Experiences on Grid production for Geant4 EGEE User Forum, CERN, 1st March 2006 P. Mendez Lorenzo, A. Ribon CERN CERN

Alberto Ribon, CERN/PH/SFT 2  Geant4  Motivation and strategy  Description of the suite  Results for the Geant4 release 8.0 (Dec 2005)  Grid experiences  Outlook Outline

Alberto Ribon, CERN/PH/SFT 3  Geant4 is a general purpose toolkit for simulating the tracking and interaction of particles through matter.  It is currently used in production in several particle physics experiments (BaBar, HARP, ATLAS, CMS, LHCb), and it has also applications in other areas, as space science, medical applications, and radiation studies.  About 500,000 C++ lines of code.  Careful testing of all of Geant4 components is needed before major releases (twice a year: June and December). Geant4

Alberto Ribon, CERN/PH/SFT 4 Our goal is to detect any difference between two Geant4 versions, by comparing a large number of physics observables. Only those distributions which are statistically different (i.e. unlikely to be originated from the same parent distribution, whatever it is) should be visually examined by someone, to understand the origin of such difference, either a bug or an improvement. As a start, we consider only calorimeter observables sensitive to hadronic physics. Motivation and strategy

Alberto Ribon, CERN/PH/SFT 5  It is very important that the regression testing is automatic, because only in this way it is possible, in practice, to consider a very large number of distributions, and use it regularly, at least before each new release.  To do that we need a statistical package that offers several statistical tests (not only Chi2 and Kolmogorov-Smirnov!), to increase the chances to spot any kind of discrepancy between two distributions. Some remarks

Alberto Ribon, CERN/PH/SFT 6  It reproduces, in a simplified way, all the LHC calorimeters: Fe-Sci, Cu-Sci, Cu-LAr, W-LAr Pb-Sci, Pb-LAr, PbWO4.  Beam particle type:  ±, K ±, K L 0, p, n, e -.  Beam energy: 1, 2, 3, …, 10, 20, 30, 40, 50, 60, 80, 100, 120, 150, 180, 200, 250, 300 (1000) GeV.  The calorimeter is a box. The user can choose: - the total thickness of the absorber (in [mm] or ) - the thickness of the active layer - the number of layers - the number and the size (in [mm] or ) of the rings for the lateral shower profile. Simplified Calorimeter setup

Alberto Ribon, CERN/PH/SFT 7

8  Observables: - total energy deposit in all active layers - total energy deposit in the whole calorimeter - energy deposit in each active layer (longitudinal shower profile) - energy deposit in each ring (i.e. radial bin) (lateral shower profile).  The program produces in output a HBOOK n-tuple, which stores all the above distributions. Then another program reads two of these n-tuples, makes the statistical tests of the distributions, and produces a.PS file whenever the p-value of a test is below a certain threshold (currently 1% ).

Alberto Ribon, CERN/PH/SFT 9  7 calorimeters x 8 particles x 24 beam energies x 5000 events x 5 Geant4 physics configurations.  About ≥ 0.07 sec/GeV GHz CPU) to simulate a hadronic shower.  Use some biasing techniques (keep 1 e - /e + /  /n every 2 or 4 with weight 2 or 4), and kill neutrons below 1 MeV, to speed up the execution.  Overall, it takes few years of CPU time, but concentrated in 1-2 weeks: need of the GRID ! CPU issue

Alberto Ribon, CERN/PH/SFT 10  G4 8.0 candidate versus G4 7.1.p01.  10 lambdas, 20 layers, 4 mm active layers, 10 rings of increasing size, starting from 0.1 lambdas; biasing for beam energies  10 GeV.  SLC 3.0.x g Run on the GRID as Geant4 Virtual Organization. ~ 120 CPUs in 7 sites in 6 countries.  ~1300 jobs per each Geant4 physics configuration. Each job that ends normally produced a tar-ball of about 3 MB size containing the results. Geant4 release 8.0 (December 2005)

Alberto Ribon, CERN/PH/SFT 11  5 GRID installations; ~ 12,000 jobs submitted to the GRID; ~ 50,000 PostScript files produced (about 10% of observables that have been checked)  ~ 99% GRID success rate (this is a significant improvements w.r.t. previous GRID deployments, thanks to a careful selections of the sites where to run).  5 Geant4 physics configurations; 3 bugs found; 1 critical issue identified (elastic scattering). Results

Alberto Ribon, CERN/PH/SFT 12 Log scale G4 8.0 cand G4 7.1.p01 Visible energy in the first ring P-value = 0.9%

Alberto Ribon, CERN/PH/SFT 13 Log scale G4 8.0 cand G4 7.1.p01 Total visible energy P-value =

Alberto Ribon, CERN/PH/SFT 14  First production: December 2004 release, as DTEAM VO; used ad-hoc scripts.  Second production: June 2005 release, as ALICE VO; used a more general framework.  Third production: December 2005 release, as GEANT4 VO (Virtual Organization). Used again successfully Patricia’s general framework, but some tests were made with the DIANE/GANGA framework. Grid experiences

Alberto Ribon, CERN/PH/SFT 15  As post-processing, using only the log files produced during the simulation, some summary.PS plots can be produced: - longitudinal shower profiles - transverse shower profiles - sampling fractions vs. beam energy - energy resolutions vs. beam energy - e/  ratios vs. beam energy  Some unphysical “jumps” are observed at 10 GeV, because biasing is not applied below such a value. Summary plots

Alberto Ribon, CERN/PH/SFT 16 QGSC Fe-Sci π + (GeV) G4 7.1.p01 G4 8.0 cand

Alberto Ribon, CERN/PH/SFT 17 QGSC Fe-Sci π + (GeV) G4 7.1.p01 G4 8.0 cand

Alberto Ribon, CERN/PH/SFT 18 It is interesting and useful to study the effects of physics changes (e.g. in multiple scattering, hadronic elastic scattering, total cross-sections, and in any other physics model), with a simplified calorimeter setup, with pure MC information, without real life complications (e.g. beam composition/profile, noise, cross-talk, clustering, reconstruction). Another use of this tool

Alberto Ribon, CERN/PH/SFT 19 Studies in simplified calorimeter setups (I) “CMS HCAL”  GeV Cu-Sci layers (6 cm Cu) 4 mm Sci 5000 events G4 7.1p01 QGSP LHEP Log scale

Alberto Ribon, CERN/PH/SFT 20 Studies in simplified calorimeter setups (II) “CMS HCAL”  GeV Cu-Sci layers (6 cm Cu) 4 mm Sci 5000 events G4 7.1p01 QGSP LHEP Log scale

Alberto Ribon, CERN/PH/SFT 21 Summary We have a tool which is useful for three purposes:  robustness testing;  regression testing;  detection of physics effects on calorimeter observables. We are using it since one year, and we are planning to deploy it even more extensively in the future.

Alberto Ribon, CERN/PH/SFT 22 Outlook (I) We aim to improve and extend this tool in the following directions :  Include more statistical tests, and study their statistical power.  Find complementary (in particular, more global and faster) ways to spot differences.  Monitor CPU time, number of steps and tracks, and other observables.  Extend to electromagnetic shower shapes, and integrate all the efforts for testing Geant4.

Alberto Ribon, CERN/PH/SFT 23 Outlook (II) As far as the Grid is concerned:  Move to the DIANE/GANGA framework.  We have asked for Geant4 dedicated queues (priority mechanism for G4 jobs sent on the Grid).  We have asked for input sandboxes up to ~30 MB (for the jobs to be submitted on the Grid, to include the candidate G4 version).  Part of this acceptance suite could be used to validate the Grid sites: non-trivial code, used by LHC experiments, but much simpler than their typical applications!

Alberto Ribon, CERN/PH/SFT 24 Acknoledgements On behalf of the Geant4 Collaboration, I would like to thank warmly Patricia, for her prompt, continuous, and excellent support! Many thanks also to the Grid community (LCG and EGEE) for enabling us to use the Grid, which is an essential ingredient of our acceptance suite. Last but not least, thanks to all the Grid sites around the world for providing the computing resources behind Geant4 VO.