117992071
Software trigger systems in High Energy Physics
2567762
The LHCb Readout System and Real-Time Event Management
The LHCb Experiment is a hadronic precision experiment at the LHC accelerator aimed at mainly studying b-physics by profiting from the large b-anti-b-production at LHC. The challenge of high trigger efficiency has driven the choice of a readout architecture allowing the main event filtering to be performed by a software trigger with access to all detector information on a processing farm based on commercial multi-core PCs. The readout architecture therefore features only a relatively relaxed hardware trigger with a fixed and short latency accepting events at 1 MHz out of a nominal proton collision rate of 30 MHz, and high bandwidth with event fragment assembly over Gigabit Ethernet. A fast central system performs the entire synchronization, event labelling and control of the readout, as well as event management including destination control, dynamic load balancing of the readout network and the farm, and handling of special events for calibrations and luminosity measurements. The event filter farm processes the events in parallel and reduces the physics event rate to about 2 kHz which are formatted and written to disk before transfer to the offline processing. A spy mechanism allows processing and reconstructing a fraction of the events for online quality checking. In addition a 5 Hz subset of the events are sent as express stream to offline for checking calibrations and software before launching the full offline processing on the main event stream.
110639465
The LHCb Run Control
LHCb has designed and implemented an integrated Experiment Control System. The Control System uses the same concepts and the same tools to control and monitor all parts of the experiment: the Data Acquisition System, the Timing and the Trigger Systems, the High Level Trigger Farm, the Detector Control System, the Experiment's Infrastructure and the interaction with the CERN Technical Services and the Accelerator. LHCb's Run Control, the main interface used by the experiment's operator, provides access in a hierarchical, coherent and homogeneous manner to all areas of the experiment and to all its sub-detectors. It allows for automated (or manual) configuration and control, including error recovery, of the full experiment in its different running modes. Different instances of the same Run Control interface are used by the various sub-detectors for their stand-alone activities: test runs, calibration runs, etc. The architecture and the tools used to build the control system, the guidelines and components provided to the developers, as well as the first experience with the usage of the Run Control will be presented
121570479
Compatibility and possible implications of the experimental results on solar neutrinos
Abstract The effect of varying the assumed value of the cross-section for the proton-proton fusion weak reaction of the solar cycle on the solar neutrino problem is discussed. It is shown that an increase of about 20% of the relevant astrophysical factor fields compatibility (within the present experimental accuracy) of the available results with theory and among themselves.
118941207
Present knowledge of the Cabibbo-Kobayashi-Maskawa matrix
A complete review of the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements and of the experimental methods for their determination is presented. A critical analysis of the relevant experimental results, and in particular of the most recent ones, allows to improve the accuracies of all the matrix elements. A chi-square minimization with the three-family unitarity constraint on the CKM matrix is performed to test the current interpretation of the CP violating phenomena inside the Standard Model. A complete and unambiguous solution satisfying all the imposed constraints is found. As a by-product of the fit, the precision on the values of the matrix elements is further increased and it is possible to obtain estimates for the important CP violation observables $sin 2\beta$, $sin 2\alpha$ and $\gamma$. Finally, an independent estimation of the CKM elements based on a Bayesian approach is performed. This complementary method constitutes a check of the results obtained, providing also the probability functions of the CKM elements and of the related quantities.
126243169
The selection crate for the L0 calorimeter trigger
1984966
NON-EQUILIBRIUM H2 FORMATION IN THE EARLY UNIVERSE: ENERGY EXCHANGES, RATE COEFFICIENTS, AND SPECTRAL DISTORTIONS
Energy exchange processes play a crucial role in the early universe, affecting the thermal balance and the dynamical evolution of the primordial gas. In the present work we focus on the consequences of a non-thermal distribution of the level populations of H2: first, we determine the excitation temperatures of vibrational transitions and the non-equilibrium heat transfer; second, we compare the modifications to chemical reaction rate coefficients with respect to the values obtained assuming local thermodynamic equilibrium; and third, we compute the spectral distortions to the cosmic background radiation generated by the formation of H2 in vibrationally excited levels. We conclude that non-equilibrium processes cannot be ignored in cosmological simulations of the evolution of baryons, although their observational signatures remain below current limits of detection. New fits to the equilibrium and non-equilibrium heat transfer functions are provided.
18035202
Dust emissivity in the submm/mm SCUBA and SIMBA observations of Barnard 68
We have observed the dark cloud Barnard 68 with SCUBA at 850  μ m and with SIMBA at 1.2 mm. The submillimetre and millimetre dust emission correlate well with the extinction map of Alves et al. (2001). The A V /850  μ m correlation is clearly not linear and suggests lower temperatures for the dust in the inner core of the cloud. Assuming a model for the temperature gradient, we derive the cloud-averaged dust emissivities (normalised to the V -band extinction efficiency) at 850  μ m and 1.2 mm. We find $\kappa_{850~\mu{\rm m}}/\kappa_{\rm V}=4.0\pm 1.0\times 10^{-5}$ and $\kappa_{1.2~{\rm mm}}/\kappa_{\rm V}=9.0\pm 3.0\times 10^{-6}$. These values are compared with other determinations in this wavelength regime and with expectations for models of diffuse dust and grain growth in dense clouds.
15395507
Self-similar Champagne Flows in H II Regions
We consider the idealized expansion of an initially self-gravitating, static, singular, isothermal cloud core. For t ≥ 0, the gas is ionized and heated to a higher uniform temperature by the formation of a luminous but massless star in its center. The approximation that the mass and gravity of the central star are negligible for the subsequent motion of the H II region holds for distances r much greater than ~100 AU and for the massive cloud cores that give rise to high-mass stars. If the initial ionization and heating are approximated to occur instantaneously at t = 0, then the subsequent flow (for r 100 AU) caused by the resulting imbalance between self-gravity and thermal pressure is self-similar. Because of the steep density profile (ρ ∝ r-2), pressure gradients produce a shock front that travels into the cloud, accelerating the gas to supersonic velocities in what has been called the "champagne phase." The expansion of the inner region at t > 0 is connected to the outer envelope of the now ionized cloud core through this shock, whose strength depends on the temperature of the H II gas. In particular, we find a modified Larson-Penston (L-P) type of solution as part of the linear sequence of self-similar champagne outflows. The modification involves the proper insertion of a shock and produces the right behavior at infinity (v → 0) for an outflow of finite duration, reconciling the long-standing conflict on the correct (inflow or outflow) interpretation for the original L-P solution. For realistic heating due to a massive young central star that ionizes and heats the gas to ~104 K, we show that even the self-gravity of the ionized gas of the massive molecular cloud core can be neglected. We then study the self-similar solutions of the expansion of H II regions embedded in molecular clouds characterized by more general power-law density distributions: ρ ∝ r-n with 3/2 < n < 3. In these cases, the shock velocity is an increasing function of the exponent n and diverges as n → 3. We show that this happens because the model includes an origin where the pressure driving the shock diverges because the enclosed heated mass is infinite. Our results imply that the continued photoevaporation of massive reservoirs of neutral gas (e.g., surrounding disks and/or globules) near the embedded ionizing source is required in order to maintain over a significant timescale the emission measure observed in champagne flows.
14593491
Galactic chemical evolution of Lithium: interplay between stellar sources
In this paper we study the evolution of 7Li in the Galaxy considering the contributions of various stellar sources: Type II supernovae, novae, red giant stars, and asymptotic giant branch (AGB) stars. We present new results for the production of 7Li in AGB stars via the hot bottom burning process, based on stellar evolutionary models. In the light of recent observations of dense circumstellar shells around evolved stars in the Galaxy and in the Magellanic Clouds, we also consider the impact of a very high mass-loss rate episode (superwind) before the evolution off the AGB phase on the 7Li enrichment in the interstellar medium. We compare the Galactic evolution of 7Li obtained with these new 7Li yields (complemented with a critical reanalysis of the role of supernovae, novae and giant stars) with a selected compilation of spectroscopic observations including halo and disk field stars as well as young stellar clusters. We conclude that even allowing for the large uncertainties in the theoretical calculation of mass-loss rates at the end of the AGB phase, the superwind phase has a significant effect on the 7Li enrichment of the Galaxy.
3230335
Beryllium abundance in turn-off stars of NGC 6752
Aims: To measure the beryllium abundance in two TO stars of the Globular Cluster NGC 6752, one oxygen rich and sodium poor, the other presumably oxygen poor and sodium rich. Be abundances in these stars are used to put on firmer grounds the hypothesis of Be as cosmochronometer and to investigate the formation of Globular Clusters. Method:We present near UV spectra with resolution R$\sim 45000$ obtained with the UVES spectrograph on the 8.2m VLT Kueyen telescope, analysed with spectrum synthesis based on plane parallel LTE model atmospheres. Results:Be is detected in the O rich star with log(Be/H)=-12.04 $\pm$0.15, while Be is not detected in the other star for which we obtain the upper limit log(Be/H)$<$-12.2. A large difference in nitrogen abundance (1.6 dex) is found between the two stars. Conclusions:The Be measurement is compatible with what found in field stars with the same [Fe/H] and [O/H]. The 'Be age' of the cluster is found to be 13.3 Gyrs, in excellent agreement with the results from main sequence fitting and stellar evolution. The presence of Be confirms the results previously obtained for the cluster NGC~6397 and supports the hypothesis that Be can be used as a clock for the early formation of the Galaxy. Since only an upper limit is found for the star with low oxygen abundance, we cannot decide between competing scenarios of Globular Cluster formation, but we can exclude that 'polluted' stars are substantially younger than 'unpolluted' ones. We stress that the Be test might be the only measurement capable of distinguishing between these scenarios.