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The LHCb experiment @ CERN

The LHCb experiment @ CERN. R. Graciani (U. de Barcelona, Spain) for the LHCb Collaboration International ICFA Workshop on Digital Divide Mexico City, October 2007. Overview. Introduction The LHCb experiment The LHCb Computing Model Making Physics @ LHCb Summary. Introduction. CERN.

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The LHCb experiment @ CERN

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  1. The LHCb experiment @ CERN R. Graciani (U. de Barcelona, Spain) for the LHCb Collaboration International ICFA Workshop on Digital Divide Mexico City, October 2007

  2. Overview • Introduction • The LHCb experiment • The LHCb Computing Model • Making Physics @ LHCb • Summary The LHCb experiment @ CERN

  3. Introduction

  4. CERN CERN is a laboratory where scientists unite to study the building blocks of matter and the forces that hold them together. The Large Hadron Collider LHC = 27 km The LHCb experiment @ CERN

  5. The structure of Matter QUARKS & LEPTONS PARTICLES: + FORCES: The Standard Model = The LHCb experiment @ CERN

  6. The Large Hadron Collider Geneva protons protons 14 TeV = 14·1012 eV The LHCb experiment @ CERN

  7. MATTER: The LHCb experiment ANTI-MATTER:

  8. Where is anti-matter? • In principle: • particles and anti-particles are produced in pairs and, • they annihilate in pairs. E = mc2 • But, our world is made out of matter. • So, where is the anti-matter? • There must be some difference to explain its absence. • One of the ingredients is CP asymmetry. The LHCb experiment @ CERN

  9. B physics @ LHCb • The aim of the experiment, is to study with very good precision: • CP asymmetry in B systems, and • rare B decays. • The Standard Model predicts differences between matter and anti-matter for B-mesons. • BaBar (@ PEP-II) and Belle (@ KEKB) experiments have recorded 500·106 bb pairs each. • But @ LHC: • there is a much larger bb cross section: • 500 μb  1012 bb pairs / year • All B-hadrons are produced: • B+(40%), B0(40%), Bs(10%), b(10%) The LHCb experiment @ CERN

  10. The LHCb Apparatus (I)  B B 679 Physicists 49 Institutions 15 Countries The LHCb experiment @ CERN

  11. The LHCb Apparatus (II) Average RAW event size: Trigger 1.0 kB Velo 5.5 kB RICH 4.3 kB Trackers 14.8 kB Muon 1.3 kB Calo 9.7 kB Total 36.5 kB The LHCb experiment @ CERN

  12. The LHCb Apparatus (III) The LHCb experiment @ CERN

  13. Taking Data Online reconstruction and selection pp collisions occur every 25 ns 35 GB/s 0.2 kHz 1 MHz 1.8 kHz 700 TB/y 40 MHz 2·1010 Evt./y LHCb selects interesting signals The result is 20 billion events with ~2 billion are full bb pairs. The LHCb experiment @ CERN

  14. Studying B decays • Final states must be fully reconstructed: • “Simple” 2 body decays: • “Easy” to find leptonic decays: • Or “complicated” multi-hadron decays: • Different physics studies require different B decays to be reconstructed. • From the first level of the trigger events are classified in different streams (up ~30). The LHCb experiment @ CERN

  15. The LHCb Computing Model

  16. Processing Data nTuple 10kB/evt DST 75kB/evt RAW 35kB/evt rDST 20kB/evt Reconstruction @ CERN + 6 Tier1’s Stripping Analysis The LHCb experiment @ CERN

  17. Simulating Data DST 250kB/evt Produced at Tier2’s, stored @ CERN + 6 Tier1’s Simulating 1 event ~ Reconstructing 100 events The LHCb experiment @ CERN

  18. Computing Resources • Reconstruction & Stripping: • @ CERN + 6 Tier1’s (CNAF, GRIDKA, IN2P3, NIKHEF-SARA, PIC, RAL). • Several iterations per year, require: • ~ 5.3 M SpecInt2000 • Monte Carlo Simulation: • @ Tier2’s • 4 billion evt./year, require: • 11.4 M SpecInt2000 • Storage: • ~ 4.0 PB of Tape • ~ 3.2 PB of Disk The LHCb experiment @ CERN

  19. Making Physics @ LHCb

  20. Analysis @ LHCb • Require full reconstruction of B hadrons from their decay products. • Many tens of channels are interesting. • Expect > 106 events for some channels • Expect < 100 events for other channels • There are many other channels. • Backgrounds, contaminations, … • Use different data samples for different parts of their analysis. The LHCb experiment @ CERN

  21. Typical analysis • Use a signal channel: O(105 evt). • Produce several selections or ntuples to study their properties. • Use few control channels: O(105 evt). • Produce several selections or ntuples to study backgrounds, systematics, contaminations,… • Use some inclusive sample: O(106 evt). • Produce several selections or ntuples to study efficiency, resolutions,… • Use Simulated data: O(105 evt). • To cross check models, hypothesis,… • Estimate: 107 evt. x 10 kB / evt. = 100 GB • Produced at Tier1’s and transfer to Local resources for further reduction/processing/analysis. • For larger statistics up to 1 TB are expected. The LHCb experiment @ CERN

  22. Typical analysis nTuple nTuple nTuple nTuple DST DST DST DST Analysis Analysis Analysis Analysis @ Tier3 Signal Control Inclusive Now the physicist iterates over these data to prepare his publications. Monte Carlo @ Tier1’s The LHCb experiment @ CERN

  23. Response for Analysis • Assume all data can be re-analyzed @Tier1’s in O(1 day). • Reasonable since all data will be on disk. • How long does the physicist need to get back the result? • 100 Mbs link @ 50 % • 100 GB / 50 Mbs = 4.5 hours • 1 TB / 50 Mbs = 45 hours The LHCb experiment @ CERN

  24. Summary

  25. Summary • Processing LHCb data will need large amounts of CPU, Storage and Networking. • LHCb has decided for a Computing Model where most of the network traffic is between Tier1’s (including CERN). • Tier2 contributions to simulation are not limited by bandwith (in total few MB/s). • Our Brazilian colleges are actively participating in the preparations for the analysis of LHCb data and are expected to contribute as successfully in the future. • Response time for analysis may be slow if “good” connectivity is not guaranteed. • LHC will start in 2008 and we hope to be at full speed by 2009. • LHCb will measure CP violation and improve our understanding of the difference between matter and anti-matter. The LHCb experiment @ CERN

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