1. Latest results of the AMS Experiment NCTS Annual Theory Meeting
NCTS, Dec. 06, 2016
Yuan-Hann Chang
National Central University

2. Special colloquium by AMS spokesman Samuel Ting
Thursday, Dec. 8, 2016, 17:00-18:00 at CERN
(Midnight in Taiwan)
“The First Five Years of the Alpha Magnetic Spectrometer on the International Space Station”
Webcast available

3. AMS is a space-borne magnetic spectrometer which measures the ridigidty, energy, charge and velocity of cosmic ray particles precisely
TRD
TOF
Tracker
RICH
ECA L 1 2
7-8
3-4 9
5-6
Time-of-Flight Counter
Transition Raditaion detector
Magnet
Silicon Tracker
Electromagnetic Calorimeter
Ring-Image Cerenkov detector 50 50 50

4. AMS was launched to the ISS by Shuttle Endeavor on May 16, 2011

5. It is a very precise particle physics detector.
AMS Research
In 5 years on ISS, AMS has collected >85 billion charged cosmic rays.
It is a very precise particle physics detector.
The data was analysed by at least two independent international teams 5

6. I. Search for Dark Matter
Positron fraction
Electron and positron spectrum
Antiproton to proton ratio

7. Search for the Dark Matter through its annihilation product: Positrons and Antiprotons in the cosmic rays.

8.  +   e+ + … Physics Result 1: Measurement of the Positron Fraction
Collision of “ordinary” Cosmic Rays produce e+, p…
Annihilation of Dark Matter (neutralinos, ) will produce additional e+, p
 +   e+ + …
M. Turner and F. Wilczek, Phys. Rev. D42 (1990) 1001
Physics Result 1: Measurement of the Positron Fraction
6.8 million e+, e− events
0.1 10
102
AMS-02 data on ISS
m=400 GeV
m=800 GeV
Collision of Cosmic Rays
Dark Matter model based on I. Cholis et al., arXiv:
6.8 million e± events, PRL 110, (2013)
Dark Matter Models
The excess of positrons is measured by
the positron fraction:
e+/(e+ + e−)
Energy (GeV)
PRL 110, (2013) 8

9. Results on the Positron Fraction from 11 million e±
Editor’s Suggestion
II. The rate of increase with energy compared with models
III. The energy beyond which it ceases to increase.
e+ /(e+ + e-)
m=800 GeV
IV. Anisotropy
 +   e+ + …
m=400 GeV
There are several questions we are answering with the measurement
I. The energy at which it begins to increase.
V. The rate at which it falls beyond the turning point.
e+, e- from Collision of Cosmic Rays
e± energy [GeV] 9

10. I. The energy at which it begins to increase10

11. The rate of increase with energy. non-existence of sharp structures.

12. III. The energy beyond which it ceases to increase
#28 12

13. V. The 2024 data beyond the Maximum.
MC simulation
Data by 2024
Pulsars
Positron fraction
Maximum
265±22 GeV
M = 1 TeV
#30 and #117
Collision of cosmic rays
I. Cholis and D. Hooper, Phys.Rev. D88 (2013)
J. Kopp, Phys. Rev. D 88 (2013)
e± energy [GeV] 13

14. AMS 2016 Positron Fraction e± energy [GeV]
Latest result based on 20 million e+, e- events
Comparison with theoretical Models
AMS 2016
Positron Fraction
M = 1 TeV
Slide #27, #117
Collision of Cosmic Rays
Model based on
J. Kopp, Phys. Rev. D 88 (2013)
e± energy [GeV] 14

15. IV. The anisotropy
The fluctuations of the positron ratio e+/e− are isotropic.
Significance
(d)
Pulsar Model : D. Hooper, P. Blasi & P. D. Serpico, JCAP 0901(2009)
Pulsars
Isotropy
Current value
Anisotropy of e+/e-
Galactic coordinates (b,l)
The anisotropy in galactic coordinates
C1 is the dipole moment
Anisotropy on e+/e- : Projected dipole measurement
Data taking to 2024, will allow to explore anisotropies of 1% 15

16. Based on 0.6 million positron events
The Electron and Positron fluxes
Based on 0.6 million positron events
Φ = C E
9,200,000
Electron Spectrum
Positron Spectrum
 =
Precise AMS measurements of the fluxes reveal several important features
Not single power laws
Both harden above 30 GeV – consistent with a contribution of an additional source
600,000
The electron flux also shows excess above 50 GeV. The rise of positron fraction is due to excess of positron, not deficit of electron. 16

17. Latest results based on 1.08 million positron events
AMS 2016
Positron Spectrum
1,080,000
Positrons
Dynamic of the pf variation – e+ becomes harder at high energies 17

18. The antiproton flux and properties of elementary particle fluxes
AMS
Dark matter
Collisions of ordinary cosmic rays
The first striking finding is that fluxes of pbar, p and positrons,
Though different in margnitude exibit the very same functional behavior above certain rigidity.
Models from
Donato et al., PRL 102, ( 2009 ); mχ = 1 TeV
Antiproton is a complementary probe, it cannot be produced in astrophysical origin like pulsars. A constant p/p ratio is surprising. 18

19. Unexpected Result: The Spectra of Elementary Particles e+, p, p
have identical energy dependence above 60 GeV e- does not.
 A challenge to theory/model: positron and antiproton are secondary cosmic rays with very different production and propagation properties. p p e+ e− 20
3x103
Electrons are different 19

20. II. Unveiling the origin and propagation of Cosmic Rays
e+ + e-
Proton
Helium
Boron
Carbon
Lithium
And their ratios.

21. Understanding the cosmic ray acceleration and propagation model is a critical to resolve the mystery of positron excess.
Example: R. Cowsik, B. Burch, and T. Madziwa-Nussinov, Ap. J. 786 (2014) (nested leaky box model, positron comes from interstellar collisions.)
Cowsik (2014)
We need to know the contribution from Astrophysics processes before assessing the Dark Matter contributions.
A good model should predict not just the positron/antiproton flux, but also the fluxes of all the other elements.

22. GALPROP program: http://galprop.standord.edu
Every flux measurement contribute to constrain the parameters.

23. With multiple charge measurement, AMS is an ideal detector to measure the ion spectra in the cosmic rays H He Li C B Be N O Mg Ne F Na Si Al P S Ar Cl K Ca Ti Fe Sc V Cr Mn Ni Co 23

24. The precision AMS measurement of the (e+ + e-) flux.
Energy Range: 0.5 GeV to 1 TeV

25. Spectral index of (e+ + e-)
Φ(e++e−) = C E
γ=−3.170 ± (stat + syst.) ± (energy scale)
E > 30 GeV
The (e+ + e-) flux versus the electron or positron energy
and the result of a single power law fit above 30.2 GeV.

26. AMS Proton Flux The proton flux AMS-02 300 million events
Our flux based 300 M events
We use high statistics proton sample to understand our detector in great details 26

27. Proton Spectrum AMS proton flux The spectrum cannot be
described by a single power law.
Proton Spectrum
Single power law is ruled out at 99.9% confidence level
single power law fit
(traditional assumption) 27

28. The AMS proton spectrum is in good agreement with the Voyager measurement outside of the Solar System when the effect of Solar modulation is properly taken into account

29. AMS Helium Flux The helium flux AMS 50 million events
Helium are the 2nd most abundant cosmic rays and are mostly produced in supernovas. 29

30. Helium Spectrum AMS Helium Flux 50 million helium nuclei Rigidity [GV]
single power law fit
Ruled out at 99.9% C.L.
Helium Spectrum
Rigidity [GV] 30

31. Protons and helium are both “primary” cosmic rays.
The AMS proton/helium flux ratio
Protons and helium are both “primary” cosmic rays.
Their rigidity ratio has traditionally been assumed to be flat.
Theoretical prediction
A. E. Vladimirov, I. Moskalenko, A. Strong, et al., Computer Phys. Comm. 182 (2011) 1156
AMS: this ratio is not flat. 31

32. Physics Result 8: The Boron flux
2.3 million boron nuclei 32

33. Physics Result 9: The Carbon flux
8.3 million carbon nuclei 33

34. Flux Ratios: Boron/Carbon and propagation
C, N, O, … + ISM  B + X
Galactic Halo C
AMS B
Galactic Disk
Cosmic Rays are commonly modeled as a relativistic gas diffusing through a magnetized plasma.
Models of the magnetized plasma predict different behavior for B/C = k Rδ. With the Kolmogorov turbulence model δ = -1/3 is expected, while the Kraichnan theory leads to δ = -1/2. 34

35. Physics Result 7: The Boron-to-Carbon (B/C) flux ratio
2.3 million boron nuclei and
8.3 million carbon nuclei

36. 2.3 million boron nuclei and 8.3 million carbon nuclei
Cowsik (2014)
A single power law in favor of Kolmogorov model is unexpected. How much room is left for a pure astrophysical explanation of the excess of positron?
\delta = \pm 0.013
\mathrm{B}/\mathrm{C} = k R^{\delta} 36

37. Simultaneous agreement between the model and the measured spectra of
Proton
Anti-Proton
Helium
Electron
Positron
Li, Be, B, C, N, O, … Fe, ….
provides very strong constraint to the parameters and the understanding of the Galactic environment (ISM, magnetic field, sources, etc.)

38. Example of systematical study of cosmic ray propagation:
A.E. Vladimirov et. al., The Astrophysical Journal 752:68 (2012)

39. Next steps for AMS: Precision measurement of the spectra of more elements in the cosmic rays. This will provide a precise set of data to constrain the cosmic ray models.
Next results: Li spectrum

40. Summary:
Excess in positron and antiproton strongly suggest the existence of an unknown source. However, we need to know the astrophysical sources with better precision.
To correctly evaluate positron and antiprotons from astrophysical origin, a precise cosmic ray acceleration and propagation model is needed.
AMS measurements of P, He, B, C spectra already provide strong constraints to the existing cosmic ray models.
Measurements of more elements (up to Fe) is being carried out.
New effects to be explained:
The spectra indices break at ~200 GeV.
The unexpected p/He ratio.
Positron/antiproton/proton follows the same power law, but not electron.
Continue taking data through the lifetime of the ISS is critical to resolve some of these issues.

41. DoE AMS Review Chairman’s Report
AMS will continue taking data through the lifetime of ISS, currently 2024.
DoE AMS Review Chairman’s Report
Barry C Barish
October 11, 2016
AMS is a very impressive state-of-the-art particle spectrometer, operating at high efficiency on the International Space Station (ISS). AMS has now been running in a data taking mode for about five years, and has accumulated and published a tremendously impressive array of results on cosmic rays. These precision result have essentially ruled out previously published anomalies that may have indicated new physics. The AMS results on a wide range of cosmic ray yields are truly impressive and provide a very good basis for the committee to evaluate both the present results and the future physics potential of AMS. In addition, the detailed reports on AMS operations have given the committee a good picture of the needs and problems involved in successfully operating the AMS instrument on the International Space Station. …
On the question of how much longer AMS should run, considering the unique nature of AMS and the low probability that a comparable instrument will operate in the foreseeable future, the committee concludes that: i) there is an obvious case to support operations through the three-year period covered by the proposal; and ii) there is a strong case for support through 2024, the currently expected operational life of the ISS. 41

42. Stay Tuned 42

43. Slope [GeV-1] Positron Fraction Zero crossing 265 ± 22 GeV Maximum
#28
Positron Fraction
Maximum
265 ± 22 GeV
e± energy [GeV] 43

44. Measurements of the proton spectrum
before AMS
Proton Spectrum
Before AMS – proton flux measurements 44

45. Measurements of helium spectrum
before AMS
Helium Spectrum
Similarly for the He – before AMS
Helium are the 2nd most abundant cosmic rays and are mostly produced in supernovas.
These were the best data before AMS. 45