Cosmic ray physics in ALICE Katherin Shtejer Díaz For the ALICE Collaboration LatinoAmerican Workshop on High Energy Physics: Particles and Strings, Havana, July 2012

2Katherin Shtejer Díaz 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 Díaz 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 Díaz HEP Havana, July 2012 Physics Topics

5Katherin Shtejer Díaz 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 Díaz 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. ddddtddddt dd     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 Díaz HEP Havana, July 2012 ALICE detector

8Katherin Shtejer Díaz 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 Díaz 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 Díaz 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 Θ y = arctan(P y /P z )  y negative A → CA → C A ← CA ← C

11Katherin Shtejer Díaz HEP Havana, July 2012 Analyses

12Katherin Shtejer Díaz HEP Havana, July 2012 Ratio   /   (near-vertical muons) CMS experiment : R  = (stat.) (syst) P<100 GeV/c L3+C experiment : R  = (stat.) (syst.) P<500 GeV/c ALICE experiment : R  = (stat.) (syst.) P<100 GeV/c

13Katherin Shtejer Díaz HEP Havana, July 2012 Ratio   /   (near-horizontal muons) ALICE : R  = (stat.) (syst.) 80<P<320 GeV/c (70 o -85 o ) MUTRON  Surface muon spectrometer at sea level, zenith 86 o -90 o, year 1984 R  = (stat.) 100<P<600 GeV/c DEIS  Surface muon spectrometer at sea level, zenith 78 o -90 o, year 1981 R  = 1.25

14Katherin Shtejer Díaz HEP Havana, July 2012 Muon Multiplicity Distribution Data taken February-August 2011 ~ 10 days live time Trigger : ACORDE + TOF Comparison with simulation CORSIKA code with QGSJET II Proton primary (relative normalization at 3 muons) Fe primary (Zoom low multiplicity)

15Katherin Shtejer Díaz HEP Havana, July 2012 High Muon Multiplicity Events (February 2010) Mean Zenith Angle : 40° Mean Azimuth Angle : 212° Density of muons : ~ 12  /m 2 Mean Zenith Angle : 41° Mean Azimuth Angle : 69° Density of muons : ~ 6  /m 2

16Katherin Shtejer Díaz HEP Havana, July 2012 High Muon Multiplicity Events (June 2011) Mean Zenith Angle : 26° Mean Azimuth Angle : 193° Density of muons : ~ 17  /m 2 Number of  Density (  /m 2 ) (1) Estimated Energy (eV) x x10 16 (1) Supposing Fe as primary, and the EAS core inside ALICE

17Katherin Shtejer Díaz HEP Havana, July 2012 Summary ALICE can study atmospheric muons with central detectors and forward muon spectrometer by measuring: number of muons, momentum, charge, direction, arrival time. Preliminary measurements of Ratio  +/  - for vertical muons ( ) with central detectors and for horizontal muons ( ) with forward muon spectrometer have been presented. More statistics is required to improve our studies. More analyses have to be performed of the muon multiplicity distribution and exploit the correlation with various observables in order to study the cosmic ray composition. Investigate the higher multiplicity events to understand their nature.

18Katherin Shtejer Díaz HEP Havana, July 2012 Inputs from:  Bruno Alessandro (a)  Mario Rodriguez Cahuantzi (b)  Arturo Fernandez Tellez (b)  Mario Sitta (a) (a) Istituto Nazionale di Fisica Nucleare, sezione di Torino, ITALY (b) Benemerita Universidad Autonoma de Puebla, MEXICO