$
$\mu^+$ beam impinging on a transversely polarized $\rm{NH}_3$ target. The
$\rho^{0}$ mesons are selected from oppositely charged hadron pairs, and the
asymmetries are extracted as a function of the Bjorken-$x$ variable, the
transverse momentum of the pair and the fraction of the energy $z$ carried by
the pair. Indications for positive Collins and Sivers asymmetries are observed.
We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard
exclusive $\rho ^0$ meson muoproduction at COMPASS using 160~GeV/$c$ polarised
$ \mu ^{+}$ and $ \mu ^{-}$ beams impinging ...on a liquid hydrogen target. The
measurement covers the kinematic range 5.0~GeV/$c^2$ $< W <$ 17.0~GeV/$c^2$,
1.0 (GeV/$c$)$^2$ $< Q^2 <$ 10.0 (GeV/$c$)$^2$ and 0.01 (GeV/$c$)$^2$ $<
p_{\rm{T}}^2 <$ 0.5 (GeV/$c$)$^2$. Here, $W$ denotes the mass of the final
hadronic system, $Q^2$ the virtuality of the exchanged photon, and $p_{\rm{T}}$
the transverse momentum of the $\rho ^0$ meson with respect to the
virtual-photon direction. The measured non-zero SDMEs for the transitions of
transversely polarised virtual photons to longitudinally polarised vector
mesons ($\gamma^*_T \to V^{ }_L$) indicate a violation of $s$-channel helicity
conservation. Additionally, we observe a dominant contribution of
natural-parity-exchange transitions and a very small contribution of
unnatural-parity-exchange transitions, which is compatible with zero within
experimental uncertainties. The results provide important input for modelling
Generalised Parton Distributions (GPDs). In particular, they may allow one to
evaluate in a model-dependent way the role of parton helicity-flip GPDs in
exclusive $\rho ^0$ production.
The production of vector mesons in deep inelastic scattering is an interesting yet scarsely explored channel to study the transverse spin structure of the nucleon and the related phenomena. The ...COMPASS collaboration has performed the first measurement of the Collins and Sivers asymmetries for inclusively produced \(\rho^0\) mesons. The analysis is based on the data set collected in deep inelastic scattering in \(2010\) using a \(160\,\,\rm{GeV}/c\) \(\mu^+\) beam impinging on a transversely polarized \(\rm{NH}_3\) target. The \(\rho^{0}\) mesons are selected from oppositely charged hadron pairs, and the asymmetries are extracted as a function of the Bjorken-\(x\) variable, the transverse momentum of the pair and the fraction of the energy \(z\) carried by the pair. Indications for positive Collins and Sivers asymmetries are observed.
We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive \(\rho ^0\) meson muoproduction at COMPASS using 160~GeV/\(c\) polarised \( \mu ^{+}\) and \( \mu ^{-}\) beams ...impinging on a liquid hydrogen target. The measurement covers the kinematic range 5.0~GeV/\(c^2\) \(< W <\) 17.0~GeV/\(c^2\), 1.0 (GeV/\(c\))\(^2\) \(< Q^2 <\) 10.0 (GeV/\(c\))\(^2\) and 0.01 (GeV/\(c\))\(^2\) \(< p_{\rm{T}}^2 <\) 0.5 (GeV/\(c\))\(^2\). Here, \(W\) denotes the mass of the final hadronic system, \(Q^2\) the virtuality of the exchanged photon, and \(p_{\rm{T}}\) the transverse momentum of the \(\rho ^0\) meson with respect to the virtual-photon direction. The measured non-zero SDMEs for the transitions of transversely polarised virtual photons to longitudinally polarised vector mesons (\(\gamma^*_T \to V^{ }_L\)) indicate a violation of \(s\)-channel helicity conservation. Additionally, we observe a dominant contribution of natural-parity-exchange transitions and a very small contribution of unnatural-parity-exchange transitions, which is compatible with zero within experimental uncertainties. The results provide important input for modelling Generalised Parton Distributions (GPDs). In particular, they may allow one to evaluate in a model-dependent way the role of parton helicity-flip GPDs in exclusive \(\rho ^0\) production.
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