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. underground 30 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 Muons with central detectors  Triggers: SPD, TOF, ACORDE Tracking : TPC  Muon multiplicity distribution  Angular distribution  Momentum and Ratio  +/  - (vertical muons 0 o -20 o ) - Muons with forward muon spectrometer Trigger and Tracking Type of events and selections Momentum and Ratio  +/  - (horizontal muons 70 o -80 o ) Data February 2010  Muon Multiplicity Distribution  High Multiplicity events

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

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/ (2010).

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 : P up and P down

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) > – |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: (Feb. 2010) Event: 3723 # of TPC tracks: 182 # of muons: 89 Some TPC tracks fail the N.of cluster cut

DATA TAKING: SUMMER 2009 # 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 Total

Trigger Type Distribution

Muon Multiplicity Distribution for the 4 Triggers

Muon Multiplicity Distribution : Data and Simulation Real data 2.5 days live timeEstimation 30 days live time

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

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

Uncorrected Muon Momentum Distribution with Pcov Vertical muons 0 o < Teta<20° No shaft effect Estimated error around 25% at P=100 GeV/c using P cov P cov : 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 negative  y 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 2009 Total time ~ 216 h → 9 days Magnetic field → 0.7 T N. Total Events → N. Events with at least one muon → 8194 N. Good events (selected) → 5876

C Side x Variables for Horizontal Muons ThetaX C Side A Side y z muon A Side Z Y X ThetaY ThetaY > 0 z z y y ThetaY < 0 ThetaY = arctg(Py/Pz) Zenith Cosmic = 90 o - |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 70 o < Zenith < 80 o 85 o < Azimuth < 95 o 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 ( ) ALICE LEVEL SURFACE LEVEL

Uncorrected Ratio  +/  - at Surface level ( )

DATA TAKING: FEBRUARY 2010 Trigger : ACORDE and SPD Time : 2.2 effective days Two events with high muon multiplicity

High Muon Multiplicity Events Time : 2.2 effective days 89 muons 182 muons Simulation Time : 30 effective days

Main Characteristics : Event with 182  Mean Zenith Angle : 40° Mean Azimuth Angle : 212° Density of muons : 12  /m 2 Mean Momentum : 123 GeV/c

Main Characteristics : Event with 89  Mean Zenith Angle : 41° Mean Azimuth Angle : 69° Density of muons : 6  /m 2 Mean Momentum : 189 GeV/c

Muon Density and Primary Energy Estimate (Simulation) A density of 6  /m 2 at ALICE level is obtained with : Primary with eV In the core of the shower 89 muons : 6  /m 2 Eprimary >= eV 182 muons : 12  /m 2 Eprimary > 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 ( ) and for horizontal muons with muon spectrometer ( ) in progress. Study and search of events of very high muon multiplicity can be a test for hadron interaction models