Context : Two years ago , the Ams-02 \xspace collaboration released the most precise measurement of the cosmic ray positron flux .
In the conventional approach , in which positrons are considered as purely secondary particles , the theoretical predictions fall way below the data above 10 GeV .
One suggested explanation for this anomaly is the annihilation of dark matter particles , the so-called WIMPs , into standard model particles .
Most analyses have focused on the high-energy part of the positron spectrum , where the anomaly lies , disregarding the complicated GeV low-energy region where Galactic cosmic ray transport is more difficult to model and solar modulation comes into play .

Aims : Given the high quality of the latest measurements by Ams-02 \xspace , it is now possible to systematically re-examine the positron anomaly over the entire energy range , this time taking into account transport processes so far neglected , such as Galactic convection or diffusive re-acceleration .
These might impact somewhat on the high-energy positron flux so that a complete and systematic estimate of the secondary component must be performed and compared to the Ams-02 \xspace measurements .
The flux yielded by WIMPs also needs to be re-calculated more accurately to explore how dark matter might source the positron excess .

Methods : We devise a new semi-analytical method to take into account transport processes so far neglected , but important below a few GeV .
It is essentially based on the pinching of inverse Compton and synchrotron energy losses from the magnetic halo , where they take place , inside the Galactic disc .
The corresponding energy loss rate is artificially enhanced by the so-called pinching factor which needs to be calculated at each energy .
We have checked that this approach reproduces the results of the Green function method at the per mille level .
This new tool is fast and allows to carry out extensive scans over the cosmic ray propagation parameters .

Results : We derive the positron flux from sub-GeV to TeV energies for both gas spallation and dark matter annihilation .
We carry out a scan over the cosmic ray propagation parameters which we strongly constrain by requiring that the secondary component does not overshoot the Ams-02 \xspace measurements .
We find that only models with large diffusion coefficients are selected by this test .
We then add to the secondary component the positron flux yielded by dark matter annihilation .
We carry out a scan over WIMP mass to fit the annihilation cross section and branching ratios , successively exploring the cases of a typical beyond-the-standard-model WIMP and an annihilation through light mediators .
In the former case , the best fit yields a p -value of 0.4 % for a WIMP mass of 264 GeV , a value that does not allow to reproduce the highest energy data points .
If we require the mass to be larger than 500 GeV , the best-fit \chi ^ { 2 } per degree of freedom always exceeds a value of 3 .
The case of light mediators is even worse , with a best-fit \chi ^ { 2 } per degree of freedom always larger than 15 .

Conclusions : We explicitly show that the cosmic ray positron flux is a powerful and independent probe of Galactic cosmic ray propagation .
It should be used as a complementary observable to other tracers such as the boron-to-carbon ratio .
This analysis shows also that the pure dark matter interpretation of the positron excess is strongly disfavored .
This conclusion is based solely on the positron data , and no other observation , such as the antiproton flux or the CMB anisotropies , needs to be invoked .