Cosmic ray physics in ALICE
Katherin Shtejer Díaz
For the ALICE Collaboration
LatinoAmerican Workshop on High Energy Physics: Particles and Strings, Havana, 15-21 July 2012
2Katherin Shtejer Díaz HEP Havana, 15-21 July 2012
Contents Motivation Cosmic Rays physics Physics Topics Extensive Air Showers (EAS) Flux of cosmic raysALICE Detector Main detectors involved in atmospheric muon detection Tracking and Reconstruction Forward Muon Spectrometer Strengths of ALICE for cosmic ray physicsAnalyses 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, 15-21 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, 15-21 July 2012
Physics Topics
5Katherin Shtejer Díaz HEP Havana, 15-21 July 2012
Extensive Air Showers (EAS)Primary Cosmic Ray
(p, He,..., Fe)+
Earth's Atmosphere
neutrino, muon component
hadroniccascade
p,n
hadronic component
e+ e- e+ e- e+ e-
e+ e- e+ e-Cherenkov &fluorescence
radiation
electromagnetic component
p nucleus anything
ee
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, 15-21 July 2012
Knee
(1 particle per m2 - year)
Ankle(1 particle per Km2 - year)
GZK cutoff
Flux of cosmics rays
- The elemental composition of primary cosmic rays and their sources for energies between the knee (~1015eV) and the Greisen-Zatsepin-Kuzmin (GZK) cutoff (~1020eV) is not well understood, because of the large discrepancies on the way the models predict the inelastic cross sections in this energy range.
ddddtd
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, 15-21 July 2012
ALICE detector
8Katherin Shtejer Díaz HEP Havana, 15-21 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
TOFTracking
ChambersTrigger
Chambers
Azimuth Angle
Zenith Angle
muon
x
y
z
9Katherin Shtejer Díaz HEP Havana, 15-21 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 event A muon interaction event
10Katherin Shtejer Díaz HEP Havana, 15-21 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
Θy = arctan(Py /Pz) y negativeA → C
A ← C
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Analyses
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Ratio / (near-vertical muons)
CMS experiment : R = 1.2766 +- 0.0032(stat.) +- 0.0032(syst) P<100 GeV/c
L3+C experiment : R = 1.285 +- 0.003(stat.) +- 0.019 (syst.) P<500 GeV/c
ALICE experiment : R = 1.275 +- 0.006(stat.) +- 0.01 (syst.) P<100 GeV/c
13Katherin Shtejer Díaz HEP Havana, 15-21 July 2012
Ratio / (near-horizontal muons)
ALICE : R =1.27 +- 0.04(stat.) +- 0.1(syst.) 80<P<320 GeV/c (70o-85o)
MUTRON Surface muon spectrometer at sea level, zenith 86o-90o, year 1984 R = 1.251 +- 0.005 (stat.) 100<P<600 GeV/c
DEIS Surface muon spectrometer at sea level, zenith 78o-90o, year 1981 R = 1.25
14Katherin Shtejer Díaz HEP Havana, 15-21 July 2012
Muon Multiplicity Distribution
Data taken February-August 2011 ~ 10 days live time
Trigger : ACORDE + TOF
Comparison with simulationCORSIKA code with QGSJET II
Proton primary (relative normalization at 3 muons) Fe primary
(Zoom low multiplicity)
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High Muon Multiplicity Events(February 2010)
Mean Zenith Angle : 40°
Mean Azimuth Angle : 212°
Density of muons : ~ 12 /m2
Mean Zenith Angle : 41°
Mean Azimuth Angle : 69°
Density of muons : ~ 6 /m2
16Katherin Shtejer Díaz HEP Havana, 15-21 July 2012
High Muon Multiplicity Events(June 2011)
Mean Zenith Angle : 26°Mean Azimuth Angle : 193°Density of muons : ~ 17 /m2
Number of Density (/m2)
(1) Estimated Energy (eV)
89
171
276
6
12
18
6x1015
1016
3x1016
(1) Supposing Fe as primary, and the EAS core inside ALICE
17Katherin Shtejer Díaz HEP Havana, 15-21 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 (00-200) with
central detectors and for horizontal muons (750-850) 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, 15-21 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