FLUKA as a new high energy cosmic ray generator

1. FLUKA as a new high energy cosmic ray generator G. Battistoni2, A. Margiotta1, S. Muraro2, M. Sioli1University and INFN of 1) Bologna and 2) Milano for the FLUKA CollaborationVery Large Volume n Telescope Workshop 2009, Athens

2. Outline Main features of FLUKA Motivations Code structure Geometry setup First results Conclusions A. Margiotta, Athens 2009

3. FLUKA - Interaction and Transport Monte Carlo code FLUKA authors:A. Fasso1, A. Ferrari2, J. Ranft3, P.R. Sala4 1 SLAC Stanford, 2 CERN, 3 Siegen University, 4 INFN Milan http://www.fluka.org • FLUKA is a general purpose tool for calculations of particle transport and interactions with matter, covering an extended range of applications (Shielding, Radiobiology, High energy physics, Cosmic Ray physics, Nuclear and reactor physics). • Built and maintainedwith the aimofincluding the best possiblephysicalmodels in termsofcompleteness and precision. • Continuously benchmarked with a wide set of experimental data from well controlled accelerator experiments. • More than 2000 users all over the world • Physics models (e.g. hadronic interaction models) built according to a theoretical microscopic point of view (no parameterizations) => High predictivity also in regions where experimental data are not available • Cosmic Ray physics with FLUKA “triggered” by: • HEP physics (e.g. atmospheric neutrino flux calculations) • radioprotection in space A. Margiotta, Athens 2009

5. Motivations • extension of the existing FLUKA cosmic-ray library to high energy region (primaries at the knee of the spectrum)  use in underground and underwater sites • use of a unique framework with high quality physics models (FLUKA) for the whole simulation, from primary interaction in the upper atmosphere to the detector level (and through the detector itself, in principle) • creation of a prediction data set (muons and muon-related secondaries) for some topic sites: presently LNGS, ANTARES and Capo Passero sites A. Margiotta, Athens 2009 5

6. Code structure • Geometry description • Generation of the kinematics (i.e. the source particles) ↔ primary cosmic ray composition model • 2 hadronic interaction models can be used: • DPMJET-II.53 • FLUKA • Output file on an event by event basis – interface between standard and user output (presently ASCII “ANTARES-like” and root output) • information on primary cosmic ray generating the shower • for each particle reaching the detector level, stores all the relevant parameters (particle ID, 3-momenta, vertex coordinates, momentum in atmosphere, information on the parent mesons etc) N.B. With FLUKA, shower generation, transport in the sea/rock, and particle folding in the detector is performed inside the same framework A. Margiotta, Athens 2009

7. Geometry setup (e.g. LNGS site) • 100 atmospheric shells • 1 spherical body for the mountain, whose radius is dynamically changed, according to primary direction and to the Gran Sasso mountain map (direction  rock depth) • 1 rock box surrounding the experimental underground halls, where muon-induced secondary are activated (e.m. and hadron showers from photo-nuclear interactions) • Underground halls: one box + one semi-cylinder • Possibility to include simultaneously more than one experimental Hall to study large transverse momentum secondaries with detector coincidences) A. Margiotta, Athens 2009

8. Geometry for underground sites z Spherical mountain whose radius is dynamically changed using a detailed topographical map Primary injection point d Atmosphere R0 R Earth A. Margiotta, Athens 2009

9. Geometry setup: LNGS halls External (rock) volume to propagate all particles down to 100 MeV m muon-produced secondaries LNGS underground halls A. Margiotta, Athens 2009

10. Some results from the simulation • Vertexes of particles entering the Hall C at LNGS • For a given site (e.g. Hall C at LNGS), possibility to parameterize all particle components reaching the underground level photons events/year electrons muons log10 Ekin (GeV) A. Margiotta, Athens 2009

11. Geometry setup (underwater) • Underwater case (e.g. ANTARES/KM3NeT) • Earth ≡ sphere of perfectly absorbing medium • sea ≡ spherical shell of water • atmosphere ≡ 100 concentricatmospheric shells • Can ≡ virtual cylindrical surface bounding the active volume (instrumented volume + 2-3 labs ) A. Margiotta, Athens 2009

12. Geometry for underwater sites Atmosphere m Sea Can Earth M. Sioli, Blois 2008

13. Primary sampling • Primary energy spectrum has the form: • Possibility to choose among different spectra (now MACRO-fit is implemented) • Sampling done re-adapting some HEMAS routines g~2.7÷3 Ecut~3000 TeV Ecut E A. Margiotta, Athens 2009

14. Technical issues (biasing)–underwater case • initialize minimum energy for primary cosmic rays: • lower bound evaluated according to muon survival probabilities  2* Ethrm • recompute “on the fly” energy thresholds: • muon survival probabilities for various depths in sea water and various muon energies at surface, evaluated with MUSIC (V. Kudryatsev) • muon energy at sea level  survival probability < 10-5 • function obtained with a fit  multiplied by 0.9 • underground case : thresholds are evaluated according to the rock map • kill in atmosphere all particles with energy lower than this threshold. • only muons with E> 20/100 GeV at the can are stored. • CPU time request optimized : FULL MC !!! A. Margiotta, Athens 2009 14

15. Some results from the simulation -1 Sea bottom = 3500 m Can radius = 1000 m height = 1000 m primaries sampled on a circle with R= 2000 m perpendicular to their direction and centered in the origin of the can muons propagated from the sea level to their geometrical intercept with the detector surface Vertexes of particles entering a KM3 detector can at 3500 m under sea level A. Margiotta, Athens 2009

16. Some results from the simulation -2 multiplicity @ can muon decoherence multiplicity meters primary energy Log (energy/TeV) A. Margiotta, Athens 2009

17. Conclusions • FLUKA can be used as a new high energy cosmic ray generator for underground and underwater physics. • Package developed using LNGS and neutrino telescope sites as examples. • It cannot substitute MUPAGE for fast simulation of atmospheric muon background. • Unique framework  significant simplification of the FULL MC chain • Next steps: • Introduce other primary cosmic ray composition models • Extensive studies with FLUKA hadronic model in progress: very encouraging results! • Some space for code optimization. • Sea level sampling • Further information: send me an e-mail. A. Margiotta, Athens 2009

19. spare slides

20. Primary C.R. proton/nucleus:A,E,isotropic The physics of CR TeVmuons hadronic interaction: multiparticle productions(A,E), dN/dx(A,E)  extensive air shower Primary p, He, ..., Fe nuclei with lab. energy from 1 TeV/nucleon up to >10000 TeV/nucleon K (ordinary) meson decay:dNm/d cosq ~ 1/ cosq p m transverse size of bundle  Pt(A,E) m short-lifetime meson production and prompt decay (e.g. charmed mesons) Isotropic ang. distr. m (TeV) muon propagation in water : radiative processes and fluctuations Multi-TeV muon transport detection:Nm(A,E), dNm/dr A. Margiotta, Athens 2009 20

21. The FLUKA hadronic interaction models(for a detailed study of their validity for CR studies :hep-ph/0612075 and 0711.2044) Relevant for HE C.R. physics > 5 GeV Elab DPM:soft physics based on (multi)Pomeron exchange DPMJET:soft physics of DPM plus 2+2 processes from pQCD

22. Phys. Rev. D 76, 052003 (2007) MINOS Charge Ratio at the Surface = 1.374 ± 0.004(stat.)(sys.) • Agreement between FLUKA simulation and MINOS data within 3% • Discrepancy systematically remarkable • No dependence on muon momentum in the atmosphere in the range considered RFLUKA μ+/μ− = 1.333 ± 0.007 L3+COSMIC (hep-ex/0408114). RFLUKA= 1.29  0.05 Rexp= 1.285  0.003(stat.) ± 0.019(sys.) 22