Anisotropy of Cosmic Ray Fluxes measured with AMS-02 on the ISS M. - PowerPoint PPT Presentation

Anisotropy of Cosmic Ray Fluxes measured with AMS-02 on the ISS M. A. Velasco, CIEMAT, Madrid (Spain) on behalf of the AMS Collaboration

O RIGIN OF THE P OSITRON E XCESS Positron spectrum shows a significant excess above 25 GeV that is not consistent with only the secondary production of positrons [Phys. Rev. Lett. 122 , 041102 (2019)] The cutoff energy (~800 GeV) is established with a significance of more than 4 σ The observation requires the inclusion of primary sources whether from a particle physics or an astrophysical origin Astrophysical point sources of cosmic ray positrons may induce some degree of anisotropy on the measured positron flux 2 M. A. Velasco – TAUP 2019

O RIGIN OF THE E LECTRON E XCESS Electron spectrum shows a significant excess above 42 GeV that is not consistent with lower energy trends [Phys. Rev. Lett. 122 , 101101 (2019)] The electron flux does not have an energy cutoff below 1.9 TeV, i.e. high energy electrons originate from different sources that positrons Astrophysical nearby sources of cosmic ray electrons may induce some degree of anisotropy on the measured electron flux 3 M. A. Velasco – TAUP 2019

O RIGIN OF P ROTON & L IGHT N UCLEI F LUX D EVIATION Proton and light nuclei fluxes measured by AMS show a deviation from a single power law above 200 GeV [Phys. Rev. Lett. 119 , 251101 (2017)] AMS Preliminary data Refer to the upcoming AMS publication This observation may require modification of cosmic ray transport models or the inclusion of local sources of high rigidity events A nearby source of cosmic ray protons or light nuclei may induce some degree of anisotropy in the high rigidity sample 4 M. A. Velasco – TAUP 2019

A NALYSIS OF THE A NISOTROPY Measurement of the cosmic ray fluxes as function of the arrival direction in Galactic Coordinates North-South Forward-Backward direction direction Z East-West X Y direction Galactic center Solar System 5 M. A. Velasco – TAUP 2019

S PHERICAL H ARMONIC E XPANSION OF CR F LUXES The directional dependence of the CR flux is described in terms of an expansion in spherical harmonics Multipolar components Real spherical harmonics basis Dipole anisotropy (ℓ=1) Dipole amplitude Dipole components East-West North-South Forward-Backward 6 M. A. Velasco – TAUP 2019

AMS S KY C OVERAGE Direction Position Geographic coordinates 12º Galactic coordinates 7 M. A. Velasco – TAUP 2019

P OSITRON A NISOTROPY Sample selection Proton background is reduced below the percent level with a selection based on cuts on E/p and the TRD and ECAL estimators For the anisotropy analysis, AMS-02 selected events are grouped into Data 5 cumulative energy ranges: E > 16, 25, 40, 65, and 100 GeV p Event Sample: AMS 6.5 years e + 9.9x10 4 e + (16 < E < 350 GeV) E/p 8 M. A. Velasco – TAUP 2019

P OSITRON A NISOTROPY The arrival directions of positron events are compared to the expected map for an isotropic flux in Galactic coordinates 16 < E < 350 GeV 9.9 × 10 4 positrons Isotropic map 9 M. A. Velasco – TAUP 2019

P OSITRON A NISOTROPY : D ETECTOR E FFICIENCIES Computation of isotropic map requires detailed understanding of detector efficiencies at different geographical locations 16 < E < 350 GeV 2% cos( θ M ) Geographical Coordinates Galactic Coordinates 16 < E < 350 GeV 10 M. A. Velasco – TAUP 2019 TRD Efficiency TRD Efficiency

P OSITRON A NISOTROPY Sky map of the relative fluctuation of the positron arrival directions in galactic coordinates 16 < E < 350 GeV The observed sky map shows no evident pattern 11 M. A. Velasco – TAUP 2019

P OSITRON A NISOTROPY : D IPOLE C OMPONENTS Galactic Coordinates ρ EW ρ NS ρ FB Results consistent with isotropy in all the dipole components and energy ranges 12 M. A. Velasco – TAUP 2019

P OSITRON A NISOTROPY : D IPOLE U PPER L IMITS Upper limits are set for each energy range Amplitude of the dipole anisotropy on e + for 16 < E < 350 GeV δ < 1.9% at the 95% C.I. [Phys. Rev. Lett. 122 , 041102 (2019)] 13 M. A. Velasco – TAUP 2019

E LECTRON A NISOTROPY In addition to the sensitivity to nearby astrophysical sources, the measurement of electron anisotropy provides a test of systematics for the positron analysis Electron sample AMS 6.5 years: 1.3 × 10 6 events (16 < E < 350 GeV) Dipole components – Galactic Coordinates ρ EW ρ NS ρ FB Results consistent with isotropy in all the dipole components and energy ranges 14 M. A. Velasco – TAUP 2019

E LECTRON A NISOTROPY : D IPOLE U PPER L IMITS Upper limits are set for each energy range Amplitude of the dipole anisotropy on e - for 16 < E < 350 GeV δ < 0.5% at the 95% C.I. [Phys. Rev. Lett. 122 , 101101 (2019)] 15 M. A. Velasco – TAUP 2019

P ROTON A NISOTROPY The arrival directions of proton events collected in the first 7.5 years are compared to the expected map for an isotropic flux in Galactic coordinates Selected events are grouped into 9 cumulative rigidity ranges with R > 18, 30, 45, 80, 150, 200, 300, 500 and 1000 GV 1.3 × 10 8 protons Isotropic map R > 18 GV 16 M. A. Velasco – TAUP 2019

P ROTON A NISOTROPY : D ETECTOR E FFICIENCIES Computation of the isotropic map requires detailed understanding of detector efficiencies at different geographical locations R > 18 GV 2% 3% cos( θ M ) Geographical Coordinates Galactic Coordinates R > 18 GV 17 M. A. Velasco – TAUP 2019

P ROTON A NISOTROPY : D IPOLE C OMPONENTS Galactic Coordinates ρ EW ρ NS ρ FB Results consistent with isotropy in all the dipole components and rigidity ranges 18 M. A. Velasco – TAUP 2019

P ROTON A NISOTROPY : D IPOLE U PPER L IMITS Upper limits are set for each rigidity range Amplitude of the dipole anisotropy on protons for R > 200 GV (2×10 6 events) δ < 0.38% at the 95% C.I. AMS Preliminary data Refer to the upcoming AMS publication 19 M. A. Velasco – TAUP 2019

H ELIUM , C ARBON & O XYGEN A NISOTROPY ► Similar analysis applied to the He, C and O samples collected in 7.5 years ► Reduced amplitude of the geographical dependence of the detector efficiencies allows to use extended detector acceptance Helium R > 18 GV 0.5% cos( θ M ) 20 M. A. Velasco – TAUP 2019

H ELIUM , C ARBON & O XYGEN A NISOTROPY All measurements found compatible with isotropy and upper limits to the amplitude of the dipole component are set Helium Helium: δ < 0.36% for R > 200 GV (2.2 × 10 6 He) Carbon: δ < 1.9% for R > 200 GV (6.1 × 10 4 C) AMS Preliminary data Oxygen: δ < 1.7% for R > 200 GV (6.3 × 10 4 O) Refer to the upcoming AMS publication Carbon Oxygen AMS Preliminary data AMS Preliminary data Refer to the upcoming AMS publication Refer to the upcoming AMS publication 21 M. A. Velasco – TAUP 2019

S UMMARY 1. The precise measurements performed by AMS on positron, electron, protons and nuclei fluxes show unexpected features that challenge the traditional paradigm of cosmic rays 2. The study of the directionality of cosmic rays, i.e. the anisotropy, provides complementary information to the spectra and may help to understand the origin of these features 3. A measurement of the anisotropy in the arrival directions of cosmic ray electrons, positrons, protons, helium, carbon and oxygen has been performed in galactic coordinates ► No deviation from isotropy has been observed and upper limits to the dipole amplitude have been quoted 4. AMS will continue taking data until the end of ISS operation, currently 2024. By that time positron statistics will allow us to reach the 1% level predicted by pulsars models 22 M. A. Velasco – TAUP 2019