1,895 research outputs found
First study of the two-body scattering involving charm hadrons
No full textThis article presents the first measurement of the interaction between charm hadrons and nucleons. The two-particle momentum correlations of pD− and pD¯ þ pairs are measured by the ALICE Collaboration in high-multiplicity pp collisions at ffiffi s p ¼ 13 TeV. The data are compatible with the Coulomb-only interaction hypothesis within ð1.1–1.5Þσ. The level of agreement slightly improves if an attractive nucleon ðNÞD strong interaction is considered, in contrast to most model predictions which suggest an overall ¯ repulsive interaction. This measurement allows for the first time an estimation of the 68% confidence level interval for the isospin I ¼ 0 inverse scattering length of the ND state ¯ f−1 0;I¼0 ∈ ½−0.4; 0.9 fm−1, assuming negligible interaction for the isospin I ¼ 1 channel.Full Tex
Conceptual design of an ALICE Tier-2 centre integrated into a multi-purpose computing facility
No full textThis thesis discusses the issues and challenges associated with the design and operation of a data analysis facility for a high-energy physics experiment at a multi-purpose computing centre. At the spotlight is a Tier-2 centre of the distributed computing model of the ALICE experiment at the Large Hadron Collider at CERN in Geneva, Switzerland. The design steps, examined in the thesis, include analysis and optimization of the I/O access patterns of the user workload, integration of the storage resources, and development of the techniques for effective system administration and operation of the facility in a shared computing environment. A number of I/O access performance issues on multiple levels of the I/O subsystem, introduced by utilization of hard disks for data storage, have been addressed by the means of exhaustive benchmarking and thorough analysis of the I/O of the user applications in the ALICE software framework. Defining the set of requirements to the storage system, describing the potential performance bottlenecks and single points of failure and examining possible ways to avoid them allows one to develop guidelines for selecting the way how to integrate the storage resources. The solution, how to preserve a specific software stack for the experiment in a shared environment, is presented along with its effects on the user workload performance. The proposal for a flexible model to deploy and operate the ALICE Tier-2 infrastructure and applications in a virtual environment through adoption of the cloud computing technology and the 'Infrastructure as Code' concept completes the thesis. Scientific software applications can be efficiently computed in a virtual environment, and there is an urgent need to adapt the infrastructure for effective usage of cloud resources
Efficient Time Frame Building for Online Data Reconstruction in ALICE Experiment
No full textAfter the Long Shutdown 2 period, the upgraded ALICE detector at the LHC will produce more than a terabyte of data per second. The data, constituted from a continuous un-triggered stream data, have to be distributed from about 250 First Level Processor nodes (FLPs) to about 1500 Event Processing Nodes (EPNs). Each FLP receives a small subset of the detector data that is chopped in sub-time frames. One EPN needs all the fragments from the 250 FLPs to build a full time frame. An algorithm has been implemented on the FLPs with the aim of optimizing the usage of the network connecting the FLPs and EPNs. The algorithm minimizes contention when several FLPs are sending to the same EPN. An adequate traffic shaping is implemented by delaying the sending time of each FLP by a unique offset. The payloads are stored in a buffer large enough to accommodate the delay provoked by the maximum number of FLPs. As the buffers are queued for sending, the FLPs can operate with the highest efficiency. Using the time information embedded in the data any further FLP synchronization can be avoided. Moreover, zero-copy and multipart messages of ZeroMQ are used to create full time frames on the EPNs without the overhead of copying the payloads. The concept and the performance measurement of the implementation on a reference computing cluster are presented
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