Direct Dark Matter Detection [A review]

As a few of you might have read in my posts, I am a professional physicist and I comment often on subjects of Dark Matter, Particle Physics and occasionally astronomy. I did my undergraduate in the UK, an MPhys in Physics and Astronomy (Masters). I followed this with a PhD in a long baseline Neutrino oscillation experiment, T2K. The subject of my theses was technical, covering aspects of photon detectors used in the T2K near detector.
I moved on after my PhD and am currently a Postdoc working for a direct dark matter search experiment.

Since I talk about things I have been involved in during my posts here I thought some of you might like to read a little bit about the types of things we do in the mysterious world of deep underground physics.

Direct searches for dark matter involve in all cases attempting to observe dark matter interacting with normal baryonic matter. The current theoretical best candidate for dark matter is the WIMP, the weakly interacting massive particle. It has mass, is electrically neutral and interacts only via the weak force, similar to that of neutrinos, only the coupling is even weaker. The reasons behind this i will not talk about in this post, but might later if there are any follow up questions.

So we are searching for the interaction of WIMPs with normal matter, typically in the form of a billiard ball type scattering event. In this event, the WIMP smacks into an atom and gives it some energy, causing it to 'recoil' this energy can be detected with current technology.

So how do we do this? and what are the challenges?

The most significant challenge are that of target mass and purity.

Target Mass - The predicted interaction cross section is extremely low, it is expressed in units of barns, it is a likelihood of an interaction occurring for any closely passing particles. Current limits on dark matter interaction cross sections are of the order 10^-44 cm^2 in affect it is like having an object that small and firing it at the earth, it is theoretically possible that with a cross section as low as this, that it will pass right through the Earth and not touch a single thing. This is in comparison to a low energy neutrino which is of the order 10^-37... Most of those will pass straight through the Earth no problem, but those we have built detectors that can observe them at a fairly low rate (one or two a day max)

So in order to give you a better chance of the event happening, you need a large amount of sensitive material! This is often both a technical and a financial problem.

Radiochemical Purity - The biggest challenge is radiation. Every material around you is radioactive, anyone who has ever seen a radiation monitor or simple Geiger counter will tell you "Hey that thing clicks every few seconds!" Well what I am trying to tell you here is that, in order to search for dark matter, you have to get the background radiation level down to 1 or 2 counts over the course of YEARS... there are a few tricks to that, but that is what we are gunning for.

That means that we have to build detectors using only the cleanest possible materials, or materials that can be cleaned to purity levels that high. We have to control every aspect of exposure and natural content of elements such as uranium and thorium. The reasons why these elements are painful for dark matter experiments is that they produce a chain of alpha decays that result in long lived elements. These elements 'grow' in and they represent a background that slowly and always increases over time. Much of these elements also love to stick to surfaces. An example being Polonium and Lead 210. Polonium is not as major an issue, though lead is terrible. It has a 22 year half life and plates out on every surface.



OK so those are the two main challenges, so what do we do? how do we reduce our backgrounds? Firstly these experiments are performed deep underground. This is both a blessing and a curse. It is a blessing because the deeper you go, the more and more cosmic rays are shielded, but it is a curse because deep underground labs tend to be in hard rock mines or tunnels. The rocks tend to be high in uranium and thorium and so give us a huge radon concentration in comparison to the surface (Radon chain gives us lead 210... bad bad bad) So typically these labs operate clean facilities where there are strict controls on moving items into the lab and in some cases moving people into the lab. Sometimes basically your day will start with a shower underground depending on the facility.

So what about the detectors themselves?
We have to screen materials that go into critical areas, or that are part of the actual active region. Active targets have to be highly purified, this is a given. I will talk about the types of detectors later, but typically if it is a Gas detector, you have to pass the gas through a cold trap, usually a charcoal trap to filter out radon. A semiconductor detector has to be grown using highly purified material. Crystal detectors have to be grown under extremely controlled conditions.

Detector materials have to be selected for purity, and any mechanical structure built wit this in mind. That means that any welding must be done as fusion welds, either pure tungsten or ceriated welds... any thorium is a big no no. That is not hard to control, but even welding tips that have been ground down on a wheel used to grind 1-2% thorium rods gives a weld that is far far too hot.

Typically good materials are stainless steel, copper, acrylic (depending on handling and type). There are a few others but those are the main ones.

Stainless steel forms a passive chromium oxide layer on its surface, this layer tends to be pure and traps radio purities inside the bulk material.

Copper can be sourced with intrinsic high purity, this is because elements that are typically found with copper ores are things like silver and gold... sooooo these ores get highly purified to recover those goodies. It can also be electro-formed, this is where you basically grow pure copper from electrolysis... amazingly pure.

Acrylic - If made with pure monomer, not slush caste using recycled material, the bulk acrylic contains what ever radioactive contaminants were in the process systems of the plant forming it. Acrylic likes to absorb things despite it being glass plastic and you don't think of it absorbing anything at all. So Radon will diffuse into the surface. Not all bad though because if you remove that surface, you end up with a nice clean and pure material to make your detector from.

-> 1 of 2

Detector Techniques
Liquid Nobel Gas - Liquid nobel gasses have interesting chemistry that they can exhibit scintillation producing UV light under nuclear recoils. Argon also has an interesting property that nuclear recoils, look completely different to electromagnetic interactions, so this allows scientists to easily distinguish between types of radiation. Nobel gas detectors can also be used as drift chambers, allowing two phase detectors to exist, where we observe the track of a recoil in the detector, and drift the charge into the gas region of the detector and observe both scintillation and ionization from the track.

Semiconductor - Create highly pure semiconductor detectors, similar to a diode in which a reverse potential is applied to the detector and when something interacts with the detector charge is drifted through the bulk of the crystal and is collected and read out.

Scintillation - Crystal detectors made from high purity scintillating materials can be used, but typically have limited use due to light output limitations from scintillators and ease of production, though these operate very similar to the above description of liquid nobel gas detectors

Bolometer detectors - These detectors are typically cryogenic, and work on the principle that a particle interaction departs energy into a material. So if you cool a semi-conductor crystal or other crystal to ultra low temperatures, Im talking of the range of mili-kelvin. The energy departed into the detector is then enough to produce a noticeable temperature change. this can be tuned in cleaver ways such that a detector is held within the superconducting transition region and a detector will briefly go normal when a particle interacts with it.

Bubble chambers - Super critical liquids have an interesting property that in order to make them boil, you do just need a little jolt of energy. C3F8 can be held at a super critical temperature and pressure in such a way that recoils from particle interactions cause nucleate boiling. So you can detect an interaction by looking for bubbles forming and pressure spikes in the detector, or even listen to the sound of the bubbles.

Hybrids - Take a few of the techniques above and apply them to your detector. An example being that of a bolometer and a semiconductor. Operate a semiconductor in its transition region and you can observe both the charge and the temperature change, if you have charge read out and phonon read out. Very complicated detector technology, but also quite amazingly powerful.


I think that covers all that come to mind, but i will maybe update if i can think of any others.

So you have your detector and you have your target, So now what do you do? Well now you construct all of it in a clean environment and you put it all in a water tank... or you build a huge shielding box around it. Despite it being underground, you still get muons from cosmic rays that you must tag and veto. This can be done simply using an outer scintillation detector or a shield tank filled with water, and you observe the Cherenkov radiation to detect the muons.

So what about backgrounds?
Well wimp interactions are thought to look exactly like nuclear recoils from neutrons, most radiation comes in the form of alphas betas and gammas... so that isn't a problem right? neutrons how do you even generate neutrons?

Well alpha particles have an annoying property that they can interact with material and produce neutrons. Cosmic rays can interact with rock and spray neutrons through the detector. This means that the design of your detector not only has to be able to have a large detector target, keep it clean, but also have a good enough shield (also clean) to stop neutrons interacting with the detector target.

So what do we do after that? Detecting Dark matter seems like a hell of a lot of trouble!

It is, it is very challenging and it is very difficult. How we prove we have observed dark matter is to account for all backgrounds that we see, make simulations of our detector and simulate it at a level were we can account for ALL parts of it and ALL radiation sources based on material assay (take a chunk of the material and count it for radio purity and use that for the simulation)
Once we have done that, we hope we can account for all our detector background and have a clear signal of dark matter despite all the backgrounds. Depending on detector design, it is also possible to perform a total background free experiment too where we expect zero backgrounds.

We can also look for an affect of annular modulation, the theory suggests that we are moving through a soup of dark matter, and such as the sun moves through this, and the Earth moves around the sun, when we are moving 'into the wind' we might expect interactions to occur more often than when we are moving 'against the wind'

the only claim of a dark matter signal thus far, is that of an annular modulation. The general scientific community does not accept this claim however because the collaboration has never opened their data set, nor do they like to talk about their analysis or how they are getting their results. Also, detectors that are of similar type have been run with higher sensitivity that have also NOT observed anything at all. So these results at the moment are quite problematic.

I hope this has been at least a little useful or fun to read. I will try and answer any relevant questions, if i know the answers to them or can offer a useful idea.

Cheers

Eros

i am not incredibly interested in dark matter unless it's the variety that leads to radical physics and engineering. but the last article i read a few days ago said that scientists have tentatively identified dark matter signatures related to sterile neutrinos. the thing is if dark matter is sterile neutrinos it does not seem to lead to much new physics as it is only a minor extension of the standard model. is that the case? what kind of odd things does sterile neutrinos as dark matter mean?

www.newscientist.com...

reply to post by ErosA433


Are detectors specifically tasked for explicit Dark Matter detection, or is data also aggregated from other sources like
Ice Cube in Antarctica and other observatories down mine shafts?

Thanks.

reply to post by AliceBleachWhite


Typically these detectors are specific to their purpose, because of the requirement for the detectors to be extremely quiet in terms of radiation, any sensitivity should be optimized to only nuclear recoils. We are entering an era where the first 1 tonne fiducial volume detector will be coming online within the Year.

IceCube is primarily a neutrino detector, in terms of optimization it is good for high energy neutrino interactions. High energy neutrino observatories are searching for potential sources of extreme astrophysical events. There are other applications to, but in terms of Dark Matter, a detector like IceCube could not do it directly despite the detector being enormous, this is because the particle interaction from a wimp nuclear recoil is tiny, any signal it produces would be attenuated too quickly travelling through the ice. What it can do though is look for a relic wimp decay... or sterile neutrinos (i think


Typically data is not aggregated from all these sources directly, but would occur as theorists look at models and look at the current state of play and try and predict observables such as for example, using a direct dark matter search to work out the interaction cross section with matter, using this to try and figure out the density of wimps in the local space, and then using that to figure out an expected relic decay rate.

If the theories are reasonable you might be able to predict cross experiments.

The difficulty with adding data sets together is that different detector technologies give you different signal bias, so typically it is not a common practice. There are groups however that are starting to look into statistically combining many data sets in a unbias manner... I am only currently aware of one person who works for CDMS who is looking at this

reply to post by stormbringer1701


Sterile neutrinos are an interesting subject, one which I am not an expert. It has to do with helicity and chirality, and the mechanism proposed to give the neutrino a very small mass. Chirality is to do with the quantum spin direction in relation to the momentum.

Helicity is a relativistic variant
Chirality is a relativistic invariant

So there is an open question, the standard model, because the neutrino was assumed to be massless, does only allow for left handed neutrinos and right handed anti-neutrinos. However because they have mass, and Helicity can be relativitistc variant, it opens the question of if Chirality is the only way to distinguish neutrino and anti-neutrinos or if neutrinos and anti-neutrinos are actually the same particle. It introduces the possibility of sterile neutrinos as a result of the model.

Science plays by the rules, the standard model gives a few predictions, and when we observe something interesting, it can open doors and possibilities. Sterile neutrinos are one such door.

What they are though is a proposed right handed neutrino which only interacts gravitationally, they also play a role in determining the left handed neutrino mass through the see saw mechanism.

The issue with the search for sterile neutrinos is that the mass of them theoretically is somewhere between 1eV and 10^15 GeV sooooo it is fairly an open playing field. This could actually be the WIMP, though the model does only give a gravitational interaction, and nothing else.

Still we can see hints of it if it is out there because it will affect aspects of neutrino oscillation physics.

Apologies if that seems rambling and not giving any clear answers. Sterile neutrinos are a definite Dark Matter candidate, and experiments such as double beta decay searches are looking for sterile neutrinos as part of their physics program.

WIMP searches however are not sensitive to them however

have you ever wondered if there was a way to make a miniaturized detector for weakly interacting particles like neutrinos or gravitons? like if you could make atoms out of smaller particles like kaons or muons and that like neutrons that are crowded by other neutrons and protons they decided to be stable when in an atomic configuration (unlike muonium or kaonium) and they had an analog to the electronic shells so that they were capable of bonding to other atoms and having chemistry analogous to normal atoms...

and the binding distance was correspondingly smaller and consequently stronger than regular atoms. and with less space between both particles and the surrounding atoms so they were much more dense and also much more massive...

so it was much harder for particles or rays to get through them without directly impacting a particle inside the material couldn't you then have more compact detectors that way? maybe a neutrino detector the size of a tablet computer or a pack of cigarettes? a graviton or gravity wave detector the size of a fishing tackle box instead of the planet jupiter? a multi-megapixel gamma ray or x ray camera the size of a nickel?

oops! i went of on a tangential stream of consciousness there!

reply to post by ErosA433


Thanks Eros, this is a field I have absolutely no experience with but find it quite fascinating. Here is a recent article regarding the exploration of dark matter in an abandon gold mine in the Black Hills in South Dakota. Question is, would there be any other benefit of performing the experiments in this environment besides the fact that the area would be used to reduce backgrounds?

Imperial College London

reply to post by stormbringer1701


Well you bring up a very very good point and already figured out a key part that i didn't really say directly.

The more massive the detector the better chance you have of seeing an interaction. The problem is however that you need to be able to observe the signal that is produced. A great material in terms of density is lead... but lead is a metal, it does not produce light when particles interact with it, you also cannot see through it.

What you are talking about is exotic matter, which is a good theoretical standing point BUT unfortunately this matter is not stable. In order to produce a working detector you need to use stable matter. You need to get away from any energy deposits in the system. Muonic atoms exist exactly analogous to regular atoms with shell structure. The issue though is that they are extremely short lived. And when they decay they give you a high energy electron and probably a gamma and a couple of neutrinos.

Hadronic atoms also exist, and are as you describe, but are also unstable due to the orbitals of the hadrons are extremely close to the nucleus and if the hadron doesn't decay as they do normally, it can interact with the nucleus in a quasi fusion reaction.

So while your idea is a good one, it is simply not feasible by physics as we understand it, and physics as we observe it. Maybe we will discover something in the future to aid this, but right now... we have what we have

Watcher777
reply to post by ErosA433

 

Thanks Eros, this is a field I have absolutely no experience with but find it quite fascinating. Here is a recent article regarding the exploration of dark matter in an abandon gold mine in the Black Hills in South Dakota. Question is, would there be any other benefit of performing the experiments in this environment besides the fact that the area would be used to reduce backgrounds?

Imperial College London

typically sensitive detectors are isolated deep underground or under water in order to reduce as much as possible spurious detections from other sources such as energetic cosmic rays, neutrons or gamma rays and so forth. also for some experiments the detector involves large volumes of water, pure gases or other mediums to increase the probability of and decrease the time interval between expected detectable events. often mine shafts are ideal for experiments that take up a lot of room too

Yeah thats about it really... underground is where we go, either underground in mines, or underground in tunnels. they are to get rid of backgrounds.

Trust me, if we could do it in nicer places, we would!

ErosA433
reply to post by stormbringer1701

 

Well you bring up a very very good point and already figured out a key part that i didn't really say directly.

The more massive the detector the better chance you have of seeing an interaction. The problem is however that you need to be able to observe the signal that is produced. A great material in terms of density is lead... but lead is a metal, it does not produce light when particles interact with it, you also cannot see through it.

What you are talking about is exotic matter, which is a good theoretical standing point BUT unfortunately this matter is not stable. In order to produce a working detector you need to use stable matter. You need to get away from any energy deposits in the system. Muonic atoms exist exactly analogous to regular atoms with shell structure. The issue though is that they are extremely short lived. And when they decay they give you a high energy electron and probably a gamma and a couple of neutrinos.

Hadronic atoms also exist, and are as you describe, but are also unstable due to the orbitals of the hadrons are extremely close to the nucleus and if the hadron doesn't decay as they do normally, it can interact with the nucleus in a quasi fusion reaction.

So while your idea is a good one, it is simply not feasible by physics as we understand it, and physics as we observe it. Maybe we will discover something in the future to aid this, but right now... we have what we have

well neutrons are not stable either unless they are bound in an atom or travelling relativistically. when by themselves they get lonely and commit suicide within about 11 minutes or so.

maybe some of these unstable particles would become stable if bound or under the influence of some sort of EM field?

or maybe there are exotic particle physics expects to find but haven't yet like a species or two or three of monopole? those would be ideal even though several of them aren't suitable either for various reasons. i got that idea off of a hard sci-fi website called orions arm which in large part only allows science props supported by peer reviewed papers with a few glaring exceptions. they have a good set of links to monopole related papers and a highly developed argument for monopole based atoms, chemistry and structural engineering and energy production based on monopole derived technology.

or how about...

you know how neutrinos arise from decay events? a parent particle decays or is otherwise disintegrated into daughter particles and energy? what if you had a gas made of the daughter particles in an exited state cooresponding to the energy component of a decay... what would happen if a neutrino then impacted with what would normally be the daughter particle(s?) is the decay chain "reversible?" could you get the normal parent particle? and if that particle can be counted perhaps by being a charged particle and being shunted by magnetic or electrical fields to a device that can register them? if the parent particle is a neutron i guess that would... nope... there are neutron detectors too. i know it would be difficult to get everything to go together right even if it were possible but occasionally it might happen?

what about an exotic atom isomere? would that prevent decay? if the decay would cause a violation of a conserved quantum or other property so long as the nuclear isomere state persisted? or a exotic atom with multiple electrical (electron analog of course ) shells in which an inner shell were excited photonically while outer shells were at their ground?




the term i neglected is "metastable" in the case of electron shells and "nucleonic isomere" in the case of nuclear shells.

Other than reading a few pages with general information, i know less about exotic matter in detail than sterile neutrinos.

You are right that some particles in bound states exhibit stability. This is due to the strong nuclear force and the neutron being bound in a nucleus. These other forms of exotic matter are more analogues to atomic structure, which has been observed in the cases of both hardronic and muonic atoms not to produce stability.

More research is obviously needed.


Sir you are a genius and you don't even know it, what you described is exactly the method used by Ray Davis in the Homestake experiment. His proposal was that, neutrinos from the sun have enough energy to do exactly what you described. His experiment searched for the following reaction

Cl 37 + nu -> Ar 37 + e-

He basically had a big tank of dry-cleaning liquid and periodically evacuated the gas space and looked for decays of Ar 37.

Extremely challenging experiment, and an experiment that was performed using a variety of different elements and shown to work by a handful of different experiments.

This was how the solar neutrino problem was discovered... that being, theoretical predictions of solar neutrino output from the nuclear reactions inside, where something like 1/3rd of what was expected. This was in fact the first hint of neutrino oscillation. The problem was eventually solved by the SNO experiment.


The issue is still that the target needs to be stable, and for direct dark matter detection, theoretically a billard ball scatter is the best we do. We don't do any kind of strong interaction.

I was "using the force" on the neutrino detector thing

i know it's not you gig or even the topic of your thread but i rarely get a chance to talk about things like this. so one more time and then i will stop, i promise:

so kaonium and muonium consist of two particles if i remember right. but what if the exotic nucleus had more particles?

that alters the strong force interaction the more particles in the nucleus. you would be shooting for an exotic analog for both neutrons and protons not to mention the electrons.

i"m using the force again. this time on the dark matter issue. though this idea is somewhat fragmentary.

there is another problem concerning neutrons. they sometimes disappear too quickly. faster that thier decay half life dictates.
it has been theorized that neutrons also oscillate to what would normally be considered an imaginary domain of the universe dubbed the mirror sector. according to the theory this translation can occur in the presence of a mirror magnetic field of .6 gauss IIRC. since mirror matter can interact with normal matter only by inelastic collisions and gravity...

www.sciencedaily.com...

1. mirror matter could be dark matter. this would suggest at least two or three ways to detect it if this were the case.

2. even if mirror matter isn't dark matter perhaps some of the details pertaining to mirror matter could be applicable to dark matter detection?

EDIT: obligatory tangential thoughts... i would dearly love a space craft window made of mirror titanium or mirror tungsten or a window or hull section i could oscillate between mundane titanium and mirror titanium by application of a mirror magnetic field coil.

gravimetric detector. the oncoming generation of gravity detectors involving optical rods may be of use for dark matter detection along the lines of your annular detection idea but via gravity variability from dark matter clouds. as a bonus they are much smaller than older attempts at gravity detectors and as yet another bonus you do away with having to worry about all that purity and shielding stuff

www.livescience.com...

reply to post by ErosA433


Great thread, thanks for making it. One thing that might be helpful for people to visualize what you're talking about is a video of an underground detection facility. I know there are numerous facilities, here's one in Canada called SNOlab and they claim this is the first time the inside of the detector has been filmed...it's pretty impressive, would this be similar to the dark matter detection facility (except this one detects neutrinos instead of dark matter)?

Inside snolab (Underground detection facility)

One thing that surprised me though, is I wouldn't let people into a food processing plant dressed like that, without hair nets, so I didn't expect to see them go into a highly sensitive detector dressed like that. Based on what you said I would have expected to see attire more along the lines of clean room stuff used by semiconductor manufacturers, or is that just for the manufacture of the detectors themselves?

You mentioned that one lab has made claims of an annual modulation but they haven't wanted to share their data set yet and it hasn't been replicated and so forth. I would be curious to know more about the various types of dark matter facilities, how they compare and contrast to one another, how they have evolved over time, etc. For example, I know that we've been looking for dark matter in underground facilities for decades, right? Yet we are still building newer detectors and facilities. Is this because the old facilities and detectors are now deemed to be inadequate in some way? I guess the null result would be one form of inadequacy, but to rephrase the question, what were the biggest drawbacks of some of the older detectors and dark matter facilities that the newer dark matter facilities are trying to improve upon? Or are some of the techniques new and different and not just improvements of the old ones?

more using the force "luuuke...I am your fa---no.


I mean something the OP said reminds me of something i came across when reading up on mach's principle and wormholes..

weakly interacting------------------------------->centauro events origin's are not entirely resolved but because they are weakly interacting events too maybe they are related to dark matter?

en.wikipedia.org...

reply to post by Arbitrageur


So I actually do spend a good portion of my time at SNOLAB so I can tell you a lot about the place. What you see there is the old SNO detector. What you see them wearing is regular clean room gear of the lab. This is in general not all that 'clean' as you point out. This is because the SNO Acrylic vessel at the time the video was made, had been sat open to mine air for a few years. Thus sending people into it it wouldn't really matter so much what they are wearing because it is already fairly dirty.

What happened was that last year, the vessel was cleaned, and portions of it were sanded, in order to take the skin layer off and remove the radioactive daughters that had settled on and in the surface. During this time a clean room was constructed over the vessel and anyone going into it would don a disposable tyvek cleanroom suit.

Once operations where complete the vessel was finally classified as clean and no one is allowed inside it at all.

It is the same for the other large construction projects, MiniCLEAN and DEAP both have clean room tents around them, and to go near them you have to put on a similar disposable suit.

Lets look at some of the labs around the world.



There are many more, but these are perhaps the more significant ones (due to size, facility support etc)
Oroville is affiliated with Sanford labs and is a underground low background counting facility, so typically this would have assay equipment for material screening, or small scale detector prototype testing.

IMB hosted a detector similar to Super Kamioka, I actually don't really know that much about that lab,from what i can find it is a tunnel dug into rock, where there is basically one experimental hall. The IMB-3 detector searched for proton decay similar to Super K

Soudan is a big facility, and houses the MINOS far detector, CDMS (cryogenic dark matter search) and NOvA (upgrade from MINOS with some extras)

Kamioka - A mine cut under a mountain rather than deep underground. This houses Super Kamiokande, KamLAND Xen, and T2K (far detector) This facility is fairly famous and has hosted science for many years. SuperK is the largest water Cherenkov detector in the world, KamLAND Xen is an upgrade of KamLAND and is a running double beta decay search.

Boulby - An operating potash mine (salt mine) with a number of experimental halls put aside for scientists to use. Salt mines are good because they give you a low background environment compared to hard rock mines... BUT salt is horrible for equipment and the mine walls slowly change shape as the salt dissolves. Working in Boulby is very good but it is a challenging environment. (Think about Salt + computer = mush)

GranSasso - A huge facility cut out from the side of a road tunnel under a mountain between Italy and France. It houses many experiments (without looking it up I could't give a big list. Though this is a lab that many people have heard of. It is mainly a neutrino physics facility and has hosted about 10 different experiments down the years. It is fairly large, but from what i have heard is not exactly an immaculate clean facility... so what will happen is that experiments will construct their own clean lab areas.

Homestake - A deep mine, though one that does not currently have a huge amount of experimental support, the US is hoping to expand this facility and make it similar to that of SNOLAB. I hear things all the time about plans but am never sure if they are funded to do it. The lab would be renamed DUSEL. The issue there is water is constantly flooding the mine and such it has to be constantly removed. That isn't as bad as it seems, but it is costly.

SNOLAB - This lab was originally just SNO, a single experiment built underground in the 6800 ft level of a Nickel mine. It has since been expanded and opened as SNOLAB which you see in the video. As it is a new lab, there are not many currently running experiments there... though many many are pegged to come online in the next year.

There is a deeper underground lab in China that is dug out of a tunnel under a mountain, BUT it really is just a gap where you can throw a detector that is self contained in a box, and not really a Lab facility. In terms of actual operating labs that are big enough for multiple experiments that you can walk around in, have dedicated support teams and are fully equipped for large operations, SNOLAB is the deepest.

While I did just point out some of them on that plot, and didn't really talk about all that much about them, It is a scrap of information i can do before I get starting work properly here.

Cheers

Eros