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

ICFA Workshop Mexico 2007 The LHCb CERN 2 Overview Introduction The LHCb experiment The LHCb Computing Model Making LHCb Summary

Introduction

ICFA Workshop Mexico 2007 The LHCb CERN 4 The Large Hadron Collider LHC = 27 km CERN is a laboratory where scientists unite to study the building blocks of matter and the forces that hold them together. CERN

ICFA Workshop Mexico 2007 The LHCb CERN 5 The structure of Matter PARTICLES: LEPTONS&QUARKS FORCES: The Standard Model = +

ICFA Workshop Mexico 2007 The LHCb CERN 6 The Large Hadron Collider Geneva protons 14 TeV = 14·10 12 eV

The LHCb experiment MATTER: ANTI-MATTER:

ICFA Workshop Mexico 2007 The LHCb CERN 8 Where is anti-matter? In principle: –particles and anti-particles are produced in pairs and, –they annihilate in pairs. E = mc 2 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.

ICFA Workshop Mexico 2007 The LHCb CERN 9 B 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 500·10 6 bb pairs each. LHC: –there is a much larger bb cross section: 500 μb  bb pairs / year –All B-hadrons are produced: B + (40%), B 0 (40%), B s (10%),  b (10%)

ICFA Workshop Mexico 2007 The LHCb CERN Physicists 49 Institutions 15 Countries The LHCb Apparatus (I) B  B

ICFA Workshop Mexico 2007 The LHCb CERN 11 The LHCb Apparatus (II) Average RAW event size: Trigger 1.0 kB Velo 5.5 kB RICH 4.3 kB Trackers14.8 kB Muon 1.3 kB Calo 9.7 kB Total36.5 kB

ICFA Workshop Mexico 2007 The LHCb CERN 12 The LHCb Apparatus (III)

ICFA Workshop Mexico 2007 The LHCb CERN 13 Taking Data 40 MHz 0.2 kHz 35 GB/s 1.8 kHz 700 TB/y 2·10 10 Evt./y pp collisions occur every 25 ns LHCb selects interesting signals Online reconstruction and selection The result is 20 billion events with ~2 billion are full bb pairs. 1 MHz

ICFA Workshop Mexico 2007 The LHCb 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 Computing Model

ICFA Workshop Mexico 2007 The LHCb CERN 16 Processing Data DST 75kB/evt RAW 35kB/evt Stripping rDST 20kB/evt Analysis Reconstruction nTuple CERN + 6 Tier1’s

ICFA Workshop Mexico 2007 The LHCb CERN 17 Simulating Data DST 250kB/evt Produced at Tier2’s, CERN + 6 Tier1’s Simulating 1 event ~ Reconstructing 100 events

ICFA Workshop Mexico 2007 The LHCb 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

Making LHCb

ICFA Workshop Mexico 2007 The LHCb CERN 20 LHCb Require full reconstruction of B hadrons from their decay products. Many tens of channels are interesting. –Expect > 10 6 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.

ICFA Workshop Mexico 2007 The LHCb CERN 21 Typical analysis Use a signal channel: O(10 5 evt). –Produce several selections or ntuples to study their properties. Use few control channels: O(10 5 evt). –Produce several selections or ntuples to study backgrounds, systematics, contaminations,… Use some inclusive sample: O(10 6 evt). –Produce several selections or ntuples to study efficiency, resolutions,… Use Simulated data: O(10 5 evt). –To cross check models, hypothesis,… Estimate: 10 7 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.

ICFA Workshop Mexico 2007 The LHCb CERN 22 Typical analysis DST Analysis nTuple DST Analysis nTuple DST Analysis nTuple DST Analysis nTuple Signal Monte Carlo Control Inclusive Now the physicist iterates over these data to prepare his Tier3

ICFA Workshop Mexico 2007 The LHCb CERN 23 Response for Analysis Assume all data can be 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 50 % 100 GB / 50 Mbs = 4.5 hours 1 TB / 50 Mbs = 45 hours

Summary

ICFA Workshop Mexico 2007 The LHCb CERN 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 LHCb will measure CP violation and improve our understanding of the difference between matter and anti-matter.