Search for time-dependent fluctuations in cosmic ray flux with the AMS-01 detector

July 23, 2008 Mercedes Paniccia - AMS Analysis Meeting

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Search for time-dependent fluctuations in Search for time-dependent fluctuations in cosmic ray flux with the AMS-01 detectorcosmic ray flux with the AMS-01 detector

PhD Thesis

Mercedes PanicciaDépartement de physique nucléaire et corpusculaire

Université de Genève

March 2008


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Short-term CR flux variations• Huge plasma emissions from the Sun (CMEs) +

Magnetic reconnection at the Earth magnetosphere• Magnetic storms, Solar Energetic Particles, Ground

Level Enhancements, Forbush decreases• Time scales from minutes to several days• Energy up to ~50 GeV/n• Disturbances to satellite operations• Geomagnetic and solar activity continously monitored

SEP Dec. 2006

SEP Dec. 2006: PAMELA

Kinetic Energy ( )


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AMS-01 Precursor Flight on Space Shuttle Discovery Mission STS-91

• June 2-12, 1998• Near Earth orbit:

– Altitude: 320-390 km– Inclination: 51.7– Period: 90 min– Attitude: variable

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.


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Searching for systematic fluctuations in cosmic ray flux

with the AMS-01 data • Cosmic ray flux measurements:

– Simplify flux measurement, enlarge acceptance– Verify by reproducing AMS-01 official cosmic ray flux

measurements

• Search for time-dependent cosmic ray flux fluctuations:– Determine mean and actual fluxes over all mission duration,

eliminating effects related to variable:detector attitudegeomagnetic position

– Search for statistically significant deviation from mean flux– Correlate with solar activity


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Cosmic ray flux measurements

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For each range of geomagnetic latitude :

Φ(i)0

(Ek ) =1

2π (1− cosϑ max )

N(i)(E k,cosϑ ,ϕ )

A(i)(E k,cosϑ ,ϕ ) ⋅T

0

2π

∑1

cosϑ max

∑ =

=1

2π (1− cosϑ max )

N( i )(Ek )

A( i)(E k ) ⋅T i = He, p, e−


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Deuteron flux above cutoff 2%

Cosmic ray flux measurementsAcceptance & Background

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Acceptance in m2 ⋅sr

A ( i )(Ek ) = 2π (1− cosϑ max ) ⋅A(i)(Ek )

Background due to particle's misidentification :

Φ(i)(Ek ) = Φ( i)0

(E k ) − Φ(i)bckg

(E k ) ; i = He, p,e−

Φ(i)bckg

(E k ) = bij

h

∑j= He,D,p,π ,e −

j≠ i

∑ (Ek, Eh ) ⋅Φ( j )0

(Eh )

Secondary pions produced on top of AMS-01 1% below 0.5 GeV

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A ( i )(Ek,cosϑ max ) = S ⋅ΩNrec as i

when gen as i

MC (Ek,cosϑ max )

Ngen as iMC

bij (Ek,Eh ) =

Nrec as iwhen gen as j

MC (Ek, Eh )

Ngen as jMC (Eh )

Estimated from AMS-01 MonteCarlo simulation:


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Event Selection I

Cosmic ray flux measurementsEvent SelectionCosmic ray flux measurementsEvent Selection

• Trigger – LVL1– LVL3 (TOF + Tracker)

• No reconstructed cluster in Anticoincidence Counter• At least one track in Tracker• At least one track in TOF ≤40°• ChargeTOF=ChargeTracker

• Signal in at least 3 TOF planes• |R/R |<0.4• p, , Z compatibility:

• Only downward going particles

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1

β= 1+

m

Ze

⎛

⎝ ⎜

⎞

⎠ ⎟2

1

R2⇒

R2

m2

1

β 2−1

⎛

⎝ ⎜

⎞

⎠ ⎟−

1

Ze

⎛

⎝ ⎜

⎞

⎠ ⎟2

< 3σ


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Event Selection II

Cosmic ray flux measurementsEvent SelectionCosmic ray flux measurementsEvent Selection

• Electron selection:– R<0– Z=-1– Isolated track– Ultrarelativistic

• Proton selection:– R>0– Z=1– |massmeas - massproton| < 3.5 mass

• He nuclei selection:– R >0– Z=2 4 2

MSoff < 200

Reduce contamination from misreconstructed pions to 10-4

Reduces contamination from misreconstructed deuterons and pions

Track quality cut


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AcceptancesCosmic ray flux measurementsCosmic ray flux measurements

• Systematics uncertainties included (taken from previous AMS01 analysis)

• Bayesian unfolding method to correct for experimental resolution (AMSUnfold in AMS Root by J. Alcaraz)


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Background Estimation

Cosmic ray flux measurementsCosmic ray flux measurements

Samplee- p He

e- -------- 10-5 10-7

p 10-6 -------- 10-6

He 10-7 <10-8 -------

• Deuterons and pions contaminations reduced to negligible levels by selection cuts

• Mutual e-, p and He contamination evaluated from MonteCarlo:


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• Data collected during Zenith pointing period (~24 hours absolute time)• Only single particles propagating toward the Earth• Events collected when the Earth was in the AMS field of view excluded• South Atlantic Anomaly excluded: 85W-25E; 0-55S


Data set


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Proton fluxComparison to previous results

Cosmic ray flux measurementsProtonsCosmic ray flux measurementsProtons

<40°: this analysis <32°: previous AMS-01 resultsM.Aguilar et al. (AMS coll.), Physics Reports, 366:331-405 (2002)

cutoff


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cutoff


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cutoff


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cutoff


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cutoff


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cutoff


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cutoff


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cutoff


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cutoff


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cutoff


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• Reproduced previous AMS01 flux measurements

(proton, electron and He nuclei )

• Background contamination negligible:– Mutual e-, p and He nuclei contaminations negligible given CR flux

magnitude– Deuterons and pions contaminations reduced by selection cuts

• Corrections for experimental resolution negligible because of large bin widths

• Use same event selection procedure to study systematic CR flux fluctuations possibly related to solar activity


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Search for time-dependent cosmic ray flux fluctuations

Shuttle geomagnetic latitude vs longitude

M

(rad

)

-3 -2 -1 0 1 2 3

-1

1

0.5

0

-0.5

M (rad)

• DATA sample: all data collected after undocking from MIR ( from June 8 18h00 UT to June 12 2h36 UT)

• For each pointing period measure average counting rate as function of geomagnetic position:

M= ; M=0; 0.2; 0.3; 0.4 ….

• Measure actual counting rate with ~1 min time sampling

• DATA sample: all data collected after undocking from MIR ( from June 8 18h00 UT to June 12 2h36 UT)

• For each pointing period measure average counting rate as function of geomagnetic position:

M= ; M=0; 0.2; 0.3; 0.4 ….

• Measure actual counting rate with ~1 min time sampling


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• Actual counting rate time sampling ~1 min

Search for time-dependent cosmic ray flux fluctuationsProtons 0.1 GeV ≤ Ek < 0.3 GeV


Actual vs Expected Counting rate

Nco

unts

/sec

flux

varia

tion

(%)

1h40 2h00 2h20 2h40 3h00 3h20 3h40 4h00 4h20

1h40 2h00 2h20 2h40 3h00 3h20 3h40 4h00 4h20


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Search for time-dependent cosmic ray flux fluctuationsProtons 0.3 GeV ≤ Ek < 1 GeV


Actual vs Expected Counting rate

Nco

unts

/sec

flux

varia

tion

(%)

1h40 2h00 2h20 2h40 3h00 3h20 3h40 4h00 4h20

1h40 2h00 2h20 2h40 3h00 3h20 3h40 4h00 4h20


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Search for time-dependentcosmic ray flux fluctuationsProtons 1 GeV ≤ Ek < 3 GeV


Actual vs ExpectedCounting rate

Nco

unts

/sec

flux

varia

tion

(%)

1h40 2h00 2h20 2h40 3h00 3h20 3h40 4h00 4h20

1h40 2h00 2h20 2h40 3h00 3h20 3h40 4h00 4h20


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Nco

unts

/sec

flux

varia

tion

(%)

1h40 2h00 2h20 2h40 3h00 3h20 3h40 4h00 4h20

1h40 2h00 2h20 2h40 3h00 3h20 3h40 4h00 4h20


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Nco

unts

/sec

flux

varia

tion

(%)

1h40 2h00 2h20 2h40 3h00 3h20 3h40 4h00 4h20

1h40 2h00 2h20 2h40 3h00 3h20 3h40 4h00 4h20


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Search for time-dependent cosmic ray flux fluctuationsProtons 30 GeV ≤ Ek < 100 GeV



Nco

unts

/sec

flux

varia

tion

(%)

1h40 2h00 2h20 2h40 3h00 3h20 3h40 4h00 4h20

1h40 2h00 2h20 2h40 3h00 3h20 3h40 4h00 4h20


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Nco

unts

/sec

flux

varia

tion

(%)

1h40 2h00 2h20 2h40 3h00 3h20 3h40 4h00 4h20

1h40 2h00 2h20 2h40 3h00 3h20 3h40 4h00 4h20


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Selection Refinement

• Observed flux variations near South Atlantic Anomaly region• Add refined South Atlantic Anomaly exclusion:

– From Box (85°W-25°E; 0°-55°S) to geomagnetic field contour E. Fiandrini et al. (AMS coll.),J. Geophys. Res, 109, (2004)

Search for time-dependent cosmic ray flux fluctuationsSearch for time-dependent cosmic ray flux fluctuations


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Searching for fluctuation evidence:

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Prob(N ≥ N(i)obs(Ek, t)) = e

−N ( i )exp (Ek ,t ) N(i)

exp(E k, t)n

n!n= N ( i )

obs (Ek ,t )

∞

∑

Prob(N ≤ N(i)obs(Ek, t)) = e


exp(Ek, t)n

n!n= 0

N ( i )obs (Ek ,t )

∑

€

Prob(N ≥ N(i)obs(Ek, t)) = e


exp(E k, t)n

n!n= N ( i )

obs (Ek ,t )

∞

∑

Prob(N ≤ N(i)obs(Ek, t)) = e


exp(Ek, t)n

n!n= 0

N ( i )obs (Ek ,t )

∑

• Calculate deviation from Poisson distribution with mean value the expected counts:

Flat for random deviations


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Prob(N≥Ncounts obs)

Prob (N≤Ncounts obs )


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Systematic fluctuation frequency


• Evidence for proton, electron and He nuclei flux fluctuation occurrence in the kinetic energy range from 0.1 GeV to 30 GeV

• Systematic fluctuation if more than 3 deviation in at least three adiacent kinetic energy bins

• Three-hour average fluctuation frequency:

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ν fluct(i) (t) =

N fluct(i) (t)

Δt(3 hours)

i = e−, p,He

Positive and negative flux variations treated separatelyTime duration and intensity not taken into account

Positive and negative flux variations treated separatelyTime duration and intensity not taken into account


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Geomagnetic activitySearch for time-dependent cosmic ray flux fluctuationsSearch for time-dependent cosmic ray flux fluctuations

• Planetary geomagnetic activity index Kp:

– Three-hour average geomagnetic field perturbations

– Data from 13 geomagnetic stations at subauroral latitudes (44°-60°)

– Disturbance level:• from 0 (quiet) to 9 (highly perturbed) in 28 steps

– Sensitive to solar particle effects

Data retrieved from Space Physics Interactive Data Resource


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Systematic fluctuation index


• Three-hour average proton flux fluctuation index:

€

Q fluct( p ) (t) =

τ h ⋅i hΔt(3 hours)h= 0

n fluct( p ) ( t )

∑

n fluct( p ) (t) : total number of systematic fluctuations

τ h : time duration of single fluctuation event

i h : percentage flux variation averaged over Nbins

Positive and negative flux variations summed togetherTime duration and intensity of systematic fluctuation considered

Positive and negative flux variations summed togetherTime duration and intensity of systematic fluctuation considered


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Systematic fluctuationsversus geomagnetic activity


• Spearman rank correlation coefficient -0.37 with 0.99 significance

Proton fluctuation index versus planetary geomagnetic activity index

Proton fluctuation index versus planetary geomagnetic activity index


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Conclusions

• Observed systematic fluctuations in He, proton and electron flux in the kinetic energy range from 0.1 to 30 GeV/n

• Biggest effects for protons• Both flux increases and decreases occurs

during active periods• Systematic decreases correlated to

geomagnetic disturbances of solar origin• Article in preparation


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THANK YOU

Documents

Search for time-dependent fluctuations in cosmic ray flux with the AMS-01 detector