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China’s dark matter space probe detects tantalizing signal

52 points by yuvalr1 9y ago

Feniks 9y ago
Number 52 with rice.
AmericanOP 9y ago
Have we ever observed annihilation? Its supposed to emit a ton of energy, right?
- aisofteng 9y ago
  Matter-antimatter annihilation? Yes, absolutely. As one starting point, see: https://en.wikipedia.org/wiki/Electron–positron_annihilation https://en.wikipedia.org/wiki/Electron–positron_annihilation
piotrkaminski 9y ago
> In its first 530 days of scientific observations, DAMPE detected 1.5 million cosmic ray electrons and positrons > "we now expect it to last 5 years" > That will allow the satellite to record more than 10 billion cosmic ray events. Assuming DAMPE continues detecting cosmic ray events at its current rate, I think the total number after 5 years would be a bit over 5 million. That's a few magnitudes off of 10 billion... Math fail, or do I misunderstand something? 1.5m / 530d * 5y * 365d/y = 5.165m
- yuvalr1 9y ago
  Your first quotation should go: > In its first 530 days of scientific observations, DAMPE detected 1.5 million cosmic ray electrons and positrons above a certain energy threshold So presumably the total number of recorded events is more than 1.5 million.
- e2e8 9y ago
  From the paper: During these ∼530 days of operation, DAMPE has recorded more than 2.8 billion cosmic ray events, including ∼ 1.5 million CREs above 25 GeV.
  - piotrkaminski 9y ago
    Ah, makes sense now -- should've gone to the source instead of trusting the article to summarize all numbers. Thanks!
fspeech 9y ago
For those interested the preprint is at https://arxiv.org/pdf/1711.10981.pdf https://arxiv.org/pdf/1711.10981.pdf The satellite carries a very large BGO calorimeter https://arxiv.org/abs/1406.3886 https://arxiv.org/abs/1406.3886
- nigwil_ 9y ago
  I noticed this paragraph about code to do this analysis: "Code availability. The numerical code has been developed with a dedicated application to the DAMPE data analysis. Due to the uniqueness of the DAMPE design and the complexity in- volved in the data analysis, the software package has limited application to the relevant community. We have opted not to make the code public." I'm just an IT guy, and not familiar with how disciplines distribute source-code for this type of analysis, but is this approach common? what does "...limited application" mean here and why not release the code?
  - shakna 9y ago
    It's frustrating but normal not to release code. It makes it easier to release further papers, with less work. Limited application means, "this is our work, all rewards should go to us", preventing others from doing any further research, so no one can "beat them to the punch", so to speak. However, on the other side, it does also prevent checking results accurately.
  - lsh 9y ago
    I'm a tech, not an academic, but I see it as part of the broader problem of science reproducibility. Software plays a huge huge part in modern science publishing and, in the case of data derived using proprietary software, it's expected we just trust the results - that the software is infallible. The comment "We have opted not to make the code public." really gets my goat, but is probably less because they sampled community opinion and found it wanting but more because it's just plain inconvenient or unknown how to publish software. Authors are not actively discouraged from publishing details about the software used (in journals in general) or including copies in the supplementing files, but the process typically has the editors (who guide the authors through the submission process) paring back the submission to just bog standard and familiar media types: image, audio, video, pdf, etc that are known quantities and can be nicely formatted in the final pdf. My small contribution to combating this has been encouraging our editors at eLife to be alert to authors using bespoke or modified software and capturing that software at a specific revision at the time of publication (https://github.com/elifesciences-publications https://github.com/elifesciences-publications) and making sure it meets some basic criteria, like being openly licensed. I'm hoping this effort will help resist general entropy and bit-rot, software moving on or getting lost, licence changes and the overall mandate of eLife to improve science publishing, which means reproducible results and software amenable to audit.
essive 9y ago
Hmmmm...scientists are still debating whether the signal is dark matter or pulsar output (high energies create electron-positron pairs). I see this recent Chinese paper debating if DAMPE can even distinguish dark matter positron remnants or pulsars - Wang et al. (2017) say this - "For the pulsar case, the latest Fermi-LAT anisotropy limits have also been taken into account. Our results show that the cases of DM annihilations to τ+τ− and all charged leptons are difficult to be distinguished from the pulsar cases by the current experiments and DAMPE"

52 points by yuvalr1 9y ago

Feniks 9y ago

Number 52 with rice.

AmericanOP 9y ago

Have we ever observed annihilation? Its supposed to emit a ton of energy, right?

aisofteng 9y ago
Matter-antimatter annihilation? Yes, absolutely. As one starting point, see: https://en.wikipedia.org/wiki/Electron–positron_annihilation https://en.wikipedia.org/wiki/Electron–positron_annihilation

piotrkaminski 9y ago

> In its first 530 days of scientific observations, DAMPE detected 1.5 million cosmic ray electrons and positrons > "we now expect it to last 5 years" > That will allow the satellite to record more than 10 billion cosmic ray events. Assuming DAMPE continues detecting cosmic ray events at its current rate, I think the total number after 5 years would be a bit over 5 million. That's a few magnitudes off of 10 billion... Math fail, or do I misunderstand something? 1.5m / 530d * 5y * 365d/y = 5.165m

yuvalr1 9y ago
Your first quotation should go: > In its first 530 days of scientific observations, DAMPE detected 1.5 million cosmic ray electrons and positrons above a certain energy threshold So presumably the total number of recorded events is more than 1.5 million.
e2e8 9y ago
From the paper: During these ∼530 days of operation, DAMPE has recorded more than 2.8 billion cosmic ray events, including ∼ 1.5 million CREs above 25 GeV.
- piotrkaminski 9y ago
  Ah, makes sense now -- should've gone to the source instead of trusting the article to summarize all numbers. Thanks!

fspeech 9y ago

For those interested the preprint is at https://arxiv.org/pdf/1711.10981.pdf https://arxiv.org/pdf/1711.10981.pdf The satellite carries a very large BGO calorimeter https://arxiv.org/abs/1406.3886 https://arxiv.org/abs/1406.3886

nigwil_ 9y ago
I noticed this paragraph about code to do this analysis: "Code availability. The numerical code has been developed with a dedicated application to the DAMPE data analysis. Due to the uniqueness of the DAMPE design and the complexity in- volved in the data analysis, the software package has limited application to the relevant community. We have opted not to make the code public." I'm just an IT guy, and not familiar with how disciplines distribute source-code for this type of analysis, but is this approach common? what does "...limited application" mean here and why not release the code?
- shakna 9y ago
  It's frustrating but normal not to release code. It makes it easier to release further papers, with less work. Limited application means, "this is our work, all rewards should go to us", preventing others from doing any further research, so no one can "beat them to the punch", so to speak. However, on the other side, it does also prevent checking results accurately.
- lsh 9y ago
  I'm a tech, not an academic, but I see it as part of the broader problem of science reproducibility. Software plays a huge huge part in modern science publishing and, in the case of data derived using proprietary software, it's expected we just trust the results - that the software is infallible. The comment "We have opted not to make the code public." really gets my goat, but is probably less because they sampled community opinion and found it wanting but more because it's just plain inconvenient or unknown how to publish software. Authors are not actively discouraged from publishing details about the software used (in journals in general) or including copies in the supplementing files, but the process typically has the editors (who guide the authors through the submission process) paring back the submission to just bog standard and familiar media types: image, audio, video, pdf, etc that are known quantities and can be nicely formatted in the final pdf. My small contribution to combating this has been encouraging our editors at eLife to be alert to authors using bespoke or modified software and capturing that software at a specific revision at the time of publication (https://github.com/elifesciences-publications https://github.com/elifesciences-publications) and making sure it meets some basic criteria, like being openly licensed. I'm hoping this effort will help resist general entropy and bit-rot, software moving on or getting lost, licence changes and the overall mandate of eLife to improve science publishing, which means reproducible results and software amenable to audit.

essive 9y ago

Hmmmm...scientists are still debating whether the signal is dark matter or pulsar output (high energies create electron-positron pairs). I see this recent Chinese paper debating if DAMPE can even distinguish dark matter positron remnants or pulsars - Wang et al. (2017) say this - "For the pulsar case, the latest Fermi-LAT anisotropy limits have also been taken into account. Our results show that the cases of DM annihilations to τ+τ− and all charged leptons are difficult to be distinguished from the pulsar cases by the current experiments and DAMPE"