Cosmic ray physics in ALICE Katherin Shtejer Daz For the ALICE Collaboration LatinoAmerican Workshop on High Energy Physics: Particles and Strings, Havana, July 2012 2Katherin Shtejer Daz HEP Havana, July 2012 Contents Motivation Cosmic Rays physics Physics Topics Extensive Air Showers (EAS) Flux of cosmic rays ALICE Detector Main detectors involved in atmospheric muon detection Tracking and Reconstruction Forward Muon Spectrometer Strengths of ALICE for cosmic ray physics Analyses Ratio +/ - (near-vertical muons) Ratio +/ - (near-horizontal muons) Muon multiplicity distribution High muon multiplicity events (february 2010) High muon multiplicity events (june 2011) Summary 3Katherin Shtejer Daz HEP Havana, July 2012 Cosmic Rays physics The understanding of the origin and nature of the most energetic particles that constitute primary cosmic rays and their interaction processes. Accelerator data and inputs are needed, particularly in the knee region of the energy spectrum of cosmic rays. Mass composition and energy spectrum of primary cosmic rays can be studied with ALICE in an energy range not available from direct measurements with satellites or balloons or from deeper ground arrays. Flux of cosmic ray muons provides a way of testing the inputs of nuclear cascade models and particle interactions at high energies. The cosmic ray muon flux provides a useful tool for calculation of neutrino fluxes, which are rather difficult to measure directly. Motivation 4Katherin Shtejer Daz HEP Havana, July 2012 Physics Topics 5Katherin Shtejer Daz HEP Havana, July 2012 Extensive Air Showers (EAS) Primary Cosmic Ray (p, He,..., Fe) + Earth's Atmosphere neutrino, muon component hadronic cascade p,n hadronic component e+e+ e-e- e+e+ e-e- e+e+ e-e- e+e+ e-e- e+e+ e-e- Cherenkov & fluorescence radiation electromagnetic component p nucleus anything e e e - e All the electromagnetic and hadronic components are absorbed by the overburden rock. Only muons with E 15 GeV reach ALICE. For this purpose three detectors are employed as triggers: - ACORDE (A COsmic Ray Detector) - TOF (Time Of Flight) - SPD (Silicon Pixel Detector)...and - TPC (Time Projection Chamber) for track reconstruction Similar processes occur in the decay of kaons producing muons with high momenta 6Katherin Shtejer Daz HEP Havana, July 2012 Knee (1 particle per m 2 - year) Ankle (1 particle per Km 2 - year) GZK cutoff Flux of cosmics rays - The elemental composition of primary cosmic rays and their sources for energies between the knee (~10 15 eV) and the Greisen- Zatsepin-Kuzmin (GZK) cutoff (~10 20 eV) is not well understood, because of the large discrepancies on the way the models predict the inelastic cross sections in this energy range. ddddtddddt dd is sensitive to the chemical composition of the primary particles ALICE may contribute to more data measurements, by registering the high energy muon distribution from cosmic rays, in a cavern 52m underground. 7Katherin Shtejer Daz HEP Havana, July 2012 ALICE detector 8Katherin Shtejer Daz HEP Havana, July 2012 Main detectors involved in atmospheric muon detection ALICE located 52 m underground 28 m of overburden rock (molasse) Detects atmospheric muons with energies 15 GeV ACORDE (A COsmic Ray Detector) - 60 scintillator modules - trigger given by the coincidence of at least 2 modules (AMU) TOF (Time Of Flight) - cylindrical Multi-Gap Resistive-Plate Chamber (MRPC) array - cosmic trigger requires one upper pad fired and one pad in the opposite lower side of TOF (OB1) SPD (Silicon Pixel Detector) - two innermost layers of silicon pixel modules very closed to the interaction point - cosmic trigger given by the coincidence of two signals of muons crossing the top and bottom halves of the external layer (SCO) Tracking and Trigger Chambers - used for horizontal muons as part of the FMS TPC (Time Projection Chamber) - for track reconstruction TPC ACORDE ITS TOF Tracking Chambers Trigger Chambers Azimuth Angle Zenith Angle muon x y z 9Katherin Shtejer Daz HEP Havana, July 2012 Tracking and reconstruction (near-vertical muons) A single muon is reconstructed by the TPC as two tracks : up, down up down One muon is counted by matching the track up with the track down A multi-muon eventA muon interaction event 10Katherin Shtejer Daz HEP Havana, July 2012 Forward Muon Spectrometer (Study of near-horizontal muons) Z Y y positive Muon momentum threshold ~ 40GeV/c (due to the rock) Length of detector ~ 13 m (from first tracking station) Interaction Point y = arctan(P y /P z ) y negative A CA C A CA C 11Katherin Shtejer Daz HEP Havana, July 2012 Analyses 12Katherin Shtejer Daz HEP Havana, July 2012 Ratio / (near-vertical muons) CMS experiment : R = (stat.) (syst) P