L. Tomassetti

Long-term drift laser frequency stabilization using purely optical reference.

We describe an apparatus for the stabilization of laser frequencies that prevents long-term frequency drifts. A Fabry–Perot interferometer is thermostated by referencing it to a stabilized He–Ne laser (master), and its length is scanned over more than one free spectral range allowing the analysis of one or more lines generated by other (slave) lasers. A digital acquisition system makes the detection of the position of all the laser peaks possible, thus producing both feedback for the thermostat and the error signal used for stabilizing the slave lasers. This technique also allows for easy, referenced scanning of the slave laser frequencies over range of several hundred MHz, with a precision of the order of a few MHz. This kind of stabilization system is particularly useful when no atomic or molecular reference lines are available, as in the case of rare or short lived radioactive species.

Experimental study of vapor-cell magneto-optical traps for efficient trapping of radioactive atoms

We have studied magneto-optical traps (MOTs) for efficient on-line trapping of radioactive atoms. After discussing a model of the trapping process in a vapor cell and its efficiency, we present the results of detailed experimental studies on Rb MOTs. Three spherical cells of different sizes were used. These cells can be easily replaced, while keeping the rest of the apparatus unchanged: atomic sources, vacuum conditions, magnetic field gradients, sizes and power of the laser beams, detection system. By direct comparison, we find that the trapping efficiency only weakly depends on the MOT cell size. It is also found that the trapping efficiency of the MOT with the smallest cell, whose diameter is equal to the diameter of the trapping beams, is about 40% smaller than the efficiency of larger cells. Furthermore, we also demonstrate the importance of two factors: a long coated tube at the entrance of the MOT cell, used instead of a diaphragm; and the passivation with an alkali vapor of the coating on the cell walls, in order to minimize the losses of trappable atoms. These results guided us in the construction of an efficient large-diameter cell, which has been successfully employed for on-line trapping of Fr isotopes at INFN’s national laboratories in Legnaro, Italy.

Light desorption from an yttrium neutralizer for Rb and Fr magneto-optical trap loading

We present here the first evidence of photodesorption induced by low-intensity non-resonant light from an yttrium thin foil, which works as a neutralizer for Rb and Fr ions beam. Neutral atoms are suddenly ejected from the metal surface in a pulsed regime upon illumination with a broadband flash light and then released in the free volume of a pyrex cells. Here atoms are captured by a Magneto-Optical Trap (MOT), which is effectively loaded by the photodesorption. Loading times of the order of the flash rise time are measured. Desorption is also obtained in the continuous regime, by exploiting CW visible illumination of the metallic neutralizer surface. We demonstrate that at lower CW light intensities vacuum conditions are not perturbed by the photodesorption and hence the MOT dynamics remains unaffected, while the trap population increases thanks to the incoming desorbed atoms flux. Even with the Y foil at room temperature and hence with no trapped atoms, upon visible illumination, the number of trapped atoms reaches 10(5). The experimental data are then analyzed by means of an analytical rate equation model, which allows the analysis of this phenomenon and its dynamics and allows the determination of critical experimental parameters and the test of the procedure in the framework of radioactive Francium trapping. In this view, together with an extensive investigation of the phenomenon with (85)Rb, the first demonstration of the photodesorption-aided loading of a (210)Fr MOT is shown.

Francium trapping at the INFN-LNL facility

A brief review of the Francium trapping experiments at the INFN-LNL facility is presented in the wide context of Atomic Parity-Nonconservation (APNC), which, as long as acquiring more precise and new spectroscopic data on the Francium isotopes, is the ultimate goal of the experiment. Due to its instability, Francium atoms must be produced continuously by a nuclear fusion–evaporation reaction into a heated Gold target hit by a beam of accelerated oxygen ions. Francium is then extracted in the ionic form and guided by an electrostatic line to the actual science chamber, where the ions are neutralized. Atoms are then cooled down and trapped in a Magneto-Optical Trap (MOT) to ensure both the availability of a sufficiently populated and stable atomic sample and to eliminate the Doppler broadening which would affect the precision of the measurements. A review of the recent improvements to the experimental apparatus and to the detection techniques that led to a sensitivity better than five atoms is presented. The final part of this paper deals with a summary of the recent results obtained by our collaboration and a short outlook for the immediate future.

Computing for the next generation flavour factories

The next generation of Super Flavor Factories, like SuperB and SuperKEKB, present significant computing challenges. Extrapolating the BaBar and Belle experience to the SuperB nominal luminosity of 1036 cm−2s−1, we estimate that the data size collected after a few years of operation is 200 PB and the amount of CPU required to process them of the order of 2000 KHep-Spec06. Already in the current phase of detector design, the amount of simulated events needed for estimating the impact on very rare benchmark channels is huge and has required the development of new simulation tools and the deployment of a worldwide production distributed system. With the collider is in operation, very large data set have to be managed and new technologies with potential large impact on the computational models, like the many core CPUs, need to be effectively exploited. In addition SuperB, like the LHC experiments, will have to make use of distributed computing resources accessible via the Grid infrastructures while providing an efficient and reliable data access model to its final users. To explore the key issues, a dedicated R&D program has been launched and is now in progress. A description of the R&D goals and the status of ongoing activities is presented.

First results from the SuperB simulation production system

The SuperB experiment needs large samples of Monte-Carlo simulated events in order to finalize the detector design and to estimate the data analysis performances. This work describes the system we developed to manage the production of the required simulated events in a fully distributed environment. The distributed infrastructure includes several sites in Europe and North America and is based on Grid services. The production of simulated events consists of: distribution of input data files to the remote site Storage Elements (SE), job submission to all available remote sites, output data transfer to the INFN-CNAF repository. The job workflow includes procedures for consistency checking, monitoring, data handling and bookkeeping metadata communication. A data bookkeeping system has been implemented in order to maintain the information associated to data files and keep track of the relations between executed jobs and their parameters and outputs. The distributed production system is operational since February 2010. Results from the first production cycles (Spring 2010 and Summer 2010) are reported.

Tracing Resource Usage over Heterogeneous Grid Platforms: A Prototype RUS Interface for DGAS

Tracing resource usage by Grid users is of utmost importance especially in the context of large-scale scientific collaborations such as within the High Energy Physics (HEP) community to guarantee fairness of resource sharing, but many difficulties can arise when tracing the resource usage of distributed applications over heterogeneous Grid platforms. These difficulties are often related to a lack of interoperability of the accounting components across middlewares. This paper brie y describes the architecture and workflow of the Distributed Grid Accounting System (DGAS) [1] and evaluates the possibility to extend it with a Resource Usage Service (RUS) [2, 3] interface according to the Open Grid Forum (OGF) sped cation that allows to store and retrieve OGF Usage Records (URs) [4, 5] via Web Services. In this context the OGF RUS and UR sped cations are critically analyzed. Furthermore, a prototype of a RUS interface for DGAS (DGAS-RUS) is presented and the most recent test results towards a full interoperability between heterogeneous Grid platforms are outlined.

Test of the photon detection system for the LHCb RICH Upgrade in a charged particle beam

The LHCb detector will be upgraded to make more efficient use of the available luminosity at the LHC in Run III and extend its potential for discovery. The Ring Imaging Cherenkov detectors are key components of the LHCb detector for particle identification. In this paper we describe the setup and the results of tests in a charged particle beam, carried out to assess prototypes of the upgraded opto-electronic chain from the Multi-Anode PMT photosensor to the readout and data acquisition system.

Francium sources at Laboratori Nazionali di Legnaro: Design and performance

A facility for the production of radioactive francium is operating at the laboratories of the Istituto Nazionale di Fisica Nucleare (INFN) in Legnaro, Italy. The goal is to collect a cold sample of radioactive atoms in a magneto-optical trap for studies in atomic, nuclear, and particle physics. Production of francium is achieved via the fusion-evaporation reaction Au197(O18,kn)215−kFr generated by a ∼100‐MeV O6+18 beam on a thick gold target. The production target is heated to ∼1200K and kept at a potential of +3kV to enhance Fr diffusion and surface desorption. Average production rates are 0.7×106ions∕s for Fr210 with a primary beam flux of 1012particles∕s, with peaks of 2×106ions∕s. Details are given on the design and construction of the production targets and on the measurements that characterize their performance.

The Legnaro francium magneto-optical trap

Laser cooling and trapping of radioactive atoms represent the new frontier in atomic physics and a new powerful tool in nuclear physics. We are setting up at the INFN-Legnaro National Laboratories a laser cooling facility that has as a first goal the realization of a 210Fr magneto-optical trap. The general outline of the experiment and the improvements of the final trap efficiency are discussed. Some preliminary results are presented.