KIAA-WAP, Peking U

2015/9/28

Implications on CRs and DM 　from the AMS-02 results

Xiao-Jun Bi ( 毕效军 )

Center for Particle and Astrophysics

IHEP, Beijing

AMS-02 changes the field of cosmic ray physics

Before AMS-02:

The model parameters are adjusted manually according to experience. As the errors are large and systematics from different experiments are not well understood, it is satisfactory by such a treatment.

AMS-02 changes the field of cosmic ray physics

After AMS-02:

Is it possible to explain these data in the same way as before, after AMS-02 provides the extremely precise measurements?

NO!NO!We propose a quantitative precise study of cosmic rays.

Aim of our study• To give a quantitative, precise explanation to the

AMS-02 results by a global fitting to the data.

• Being a powerful tool we adopt Galprop to calculate the CRs propagation.

• We adopt MCMC algorithm to give a global fitting to data, so that we can 1, precisely explain the data; 2, precisely determine the properties of new sources (DM or astrophysical); 3, reveal some subtle effects hid in data.

Bkg+pulsar (or DM) to fit the data

1 ， propagation of charged particles is treated by Galprop. We fit the parameters to data by MCMC

2, Note: Note: pulsar and DM are just taken as two typical benchmark models. Certainly there are many other possibilities.

1, we adopt the method to fit the AMS-02 (2013) positron fraction together with the Fermi-LAT electron/positron spectrum. Both pulsar and DM scenarios are studied.2, It seems the data can be fit well. However, the χ2/dof=1.8; 6σ excluded by data. 3, Fermi data is not consistent with AMS02 data considering large systematics. 4 ， We fit without including the Fermi data. χ2/dof=52/80; perfect fit to data!

Yuan, Bi, Chen, Guo, Lin, Zhang, 1304.1482

Comments:1, PAMELA has higher positron fraction with larger errors which leads to consistency with Fermi spectrum. 2, It is the high accuracy of AMS-02 measurement that leads us to draw the conclusion of inconsistency between Fermi and AMS-02.

1304.1482

宇宙线中的电子加正电子能谱与以往实验的比较

流量

x E

3 (s s

r m

2

GeV

)-1

能量(GeV)

AMS-02 重要结果：以前的实验结果是错误的

1409.6248

Conclusions of the quantitative study I• There is a new break at the primary electron spectrum

Comments: 1 ， This is similar to the case of proton spectrum measured by AMS2. The electron break is at ~60GeV with Δγ ≈ 0.3.2, again precise fit! without second break the fitting to the DM parameters should be wrong, as a wrong background is adopted! （ Without a sufficient understanding of background, we can never understand the signal correctly. ）

3, subtle effect is hid behind the precise data, only by quantitative study can it be revealed.

"Advances in Cosmic Ray Science" Waseda University

Electrons can provide additional information about the GCR source

• High energy electrons have a high energy loss rate E2

– Lifetime of ~105 years for >1 TeV electrons

• Transport of GCR through interstellar space is a diffusive process– Implies that source of high energy electrons are < 1 kpc away

• Electrons are accelerated in SNR• Only a handful of SNR meet the

lifetime & distance criteria• Kobayashi et al (2004)

calculations show structure in electron spectrum at high energy

Conclusions of the quantitative study II

Both astrophysical sources, like pulsars, or dark matter can give good fit the AMS-02 data. AMS02 data can not distinguish the two scenarios.

• The AMS-02 positron(pbar) data do not favor the diffuse+reacceleration propagation model, but the convection model.

Conclusions of the quantitative study III

Systematic uncertainties in the model

• Uncertainties from the propagation parameters• Solar modulation• Interaction cross sections• Minor ones …

The AMS-02 data is precise enough. However, the theoretical model has large uncertainties. This is the main difficulty for precise study. We study how the uncertainties affect the fitting to the data. The model uncertainties includes

Yuan & Bi, JCAP03, 033 (2015)

Propagation uncertainties

Solar modulation

Strong interaction models

AMS-02 pbar/p results

Summary • AMS-02 opens a new era for precise study of cosmic

rays. The subtle effects from background and/or from dark matter can be revealed by a quantitative study.

• We found interesting effects, such as the new break of the primary electron spectrum, the constraints on the cosmic ray propagation model from AMS-02 data.

• Both DM and pulsar give good explanation to data, (but DM is strongly constrained by Fermi).

• Excess of antiproton is not significant. Constraint on DM annihilation can be derived. DM improves fit to data.