Implication of AMS-02 positron fraction measurement Qiang Yuan (yuanq@ihep.ac.cn) Institute of High Energy Physics, Chinese Academy of Sciences Collaborated with Xiaojun Bi, Guo-Ming Chen, Yi-Qing Guo, Su-Jie Lin and Xinmin Zhang 2013-05-09@KIAA, Multi-messenger workshop
AMS02: Phys. Rev. Lett., 2013, 110, 141102
Outline Introduction to cosmic rays Standard model of Galactic cosmic rays Implication of AMS-02 result Conclusion
100 year of discovery Discovered by V. Hess (and some other scientists) ~1912 V. Hess won Nobel Prize in Physics in 1936
Two golden ages of cosmic ray study 1930s-1950s 1932: positron discovered by C. Anderson 1936: muon discovered by C. Anderson and S. Neddermeyer 1946: kaon discovered by G. Rochester and C. Butler 1947: pion discovered by C. Powell 1949: mu-atom discovered by W. Chang ( 张文裕 ) Nowadays Connection with dark matter searches
Detection of particle dark matter
Indirect detection of dark matter Sun Galaxy Cluster Deep extragalactic space and early Universe Baltz et al. 2008
Summary of the measurements of cosmic rays Better to search for DM signal in antiparticles (secondary) due to lower background gamma-rays and neutrinos are also good due to the simple propagation
Galactic cosmic rays: general picture Two unknowns: source and propagation A. W. Strong
Disentangle the source and propagation information Secondary/primary ratio: grammage Unstable/stable of secondary particles: residual time Propagation parameters Source parameters e+, pbar,
PAMELA observation of the positron fraction and pbar/p ratio 2009, Nature, 458, 607 2010, PRL, 105, 121101 Positron has an excess, but no excess from antiprotons!
Several measurements of the electron+positron spectra ATIC, 2008, Nature, 456, 362 Fermi, 2010, PRD, 82, 092004 HESS, 2009, A&A, 508, 561 ATIC shows a peak Fermi shows a smooth bump ATIC/HESS shows a cutoff
To explain simultaneously positron and electron data, we need exotic electron/positron sources. Solar modulation of low energy part
Models Dark Matter Annihilation or decay Leptonic, quark or gauge bosonic final states Smooth or subhalo Many can work but some general conclusions: TeV scale DM Lepton dominated Large annihilation or decay rate Astrophysical Pulsar, SNR, GRB Various populations of SNRs SNR+PWN+SNR/MC Hadronic or leptonic Single or population Burst or continuous injection
CosRayMC: MCMC fitting tool of cosmic ray propagation (Implement the GALPROP code with MCMC sampling) Necessary when large amount data are available Better and easier to constrain the parameters Study the global feature of the model with less bias Full investigation of the high-dimensional correlated parameter space Liu, J. et al., 2010, 2012a, 2012b
Whatever the real physics is, it is possible to parameterize the exotic source component and fit the model parameters from the data Pulsar like scenario Dark matter scenario
Almost indistinguishable between pulsars and dark matter models in the PAMELA era Liu, J. et al., 2012b
What can AMS-02 precise data can tell us? We do the same global fit with pulsar and dark matter scenarios, based on the currently available high quality data (AMS-02 e+/(e+e-), PAMELA e-, Fermi-LAT e+e-)
Determining the propagation parameters
Pulsars as the extra sources of e+e-
DM annihilation to muon pair
DM annihilation to tauon pair
Summary of goodness of fitting It is difficult to fit simultaneously the AMS-02, PAMELA and Fermi-LAT data, which means there might be intrinsic discrepancy of the measurements Pulsars seem to be better to fit the data than DM scenarios
Comparison of different data sets N. Mori, TeVPA 2012 We do observe tension between PAMELA and Fermi data at low energies, but not significant enough. AMS-02 data makes it more significant!
Why pulsars can be better? The positron spectrum from DM is generally too hard while the current AMS-02 data requires softer spectrum
Another difficulty for DM models: constraints from gammarays and/or antiprotons
Pulsars as natural explanation (based on the ATNF pulsar catalog) Yin et al., arxiv:1304.4128
arxiv:1304.1997
arxiv:1304.1840
arxiv:1304.2800
Solutions
AMS-02 measurement of the e+/e- spectra
Spectral hardening of the primary electron spectrum (like what was observed for cosmic ray nuclei) Feng et al. (2013), Cholis & Hooper (2013), Yuan & Bi (2013) PAMELA, 2011, Science Yuan & Bi, arxiv:1304.2687
Asymmetric decaying dark matter Feng & Kang, arxiv:1304.7492
Additional pure e- source (Vela SNR) Gaggero et al., arxiv:1304.6718
Additional signature at ~100 GeV? Y.-Z. Fan et al.
Conclusion There might be tension between AMS02/PAMELA and Fermi-LAT data (under the current theoretical frame) Pulsar scenario can basically fit the data Dark matter scenario fits worse than the pulsar scenario, because the positron spectrum from DM is in general too hard Dark matter scenario will further suffer from strong constraints from gamma-rays and antiprotons Systematic study on-going
谢谢
Charge-sign dependent solar modulation Maccione, 2013, PRL