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Author Topic: Do we know the identity of Dark Matter?  (Read 3156 times)

Offline imatfaal

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Do we know the identity of Dark Matter?
« on: 03/04/2013 18:00:43 »
The long awaited and trailed announcement from the AMS Collaboration is here

 SPECIAL CERN-EP Seminar on Wednesday 3rd of April 2013
 "Recent results from the AMS experiment"
 by Prof. Samuel TING (Massachusetts Inst. Of Technology (US))
https://indico.cern....y?confId=244334

NASA TV BRIEFING DISCUSSES ALPHA MAGNETIC SPECTROMETER RESULTS
 NASA will hold a news conference at 1:30 p.m. EDT on Wednesday, April 3, to discuss the first results of the Alpha Magnetic Spectrometer (AMS) experiment.

 For NASA TV streaming video, scheduling and downlink information, visit:
http://www.nasa.gov/ntv

AMS Draft Press Announcement (cannot find final version) http://ams.nasa.gov/AmsScientificPublications.html
 
BBC - http://www.bbc.co.uk/news/science-environment-22016504

Nature http://www.nature.com/news/space-station-experiment-deepens-antimatter-enigma-1.12718

Space,com http://www.space.com/20488-nasa-astrophysics-discovery-ams.html  (although can you trust an astro site that cannot convert EDT to GMT???)

Science Magazine http://news.sciencemag.org/sciencenow/2013/04/two-billion-dollar-cosmic-ray-de.html



The know-nothing bozzo version is a little disappointing.  What the AMS Colab are announcing is at present confirmation of the previously hinted at positron excess - more positrons (anti matter electrons) than would be expected in open space.  This is not new but previous evidence was compromised and unconvincing.  The AMS detects from the whole sky (so rules out a localized source), was designed to tell positrons from electrons (so does not suffer from the possible problem of using deflecting by earths magnetic field to distinguish), and can accurately tell that these are the light positrons rather than much heavier protons.  From my early reading this confirmation of (lower energy) positron excess is well documented and evidence by the AMS data and is accurate to a high significance. 



The more interesting bit is that the theory suggested that the level of positron excess should fall with measured energy - but it clearly shows a dip and rise.  There is something which is annihilating or decaying to positrons which is outside of current theory.  The idea is that this unknown is dark matter.

 

Even more speculative is the fact that after a rise - at around 250-300 GeV - the curve starts to flatten off.  It would make sense that you cannot get dark matter particles to produce positrons of a higher energy than the parent particle - is this flattening off the sign of the energy of a dark matter particle?
« Last Edit: 10/04/2013 12:34:57 by chris »


 

Offline CPT ArkAngel

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Re: AMS announcement on Dark Matter
« Reply #1 on: 03/04/2013 21:43:17 »
A cold Dark Matter particle being 250 to 300 times heavier than the proton must produce black holes or other strange objects...
 
 

Offline syhprum

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Re: AMS announcement on Dark Matter
« Reply #2 on: 03/04/2013 23:09:09 »
The article can be found here


http://physics.aps.org/articles/v6/40
 

Offline imatfaal

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Re: AMS announcement on Dark Matter
« Reply #3 on: 03/04/2013 23:59:35 »
The article can be found here


http://physics.aps.org/articles/v6/40

Thanks. Will try and read it.  I will probably only really understand the huge list of names making up the collaboration.
A cold Dark Matter particle being 250 to 300 times heavier than the proton must produce black holes or other strange objects...
 

Why so?   Black holes are entities for which the schwarzchild radius is greater than the predicted physical radius -  what information about density, substructure, size of a dark matter particle allows you to know this about a particle from just its energy?.i cannot look it up as I am on mobile but what are the weights of the massive rare particles - surely a tip quark is already about 180 GeV and what is a plutonium atom (I am guessing a shade over 200)?   My point is that we know next to nothing about these particles so have to be careful ascribing properties to them.
« Last Edit: 04/04/2013 00:04:45 by imatfaal »
 

Offline CPT ArkAngel

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Re: AMS announcement on Dark Matter
« Reply #4 on: 04/04/2013 00:53:17 »
You can't compare the sizes of elementary particles to atoms sizes.

Dark matter particles don't interact with EM, only weakly and gravitationally, they don't form atoms.

A hypernova does form a black hole from a starting radius much larger than the Schwarzschild radius.
« Last Edit: 04/04/2013 00:54:50 by CPT ArkAngel »
 

Offline Bill S

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Re: AMS announcement on Dark Matter
« Reply #5 on: 04/04/2013 03:12:48 »
 

Offline syhprum

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Re: AMS announcement on Dark Matter
« Reply #6 on: 04/04/2013 09:16:51 »
It is a long time since I was lectured on logarithmic notation so I was  little confused by the graphs where the vertical axis is labelled logarithmically while the horizontal axis is labelled by a mixture
I took me a little while to appreciate that 10^-1 = 0.1 while 1=10^0 and 10=10^1
 

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Offline Pincho

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Re: AMS announcement on Dark Matter
« Reply #7 on: 04/04/2013 12:30:54 »
Shrunk
I'm not going to throw the thread off topic, so here is a link to my version...

http://www.thenakedscientists.com/forum/index.php?topic=47070.msg408327#msg408327
 

Offline imatfaal

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Re: AMS announcement on Dark Matter
« Reply #8 on: 04/04/2013 15:09:41 »
You can't compare the sizes of elementary particles to atoms sizes.
Of course you can - when you have no idea of the internal structure of the dark matter particle you use every aid or comparison you can. 
Quote
Dark matter particles don't interact with EM, only weakly and gravitationally, they don't form atoms.
Who said they did?  You claimed knowledge of how a massive - yet otherwise completely unknown particle would behave.  I showed that particles of that around mass exist as both elementary and composite particles

Quote
A hypernova does form a black hole from a starting radius much larger than the Schwarzschild radius
. That why I said predicted physical radius - the hypernova only forms when the density is changed by the implosion and throwing off of exterior, this changes the density and results in an object with an external s'child radius. Anything with enough mass in a small enough volume forms a black hole.  As you have no possible knowledge of the density of a dark matter particle you cannot say whether it would form a black hole or not.  Mass is not enough to predict whether something will form a black hole - we use it as a shortcut for stars because all stars mass / density / radius are all linked by the same formulae. 

 

Offline Pmb

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Re: AMS announcement on Dark Matter
« Reply #9 on: 04/04/2013 18:14:41 »
The long awaited and trailed announcement from the AMS Collaboration is here

 SPECIAL CERN-EP Seminar on Wednesday 3rd of April 2013
 "Recent results from the AMS experiment"
 by Prof. Samuel TING (Massachusetts Inst. Of Technology (US))
https://indico.cern....y?confId=244334
This link is erroneous. Can you post the entire link please?
 

Offline imatfaal

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Re: AMS announcement on Dark Matter
« Reply #10 on: 04/04/2013 18:26:55 »
https://indico.cern.ch/conferenceDisplay.py?confId=244334

Sorry about that.  Not sure if the link will get you access to a recording now that the event is passed
 

Offline CPT ArkAngel

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Re: AMS announcement on Dark Matter
« Reply #11 on: 04/04/2013 21:26:15 »
It is all about likelihood.

First, the only known dark matter particles are the neutrinos. This is the first track.

Second, not interacting with the EM and the strong forces is a strong evidence that it should be found as an elementary particle. It is what they are looking for.

Third, the size of an elementary particle is related to the Compton or De Broglie wavelength, this is standard QM, fool proof. Meaning the size is smaller as mass increases. So the size of 300 GeV dark matter elementary particle is smaller than the size of the proton by more than a factor of 300 because the proton is not elementary.

Four, in all experiments to date, none have seen a hint of a dark matter particle but the neutrinos.

Five, if there is five times the amount of dark matter over matter, it is easy to guess that this dark matter is pretty stable... Like proton and electron, and neutrinos...

From basic physics, the likelihood of finding a stable dark matter particle decrease with mass, most certainly at higher mass than the proton mass because of the high density objects it could produce and not observed. Like i said, it is all about likelihood...

I must admit that how dark matter could clumps is opened to discussion.
 
« Last Edit: 04/04/2013 21:31:35 by CPT ArkAngel »
 

Offline imatfaal

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Re: AMS announcement on Dark Matter
« Reply #12 on: 05/04/2013 10:16:26 »
It is all about likelihood.

First, the only known dark matter particles are the neutrinos. This is the first track.

Second, not interacting with the EM and the strong forces is a strong evidence that it should be found as an elementary particle. It is what they are looking for.

Third, the size of an elementary particle is related to the Compton or De Broglie wavelength, this is standard QM, fool proof. Meaning the size is smaller as mass increases. So the size of 300 GeV dark matter elementary particle is smaller than the size of the proton by more than a factor of 300 because the proton is not elementary.

The Compton wavelength and the de Broglie are not the same .  The compton is the wavelength of a photon with the same energy as the rest mast of a particle - its the size below which quantum effects become crucially important when describing a particle.   You will have to point me to where it explains how the compton determines the size of a particle.

The de Broglie wavelength is the wavelength of a matter wave and is based on the momentum (not just the mass) of the particle - whilst the de broglie wavelength on an electron does relate to bohr radius I know of know other constraint to particles size.  For your guidance we can emprically observe the de broglie radius of macromolecules now (which are most often in the picometre order of magnitude but is dependent on their velocity as well) - these molecules have actually size in the nanometre range.   Again you will have to point me to where someone explains that the de broglie wavelength constrains size

Quote
Four, in all experiments to date, none have seen a hint of a dark matter particle but the neutrinos.
  Which is why it is pretty futile to speculate on the makeup/decay pattern/internal structure

Quote
Five, if there is five times the amount of dark matter over matter, it is easy to guess that this dark matter is pretty stable... Like proton and electron, and neutrinos...

From basic physics, the likelihood of finding a stable dark matter particle decrease with mass, most certainly at higher mass than the proton mass because of the high density objects it could produce and not observed. Like i said, it is all about likelihood...

But your first comment was not about likelihood - it was pretty clear:
 
"A cold Dark Matter particle being 250 to 300 times heavier than the proton must produce black holes or other strange objects.."

And so far your arguments have been general and quite correct about areas not specific to the question- but you are dogmatic about which comparisons can be used in an area in which we have practically zero knowledge and still  you haven't backed up that statement at all 
« Last Edit: 05/04/2013 10:22:21 by imatfaal »
 

Offline CPT ArkAngel

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Re: AMS announcement on Dark Matter
« Reply #13 on: 05/04/2013 22:41:51 »
The Compton wavelength and the De Broglie wavelength are two parts of the same element. The first is the wave of a free elementary particle at rest (producing quantized spin and magnetic moment) and the second is the wave of its momentum, related to the path in Bohm-De Broglie interpretation. De Broglie wavelength is an extension of Compton wavelength.

http://en.wikipedia.org/wiki/Compton_wavelength
http://en.wikipedia.org/wiki/Electron_diffraction

You can say that CDM (cold dark matter) could form tiny solar system-like atoms which are stable enough and only binded by gravity. You would be right for CDM in vacuum, but what would happen inside planets and stars? This is where comes from the unlikelihood of a heavy CDM particle.

Yes, I was dogmatic by using "must". I should have used "could". In theoretical science, we should never use "must" but "could". Sorry Matt!
« Last Edit: 05/04/2013 23:14:11 by CPT ArkAngel »
 

Offline imatfaal

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Re: AMS announcement on Dark Matter
« Reply #14 on: 08/04/2013 10:12:19 »
The Compton wavelength and the De Broglie wavelength are two parts of the same element. The first is the wave of a free elementary particle at rest (producing quantized spin and magnetic moment) and the second is the wave of its momentum, related to the path in Bohm-De Broglie interpretation. De Broglie wavelength is an extension of Compton wavelength.

http://en.wikipedia.org/wiki/Compton_wavelength
http://en.wikipedia.org/wiki/Electron_diffraction
  But neither of those pages state how either de broglie or compton constrain particle size.  I gave you an example of a macromolecule that has a wavelength many orders of magnitude lower than the nearest idea of its physical radius


Quote
You can say that CDM (cold dark matter) could form tiny solar system-like atoms which are stable enough and only binded by gravity. You would be right for CDM in vacuum, but what would happen inside planets and stars? This is where comes from the unlikelihood of a heavy CDM particle.

Yes, I was dogmatic by using "must". I should have used "could". In theoretical science, we should never use "must" but "could". Sorry Matt!

You're quite right it is far to easy to lose the shades of grey that inhabit most of science.  Prior to the LHC the best bet was a super-symmetric partner particle - and they are expected to all be in the GeV range and higher; I think that has been knocked on the head by the lack of anything new other than Higgs in that mass/energy range.  I think we risk missing important things if we insist on constraining completely new ideas and virgin territory with rules and laws that may or may not apply
 

Offline yor_on

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Re: AMS announcement on Dark Matter
« Reply #15 on: 10/04/2013 00:36:21 »
Want to know my opinion?
No dark matter.
 

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Re: AMS announcement on Dark Matter
« Reply #15 on: 10/04/2013 00:36:21 »

 

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