1. Detection of atmospheric muons using ALICE detectors
B. Alessandro, V. Canoa, A. Fernández, M. Rodríguez, M. Subieta
for the
ALICE Collaboration

2. ALICE Experiment at LHC
ALICE located 40 m. underground
30 m of rock (molasse)
10 m of air
Threshold Muon Energy ~ 15 GeV
MRC – Alice Day meeting ICN-UNAM, Feb. 26th 2010

3. ALICE Experiment during assembly

4. Detectors used for cosmics in the central part :
Trigger : ACORDE, TOF, SPD Tracking : TPC
Detectors used for horizontal muons :
Trigger Muon Chambers Tracking Muon Chambers

5. Study of the runs taken during summer 2009 with trigger for cosmics
Muons with central detectors : August-Sept, 2009
Triggers: SPD, TOF, ACORDE
Tracking : TPC
Type of events
- Muon multiplicity distribution
Angular distribution
Momentum resolution analysis
Momentum spectrum
Ratio mu+/mu- (not presented in progress)
Muons with muon spectrometer : August-Sept, 2009
Trigger and Tracking
Type of events and selections
- Final Remarks

6. Trigger Detectors ACORDE : 60 scintillators Trigger coincidence of two
scintillators : 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 when
muon cross two layers : SCO

7. Tracking Detector and type of events
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/ (2010).
Muon Interaction Event
Standard Muon Event (multimuon)

8. Single muon up up down down
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

9. 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| < 165 cm
DeltaDist < 2 cm for matching
Tested with real multimuon events (up to 200 tracks)

10. Reconstruction of CR - events with ACORDE , SPD + TPC
Run: (Feb. 2010)
Event: 3723
# of TPC tracks: 182
# of muons: 86
Some TPC tracks fail the N.
of cluster cut

11. DATA TAKING: SUMMER 2009 # Run Time [h] # Events OB3 OCP AMU
# Events Mu > 0
OB3 OCP
Purity Rate OB3 [Hz]
Purity Rate OCP [Hz]
Purity Rate AMU [Hz]
# Interaction Events #
Multi- Mu Events
83811
9.48
719832 20 1
0.03
152
83775
1.27
580925
148666
30.1
1.8
0.05 29 19
83802
1.05
382985
81830
20.5
1.1 18 15
84148
6.4
682773 28
1.6
0.04
103 98
84205
4.5
424331
24.7
1.4 84 76
84254 7
587554 22
1.3 99 81
84389
2.23
599723
151642
17.8 33 34
84420
5.12
495292
25.4 80 92
84455
4.43
478493
28.3 82
84479
377985
96761
1.5
84993
1.52
460389
120291
20.7
1.2 17 24
85024
1.35
493870
128554
24.9
85031
0.51
304872
79945 41
2.4
0.06 9 10
85032
0.43
14388
3759
2.3
0.13
0.004
85034 11
24.4
197
161
Total
57.29
957
880

12. Trigger Type Distribution

13. Muon Multiplicity Distribution for the 4 Triggers

14. Muon Multiplicity Distribution for : TOF Single and TOF Cosmic Trigger

15. Angular Distributions
Azimuth Angle
C Side
A Side
Zenith Angle y z
muon
Zentih & Azimuth Angles for Cosmics Y x
C Side Z
A Side X

16. Zenith and Azimuth Distribution of Muons

17. A SIDE C SIDE Zenith Angle y A Side C Side z Azimuth Angle x SHAFT

18. Definition and Study of the Muon Momentum
Selected events with one muon reconstructed (2 tracks)
Three definitions of the momentum : Pweight, Pmean, Pcov
Pcov : Momentum obtained fitting
the whole track length of the muon
(up and down as one track)

19. Muon Momentum Resolution calculated with Data for Pweight and Pmean
How to improve the resolution :
From simulation program we see that the measurement of the momentum using the fit of the whole muon track length (Pcov) instead of using up and down separately (Pweight) improve the resolution by a factor ~ 3.
Best resolution using :
Pcov
Resolution at 100 GeV/c ~ 50% using up and down separately (Pweight)
Resolution at 100 GeV/c ~ 20% using the whole muon track length (Pcov)

20. Uncorrected Muon Momentum Distribution with Pcov
Vertical muons
0o<Teta<20o
Estimated error around 20% at P=100 GeV/c
using Pcov
Resolution obtained with March 2010 TPC calibration.
Improvments expected with the new calibration.

21. Future results with central detectors (vertical muons)
EXPECTED FROM ALICE
Measurement of Muon Momentum Distribution up to 200 GeV/c
Measurement of Ratio mu+/mu- up to 200 GeV/c
Studies of the correlation between Number of muons and their Momenta (composition studies ?)

22. Study of Horizontal Muons with Muon Chambers
Qy negative
Qy positive
Muon momentum threshold ~ 4GeV/c (due presence of absorbers)
Length detector ~ 17 m (from the interaction point)
Length detector ~ 13 m (from first tracking station)

23. Data Sample Runs of August and September 2009
Total time ~ 240 h → 10 days
Magnetic field → 0.5 T
N. Total Events →
N. Events with at least one muon → 8194
N. Good events (selected) → 5876

24. Variables for Horizontal Muons
ThetaY > 0 z y
ThetaY < 0
ThetaY y
muon
ThetaY = arctg(Py/Pz)
Zenith Cosmic = 90o - |ThetaY|
ThetaX = arctg(Px/Pz)
A Side
C Side z
A Side Z Y X
ThetaX x
C Side

25. Type of Events (run 81249) Good event Event 43 P → 28.25 GeV/c
ThetaY → 12.6 Deg
ThetaX → 9.2 Deg
Event 613
P → GeV/c
ThetaY → Deg
ThetaX → 2.1 Deg

26. Selection of good events
Cut to select “good events” :
ThetaY > 0

27. Angular Distributions

28. Momentum in interval of zenith angles

29. Energy loss from Surface to ALICE

30. Uncorrected Muon Momentum Distribution (700-800)

31. 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 Muon Momentum Distribution and Ratio mu+/mu- for vertical muons with the central detectors (00-200) and for horizontal muons with muon spectrometer ( )