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Nicole Ackerman | SLAC | USA

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Data: Women in Physics

Tuesday, October 13th, 2009

This is a response to Lucie’s post “powerchick”.

It is true that Poisson statistics can make it difficult to tell when a situation involving few people agrees with a “null hypothesis”. I’ve done a calculation like this once when teaching an undergraduate class. The class was not very large (~40) and it was about 30% female. After a few weeks, many people had dropped. Looking at the names, I noticed that a higher percentage of female students had dropped the course. Before getting too concerned I calculated out the numbers. My null hypothesis was that the percent of male students who dropped the course was the “normal” percent of students (male and female) that would drop the class. Then I could calculate what percent of the time I would see this number of women (or more) drop the class, not based on a gender bias, but based on statistical fluctuations. I found that the answer was between 30 and 40% (I don’t have the numbers any more). Had the number been 5%, the idea that there was something extra making women drop the class would be reasonable. But really, the effect was just statistical fluctuations.

HOWEVER – had I taught the class over many years, I could have gathered greater statistics. If in every case slightly more female students dropped than expected from the male students dropping rate then I could see a statistically significant effect over time, though not in each measurement. This happens in physics when there are few events. One great example of this is the search for solar neutrinos in the Homestake Mine (data shown below). Each measurement has very large error bars, such that the data could not really determine whether the prevailing model was correct or not. But when you look at the data over multiple measurements, the error bars are reduced (see the point to the right) and it becomes clear that the data does not match what theory had predicted.

When dealing with issues regarding women and racial minorities in the sciences (and especially physics), the numbers are so low that evidences of bias or discrimination will often be dismissed as statistically insignificant or “anecdotal”. But when (here in the US) less than a dozen African-Americans get a PhD in physics a year, or graduate schools see 3 women enter their physics PhD program, the issue cannot be ignored until the data becomes large enough to see something statistically significant. Many patterns can be seen – perhaps not within a certain school or experiment – that point to issues of bias in physics. I will create a post later with links to some of the studies.

When the sample sizes are small, we must keep in mind that if the null hypothesis was “women are being treated differently” we wouldn’t be able to disprove it either.

Solar Neutrino Data from Homestake Experiment

Solar Neutrino Data from Homestake Experiment


Physics is like…

Tuesday, September 29th, 2009

A lot of topics in physics are explained through analogy. While objects rolling down a ramp or colliding are phenomena people have experience with every day, quantum mechanics and relativity are not part of our daily awareness. They are introduced, conceptually, through descriptions we can understand but that don’t fully encompass what is going on. But seeing as “time slows down” and “the cat is both dead and alive” are hard enough to figure out, the analogies are a good place to start.

Non-quantum cats (in Erice)

Non-quantum cats (in Erice)

Particle physicists spend a lot of time on analogies, likely because our work is so far from what most people deal with daily and requires relatively advanced math. While I think neutrino mixing is ‘straight-forward’ and easy to understand from the math, those equations won’t help my non-physics family and friends. How then, can we explain it? At the International Nuclear School in Erice, Prof. Christian Weinheimer presented an experimental parallel with polarized light. A laser beam is polarized, passed through a birefringent crystal, and then split to have each polarization measured with photodiodes. While his talk was geared towards neutrino physicists, the hope was that we could take the technique back and present it to advanced high school and early university students. I’m not sure how many high school students in the US understand polarized light, but it should certainly work with early university students. Not only is the mixing conceptually similar, but the math works in a very similar way as well.

I find myself attempting to explain my experiment and the physics I work on to people who have not had university (or even high school) physics. I think I have finally come up with a good analogy for the design of EXO-200, a time projection chamber. While scintillation light and ionization are not familiar to many people, lightning is. When a decay occurs in our detector, it is like a flash of lightning. The light we see is immediate, followed some time later by the ‘thunder’ (for us, ionization). By measuring the difference in time between the ‘lightning’ and ‘thunder’ we can tell how far away the decay occurred. The biggest flaw in this is that normally light gives information about how big and what orientation the lightning strike was, while thunder only gives a rough direction. For us, it the other way around – the light can’t tell us much about where the decay way but the ionization (‘thunder’) does.

Hopefully I will improve my own physics analogies over time, or hear good ones that others have developed. My recent favorite is comparing dark matter to the unsocial people at a party. Not only does it capture the physics – freeze out, unseen interactions – it also brings to mind the anti-social stereotype that haunts physicists. This should make the analogy easier to remember! My current quest is to find a good analogy for the Taylor Series Expansion. Given enough time and something to write on, I can explain it to someone who knows what the sine wave is. I haven’t found a good way to explain it quickly – to cashier at a store – or to someone who doesn’t know about the sine wave.


Physics on the Mountain of God

Friday, September 18th, 2009

I am writing this post from one of the most beautiful places I have ever been, Erice, in Sicily. My trip to Rome was enjoyable, but two days ago I began the raison d’être of my 20-hour flight to Italy. The so-called “Nuclear School” is focusing entirely on neutrinos, with a surprising amount of talks relating to double beta decay. At most of the particle physics conferences I have attended the majority of the focus is on accelerator physics, including accelerator-based neutrino physics. Double beta decay is often relegated to a sparsely-attended parallel session.

But certainly this school at the Ettore Majorana Center for Scientific Culture is unlike anything I have ever attended before. As the large tour bus ascended the mountain from Palermo to Erice, I realized that I could not be in more incredible company. Many of the papers that I have worked hard to understand were written by attendees of this school. I was astounded by the amount I learned in just the first day! My favorite talks so far have been the ones covering theory, since it is not something I have been exposed to. This is the most excited I have ever been about my field.

I look forward to the proceedings being available so that I can go back and slowly try to piece together some of the details I was unable to absorb during the fast-paced talks. A talk was just presented on the importance of double beta decay in particle, nuclear, and atomic physics. I was eagerly awaiting the final section of the talk, as I couldn’t imagine what it would include. I believe (and forgive a young experimentalist if I misrepresent this) that there is an argument that it is possible to have atomic oscillations due to a box diagram with the same sort of couplings as neutrinoless double beta decay. This makes sense on first glance, since it resembles the oscillations seen in K (and other) mesons. I was too busy trying to absorb this concept to fully understand the consequences, but I believe it could result in measurable differences in atomic physics. I certainly hope to read more on this, once my brain is no longer running at full speed!

Even aside from the physics, this is a very enjoyble event. The town and view are incredible – which I will share when I can connect my camera to a computer. The food is good, and the nightly marsala receptions are even better. I’ve met a fair number of people and had great conversations on research, travel, and the details of our lives that make us human, in addition to scientists. I am surviving quite nicely without my laptop, though my lack of Italian has been a bit more of a problem. I can’t believe that I really get to spend a week here, and while I will be sad to go, I will be excited to get back and work on contributing to the field I am so proud to be a part of!


What a whirlwind!

Thursday, September 10th, 2009

In just a few hours I depart for Italy. I am greatly looking forward to visiting Rome and learning all about neutrinos at the Erice Nuclear School. I’m not sure which one I’m more excited about! I think I have everything in order – the places I want to visit, where I am staying, Italian phrasebooks, and emergency contacts. I’ve decided not to take my laptop, so I may not post at all for the next two weeks. After that I hope I will have many exciting stories to share about Italy, Erice, and the current state of neutrino physics. Before the jet lag wears off I will be on my way to New Mexico to take a commissioning shift on EXO. I will document “a day in the life of a miner” for you – it has been over a year since my last trip to WIPP and this will be my first commissioning shift!

Now, perhaps you are wondering how I (a computer-tethered physicist) will live without my laptop for two weeks. I won’t have any sort of working cell phone there or small wireless device either. I will be completely cut off! I think I can survive since I had no problem being cell-phone free for 3 months when I was last in Europe. I like to think of myself as not being gadget-dependent, though I will admit to buying a new digital camera for this trip. I had originally planned on bringing my laptop, but the cons finally outweighed the pros. I won’t have free internet in Rome, I’ll have to carry it with me in Rome the entire time, it might get stolen or damaged, and I might be tempted to check my e-mail instead of paying attention to the talks at Erice. What had previously outweighed all of that was the need to finish a paper. My conference proceedings needed to be submitted shortly after I return from Italy, so I had imagined spending some time on the paper. Amazingly, I finished it this weekend and already posted it to arxiv. While it is only a conference proceedings, it is only the 2nd paper ever to have my name on it and the first one I actually wrote. I think I should celebrate with a bit of a trip, don’t you think?


My “first” Collaboration meeting

Tuesday, September 1st, 2009

I’m really enjoying my time with my EXO collaborators in Sudbury, Canada.  While this isn’t my first collaboration meeting by most definitions, this is the first time I really have gotten the complete experience.  While on BaBar I called into collaboration meetings for a few talks, but never attended the whole thing.  All previous EXO collaboration meetings were at SLAC, so I didn’t have the experience of  leaving my normal environment to focus 100% on EXO or going out for drinks with my colleagues every night.

I’m noticing that there are many nuanced differences between this collaboration meeting and any sort of other meeting or conference.  First of all is the schedule.  We have many days filled with talks, so the chair of each session is trying to keep us on time.   However, it was realized at some point that the conversations we are having are absolutely essential and the reason we are having this meeting!  But even with the discussions between groups regarding the content of the talks, we are still only an hour behind after the third day.  I’ve seen much worse scheduling at conferences!  Almost all of the speakers are observing their time limit, which helps.  I will definitely claim that I talked for my allotted 30 minutes but that there was 10 minutes or so of discussion that made me go over.

Another big difference is the friendliness of everyone. While I work closely with many people here, there are others I’ve never met. Yet we all have lunch together and it seems as if everyone just sits down with whoever. While I try to meet new people at conferences, I am not very successful. Here however, I know I will be interacting with everyone again (many times) so I need to learn names and get to know them – and that there is plenty we can talk about right away! I have even learned a lot about the people I already knew, over drinks and dinner. Unfortunately, dinner plans have been difficult to arrange without the last-minute cell phone contact we’ve all become used to.

While I’m more exhausted than I knew I would be and I got a lot less done than I anticipated, I’m still a little sad to head home. I look forward to future opportunities to come up to SNOLAB (and the exciting bars of Sudbury) and I also look forward to future EXO collaboration meetings, regardless of where they are.


A tour of SNOLAB

Saturday, August 29th, 2009

Our EXO Collaboration meeting began with an excellent tour of the SNOLAB facility. Our guide – Samantha – did a wonderful job of leading our exceedingly large group through the mine and answering all of our questions. While it is not my first time underground – I’ve possibly logged 220 hours underground already at WIPP – this was the deepest I’ve ever been. While WIPP is 2150 ft underground, it is still above sea level. SNOLAB is 2km underground (currently the deepest science facility in the world), which is about 5600 ft below sea level. The depth certainly is noticeable: while both involve pressure changes as you descend in the alarmingly-loud lift, at SNOLAB the pressure change is much greater and the ambient rock temperature is 42C (108F) once you reach the bottom. I was quite concerned that this would make the faciilty a giant sauna – and we were warned to wear little clothing under the mine gear – but it wasn’t too bad. At least, I’ve been as sweaty at WIPP after a long walk and there the temperature is close to room temperature.

I was surprised by certain differences in the mines themselves. The mine SNOLAB is located in (Vale/Inco) is a nickel mine, while WIPP is a salt mine. This makes the mining process very different, especially since SNOLAB is located in a private mine run for profit while WIPP is a government facility for storing nuclear waste. Hence, Vale/Inco is concerned with getting as much nickel ore out as quickly as possible, while WIPP just wants a place to put the nuclear waste (as safely as possible). One big difference is the size – while I’m not sure how big the Vale/Inco mine is in itself, the area we were in today was certainly a small fraction and it likely rivaled the entire size of WIPP. Another is the size and condition of the drifts – at WIPP most of the drifts are very large, flat, and wide, while we walked through some much smaller areas today. There are tracks running through the drifts at the Vale/Inco mine for the carts they use, while at WIPP things tend to be more vehicular. This meant we did more walking today than we usually do at WIPP!

Perhaps the biggest difference (to me) was that SNOLAB has toilets. Proper toilets. WIPP mostly has porta-jons, while there is at least one mini-sewage treatment toilet underground at WIPP (it is a glorified porta-jon). At WIPP, the port-jons are scattered throughout the underground and are pumped out a few times a week. This fills the downwind drifts with an absolutely horrible stench that is overpowering even inside our clean rooms! In the underground at Vale/Inco they have a small sewage treatment facility that can support about 100 people (the SNOLAB facility currently is supporting about 40) and only a small amount of waste needs to be shipped above ground. There seemed to be no smell, even when looking directly into the open treatment tank.

Of course, the most meaningful difference is that everywhere at WIPP that isn’t within our cleanrooms is a salty environment. SNOLAB is a large, class-2000 (or better) clean room facility. Once they finish the expansion, they will have about 5000 m2 of clean room facility. Our clean room facility for EXO-200 is something close to 60 m2 (though it is a “more clean” area than SNOLAB). At WIPP we go in and out of the clean rooms, changing between clean room suits and mine gear. We have to leave the clean room if we want to eat something, use the porta-jon, or scratch our head. At SNOLAB, you leave your mine clothes at the door, take a shower, and put on clean room gear. Then you enter an area where there are physics experiments, computers, eating facilities, and toilets. It was quite civilized!

I’m very impressed with the lab. Not only is there an unimaginably large area – kilometers underground – that has complete infrastructure for scientific work, but it has been implemented at the class-2000 clean room level. Every cable and piece of support structure has been cleaned by hand. There are indescribably huge caverns for future experiments – it feels like walking into the bottom of a professional football arena. And then, crowning it all, is the SNO detector.

The SNO detector has a special place in physics history, because it is (more or less) where measurements were made that proved that neutrinos oscillated. And that meant they had mass. While SNO wasn’t the first experiment to measure solar neutrinos, it did it in a way that was more definitive than previous experiments. This has special meaning for me, as I was in high school at the time and remember when the science magazines covered their first results in 2001. This was the experiment that showed me we didn’t yet know everything about particle physics.

The SNO detector is still there, being refitted to look for a different types of reactions, including neutrinoless double beta decay. I won’t hold it against it that it will be competing with EXO, because it is the most beautiful thing I have ever seen. It is a huge sphere, covered with photomultiplier tubes (PMT’s) looking inwards, with a few looking outside the detector. For most of its operation it was filled with heavy water, where PMT’s would detect rings of light left by relativistic particles. Because it was empty, we were able to look both inside and outside the detector, from above. At 6m in radius, it is a large structure. But more importantly, it is impressive in its perfection. Over a million pieces were brought into the mine to be assembled, including acrylic pieces that form the sphere itself. They were carefully bonded together and inspected, and then carefully sealed. The PMT’s are themselves impressive on their own, but this has a large quantity are precisely installed.

It felt like viewing an ancient cathedral. No picture will be able to capture how small it makes you feel. Numbers alone do not do it justice. Realizing how many people poured their effort into it and how its influence has been felt around the world and how close you are to the location where the most important neutrinos were – it makes history seem so small – how else could someone so insignificant as me get so close to it. It was quite awe inspiring.


Occupational Hazards

Wednesday, August 26th, 2009

As a physicist, it is easy to imagine that the majority of our occupational hazards can be prevented with good safety practice. We all go through extensive training regarding radiation, cryogenics, lasers, heavy equipment, electricity, power tools, ladders, and even computer use. I’ve found myself a victim of one of those tragedies that often afflicts my profession: chronic wrist pain.

I do not have a simple RSI like Carpal Tunnel. I did something bad to it when machining a few years ago, which was aggravated by how I was carrying my bike up and down stairs. Soon I found myself having difficulty doing dishes and getting dressed. So I saw a doctor, took some ibuprofen, and kept my wrist in a brace during any significant lifting. Of course, this is my dominant hand I injured.

Eventually the pain stopped, but reoccurred after a few months. It was re-triggered by torquing my wrist too far back. The pattern repeated for a while with the latest occurrence beginning about 2 weeks ago. Now it has even begun to hurt when typing, so I revisited the clinic (where I was given a totally different diagnosis) and began physical therapy. Of course, this injury now coincides with the preparation of a talk and the writing of a paper, so typing is not something I can currently avoid.

Tomorrow I leave for Canada for the second EXO Collaboration meeting of the year. I’m quite excited to visit SNOLab and to give my wrist a chance to heal some. When I’m a work I’m either lifting things or typing, so a week of talks will be a welcome break. While I could be tempted to update documentation during the talks, I have a great excuse to close the laptop lid and not multi-task: another occupational hazard!


Preparing for a Foreign Trip

Tuesday, August 11th, 2009

My recent trip to Detroit was relatively unusual in that I was traveling to a place I know. My past travel for conferences and other business has always been to a city I’m unfamiliar with. Usually I have to navigate the public transportation between a strange airport and a hotel I’ve never been to before. Now I get to do this in another country.

In September I am traveling to Italy to attend the 31st Course in Nuclear Physics in Erice at the Ettore Majorana Foundation and Centre for Scientific Culture. Since I have 20 hour of travel time to get to Europe, I’m spending a few days in Rome before the school. I’ve never been to Italy before, so I’m looking forward to seeing the city of Rome and some of Sicily. I’m less excited about navigating Italy by myself when I don’t know any Italian!

While my preparation for the trip began many months ago – foreign travel requires 90 days pre-approval by the DOE – I have been putting a lot of time into it recently. I booked my flight from Rome to Palermo last week and today I booked my hostel in Rome. I’ve downloaded a bunch of “learn Italian” podcasts, but I haven’t been paying enough attention to them to learn any phrases. I am slowly learning the sound of the language, which I usually end up pronouncing like Spanish. I certainly hope to pick up some survival phrases before I leave, but I face a few challenges. First, I have a few deadlines occurring right after my trip, so I either have to have the work done before I leave or do the work while in Italy. Second, I really want to read up on neutrino theory before I attend the school. Third, I have to figure out what I want to actually see in my short stay in Rome. Finally, the majority of the time between now and my Italy trip is taken up by a collaboration meeting in Canada. This is a juggling feat I do not feel ready for!


DPF in Detroit (part II)

Monday, August 3rd, 2009

I’ve made it to the last day of DPF. I’ve had a great time listening to physics talks, seeing Detroit, and spending time with family. Unfortunately I haven’t met as many people as I had hoped to. It turns out that in addition to at least one other QD blogger who is here, some Cosmic Variance bloggers are here as well.

DPF 2009 Logo

DPF 2009 Logo

I realized that the “logo” for the conference is one of the most clever combinations of physics iconography and cultural symbols. The dotted lines with arrows represent Feynman Diagrams, the loops being very common in searches for new physics. Hopefully it doesn’t take too much imagination to see the car that the logo is as well. Being (more or less) a Detroit native, I can tell you there is nothing that represents the Motor City better!


Security in Science

Thursday, July 30th, 2009

SLAC is different from many other DOE facilities in that the public (with ID) can enter. There is a radiation fence that the public is not allowed past (without proper escort) but SLAC is open – from a security point of view – since weapons and other “top secret” type government work is not done there.

Unfortunately, there was a recent act of vandalism at a SLAC facility – the Stanford Synchrotron Radiation Lightsource. More unfortunately, this vandalism was not just someone spray-painting something offensive on the wall. A few thousand samples of crystallized protein were removed from their liquid nitrogen storage, hence destroyed. While these samples are replaceable, it will require time and money. The samples are estimated to be worth half a million dollars.

This was a shock to the SLAC community. I wondered who could do such a thing. Were they a disgruntled (former?) graduate student, a competing experimenter, or someone who is anti-science (and a bit crazy)? This may cause security to significantly increase at SLAC, which would be regrettable if it means that the Stanford (and wider) community can not come to SLAC for talks. I wonder if CERN has increased security measures in fear of people trying to somehow stop the LHC “from destroying the world”. There have been violent attacks upon scientific facilities before, and there are people out there who genuinely think the LHC will somehow cause harm. I’m sure Dan Brown’s books don’t help people trust CERN either.

The FBI investigated the incident and has made an arrest. It turns out that she is a former employee who felt overworked and was fired from the group about a month ago. I’m somewhat glad this is the answer – it doesn’t point to an anti-science terrorist group or a maliciously competitive experimental culture. Hopefully this does not change the open culture of SLAC. I must also add that while groups and advisors vary, I find that SLAC groups seem to expect more reasonable workloads than many University groups out there. This act is a reflection of her, and not the SLAC work environment.