1. US ATLAS Physics & Computing
ATLAS Data Challenges
US ATLAS Physics & Computing
ANL
October 30th 2001
Gilbert Poulard
CERN EP-ATC

2. ATLAS Plenary-18 October 2001
Outline
ATLAS Data Challenges & “LHC Computing Grid Project”
Goals
Scenarios
Organization
ATLAS Plenary-18 October 2001

3. From CERN Computing Review
CERN Computing Review (December February 2001)
Recommendations:
organize the computing for the LHC era
LHC Grid project
Phase 1: Development & prototyping ( )
Phase 2: Installation of the 1st production system ( )
Software & Computing Committee (SC2)
Project accepted by the CERN council (20 September)
Ask the experiments to validate their Computing model by iterating on a set of Data Challenges of increasing complexity
However DC’s were in our plans
ATLAS Plenary-18 October 2001

4. LHC Computing GRID project Phase1:
Prototype construction
develop Grid middleware
acquire experience with high-speed wide-area network
develop model for distributed analysis
adapt LHC applications
deploy a prototype (CERN+Tier1+Tier2)
Software
complete the development of the 1st version of the physics application and enable them for the distributed grid model
develop & support common libraries, tools & frameworks
including simulation, analysis, data management, ...
in parallel LHC collaborations must develop and deploy the first version of their core software
ATLAS Plenary-18 October 2001

5. ATLAS Plenary-18 October 2001
ATLAS Data challenges
Goal
understand and validate:
our computing model, our data model and our software
our technology choices
How?
In iterating on a set of DCs of increasing complexity
Start with data which looks like real data
Run the filtering and reconstruction chain
Store the output data into our database
Run the analysis
Produce physics results
To study
Performances issues, database technologies, analysis scenarios, ...
To identify
weaknesses, bottle necks, etc… (but also good points)
ATLAS Plenary-18 October 2001

6. ATLAS Plenary-18 October 2001
ATLAS Data challenges
But:
Today we don’t have ‘real data’
Needs to produce ‘simulated data’ first
so:
Physics Event generation
Simulation
Pile-up
Detector response
Plus reconstruction and analysis
will be part of the first Data Challenges
we need also to “satisfy” the ATLAS communities
HLT, Physics groups, ...
ATLAS Plenary-18 October 2001

7. ATLAS Plenary-18 October 2001
ATLAS Data Challenges: DC0
DC0 November-December 2001
'continuity' test through the software chain
aim is primarily to check the state of readiness for DC1
We plan ~100k Z+jet events, or similar
To validate the software:
issues to be checked include
G3 simulation running with the ‘latest’ version of the geometry
reconstruction running
Re-analyze part of the Physics TDR data “reading from & writing to Objectivity”
Would test the “Objy database infrastructure”
Complementary to the “continuity test”
ATLAS Plenary-18 October 2001

8. ATLAS Plenary-18 October 2001
ATLAS Data Challenges: DC1
DC1 February-July 2002
reconstruction & analysis on a large scale
learn about data model; I/O performances; identify bottle necks …
use of GRID as and when possible and appropriate
data management
Use (evaluate) more than one database technology (Objectivity and ROOT I/O)
Learn about distributed analysis
should involve CERN & outside-CERN sites
site planning is going on, an incomplete list already includes sites from Canada, France, Italy, Japan, UK, US, Russia
scale 107 events in days, O(1000) PC’s
data needed by HLT & Physics groups (others?)
Study performance of Athena and algorithms for use in HLT
simulation & pile-up will play an important role
checking of Geant4 versus Geant3
ATLAS Plenary-18 October 2001

9. ATLAS Plenary-18 October 2001
ATLAS Data Challenges: DC1
DC1 will have two distinct phases
First, production of events for HLT TDR, where the primary concern is delivery of events to HLT community;
Second, testing of software (G4, dBases, detector description,etc.) with delivery of events for physics studies
Software will change between these two phases
Simulation & pile-up will be of great importance
strategy to be defined (I/O rate, number of “event” servers?)
As we want to do it ‘world-wide’ we will ‘port’ our software to the GRID environment and use as much as possible the GRID middleware (ATLAS kit to be prepared)
ATLAS Plenary-18 October 2001

10. ATLAS Plenary-18 October 2001
ATLAS Data Challenges: DC2
DC2 Spring-Autumn 2003
Scope will depend on what has and has not been achieved in DC0 & DC1
At this stage the goal includes:
Use of ‘TestBed’ which will be built in the context of the Phase 1 of the “LHC Computing Grid Project”
Scale at a sample of 108 events
System at a complexity ~50% of system
Extensive use of the GRID middleware
Geant4 should play a major role
Physics samples could(should) have ‘hidden’ new physics
Calibration and alignment procedures should be tested
May be to be synchronized with “Grid” developments
ATLAS Plenary-18 October 2001

11. ATLAS Plenary-18 October 2001
DC scenario
Production Chain:
Event generation
Detector Simulation
Pile-up
Detectors responses
Reconstruction
Analysis
These steps should be as independent as possible
ATLAS Plenary-18 October 2001

12. ATLAS Plenary-18 October 2001
Production stream
“OO-db” is used for “OO database”, it could be Objectivity, ROOT/IO, …
ATLAS Plenary-18 October 2001

13. ATLAS Plenary-18 October 2001
DC1
Ntuple
Pythia, Isajet,
Herwig,
MyGeneratorModule
HepMC
Obj., Root
ATLFAST OO
GENZ
G3/DICE
RD event ?
OO-DB ?
ATHENA
reconstruction
Comb. G4
Obj.
Missing:
-- filter, trigger Detector description
-- HepMC in Root Digitisation
-- ATLFAST output in Root (TObjects) -- Pile-up
-- Link MC truth - ATLFAST
-- Reconstruction output in Obj., Root
-- EDM (e.g. G3/DICE , G4 input to ATHENA)
Ntuple-
like
ZEBRA
ATLAS Plenary-18 October 2001

14. ATLAS Plenary-18 October 2001
Detector Simulation
Geant3 and Geant4
For HLT & physics studies we will use Geant3
Continuity with past studies
ATLAS validation of Geant4 is proceeding well but not completed
Detector simulation in Atlsim (Zebra output)
Some production with Geant4 too
Goals to be defined with G4 and Physics groups
It is important to get experience with ‘large production’ as part of G4 validation
it is important to use the same geometry input
In the early stage we could decide to use only part of the detector
it would also be good to use the same sample of generated events
Detector simulation we propose to use the FADS/Goofy framework
Output will be ‘Hits collections’ in OO-db
Detector responses (& pileup) has to be worked on in new framework
ATLAS Plenary-18 October 2001

15. ATLAS Plenary-18 October 2001
Reconstruction
Reconstruction
we want to use the ‘new reconstruction’ code being run in Athena framework
Input should be from OO-db
Output in OO-db:
ESD (event summary data)
AOD (analysis object data)
TAG (event tag)
ATLAS Plenary-18 October 2001

16. ATLAS Plenary-18 October 2001
Analysis
We are just starting to work on this but
Analysis tools evaluation should be part of the DC
It will be a good test of the Event Data Model
Performance issues should be evaluated
Analysis scenario
It is important to know the number of analysis groups, the number of physicists per group, the number of people who want to access the data at the same time
It is of ‘first’ importance to ‘design’ the analysis environment
to measure the response time
to identify the bottle necks
for that users’ input is needed
ATLAS Plenary-18 October 2001

17. ATLAS Plenary-18 October 2001
Data management
It is a key issue
Evaluation of more than one technology is part of DC1
Infrastructure has to be put in place:
For Objectivity & ROOT I/O
Software, hardware, tools to manage the data
creation, replication, distribution
discussed in database workshop
Tools are needed to run the production
“bookkeeping” , “cataloguing” …
Run number, random number allocation, …
Working group now set-up
Job submission
Close collaboration with ATLAS Grid (validation of Release 1)
ATLAS Plenary-18 October 2001

18. ATLAS Plenary-18 October 2001
DC1-HLT - CPU
Number of events
Time per event sec SI95
Total time
Sec
SI95
Hours
simulation
107
3000
3 * 1010
reconstruction
640
6.4 * 109
2 * 106
ATLAS Plenary-18 October 2001

19. ATLAS Plenary-18 October 2001
DC1-HLT - data
Number of events
Event size MB
Total size GB TB
simulation
107 2
20000 20
reconstruction
0.5
5000 5
ATLAS Plenary-18 October 2001

20. DC1-HLT data with pile-up
Number of events
Event size MB
Total size GB
Total size TB
2 x 1033
1.5 x 106
(1) 2.6
(2) 4.7
4000
7000 4 7
1034
(1) 6.5
(2) 17.5
10000
26000 10 26
In addition to ‘simulated’ data, assuming ‘filtering’ after simulation (~14% of the events kept).
(1) keeping only ‘digits’
(2) keeping ‘digits’ and ‘hits’
ATLAS Plenary-18 October 2001

21. ATLAS Plenary-18 October 2001
Ramp-up CERN
Week in 2002
ATLAS Plenary-18 October 2001

22. ATLAS Plenary-18 October 2001
What next
This week:
Have an updated list of goals & requirements prepared with
HLT, Physics communities
simulation, reconstruction, database communities
people working on ‘infrastructure’ activities
bookkeeping, cataloguing, ...
Have a list of tasks
Some Physics oriented
But also like testing code, running production, …
with ‘established’ responsibilities and priorities
And working groups in place
You can join
ATLAS Plenary-18 October 2001

23. ATLAS Plenary-18 October 2001
What next
In parallel
Define ATLAS validation plan for
EU-DataGrid Release 1
ATLAS software for DC0 and DC1
Understand the involvement of Tier centers
Insure that we have the necessary resources
@ CERN and outside CERN
We have already some input and a ‘table’ is being prepared
“And turn the key”
ATLAS Plenary-18 October 2001