F. Ledroit

Implementation and Performance of the High-Level Trigger electron and photon selection for the ATLAS experiment at the LHC

The ATLAS experiment at the Large Hadron Collider (LHC) will face the challenge of efficiently selecting interesting candidate events in pp collisions at 14 TeV center of mass energy, while rejecting the enormous number of background events, stemming from an interaction rate of up to 10 Hz. The First Level trigger will reduce this rate to around O(100 kHz). Subsequently, the High Level Trigger (HLT), which is comprised of the Second Level trigger and the Event Filter, will need to further reduce this rate by a factor of O(10). The HLT selection is software based and will be implemented on commercial CPUs, using a common framework built on the standard ATLAS object oriented software architecture. In this paper an overview of the current implementation of the selection for electrons and photons ∗ S. Armstronga, A. dos Anjosb, J. T. M. Bainesc , C. P. Beed, , M. Bigliettie , J. A. Bogaertsf , V. Boisvertf , M. Bosmang , B. Caronh , P. Casadog , G. Cataldii , D. Cavallij , M. Cervettok , G. Comunel , P. Conde Muinof , A. De Santom , M. Diaz Gomezn, M. Dosilg , N. Ellisf , D. Emeliyanovc , B. Eppo, S. Falcianop , A. Farillaq , S. Georgem , V. Gheteo, S. Gonzalezr , M. Grothef , S. Kabanal , A. Khomichs, G. Kilvingtonm , N. Konstantinidist , A. Kootzu, A. Lowem, L. Luminarip, T. Maenof , J. Masikv , A. Di Mattiap , C. Meessend , A. G. Mellob , G. Merinog , R. Mooreh, P. Morettinik , A. Negriw , N. Nikitinx , A. Nisatip , C. Padillaf , N. Panikashviliy , F. Parodik , V. Perez Realel , J. L. Pinfoldh, P. Pintof , Z. Qiand, S. Resconij , S. Rosatif , C. Sanchezg , C. Santamarinaf , D. A. Scannicchiow , C. Schiavik , E. Segurag , J. M. de Seixasb , S. Sivoklokovx , R. Solukh, E. Stefanidist , S. Sushkovg , M. Suttont , S. Tapproggez , E. Thomasl, F. Touchardd, B. Venda Pintoaa, V. Vercesiw , P. Wernerf , S. Wheelerh,bb , F. J. Wickensc , W. Wiedenmannr , M. Wielerscc , G. Zobernigr aBrookhaven National Laboratory (BNL), Upton, New York, USA. bUniversidade Federal do Rio de Janeiro, COPPE/EE, Rio de Janeiro, Brazil. cRutherford Appleton Laboratory, Chilton, Didcot, UK. dCentre de Physique des Particules de Marseille, IN2P3-CNRS-Université d’Aix-Marseille 2, France eUniversity of Michigan, Ann Arbor, Michigan, USA. f CERN, Geneva, Switzerland. g Institut de Fı́sica d’Altes Energies (IFAE), Universidad Autónoma de Barcelona, Barcelona, Spain. hUniversity of Alberta, Edmonton, Canada. iDipartimento di Fisica dell’Università di Lecce e I.N.F.N., Lecce, Italy. jDipartimento di Fisica dell’Università di Milano e I.N.F.N., Milan, Italy. kDipartimento di Fisica dell’Università di Genova e I.N.F.N., Genova, Italy. lLaboratory for High Energy Physics, University of Bern, Switzerland. mDepartment of Physics, Royal Holloway, University of London, Egham, UK. nSection de Physique, Université de Genève, Switzerland. oInstitut für Experimentalphysik der Leopald-Franzens Universität, Innsbruck, Austria. pDipartimento di Fisica dell’Università di Roma “La Sapienza” e I.N.F.N., Rome, Italy. qDipartimento di Fisica dell’Università di Roma “Roma Tre” e I.N.F.N., Rome, Italy. rDepartment of Physics, University of Wisconsin, Madison, Wisconsin, USA. sLehrstuhl für Informatik V, Universität Mannheim, Mannheim, Germany. tDepartment of Physics and Astronomy, University College London, London, UK. uFachbereich Physik, Bergische Universitat Wuppertal, Germany. vInstitute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic. wDipartimento di Fisica Nucleare e Teorica dell’Università di Pavia e INFN, Pavia, Italy. xInstitute of Nuclear Physics, Moscow State University, Moscow, Russia. yDepartment of Physics, Technion, Haifa, Israel. zInstitut für Physik, Universität Mainz, Mainz, Germany. aaCFNUL Universidade de Lisboa, Faculdade de Ciências, Lisbon, Portugal.bbUniversity of California at Irvine, Irvine, USA. ccUniversity of Victoria, Victoria, Canada. in the HLT is given. The performance of this implementation has been evaluated using Monte Carlo simulations in terms of the efficiency for the signal channels, rate expected for the selection, data preparation times, and algorithm execution times. Besides the efficiency and rate estimates, some physics examples will be discussed, showing that the triggers are well adapted for the physics programme envisaged at LHC. The electron and photon trigger software is also being exercised at the ATLAS 2004 Combined Test Beam, where components from all ATLAS subdetectors are taking data together along the H8 SPS extraction line; from these tests a validation of the selection architecture chosen in a real on-line environment is expected.