1. Detection of atmospheric muons @ ALICE-LHC experiment Seminario del Cuerpo Académico de Partículas, Campos y Relatividad General Dec. 8th. 2010 M. Rodríguez Cahuantzi

2. With the ALICE’s detectors it is possible to detect those muons coming from the cosmic ray that reaches the P2 with the use of ACORDE, TOF and SPD trigger + TPC track reconstruction. ALICE located 40 m. underground 30 m of rock (molasse) 10 m of air Threshold Muon Energy ~ 15 GeV

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.  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  Muons with muon spectrometer : August-Sept, 2009 Trigger and Tracking Type of events and selections Momentum spectrum - Final Remarks Study of the runs taken during summer 2009 with trigger for cosmics

6. Trigger Detectors 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 : triggers when a muon crosses two layers of SPD detector: SCO. ACORDE : 60 scintillators Trigger coincidence of two scintillators : AMU or SL0 (Single Muon Trigger)

7. ACORDE geometry scheme

8. The TOF detector covers an effective area for all φ and 45 ≤ θ ≤ 135. This area is around 160 m 2. It will identify charged particles. Temporal resolution < 100 ps Efificiency > 95 %

9. TOF trigger TOF clusters (magnetic field: 0.5 T) TOF clusters (magnetic field: 0 T) Tracks reconstructed by the TPC

10. 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).

11. TOF TPC TRD YOKE TOF TPC TRD YOKE

12. The algorithms for reconstruction of tracks in the TPC have been created mainly for heavy ions collisions. These methods have been adapted and improved continuously during the analysis of CR – events which have a completely different topology. Time stamp: 2009-11-23 16:13:37

13. Single muon A muon is reconstructed by the TPC as two tracks : up, down up down A matching algorithm connects track up with down to count one muon The momentum is given for the two tracks : Pup and Pdown

14. 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) Algorithm for matching TPC tracks

15. # Run Time [h] # Events OB3 OCP AMU # Events Mu > 0 OB3 OCP AMU Purity Rate OB3 [Hz] Purity Rate OCP [Hz] Purity Rate AMU [Hz] # Interaction Events # Multi- Mu Events 838119.4834225997198322010.03152 837751.2758092514866630.11.80.052919 838021.053829858183020.51.10.031815 841486.42720090682773281.60.0410398 842054.5168117142433124.71.40.048476 8425472330994587554221.30.039981 843892.2359972315164217.810.033334 844205.12195877649529225.41.40.048092 844554.43 188398247849328.31.60.049882 84479 13779859676125.41.50.041918 84993 1.5246038912029120.71.20.031724 85024 1.3549387012855424.91.40.0418 85031 0.5130487279945412.40.06910 85032 0.431438837592.30.130.00410 85034 113906585102359024.41.40.04197161 Total 57.295223313957880

16. Trigger Type Distribution

17. Muon Multiplicity Distribution, 4 trigger types

18. Muon Multiplicity Distribution: TOF Single and TOF Cosmic Trigger

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

20. Zenith and Azimuth Distribution of Muons

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

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

23. 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) Muon Momentum Resolution calculated with Data for P weight and P mean

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

25. #Run Time (hours) # of Events Reconstructed # of Events trigger SCO # of Events trigger: OSH2 # of Events trigger AMU Event rate (Hz) Rec. Pass2(%) 10943212.93382764402874146310.72100 1094773.493821769786212410.75100 1095475.21410627051175518960.74100 1095762.36245117051478620.75100 1095804.59119822090988516420.72100 DATA TAKING: FEBRUARY 2010

26. We found one event with high multiplicity of muons triggered by AMU. SPD trigger: register multi-muon + muon+iron events Winter 2010 data

27. A high multiplicity event, triggered by aco_multi

28. VERY high muon multiplycity event!! Run: 109547 Chunk: 109547020.10 Event: 3723 # of tracks: 182 # of muons: 86

29. Same muon bundle event, other views

30. World ratio ~ 1.3, P < 100 GeV/c ALICE uncorrected ratio ~1.31, P < 100 GeV/c Ratio

31. Θ y negative Θ y 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) Study of Horizontal Muons with Muon Chambers

32. Data Sample Runs of August and September 2009 Total time ~ 240 h → 10 days Magnetic field → 0.5 T N. Total Events → 200372 N. Events with at least one muon → 8194 N. Good events (selected) → 5876

33. 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 → 10.42 GeV/c ThetaY → -18.8 Deg ThetaX → 2.1 Deg

34. Angular Distributions

35. Momentum in interval of zenith angles

36. Energy loss from Surface to ALICE

37. Uncorrected Muon Momentum Distribution (70 0 -80 0 )

38. Conclusions We found that around 12 % of ACORDE triggers (AMU>=4), reconstructed as a muon by the TPC. For AMU>=6 we got around 57 % of trigger purity !!! The rate for AMU>=3 ~0.32 Hz  1152 events/hour, purity trigger ~ 9% In around 20 days of data taking we will have ~552960 events with AMU >=3, with 9% of trigger purity we will have around 55,296 events with at least one track reconstructed by the TPC.

39. 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 (0 0 -20 0 ) and for horizontal muons with muon spectrometer (70 0 -80 0 )

40. The End.. Thank you very much for your attention and for your comments …

41. Backup slides

42. We can see the systematic by the TPC charge reconstruction @ 100 clusters for p > 180 GeV/c Backup slides

43. Cut @ 50 clusters

44. Backup slides Cut @ 100 clusters

45. Backup slides In red we have the multi muon bundle events. In blue the interaction events. We can distiguish with at least 5 muons reconstructed.

46. Backup slides Good PID for lower values of momentum reconstructed by the TPC

47. Backup slides Good correlation for P reconstruction @ both TPC sides.

48. 13 Después de aplicar el algoritmo de identificación de muones a partir de las trazas reconstruidas por la TPC tenemos una estimación del número de muones que atraviesan ALICE. Mayor frecuencia en el sistema de disparo para TOF. Se encuentran eventos con buena multiplicidad de muones. Backup slides

49. 14 19.7 o C 18.2 o C Lado A Lado C Identificación de trazas para μ + (traza Up y traza Down) Buen reconocimiento de trazas inclusive para μ + con altos momentos. Backup slides

50. 15 Para el caso de μ - se está observando un decremento en la resolución de la reconstrucción de los mismos por la TPC en el lado C. Para momentos altos se va perdiendo la resolución en la reconstrucción. Cluster > 100 Backup slides

51. Muy buena correlación entre las trazas reconstruidas y los candidatos a μ. Backup slides

52. Tenemos una buena reconstrucción para los parámetros internos y externos de la TPC. En esta corrida encontramos un evento con 459 trazas reconstruidas y 220 candidatos a μ. Backup slides

53. Para el evento 6353 tenemos Parámetros externos Parámetros internos Como se puede ver hemos encontrado una buena densidad de candidatos a trazas de μ. Backup slides

54. La mayoría de las trazas tienen dirección en Φ de 125 0 y 107 0 en la dirección θ. Por favor compárese con el evento reconstruido por DELPHI (127 μ) Backup slides