Implication of AMS-02 positron fraction measurement Qiang...
Transcript of Implication of AMS-02 positron fraction measurement Qiang...
Implication of AMS-02 positron fraction
measurement
Qiang Yuan
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
• Introduction to cosmic rays
• Standard model of Galactic cosmic rays
• Implication of AMS-02 result
• Conclusion
Outline
100 year of discovery
Discovered by V.
Hess (and some
other scientists)
~1912
V. Hess won Nobel
Prize in Physics in
1936
• 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
Two golden ages of cosmic ray study
Indirect detection of dark matter
Deep extragalactic
space and early
Universe
Sun
Galaxy
Cluster
Baltz et al. 2008
Better to search for
DM signal in anti-
particles (secondary)
due to lower
background
gamma-rays and
neutrinos are also
good due to the
simple propagation
Summary of the measurements of cosmic rays
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
Positron has an “excess”, but no excess from antiprotons!
2009, Nature, 458, 607 2010, PRL, 105, 121101
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
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
Models
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-)
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
We do “observe” tension between PAMELA and Fermi
data at low energies, but not significant enough. AMS-02
data makes it more significant!
N. Mori, TeVPA 2012
Why pulsars can be better?
The positron
spectrum from DM
is generally too
hard while the
current AMS-02
data requires
softer spectrum
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
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