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Posts Tagged ‘COUPP’

Fermilab planning a busy 2012

Tuesday, January 3rd, 2012

This column by Fermilab Director Pier Oddone first appeared in Fermilab Today Jan. 3 .

We have a mountain of exciting work coming our way!

In accelerator operations, we need to give enough neutrinos to MINERvA to complete their low-energy run, enough anti-neutrinos to MiniBooNE to complete their run and enough neutrinos to MINOS to enable their independent neutrino velocity measurement that will follow up on last year’s OPERA results. We need to provide test beams to several technology development projects and overcome setbacks due to an aging infrastructure to deliver beam to the SeaQuest nuclear physics experiment. And we need to do all of this in the first few months of the year before a year-long shutdown starts. During the shutdown, we will modify the accelerator complex for the NOvA era and begin the campaign to double the number of protons from the Booster to deliver simultaneous beams to various experiments.

In parallel with accelerator modifications, we will push forward on many new experiments. The NOvA detector is in full construction mode, and we face challenges in the very large number of detector elements and large mechanical systems. Any project of this scale requires a huge effort to achieve the full promise of its design. We have the resources in our FY2012 budget to make a lot of progress toward MicroBooNE, Mu2e and LBNE. We will continue to work with DOE to advance Muon g-2. All these experiments are at an important stage in their development and need to be firmly established this year.

At the Cosmic Frontier, we will commission and start operation of the Dark Energy Survey at the Blanco Telescope in Chile, where the camera has arrived and is being tested. In the dark matter arena we will commission and operate the 60 kg COUPP detector at Canada’s SNOLAB and continue the run of the CDMS 15 kg detector in the Soudan Mine while carrying out R&D on future projects. We continue to have a major role in the operation of the Pierre Auger cosmic-ray observatory. In addition we should complete the first phase of the Fermilab Holometer, which will study the properties of space-time at the Planck scale.

At the Energy Frontier, we play a major role in the LHC detector operations and analysis. It should be a fabulously exciting year at the LHC as we push on the hints that we already see in the data.

Beyond construction and operation of facilities we continue our R&D efforts on the superconducting RF technology necessary for Project X and other future accelerators. We will be building the Illinois Accelerator Research Center and moving forward to connect our advanced accelerator program with industry and universities. Our rich program on theory, computation and detector technology will continue to support our laboratory and the particle physics community.

If we accomplish all that is ahead of us for 2012, it will be a year to remember and celebrate when we hit New Year’s Day 2013!


This story first appeared in Fermilab Today Oct. 10.

The 1970s were a thriving time in the world of physics, heralding such milestones as the development of the Standard Model and the discovery of the bottom quark. Now scientists at Fermilab are bringing some experimental pieces of that era back – bubble chambers and fixed-target physics.

Mike Crisler, a Fermilab scientist working on COUPP, is building the chambers for the CITRE experiment. Photo: Reidar Hahn

Peter Cooper, a Fermilab physicist, is heading a new experiment calibrating the classic bubble chamber technology, which is used today to search for dark matter.

The Chicagoland Observatory for Underground Particle Physics (COUPP) collaboration looks for bubbles in chambers filled with a compound containing carbon, fluorine and iodine. The fluid is superheated beyond the boiling point but has no rough surface to form bubbles. When a specific type of particle interacts in the chamber, it can deposit enough energy to boil the fluid and make a bubble. Electrons do not produce bubbles, while a dark matter particle interacting with a nucleus can – making this the key for dark matter detection.

“When a bubble forms, we notice it in the pictures,” Cooper said of the chamber technology. “The bubbles in the fluid are slow enough that high-speed cameras will capture the changes through continuous still shots. We’re making the world’s most boring movie.”

However, scientists are uncertain about the energy it takes to create a bubble in the chamber, which directly influences the sensitivity of the experiment.

The new experiment, named COUPP Iodine Recoil Threshold Experiment (CIRTE), will calibrate the energy threshold of the COUPP bubble chambers so that the COUPP dark matter results are on a firmer foundation. Scientists will fire pions, the lightest meson, in the Fermilab Test Beam Facility at a tiny pen-sized bubble chamber to measure how much energy needs to be deposited in the chamber to form a bubble.

The CITRE collaborators will use a fixed-target technique called elastic scattering of pions. The pions interact with iodine, the target nucleus in the COUPP bubble chambers with the most sensitivity to the most popular dark matter candidates. The pions are surrogates for dark matter – the bubble chamber sees them both in the same way by observing the bubble from the recoiling iodine.

Unlike dark matter, however, pions can be easily observed with other detectors on both sides of the bubble chamber, allowing COUPP scientists to know how much energy the pion gave to a scattered iodine nucleus.

Cooper and his team are currently running preliminary beam tests on solid carbon, fluorine and iodine targets to ensure that they understand how the experiment will work, in preparation for putting an actual bubble chamber in the beam. By watching how the pions interact with each target, they can determine how the pions should behave once the bubble chamber is in place.

However, the bubble chamber will only be able to produce one measurable bubble per beam spill, or one cycle of the accelerator. After the one bubble appears, the entire chamber needs to be recompressed in order to reset the contents.

The current COUPP chamber operates at the underground SNOLAB in Canada. Being deep below the surface allows scientists to suppress background events, such as those from cosmic rays. That bubble chamber is already setting limits on dark matter interactions that approach the best in the world. But they are hampered by the uncertainty on the energy threshold. With a little help from CIRTE, the COUPP experiment will be on a solid foundation as its search for dark matter increases.

—Brad Hooker


Science is full of surprises such as this laboratory flooding at Yale. Credit: Caitlin Casey

Hi everyone, it’s been a few weeks since I did my introductory post  on who I am (my name is Hugh) and what I’m working on (dark matter detection with bubble chambers, as part of the COUPP collaboration). I fear it has been too long for there to be any continuity between the previous post and this one, so I figured I’d go in a different direction and talk a bit about the uncertainty (or unexpected challenges) of working in science.

I decided on this topic after I just spent a few minutes clicking through the past week of entries here on Quantum Diaries. There really is quite a lot of information being posted here (including a really nice, detailed description of the Higgs boson, which was useful to me).I’m particularly enjoying Bob Peterson’s description of his journey around the world. We’re certainly covering a wide range of topics.

One thing I did notice is that people are writing a lot of explanations – how things work, how their detectors work, what we’re trying to discover. I think this is really good stuff and I’m glad we’re writing about it, but it does give the impression that we generally know what is going. Unfortunately, my experience, and therefore the subject of this post, is that a lot of the time my experiments do not go as expected and I often find myself rather confused (I suspect that other people have the same experience, but I’ll be safe and speak only for myself here).

First, experimental physics never goes exactly the way you planned it. Something always goes wrong. To give a particularly disastrous example, my lab flooded once in when I was at Yale for graduate school. Most experiments have some form of basic monitoring system called “slow control.” The slow control is constantly taking measurements of the pressure or temperature of a system and reading back to some kind of database. Often, they will be set up to send the experimenter a warning of some kind when a reading is out of safe range – for example, if a pressure gets too high. On this particular occasion, I was running a chamber filled with liquid neon, which is a liquid at minus 248 degrees Celsius (or 25 Kelvin). I think it was a Friday or Saturday and I was out to dinner with a friend when I got a text message – “ALARM: T1 out of range! T1 > 28 K!” – that the temperature was rising and therefore pressures might be getting a bit high. While there was no physical danger due to the safety systems that are engineered into experiments like these, often the safety systems will not protect against the loss of the experimental run itself, which in this case would have cost me several months and delayed my graduating. And I wanted to graduate.

I broke a few traffic laws on the way to my lab (fortunately I was not too far away) and was faced with the scene shown in the picture. It may be slightly hard to tell, but normally there is a large 4-foot by 8-foot pit in the middle, where the stainless steel cylinder is sitting, but in the picture the pit is completely full of water. There is rather a lot of expensive equipment sitting around the room, also in water. I ran down the stairs, shut everything off, found the source of the flood (a plumbing connection that had burst) and prayed that it would be OK; which, thankfully, it largely was. I had managed to shut off the water before it could damage any of the more sensitive pieces of equipment. The only thing that broke was a single fuse in my cooling system, and I ended up losing only two weeks.

That’s equipment failure, and that does happen often. And we try to learn from these incidents to make our experiments safer and more robust (in the previous example, the slow control alarms worked perfectly and a freak flooding accident did no permanent damage) However, at least it’s generally pretty easy to tell when something physical in the experiment has broken down (although the cause can be elusive).

Screen shot of the slow-control system. Credit: Hugh Lippincott

If you’ve been paying attention to recent popular physics news, you’ll have noticed that various “excesses” are all over the place at the moment (in dark matter, at CDF at Fermilab, at the LHC). These are examples of data that we do not fully understand, and we really don’t know what is going on yet.

In the next post, I’ll talk a little bit about the current run of COUPP, which produced some really strange results back in November and December that we’re still trying to figure out.

—  Hugh Lippincott


Hugh Lippincott installs a COUPP bubble chamber.

In keeping with the introductory series of posts you’ve seen in this blog from Fermilab experiments, I guess I’ll introduce myself as well. My name is Hugh Lippincott. I’m a postdoc at Fermilab, where I work on an experiment looking for dark matter called COUPP (the experiment is COUPP, not the dark matter. The dark matter is WIMPs, or weakly interacting massive particles).

If you’ve been reading these posts, you’ll know by now that all experiments and many physics concepts have some kind of acronym or cute name, and ours is no different. The acronym stands for Chicagoland Observatory for Underground Particle Physics, but no one thinks of it like that, it’s just COUPP. The real debate is whether the two Ps are silent or not, and we’ve been known to have long debates inside the collaboration about this. I tend to think of it as silent, the way the P sounds when you say coup,  as in overthrowing the state. But if you prefer to think of sounding more like the P in coupe,  a small car, be my guest. Maybe we can have an Internet poll or something in the future and solve that problem once and for all.

This is not actually my first attempt at blogging (although I really do detest that verb and will try to avoid using it henceforth). I wrote several posts at physicsformom.blogspot.com where I attempted to explain a somewhat significant chunk of dark matter physics in a way that could hold my mother’s attention. In this, as in so many things, I came up a bit short, and I haven’t posted anything there for months, but I actually think the three introductory posts on what dark matter is hold up OK. So, instead of going back over all that here, I’ll risk losing half of my audience by being a lazy scientist and ask you to review those posts if you want more information.

Double click on the above icons to see the bubble chamber in action.

I’ll talk more about COUPP and anything else going on as I continue writing. For now, I’ll just say the COUPP collaboration is building a series of bubble chambers , which essentially means it is  literally watching a jar of fluid waiting for bubbles to appear. For example, the accompanying movie shows a neutron (produced by a neutron source placed near the detector) that has scattered four times in our chamber we’ve recently installed in a deep underground site called SNOLAB in Ontario, Canada). This particular event is pretty recent, from a chamber called COUPP-4 since it has 4 kg of fluid.

As I mentioned here ( I’m referencing myself again), bubble chambers were used in the heyday of particle physics when it seemed like new particles were being discovered and understood every two weeks.  We’re now using the same technology, just in a new way.  A bubble chamber is a jar filled with a superheated liquid, or liquid that is hotter than its boiling point. The liquid wishes it were boiling but can’t because there is nowhere to make a bubble. I’m not sure if that entirely makes sense, so I’ll try again. When you boil a pot of water, you see bubbles form first on the metal of your pot. That’s partly because a bubble needs a place to be born, called a nucleation site. In general, this can be an impurity or a rough surface like the metal of the pot or anywhere where a little pocket of gas can form and then grow. Without these impurities or surfaces, the liquid can’t boil, and instead becomes superheated – a very unstable state where any input at all (such as an interacting dark matter particle) that can nucleate a bubble will cause rapid boiling.

Some of you may be familiar with this phenomenon if you’ve ever tried to boil clean water in a ceramic mug in the microwave. In fact, there was a Mythbusters episode about it and a host of other videos on YouTube. What they show is that superheated water will boil (or explode) very suddenly as soon as anything that can create a bubble touches the water.

In our bubble chambers, the bubble is created by particles interacting in the chamber. For example, in the movie above, a neutron scattered and deposited heat in four places, creating four bubbles. We superheated the fluid, making sure that there was nothing else in there to nucleate bubbles, and then waited until some radioactive particle zipped through. When we saw a bubble, we knew something had interacted in the fluid.  And that’s how a bubble chamber works.

— Hugh Lippincott