flowbion.blogg.se - Electron capture

Electron capture free#

For example, there are lots and lots of types of events that occur, within the Standard Model alone, that also create signals that would show up in any detector. Sure, you can envision a detector where you make some sort of chamber that’s sensitive to these interactions, but the problem then becomes creating a detector that isn’t going to give you all sorts of false positive signals as well. Credit: Nicolle Rager Fuller/NSF/IceCubeīut detecting a nuclear recoil event from a dark matter interaction is no easy task. The XENON detector leverages this idea spectacularly, making it one of the world’s most sensitive particle detection experiment.

Electron capture free#

When an incoming particle strikes an atomic nucleus, it can lead to the production of free charges and/or photons, which can produce a signal visible in the photomultiplier tubes surrounding the target.

And this is where we get our motivation for building detectors, like XENON, LZ, PANDA, and others, to directly interact with these WIMPy particles. If such a species of particle exists, it should also be present in our own galaxy, permeating the galactic halo, and also flying through the Earth all the time as we orbit around the Sun and as our Solar System moves through the Milky Way.

WIMPy dark matter isn’t the only possibility for what dark matter could be, of course, but this scenario - in part because it’s so general and in part because there are so many specific realizations that would lead to the generation of large numbers of WIMPy particles in the early Universe - is definitely worth exploring. The WIMP scenario generally arises whenever you have a massive species of particle that’s created early on, then ceases to be created as the Universe expands and cools, but that particle species only partially annihilates away, leaving a substantial relic abundance that can persist until the present day, making up the dark matter we now observe. That’s a quite general scenario for making WIMPs, which would then form cold dark matter halos around galaxies, clusters of galaxies, and all large-scale gravitationally bound structures.

And, if there’s a species of heavy, neutral particle that’s stable and that interacts only very weakly (and, of course, that gravitates, since it has mass), that species should persist even to the present day.

Eventually, particles that only interact weakly (not necessarily through the weak force, but “weak force” or even more weakly) “decouple” from the primordial plasma, meaning that they stop scattering off of or interacting with other particles, including particles of their own species.

As the Universe expanded and cooled, the more massive, unstable particles (and antiparticles) decayed away, leaving only stable ones as there’s no longer enough energy to make new unstable particle-antiparticle pairs.

The hot Big Bang occurred, filling the Universe with a bath of extremely energetic particles (and antiparticles), that collided, interacted, annihilated, and created new particle-antiparticle pairs via Einstein’s E = mc².

It’s a remarkable experimental achievement, and one that illustrates just how experimental physics progresses. In a remarkable experimental achievement, the XENON collaboration just announced, via a public talk from Daniel Wenz, their tightest constraints on WIMP dark matter, enough to rival the currently world-leading LZ collaboration, with even better results expected in the very near future. These classes of particles - that interact only very weakly but that have large rest masses - are collectively known as WIMPs: Weakly Interacting Massive Particles. This dark matter must be cold (i.e., moving slow compared to the speed of light) at even early times, teaching us that if it ever were in thermal equilibrium with the “primordial particle soup” of the hot Big Bang, it must be quite a massive species of particle. We call this massive species of matter that must exist, but whose nature remains unknown, dark matter. Additionally, observations of individual galaxies, of groups and clusters of galaxies, of the cosmic microwave background, and of the large-scale structure of the Universe all paint the same picture: a Universe where 5/6ths of the mass out there isn’t made of any Standard Model particle, but rather is invisible, cold, and non-interacting except through the gravitational force.

When we add up all of the normal matter - stuff made up of quarks and charged leptons - we find that it’s only responsible for about 1/6th of the total “mass” that must be out there. When it comes to the question of “What makes up the Universe?” the Standard Model simply doesn’t add up.