measurement of the p ratio using the moon shadow with the l3...

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Measurement of the p/p ratio

using the Moon shadow with the L3 detector

Jean-Francois PARRIAUDon behalf of the L3 collaboration

☛ L3+Cosmics: experimental setup and topics

☛ Principle of the Moon shadow technique

☛ Observation of the Moon shadow in L3+Cosmics

☛ p/p ratio: measurement and limits

☛ Conclusion

L3+C

– 38 –

Fig. 10.— The p /p ratio at the top of the atmosphere obtained in this work compared with

previous measurements (Buffington, Schindler, & Pennypacker 1981; Golden et al. 1984;

Bogomolov et al. 1987, 1990; Salomon et al. 1990; Stochaj et al. 1990; Mitchell et al. 1996;

100 1000

0.01

CAPRICE

1.0

0.1

Ant

ipro

ton/

prot

on r

atio

10-5

10-4

Caprice

10

Kinetic energy (GeV)

-3

10-6

1 10

June 19 2002 Measurement of the p/p ratio using the Moon shadow with the L3 detector (page 1) Jean-Francois PARRIAUD

on behalf of the L3 collaboration

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L3+

Cosm

ics:

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L3+Cosmics: topics

2 years running: 1999-2000

Statistics: 12x109 muon events

Topics:

✦ Muon momentum spectrum in the 20-2000

GeV/c range at the % level

✦ Primary composition around the “knee”

✦ Gamma-Ray Bursts, point sources

✦ Moon shadow

✦ . . . 0

2000

4000

6000

0 50 100 150 200

time (days)

Eve

nts

/ 10

6

Year 2000 Year 1999




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Moon shadow

Cosmic rays are blocked by the Moon.

(Clark 1957)

=⇒ Deficit of cosmic rays in the direction

of the Moon.

☛ Size of the deficit → angular resolution

of the experiment.

☛ Position of the deficit → pointing error.

Observed in the 90’s (SOUDAN, MACRO,

CASA . . .)

N

W

E

Moon

Earth




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Moon shadow

Geomagnetic field: positively charged par-

ticles deflected to the East

=⇒ Deficit appears shifted to the West.

=⇒ If present, antimatter in cosmic rays

will induce a deficit on the opposite side.

☛ Earth-Moon = ion spectrometer (Urban

et al., ARTEMIS experiment)

Deflection � 1◦E(TeV/c)

GENEVA (6.02◦N, 46.25◦E)

Earth

Moonshadow

E

for protons

W

N

p

p

pB

Moonshadow for anti-protons

Moon




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Moon shadow

Sky seen by L3+C:

1 pixel = 1 direction

Moon trajectory:

Deflection = f(Moon location)

sin(θz).sin(αz)

sin(

θ z).c

os(α

z)




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Observation of the Moon shadow in L3+Cosmics

f(θ) = λ · (1 − ε · R2Moon

2·σ2 · e− θ2

2·σ2 )

600

610

620

630

640

650

660

670

680

690

0 0.5 1 1.5 2 2.5 3 3.5 4

17.18 / 17λ 662. ±2.σ 0.54 ±0.10ε 0.72 ±0.21

Angle with deficit centre (°)

Eve

nt d

ensi

ty (e

vt .moo

n-1)

375

400

425

450

475

500

525

550

575

0 0.5 1 1.5 2 2.5 3 3.5 4

16.75 / 17λ 536. ±2.σ 0.35 ±0.06ε 0.83 ±0.19

Angle with deficit centre (°)

Eve

nt d

ensi

ty (e

vt .moo

n-1)

Experimental angular resolution:

✦ Angle between muon and primary particle

✦ Multiple scattering in molasse

✦ Detector angular resolution

+ Moon shadow elongation by geomagnetic field




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Determination of the pointing error

|pµ| > 100 GeV/c, use of the local coordinates system Zenith vs Azimuth

Background: Moon’s path in the sky, delayed in time.

Substracted to source map → Moon effect.

Smoothing: uniform distribution.

Result in standard deviations from normal distribution.

x = Azev - Azmoon (°)

y =

θzev

- θz

moo

n (°

)

x = Azev - Azmoon (°)

y =

θzev

- θz

moo

n (°

)

Comparison Data-MC: pointing error � 0.1◦.




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Observation of the geomagnetic field effect

Deflection = ∆θ · −−−→udefl

∆θ = f(Az, θz, pproton(unknown))Simulation: −−−→udefl = g(Az, θz)

Horizontal axis = - −−−→udefl

=⇒ Deficit along this axis.

65 − 100 GeV/c: ∆x = 0.8◦

> 100 GeV/c: ∆x = 0.25◦

Parallel to deflection (°)

Ort

hogo

nal

to d

efle

ctio

n (°

)


Ort

hogo

nal t

o de

flec

tion

(°)


Ort

hogo

nal t

o de

flec

tion

(°)


Ort

hogo

nal

to d

efle

ctio

n (°

)




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Determination of the angular resolution

Geomagnetic field → horizontal axis.=⇒ Projection on vertical axis: angular resolution only.

-50

0

50

100

150

-3 -2 -1 0 1 2 3

87.32 / 67

Angle from Moon centre (°)

Num

ber

of e

vent

s

λ 122. ±26.resolution 0.39 ±0.10x0 -0.22 ±0.11

-100

-50

0

50

100

150

-3 -2 -1 0 1 2 3

92.07 / 67

Angle from Moon centre (°)

Num

ber

of e

vent

s

λ 100. ±16.resolution 0.18 ±0.05x0 -0.04 ±0.04

Difference with previous estimates due to geomagnetic field.




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Search for antimatter

Simulation: “anti-shadow” symmetric to Moon shadow.

|pµ| > 100 GeV/c.


Ort

hogo

nal t

o de

flec

tion

(°)


Ort

hogo

nal t

o de

flec

tion

(°)




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Measurement of the p/p ratio

|pµ| > 65 GeV/c, deflection coordinates system.

Hypothesis: p, p spectrums with same index.

Maximum likelihood fit:

f(x, y) = ax + by + c︸︷︷︸plane

−N [G(x0, y0, σ)︸︷︷︸p deficit

+ r︸︷︷︸p/p ratio

G(−x0,−y0, σ)︸︷︷︸p deficit

]

=⇒ Moon shadow observation with 8σ significance.

Simulation → uncertainty on the measured ratio.

Preliminary measurement:r = − 0.1 ± 0.15 → r < 0.25 (90% C.L.)

∆lnL 31. 5

Missing events 944. ±320.

x0 0.41◦± 0.14

y0 - 0.05◦± 0.05

r - 0.1 ± 0.15 0

0.025

0.05

0.075

0.1

0.125

0.15

0.175

0.2

0.225

2 4 6 8 10 12 14 16 18 20Missing events (x103)

unce

rtai

nty

on r

atio




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Conclusion

☛ The Moon shadow has been observed with 8σ significance.

☛ Preliminary measurement of p/p ratio is − 0.1 ± 0.15 for a primary energy between .5 TeV and 1 Te

(from MC).

90% C.L. upper limit is 0.25At the moment, 33% of events reconstructed.

With full statistics, uncertainty on the ratio could be reduced down to 0.09.

☛ HEP detectors can be used for muon astronomy with success.

implementation relatively unexpensive

continuously monitored

designed for 10 years of running




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Earth-Moon system simulation

Generate protons around the Moon location

and remove protons hitting the Moon

�Generate protons at the Moon location

From the Moon to the Earth

�From the Earth to the Moon

✦ p spectrum ⇐= data µ spectrum and MC

✦ p generated within 0.27◦ from θMoon −∆θp−−−→udefl

✦ p tracked through geomagnetic field (IGRF

model) up to 5 Earth radii from the Earth

✦ p trajectory prolongated → Earth-Moon distance

✦ Check that p hits the Moon

B

North

Earth

L3

Earth

Moon




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Deflection coordinates system

Moon

Earth

Obs

Moo

n

Udefl

UdeflMoonobs




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Muon momentum spectrum

pµ / GeV

P3 Dµ(P

) (cm

-2 s

-1 s

r-1 /G

eV2 )

Nottingham 1967Kiel 1971AMH 1971MARS 1975AMH 1979Nottingham 1983MASS 1993CAPRICE 1994CAPRICE 1997

L3+C preliminary

10

0.1

0.2

0.3

0.4

0.5

0.6

102

103




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Muon charge ratio

Hayman 1962

Nottingham 1984

Nottingham 1971Durgapur 1972Durham 1975

CAPRICE 1994+1997others

L3+C preliminary

pµ / GeV

R µ

only data points with error smaller than 10% are shown1

1.2

1.4

1.6

1.8

2

10 102

103



measurement of the p ratio using the moon shadow with the l3...

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