Fermilab Experiments. Daniel Wicke (Bergische Universität Wuppertal) Outline. (Accelerator, Experiments and Physics) Computing Concepts

Transcription

1 Fermilab Experiments CDF Daniel Wicke (Bergische Universität Wuppertal) Outline Motivation (Accelerator, Experiments and Physics) Computing Concepts (SAM, RACs, Prototype and GRID) Summary 30. Oct

2 The p p Accelerator Tevatron Circumfence 7 km. Run I ( ) Run II (since 2001) p p collisions 2 experiments, CDF and DØ, record events. Daniel Wicke, Fermilab Experiments, The p p Accelerator Tevatron 30. Oct

3 The Tevatron Daniel Wicke, Fermilab Experiments, The p p Accelerator Tevatron 30. Oct

4 CDF Collider Detector at Fermilab International coll. of 53 institutes, 550 physicists; From Germany: Karlsruhe Daniel Wicke, Fermilab Experiments, CDF 30. Oct

5 DØ International collaboration 76 institutes, 550 physicists From Germany: Aachen, Bonn, Mainz, München, Wuppertal. Dimensions: m 3 Daniel Wicke, Fermilab Experiments, DØ 30. Oct

6 Physics The Top Quark Discovered by CDF and DØ in The heaviest of all fermions. Strong interaction with Higgs. Decay before it hadronises. Decays to bw (nearly) 100%. Signature: 2b-jets + at least 4 jets 2b-jets + missing E t + lepton(s) Daniel Wicke, Fermilab Experiments, Physics 30. Oct

7 A real (CDF) event e + 4 jet event 40758_ September, 1992 MET fit neutrino jet #4 e + jet #3 jet #1 jet # TWO jets tagged by SVX fit top mass is GeV e +, Missing E t, jet #4 from top jets 1,2,3 from top ( 2&3 from W ) jet #2 LEGO view 5 centimeters Tevatron beam pipe jet #3 jet #1 SVX tags jet #4 Two Vertex Views ( note scales ) e + 3 meters Tracking View Primary Vertex Secondary Vertex Ellipses 5 mm Daniel Wicke, Fermilab Experiments, Physics 30. Oct

8 Run IIa The Higgs Boson The strangest particle in the Standard Model. Remainder of elektroweak symmetry breaking. Responsible for masses of elemetary particles. Not yet observed. CDF & DØ combined senistivity to the Higgs: Run IIb Signature: 2b-jets 2W Bosons Daniel Wicke, Fermilab Experiments, Physics 30. Oct

9 Background: QCD Production of light quarks (udscb) results in 2 or more jets. Gluon radiation may add more jets. These event can t be fully suppressed in realtime. σ p p tot 70mb σ p p t t 6.6pb σ p p H 0.7pb (for M H = 116 GeV) σ p p t t σ p p tot 10 9 Daniel Wicke, Fermilab Experiments, Physics 30. Oct

10 Computing Concepts Demands Top and Higgs are difficult to recognise in realtime. To find sufficiently many top- and Higgs-events a large number of reactions must be recorded. CDF and DØ record 500GB/day each. Another 1100GB/day come from processing the raw data. This sums up to 200m of CDs per year. Providing facilities to analyse these data is a big challenge. Daniel Wicke, Fermilab Experiments, Computing Concepts 30. Oct

11 Optimised use of local resources Problem It is impossible to store all data on disks: Tape access is the major bottleneck. Base of improvements The order of events in the dataset has no meaning. Optimisation Don t loop through file lists. Request datasets. The order in which files corresponding to a dataset are processed may change. The system optimises the order to minimise tape access and tape mounts. Sequential Access through Metadata: SAM Daniel Wicke, Fermilab Experiments, Computing Concepts 30. Oct

12 Worldwide Distribution of Data Problem For the most frequently used data the I/O rate to disks limits performance. Base of improvements Setup copies of these most frequently used data. Regional Analysis Centers (RACs) Hold all Thumbnails. Provide computing power to process these allows full physics analysis. Hold 10% of full DST. allows distributed reprocessing. Serves as intermediate cache for institutions. Daniel Wicke, Fermilab Experiments, Computing Concepts 30. Oct

13 Worldwide Distribution of Data (II) Several centers are already in use for Monte Carlo production. GridKa will be the first regional analysis center. DØ is setting up a Prototyp at GridKA. Daniel Wicke, Fermilab Experiments, Computing Concepts 30. Oct

14 RAC Prototype Specifications The prototype should implement the following major features of a full RAC: Continuously and immediate transport of thumbnails from Fermilab to GridKa disks. Fetching files available at the prototype from associated institutes. Automatic installation of DØ-software updates. Goals Proof of principle for RAC concept. Provide a working analysis environment for DØ-Germany. Check needed resources and its scalability (mostly network). Daniel Wicke, Fermilab Experiments, Computing Concepts, Prototype 30. Oct

15 Status of Prototype at GridKa 1. Continuously and immediate transport of thumbnails Up and running since end of August: a cronjob every 2h. 400GB thumbnails transported without problems (total of 1TB in cache). To determine detailed parameters (e.g. retry rate, failure rate, etc.) we need tools/scripts to analyse log-files from the expert. Crosscheck of histogramms in work. Daniel Wicke, Fermilab Experiments, Computing Concepts, Prototype 30. Oct

16 Results: Transfer Speed Integrated size of arriving files as function of time: Transport from FNAL to GridKa "speedtest1b.out" usi 1:7 2 3MB/s = 15 25Mbit/s (averaged over 7 hours). larger gaps in the transport decreased effective speed MB/s thereafter day in Sep A direct disk to disk bbftp yields upto 30MB/s=125Mbit/s. Daniel Wicke, Fermilab Experiments, Computing Concepts, Prototype 30. Oct

17 The GRID Problem Network, CPU and Diskspace availability will be constantly changing. Communication lines need to be configured explicitly. Base of improvements Dynamic adaption to actual situation. Optimised use of globally distributed resources: The GRID Retrieve data from remote disks with best availability. Submit jobs to centres for which they re best suited. Base these decisions on current status of the systems. Requires Common protocols for data and status information exchange. The GRID Daniel Wicke, Fermilab Experiments, Computing Concepts, GRID 30. Oct

18 SAM Grid Common CDF-DØ effort to finalise this for Run IIb (2005). Daniel Wicke, Fermilab Experiments, Computing Concepts, GRID 30. Oct

19 Summary Tevatron experiments need to handle huge amounts of data (now). The load of data poses a big challenge on the computing structure. optimised use of local resources (SAM) global distribution of data (RACs) optimised use of global resources (GRID) CDF and DØ aim to a fully GRID enabled environment at latest in (among) the first running experiments to exploit the GRID. Daniel Wicke, Fermilab Experiments, Summary 30. Oct