Transcript Indirect Dark Matter Search with AMS-02 Stefano Di Falco

Indirect
Dark Matter Search
with AMS-02
Stefano Di Falco
INFN & Universita’ di Pisa
for the AMS collaboration
Indirect search for Dark Matter
nn
Direct production
Decay of W
Decay of Heavy Quark
Decay of Charged Pions
Photons
Direct Production : Eg = mX
EGRET
Decay ofg Neutral
Pions
excess?
AMS
a multichannel approach
e+e-
Direct production: Ee = mX
Decay of W,
Decay ofe+Heavy
Quark
HEAT
Decay ofexcess?
Leptons and Charged Pions
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pp, (dd)
No direct production
Hadronization : Eh << mX
p excess?
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The AMS (Alpha Magnetic Spectrometer) experiment
AMS-01
AMS-02
1998
2008*-…
10 days on Space Shuttle Discovery
3 years on ISS
- He/He < 1.1·10-6
- very nice measurements of primary and
secondary p, p, e-, e+, He, and D spectra
from ~1 to 200 GeV
- Superconducting magnet
- New detectors
- ANTIMATTER SEARCH: He/He < 10-9
- COSMIC RAY FLUXES up to Z=26
- DARK MATTER SEARCH
(Phys. Rept. vol. 366/6 (2002) 331)
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*ready for launch date
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The AMS detector
TRD (Transition Radiation Detector):
1m
20 layers of Foam + Straw Drift Tubes (Xe/CO2 )
3D tracks, e/h separation>102 rej. up to 300 GeV
~2 m
AMS Weight: 7 Tons
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1 out of 328 Straw tube Modules
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The AMS detector
TOF (Time of Flight):
1m
2+2 layers of scintillators, Dt =~160ps
Trigger, Z separation, b with few % precision
~2 m
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2 out of 4 layers
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The AMS detector
Superconducting Magnet:
1m
12 racetrack coils & 2 dipole coils cooled to
1.8° K by 2.5 m3 of superfluid He
Contained dipolar field: BL2 = 0.85 Tm2
~2 m
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Technological challenge:
first superconducting magnet operating in space
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The AMS detector
Tracker:
1m
8 layers double sided silicon microstrip detector
sR(igidity)<2% for R<10 GV, R up to 2-3 TV, Z separ.
~2 m
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The AMS detector
RICH (Ring Imaging CHerenkov):
2 Radiators: NaF (center), Aerogel(elsewhere),
b with 0.1% precision, Z and isotopes separation,
(2% precision on mass below 10 GeV/n)
1m
radiator
reflector
PMT plane
~2 m
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The AMS detector
ECAL (Electromagnetic Calorimeter):
1m
Sampling: 9 superlayers of Lead+Scint. Fibers
trigger, e, g detection: sE(nergy) <3% for E>10 GeV,
3D imaging: e/h separation>103 rej
~2 m
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Expected particle fluxes
p and He from AMS-01
e+, e- and g from Moskalenko & Strong*
e+/p ~ 5·10-4 @ 10 GeV
e+/e- ~ 10-1 @ 10 GeV
ggalactic center/p ~ 10-4 @ 10 GeV
ggalactic center/e-~ 10-2 @ 10 GeV
Very high particle identification needed
*ApJ 493 (1998) 694
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AMS response to positrons and protons
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TRD signal
X rays from transition radiation
No signal if g<103 (E<300 GeV)
Rejection factor 102-103
up to 300 GeV
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AMS response to positrons and protons
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TOF signal
t~4ns, Dt~160ps
bTOF ~ 1, |Z|=1,
•Reject upgoing particles
•Reject p up to 1.5 GeV
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(kinetic energy)
•Reject He (|Z|=2)
bTOF ~ 0.92±[email protected], |Z|=1
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AMS response to positrons and protons
P
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•Charge determination:
Positive curvature
(with TOF): Z= +1
reject e- and He++
•Rigidity measurement
(E/p matching):
Positive curvature
(with TOF): Z= +1
Resolution in Rigidity (%)
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Tracker signal
Rigidity (GV)
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AMS response to positrons and protons
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RICH signal
q~17° (41° at center), Dq~0.2°
Np.e. ~7 (4 at center)
•Reject p up to 10 GeV
bRICH ~ 1, |Z|=1,
(kinetic energy)
•Reject He (|Z|=2)
bRICH~0.996±0.001@10GeV,
|Z|=1
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AMS response to positrons and protons
ECAL signal
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Electromagnetic shower:
• prompt
• known longitudinal profile
• recoverable leakage
• narrow
• strongly collimated
~16X0
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Hadronic shower:
• not prompt
• wrong longitudinal profile
• unrecoverable leakage
• wide
• weakly collimated
~1lI
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Rejection factor ~103
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AMS response to positrons and protons
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ECAL+Tracker: E/p matching
E/P > 1-(sTrackersECAL)/E
sTracker(E)/E = 0.05%·E(GeV)  3% (E>50GeV)
sECAL(E)/E = 12%/sqrt(E(GeV))  2%
Radiative tail
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Positron and background acceptance
Results from a montecarlo study using discriminant analysis*
Kinetic energy (GeV)
Kinetic energy (GeV)
Acceptance for e+:
~0.045 sr m2 from 3 to 300 GeV
Rejection factor for p : ~105 **
Rejection factor for e-: ~104
* P. Maestro, PhD Thesis, 2003
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** Including a ~7 flux factor improvement because <Edep>~Ekin/2 )
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S. Di Falco, Indirect dark matter search with AMS-02
Number of Positrons in 3 years
In 3 years AMS will collect
O(105) e+ with 10<E< 50 GeV
[ O(102) for HEAT ]
Total contamination: ~4%
Reconstructed energy (GeV)
Good sensitivity up to 300 GeV
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Positron fraction: statistical error in 3 years
The positron fraction e+/(e++e-) is preferred to the e+ flux because is less
sensitive to uncertainties on cosmic-ray propagation and solar modulation
Parametrization of the
standard prediction
for positron flux*
(without Dark Matter)
Errors are
statistical only
*Baltz et al., Phys. Rev. D 59, 023511
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Possible scenarios from neutralino annihiliation
Example of neutralino annihiliation signal observed by AMS with the boost
factors found by Baltz et al.* to fit the HEAT data and motivated with a
inhomogenous dark matter density (clumpiness)
 gaugino dominated
m= 340 GeV, boost factor=95
e+ primarily from hadronization
 gaugino dominated
m= 238 GeV, boost factor=116.7
hard e+ from direct gauge boson decay
*Baltz et al.; Ph.Rev D65, 063511
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More neutralino scenarios: needed boost factors
The mimimal boost factor to see the LSP annihilation at 95% C.L. in the positron
channel in 3 years is reduced if the gaugino mass universality condition in mSugra is
relaxed*
mSugra :
• m1/2 = M1 = M2 = M3
Relaxing gaugino mass universality :
•Gluino Mass : M3 = 50% m1/2
• tan b = 10
*J. Pochon, PhD Thesis, 2005
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Possible positron signals from Kaluza-Klein model
Kaluza-Klein model are interesting because allow for direct production
of e+e- pairs in the annihilations of the LKP (B1)
Boost factors needed:**
~O(102) to fit HEAT data
~110 for discovery
much steeper raises can fit HEAT data*
Positron fraction e+/(e++e-)
 AMS 3 years Signal with Boost
*J.Feng,Nucl.Phys.Proc.Suppl.134 (2004) 95
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adjusted on HEAT data + Bg
∆ AMS (3 years) Signal with Boost at
visibility limit + Bg
—
Background ( no DM)
**J Pochon & P Salati
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Dark Matter annihilation into photons
●
●
The center of the
galaxy can be a very
intense point-like source
of gammas from dark
matter annihilations.
Unlike positrons,
gammas travel long
distances and point to
the source
The annihilation signal could be enhanced by a cuspy
profile of the DM density at the galaxy center (supermassive black hole (SMBH), adiabatic compression,...)
●
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Photon detection in AMS
Photon conversion:
Direction (angle): from Tracker
Energy: from Tracker (and ECAL)
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Single Photon (direct measurement)
Direction (angle): from ECAL
Energy: from ECAL
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Gamma energy and angular resolution
Energy resolution
6%
3%
~1o
Angular resolution
0.02o
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Main backgrounds to Photons
Conversion mode
d rays
Rejection factor: >105(p), 4·104(e)
Using: TRD veto, invariant mass
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Single Photon mode
Secondaries (p0) from p interactions
Rejection power: 5·106
Using: veto on hits, g direction
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Acceptance (m2.sr)
Gamma acceptance and effective area
GeV
Max Acceptance:
Conversion mode:
Field of view:
0.06 m2·sr
Single photon mode: 0.097 m2·sr
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Conversion mode:
~43°
Single photon mode: ~23°
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AMS-02 Exposure to g from galactic center
51º latitude
Conversion mode (sel. acc.)
GC : ~ 40 days
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Revolution : 90’
Single photon mode (geom. acc.)
GC : ~ 15 days
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Statistical significance (single photon mode)
Statistical error on
photon spectrum
from galactic center
(AMS 3 years):*
68% C.L.
95% C.L.
Good sensitivity
between 3 and 300 GeV
* F. Pilo, PhD Thesis, 2004
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E (GeV)
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Gamma sensitivity to neutralino annihilation
E2Flux (GeV/cm2s)
Example*: m = 208 GeV (AMS 1 year)
Egret
— Background
— Signal
— Background + Signal
— Background
— Signal
— Background + Signal
* L. Girard. PhD Thesis,2004
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E (GeV)
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Gamma sensitivity for different halo profiles
Kaluza-Klein & SuSy Models Scan for different halo profiles*:
*A. Jacholkowska et al., astro-ph/0508349
**Navarro, Frenk & White, ApJ 490 (1997) 493
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Antiproton detection in AMS
Main Backgrounds:
• Protons: charge confusion, interactions with
the detector and misreconstructed tracks.
• Electrons: beta measurement, e/h rejection
Antiproton signal:
-Single track in TRD + Tracker
- Z = -1
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Rejection :
p : > 106
(ToF, Rich …)
e- : > 103-104
TRD /Ecal
Acceptance :
1-16 GeV : 0.160 m2·sr
16-300 GeV : 0.033 m2·sr
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Antiproton flux measurement with AMS
Current Measurements:
large errors below 35 GeV,
AMS-02 *
Conventional p flux
with Statistical Errors (3 years)
Range 0.1 to ~ 500 GeV
*V. Choutko (2001)
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Possible DM signal in Antiproton spectrum
Low Energy Spectrum well explained by secondary production.
There is room for a signal at high energy (10 – 300 GeV):*
1)
M=964 GeV
(x4200)
2)
M=777 GeV
(x1200)
However models require a boost factor.
* P. Ullio (1999)
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Conclusions
The AMS experiment, during its 3 year mission, will be
able to measure simultaneously and with unprecedented
precision the rates and spectra of positrons, gammas
and antiprotons in the GeV-TeV range, looking for an
excess of events that could hint for a dark matter
annihilation signal.
Several models for dark matter candidates can be
constrained by the new AMS data.
The AMS simultaneous measurements of other
fundamental quantities (p and e spectra, B/C ratio,…)
will help to refine the astrophysical predictions
enhancing the compelling evidence for a dark matter
signal.
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Backup
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Background flux calculations
F(m-2 s-1 sr-1 GeV-1) = φbg + φsignal
Local Background Flux determined by propagation of CR
yield per unit volume through simulation (GALPROP)
CR source distribution and
spectrum (index, abundances)
Gas (HI,H2,HII…)
distribution
Diffusion model (reacceleration,
diffusion) and parameters (D,size
h, cross-sections…)
Physical background:
• Antimatter channels:
secondary products from cosmic ray spallation in the interstellar medium;
• Gamma ray channel:
diffuse Galactic emission from cosmic ray interaction with gas (π0 production,
inverse Compton, bremsstrahlung)
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Signal flux calculations
F(m-2 s-1 sr-1 GeV-1) = φbg + φsignal
Local Flux determined by propagation of CR yield per unit
volume through simulation (GALPROP)
(propagation model and
parameters …)
CR yield per unit volume (r,z,E) ≡ gann(E).*<σv>*(ρχ(r,z) /mχ)2
ASTROPHYSICS
Rotational velocity
measurements
DM density profile shape
(+ “boost factors*”)
COSMOLOGY
WMAP (+…) constraints on
h2
HEP
gann(E) ≡ particle production
rate per annihilation
mχ ≡ neutralino mass
<σv> ≡ coannihilation crosssection
Accelerator constraints
SUSY parameter space
(5+…)
ρχ(r,z) ≡ density distribution
Boost factors: clumpiness,cuspiness, baryon interaction, massive central black hole…
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Indirect Search: neutralino annihilation
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Indirect Search: neutralino annihilation
Charged:
Propagation G
•diffusion model
•earth vicinity
Cosmology
•Nominal Local density of Dark Matter: 0.3
GeV/cm3
•Distribution:
•Clumps <2 > = Boost <>2
•Halo shape
(Galactic Centre)
Particle Physics
•models: sanni , annihilation
channels and mX
•should be compatible with
DM Relic Density
Gamma:
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Antideuterons
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Antideuterons
●
●
Antideuterons have never been measured in CR
could be an alternative channel to look for dark matter signals.
Claim: almost background-free channel at low energies
DM signal
Spallation
spectrum
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1 /GeV/year
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Antideuterons
Spallation
spectrum
Estimate of AMS potential under study:
focused on low momenta, antiproton flux
is the main background – need 105
discrimination - mass resolution is
crucial!
tertiary
component
TOA flux prediction is even less optimistic
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Some favourites Dark Matter candidates
•
Models of Supersymmetry : mSugra
– 5 parameters:
• m0
: scalar mass
• m1/2
: gaugino mass
• A0
: sleptons and squarks coupling
• tan b : ratio of VED of the Higgs doublets
• sign() : Higgs mass parameter
– R-parity conservation
• Ligthest Susy Particle stable : Neutralino
•
Extensions à la Kaluza-Klein: 2 working models with Extra Dimensions
– Universal Extra Dimensions (UED)
• all SM particles propagates in X-dimensions
• Lightest First Excitation Level is stable : B(1) ( ~g(1) )
– Warped Grand Unified Theories
• Z3 symmetry to ensure proton stability
• Lightest Z3 charged particle is stable (nR(1) )
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Positron fraction after 3 years: AMS and PAMELA
AMS
PAMELA
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Antiproton expected flux (without DM)
Uncertainty mainly due to
present determination of B/C
Low Energy Spectrum well explained by secondary production.
The prediction are very sensitive to the physics details of cosmic ray propagation,
particularly at low momentum. This is controlled by secondary/primary ratios,
like B/C. AMS will measure the B/C ratio with high precision
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B/C measurement in AMS
Charged nuclei
Charge(Z): from TOF, Tracker and RICH
Rigidity(R): from Tracker and Magnet
Velocity(b): from TOF and RICH

Mass and Charge
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Gamma detectors in space
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AMS response to positrons and protons
E/P > 1-(sTrackersECAL)/E
X rays from transition radiation
q~17° (41°
at center), Dq~0.2°
Electromagnetic
shower:
•Charge
determination:
sTracker(E)/E = 0.05%·E(GeV)
 3% (E>50GeV)
• (4
prompt
N
~7
at
center) ++
p.e.
Positive
curvature
t~4ns, Dt~160ps
reject
e- and
He
sECAL(E)/E = 12%/sqrt(E(GeV))

2%
• known
longitudinal
profile
(with
TOF):
Z=
+1
b
~
1,
|Z|=1,
TOF
•Reject p up to 10 GeV
bRICH ~ 1, |Z|=1,
~16X0
P
r
o
t
o
n
• recoverable
leakage
•Rigidity
measurement
• narrow
(kinetic energy)
(E/p• strongly
matching):
collimated
•Reject
upgoing particles
•Reject
He (|Z|=2)
Resolution in Rigidity (%)
P
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ECAL+Tracker:
ECAL
E/p matching
TRD
TOF
Tracker
RICH
signal
signal
signal
•Reject p up to 1.5 GeV
(kinetic energy)
Hadronic
shower:
No signal if g<103 (E<300 GeV)
Radiative
tail
•Reject
He (|Z|=2)
• not prompt
• wrong longitudinal profile
Positive curvature
• unrecoverable leakage
(with TOF): Z= +1
factor 102-103
• Rejection
wide
up to 300 GeV
• weakly
collimated
bRICH
~
~
0.996±0.001@10GeV
0.92±[email protected],
,
|Z|=1
TOF
|Z|=1
Rigidity (GV)
~1lI
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Rejection factor ~103
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The AMS detector
TRD (Transition Radiation Detector):
20 layers of Foam + Straw Drift Tubes (Xe/CO2 )
3D tracks, e/h separation>102 rej. up to 300 GeV
TOF (Time of Flight):
2+2 layers of scintillators, Dt =~160ps
Trigger, Z separation, b with few % precision
Superconducting Magnet:
1m
Nb-Ti coils in superfluid He(1.8  K).
Contained dipolar field: BL2 = 0.85 Tm2
Tracker:
8 layers double sided silicon microstrip detector
sR(igidity)<2% for R<10 GV, R up to 2-3 TV, Z separ.
RICH (Ring Imaging CHerenkov):
2 Radiators: NaF (center), Aerogel(elsewhere),
b with 0.1% precision, Z and isotopes separation,
(2% precision on mass below 10 GeV/n)
ECAL (Electromagnetic Calorimeter):
~2 m
La Thuile, March 2006
Sampling calorimeter: Lead+Scint. Fibers
trigger, e, g detection: sE(nergy) <3% for E>10 GeV,
3D imaging: e/h separation>103 rej
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