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

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

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

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

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

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

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

 +   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:0810.5344 6.8 million e± events, PRL 110, 141102 (2013) Dark Matter Models The excess of positrons is measured by the positron fraction: e+/(e+ + e−) Energy (GeV) PRL 110, 141102 (2013) 8

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

I. The energy at which it begins to increase 10

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

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

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) 023013 J. Kopp, Phys. Rev. D 88 (2013) 076013 e± energy [GeV] 13

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) 076013 e± energy [GeV] 14

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

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

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

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, 071301 ( 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

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

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

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) 124 (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.

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

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

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

Spectral index of (e+ + e-) Φ(e++e−) = C E γ=−3.170 ± 0.008 (stat + syst.) ± 0.008 (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.

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

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

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

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

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

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

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

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

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

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

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 = -0.352 \pm 0.013 \mathrm{B}/\mathrm{C} = k R^{\delta} 36

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.)

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

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

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.

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

Stay Tuned 42

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

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

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