Cosmic ray physics in ALICE

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


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


Physics Topics


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


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.


ALICE detector


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


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


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


Analyses


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


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


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)


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


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


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.


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

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Cosmic ray physics in ALICE