The Performance of the ALICE experiment for cosmic ray physics
B. Alessandro, V. Canoa, A. Fernández, M. Rodríguez, M. Subieta
for the
ALICE Collaboration
ALICE Experiment at LHC
ALICE located 40 m. underground30 m of rock (molasse)10 m of air
Threshold Muon Energy ~ 15 GeV
ALICE Experiment during assembly
Detectors used for cosmics in the central region :Trigger : ACORDE, TOF, SPD Tracking : TPC
Detectors used for horizontal muons :Trigger Muon Chambers Tracking Muon Chambers
Study of the cosmic runs taken during Summer 2009 and February 2010
Data Summer 2009 -Muons with central detectors
Triggers: SPD, TOF, ACORDE Tracking : TPC Muon multiplicity distribution Angular distribution Momentum and Ratio +/- (vertical muons 0o-20o)
- Muons with forward muon spectrometer • Trigger and Tracking• Type of events and selections• Momentum and Ratio +/- (horizontal muons 70o-80o)
Data February 2010 Muon Multiplicity Distribution High Multiplicity events
Trigger DetectorsACORDE : 60 scintillatorsTrigger coincidence of twoscintillators : AMU
TOF cylinder of MRPC surrounding the TPC two types of trigger :1 pad up 1 pad down +- 3 pads : TOF Single (OB3)4 pads everywhere : TOF Cosmic (OCP)
SPD small detector trigger whenmuon cross two layers : SCO
Tracking Detector and type of events
Muon Interaction Event
Standard Muon Event (multimuon)
TIME PROJECTION CHAMBER (TPC) :ALICE TPC Collaboration, J. Alme et al., "The ALICE TPC, a large 3-dimensional tracking device with fast readout for ultra-high multiplicity events.", Physics. Ins-Det/10011950 (2010).
Single muon A muon is reconstructed by the TPC as two tracks : up , down
up up
down down
A matching algorithm connects track up with down to count one muon The momentum is given for the two tracks : Pup and Pdown
Algorithm for matching TPC tracks• Find parallel tracks, match the TPC
tracks, count the muons (single TPC track, matched TPC tracks)– N. TCP clusters > 30 (matched tracks)– N. TPC clusters > 50 (single tracks)– P > 0.5 GeV– Cos(DeltaDirection) > 0.990– |Z-Zo| < 250 cm |X-Xo| < 250 cm – DeltaDist < 2 cm for matching
• Tested with real multimuon events (up to ~ 200 muons)
Reconstruction of CR - events with ACORDE , SPD + TPC
Run: 109547 (Feb. 2010)Event: 3723# of TPC tracks: 182# of muons: 89Some TPC tracks fail the N.of cluster cut
DATA TAKING: SUMMER 2009 # Run Time
[h]# Events
OB3OCPAMU
# Events Mu > 0
OB3 OCPAMU
Purity Rate OB3 [Hz]
Purity Rate OCP [Hz]
Purity Rate AMU [Hz]
# Interaction
Events
# Multi- Mu Events
83811 9.48 3422599 719832 20 1 0.03 152 152
83775 1.27 580925 148666 30.1 1.8 0.05 29 19
83802 1.05 382985 81830 20.5 1.1 0.03 18 15
84148 6.4 2720090 682773 28 1.6 0.04 103 98
84205 4.5 1681171 424331 24.7 1.4 0.04 84 76
84254 7 2330994 587554 22 1.3 0.03 99 81
84389 2.23 599723 151642 17.8 1 0.03 33 34
84420 5.12 1958776 495292 25.4 1.4 0.04 80 92
84455 4.43 1883982 478493 28.3 1.6 0.04 98 82
84479 1 377985 96761 25.4 1.5 0.04 19 18
84993 1.52 460389 120291 20.7 1.2 0.03 17 24
85024 1.35 493870 128554 24.9 1.4 0.04 18 18
85031 0.51 304872 79945 41 2.4 0.06 9 10
85032 0.43 14388 3759 2.3 0.13 0.004 1 0
85034 11 3906585 1023590 24.4 1.4 0.04 197 161
Total 57.29 5223313 957 880
Trigger Type Distribution
Muon Multiplicity Distribution for the 4 Triggers
Muon Multiplicity Distribution : Data and Simulation
Real data 2.5 days live time Estimation 30 days live time
C Side
A Side
Zenith & Azimuth Angles for Cosmics
x
Angular Distributions
Azimuth Angle
C SideA Side
Zenith Angley
z
muon
Z
Y
X
A SIDE
C SIDE
SHAFT
SHAFT
Zenith Angle y
x
z
Azimuth Angle
C Side
A Side
Uncorrected Muon Momentum Distribution with Pcov
Vertical muons0o< Teta<20°No shaft effect
Estimated error around 25% at P=100 GeV/cusing Pcov
Pcov : Momentum obtained fitting the whole track length of the muon (up and down as one track)
Ratio +/- (vertical muons)
World Ratio ~ 1.28 P<100 GeV/c
Alice Uncorr. Ratio ~ 1.31 P<100 GeV/c
Study of Horizontal Muons with Forward Muon Spectrometer
y negativey positive
Muon momentum threshold ~ 40GeV/c (due to the rock)
Detector length ~ 17 m (from the interaction point)
Detector length ~ 13 m (from first tracking station)
Data Sample
Runs of August and September 2009Total time ~ 216 h → 9 days Magnetic field → 0.7 TN. Total Events → 200372N. Events with at least one muon →
8194 N. Good events (selected) → 5876
C Side
x
Variables for Horizontal Muons
ThetaX
C SideA Side
y
z
muon
A Side
Z
Y
X
ThetaYThetaY > 0
z z
y y
ThetaY < 0
ThetaY = arctg(Py/Pz)Zenith Cosmic = 90o - |ThetaY|
ThetaX = arctg(Px/Pz)
Selection of good events
Cut to select “good events” :ThetaY > 0 5876 events
Angular Distributions and Selection of the events
70o< Zenith < 80o
85o< Azimuth < 95o 5876 events after these cuts 2862 events
Energy loss from Surface to ALICE
Simulation to obtain the energy loss by + and - crossing the rock from Surface to ALICE experiment at different Zenith Angles
Uncorrected Muon Momentum Distribution (700-800)
ALICE LEVEL
SURFACE LEVEL
Uncorrected Ratio +/- at Surface level (700-800)
DATA TAKING: FEBRUARY 2010
Trigger : ACORDE and SPDTime : 2.2 effective daysTwo events with high muon multiplicity
High Muon Multiplicity Events
Time : 2.2 effective days89 muons182 muons
SimulationTime : 30 effective days
Main Characteristics : Event with 182
Mean Zenith Angle : 40°Mean Azimuth Angle : 212°Density of muons : 12 /m2
Mean Momentum : 123 GeV/c
Main Characteristics : Event with 89
Mean Zenith Angle : 41°Mean Azimuth Angle : 69°Density of muons : 6 /m2
Mean Momentum : 189 GeV/c
Muon Density and Primary Energy Estimate (Simulation)
A density of 6/m2 at ALICE level is obtained with :•Primary with 1016 eV•In the core of the shower
89 muons : 6 /m2 Eprimary >= 1016eV 182 muons : 12/m2 Eprimary > 1016 eV
Final Remarks• ALICE can study atmospheric muons with central
detectors (vertical muons) measuring : Num. of muons, Momentum, Charge, Direction.
• In the future analysis of the correlations of these quantities for composition studies ????
• Measurement of the Ratio +/- for vertical muons with the central detectors (00-200) and for horizontal muons with muon spectrometer (700-800) in progress.
• Study and search of events of very high muon multiplicity can be a test for hadron interaction models
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