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Nicole Ackerman | SLAC | USA

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Double shift in the desert

Wednesday, March 10th, 2010

Last night was a very late night – we were underground from the beginning of the day shift to the end of the swing shift. We had to complete a ‘pump and purge’ process on our plumbing so we could pump down overnight. This process cleans out the pipes our xenon will be in, which is essential to prevent the xenon from becoming contaminated.

We started the 45 minute drive back to our house around 11:45 PM. Being in the desert in the middle of the night is amazing. From WIPP we could see Carlsbad (45 minutes away) because there were no hills or trees in the way and we were slightly elevated. I don’t simply mean seeing a glow in the sky due to light pollution, but really seeing the town itself. We pulled off the road to look at stars. Few times in my life have I seen so many stars – it would have surpassed all of them had there not been a bright oil derrick right behind us. In the 5 minutes we were stopped we saw a few shooting stars – one brighter than any star and that traversed almost half the sky. Our soundtrack were coyotes howling in the distance. This isn’t the occasional howl that defines the sound of the desert in movies, but a constant din of coyotes that sounded far enough away to not worry. It was amazing enough to make me want to work 16 hours again to witness it. But not today.


Imagining my next tattoo

Monday, March 8th, 2010

I was quite surprised to see an article on the main NY Times website this morning on complex numbers.

Imaginary Roots and Chaos (NY Times)

Imaginary Roots and Chaos (NY Times)

I thought the article was good both for the mathematical content and for the prose:

Complex numbers are magnificent, the pinnacle of number systems. They enjoy all the same properties as real numbers — you can add and subtract them, multiply and divide them — but they are better than real numbers because they always have roots. You can take the square root or cube root or any root of a complex number and the result will still be a complex number.

Eulers Formular: Linking angles, exponentials, and the imaginary plane

Eulers Formular: Linking angles, exponentials, and the imaginary plane

One of the things the article doesn’t mention (which is ok, I didn’t expect a textbook) is the polar representation of complex numbers. Real positive numbers correspond to an angle of 0 and real negative numbers correspond to an angle of 180 degrees or π (pi) radians. The name ‘imaginary’ numbers lead one to imagine that this part of math is just a game with rules – not anything based in nature. But quantum mechanics is full of them – any quantum mechanical phenomena we witness could not be explained without complex numbers. The ‘imaginary’ part is the phase – something that is not observable but is carried along. For instance, a wave has a phase and an amplitude. What we measure is the amplitude. But if two waves interact, their phases interact and the waves could be ‘in phase’ (adding amplitude) or ‘out of phase’ (subtracting amplitude). It is relatively straightforward in the world of complex numbers.

Here is the finale of complex numbers: Euler’s Identity. It brings together the 5 most important numbers in math

  • Start with e, the base of the exponential.
  • When raised to an imaginary power (i), it is a rotation in the complex plane.
  • What angle to rotate it? How about π (pi), the magic number of circles.
  • e^iπ (e to the i pi) rotates from 1 halfway around the complex plane, resulting in -1.
  • This gives us 3 numbers – the final numbers are 1 and 0.

So Euler’s Identity becomes:
I considered this for a long time for a tattoo. I hope to find something this elegant in physics for my next tattoo, or else someone might mistake me for a mathematician.


Party in the salt mine!

Saturday, March 6th, 2010

Once again, I am blogging from a salt mine in New Mexico. This will be my last trip to WIPP for a while since I will be teaching next quarter and then will have a bit of early summer travel. Also – we are almost “done”. Well, done with the part where we need hands here doing things. Our detector is in the cryostat and the electronics are installed and relatively soon the lead wall will be built in front. So by time I can fit a trip into my schedule, there might not be anything for me to do here.

In the past I’ve been here with one other physicist and our two local techs- this time our area feels crowded! Next week is “40 hour training”, which is the first step to someone becoming a miner. Any collaborator who wants to come underground and work needs to have completed 40 hour training, which really is an entire week. We currently have about 5 people who are here to take that, plus myself, our tech from SLAC, our 2 local techs, and a post-doc who lives here. Next week most people will be above ground in training, but now many of them are underground with us becoming familiar with our area (but not allowed to do work).

The disadvantages of having so many people is that our underground office has 2 computers, 6 chairs, and really enough space for only about 4 people comfortably. This is only an issue around lunchtime. Additionally, the entrance to the clean room has enough space for about 4 persons’ gear. It is a great advantage for dinner though – more people can take turns cooking and there is more motivation to cook something decent (rather than nachos every night) if it is for 4 people rather than only 1 or 2. Additionally, it means more options on the weekend – one car can go hiking, another up to Artesia. When there are few enough people for us to not need to rent a car, we only have one local vehicle to get around with and few people are allowed to drive it.

The final issue is that our two rental houses have 6 beds and I didn’t “sign up” for a bed early enough. I hate to spend our money on a hotel, so I’ll either be sleeping on the couch or using an air mattress. So if I end up on the floor in someone else’s room it might get to be a bit of a slumber party!


Neutrinos: A question and an answer

Friday, March 5th, 2010

We often rely on photons – light – to understand the world around us. Sight is the primary faculty through which many of us navigates through the world. Additionally, light has been invaluable in understanding many phenomena, even when they are very small or very far. The way photons interact with atoms makes it possible to look at distant stars and determine their chemical makeup. We can theorize what processes are at work in distant astrophysical bodies based on the type of photons – xrays, gamma rays, radio waves – that reach us. All of this is possible due to our understanding of light.

We don’t understand the neutrino. We still have to guess about some of its most fundamental properties. But some of its properties – like how infrequently it interacts – make it very useful for studying phenomena that we can’t use light to study (completely). Photons, being the particle of electromagnetic force, interact with strong magnetic fields and most types of matter. Distant light might be deflected or absorbed by objects on their path from source to telescope. Neutrinos can pass right through gas clouds and come straight to Earth – allowing astrophysical observations where they weren’t always possible before.

A known property of the (anti)neutrino is that it is created during beta decay – this is how it was initially “found”. This means that in many types of radioactive decay, neutrinos are emitted, with specific ranges of energy depending on what is decaying. This was one of the earliest “uses” of neutrinos: looking at neutrinos from the sun to check if we understood the nuclear processes going on inside. This work is still being done, on wider energy scales, to check that our theory of the sun is correct. We know how many neutrinos of each energy we should see based on the predicted rates of different nuclear processes. Few of these processes give of photons – and many occur deep inside the sun where photons couldn’t escape – so neutrinos are the only way of verifying they occur.

Geo-neutrinos are one of the newest tools that bridge particle physics and more ‘practical’ observational science. How do we know what the core of the Earth is doing – is it a big nuclear reactor? The temperature of the Earth is a clue, but isn’t enough to know. By looking for the neutrinos coming from the center of the Earth we can understand how much radioactivity is at the core. These measurements can be done by detectors that are measuring solar neutrinos, like Borexino. They just published a paper that puts a limit on the power generated in the Earth by radioactivity. There is still a lot of room left for more experiments in this field to further improve our understanding – the Borexino result is based on about 10 neutrinos.


Scientists in Washington

Thursday, March 4th, 2010

This past week saw a flock (herd, swarm, or perhaps rookery) of particle physicists arrive in Washington DC (from around the US and CERN) to speak with congressional offices about particle physics and funding. Our goals were many: gain support for the President’s budget request for the Department of Energy (DOE) Office of Science and National Science Foundation, thank congresspeople for their past support of science, explain the larger benefits (and applications) of particle physics research, visit executive offices (DOE,budget,NSF), eat some Chinese food, and show how great physicists can look in suits. All of these goals were accomplished.

This was my first year on the trip, and I hope to do it again next year. I did find it intimidating to call congressional offices and ask for an appointment, but the actual visits were enjoyable. There were some interesting and challenging questions, such as “What is the environmental impact of the work you do at SLAC?” from an office with a big focus on green issues. One of the topics I often discussed was the practical application of accelerators and particle physics detector technologies used for the treatment of plastics and medical imaging, replacing toxic chemicals or radioactive materials. This loses a lot of its benefit if we end up harming the environment. I found a detailed report discussing a variety of aspects of SLAC’s environmental impact and shared it with the staffer who had asked me the question. This is one of the most valuable aspects of the trip – making sure that the people who are making big decisions (especially about our funding!) have all of the information they need.

Most appointments are with staffers and not the actual Senators and Representatives, but if the person we are meeting with is a science staffer it means they are relatively knowledgeable about physics research. Conversations included how New Mexico has both suffered and benefited from the nuclear science that has been done there, how rural Ohio suffers from a lack of broadband access, and how a new project in Michigan will help the economy. It felt amazing to be participating in government – to feel like as an individual citizen I can go in and make a difference.


Nature 1, Science 0

Thursday, January 21st, 2010
Our detector, finally inserted into the TPC

Our detector, finally inserted into the TPC

While it seems like the pace on EXO has been at 110% for over a year now, things have been ramping up even more lately. We had a ‘software week’ the first week of January where analysis, DAQ, event displays, and many other code-related tasks were discussed. I walked away with many things to do and a very short time period in which most needed to be done.

I walked away… into the salt mine. I’ve been in New Mexico at WIPP – where EXO-200 is installed – since Jan 11th and I will be here until the end of the month. I’m spending most of my time in the cleanroom working towards sealing up the cryostat – now with the detector inside. My coding work has been getting done in the evenings and has proved to be more of a challenge than I had originally anticipated.

Then – nature strikes. It is the ‘rainy season’ in California right now and apparently the weather has been proving exactly how rainy it can be. Tuesday morning SLAC and Stanford lost power due to a storm. We figured that out here at WIPP when we couldn’t access the collaboration wiki where we keep all of the documentation. No one was allowed on site with the power off, so we had a hard time getting ahold of collaborators. We get a bit done and then head home. I start up my laptop and try to ssh in… with no luck, of course. I couldn’t access any of the code I am working on since it all is on SLAC servers.

We ended up spending 2 days without documentation, without SLAC-based e-mail, without a way to access files at SLAC (like important engineering drawings), and without a way for our collaborators to get us supplies from SLAC. Never before has California rain had such an impact 2000 ft underground in New Mexico!


A Very Exciting Week

Wednesday, December 16th, 2009

Without a good way to tie three disparate topics together, I will go through the excitement chronologically:

SLAC public tours have started up again! On Tuesday the first public tour (in about 2 years) took place. I was not guiding the tour, but tagged along to prepare for future tours. There were about 10 people on the tour, a nice group (in both size and temperament) for the first run. The tour seemed quite successful and we all learned lessons for future tours. I was really impressed by the questions that were asked, and how well the tour guide, Keith Bechtol, was able to answer them. I have a lot of studying to do in order to know the cross section of the electron bunches, the expected radiation doses at a variety of locations around the lab, the use schedule for LCLS, and all of the dates of construction and discoveries! While I anticipate lots of WIPP travel in the next few months, I hope that I can lead a few tours in between trips. I’m certainly happy to see tours running again.

I’m blogging from an airplane right now– how futuristic is that? My understanding is that those of you in Europe have had wireless (and cell phones?) on planes for a while, but this is the first flight I’ve used wireless on. Right now it is a free trial, and I’m not yet convinced that I’d pay $13 for this for a flight, unless it was a very long flight.

Of course, the reason I’m on the airplane is more exciting: holiday travel! I’m traveling to Ohio to spend almost two weeks with family and I could really use the break. I saw snow last year there, so I’m eager to see if I can actually have a white Christmas this year. Certainly the mountains we are flying over right now are snow covered, but it isn’t quite the same thing.

The future is always the most exciting, right? Tomorrow (in exactly 25 hours) the new CDMS results will be announced. Thanks to many rumours, there has been some speculation that CDMS may have seen something. Since CDMS is an incredibly sensitive experiment that has a very tiny background, something is actually saying a lot. Their past results have been that they saw zero events. No background events, no signal. So seeing anything would be a change, and it wouldn’t take too many events (like 6) for it to not be consistent with background – ie, EVIDENCE FOR DARK MATTER!

I haven’t been this excited since the MiniBooNE results were announced when I was an undergrad at MIT. That experiment was testing the (unexpected) results of a previous experiment, LSND. If MiniBooNE confirmed the LSND results, it would imply there was something strange in the neutrino sector (like a sterile neutrino). The MiniBooNE results were consistent with the “standard” neutrino model – the audience was palpably disappointed. Of course, the structure of these talks are that the first 45 minutes or so describe the experiment, analysis methods, and possible backgrounds without announcing the actual results. At the end of the talk the “box is opened” and everyone either starts discussing it with their neighbours or runs out of the room to go and write a theory to match the new data. I think those are 45 of the most excruciatingly exciting minutes possible in science.

But since my present status is flying away from SLAC at 582 mph, I won’t be at SLAC for the talk tomorrow given by Prof. Cooley of Southern Methodist University. There are simultaneous announcements occurring at Fermilab and SLAC, both being webcasted. I will be tuning in from three timezones away, hoping for a birthday present of dark matter. I can’t imagine anything I would rather receive for my 25th birthday than a breakthrough in our understanding of the universe.


SLAC kills millions!

Friday, December 11th, 2009

Only in TV land, of course. A show in the US called FlashForward had a recent episode (that I keep meaning to watch but just… can’t… bring myself to do it) where a lab that resembles SLAC in its location and research kills 20 million people via plasma-wakefield acceleration experiments. I was planning on pulling apart the bad information in the episode, but the SLAC communications office has done it for me!.

Is there any way that plasma-wakefield experiments could cause a “flashforward”?
No. Plasma-wakefield acceleration is just an advanced technique to boost particles to high energies, something that particle physicists have been doing for decades. Even the most speculative theories rooted in real physics make no prediction that anything like a flashforward could occur.

“Although we can use particle accelerators to essentially look backward in time to recreate the conditions of the universe soon after the big bang, there is no known way to look into the future,” says Mark Hogan, chief experimental scientist for the plasma wakefield program at SLAC’s FACET.

While I always cringe to see science represented this way, it is nice to see that CERN isn’t the only lab portrayed as apocalyptic! The conversations about particle physics due LHC publicity (good and bad) is a great chance to educate the public, as many of you have done. Hopefully plasma-wakefield gets a bit of (good!) attention after this episode since it has so much potential.


EXO Night Shift

Wednesday, November 4th, 2009

I sit here at the SLAC Surface Control Center for EXO. I was originally supposed to be at WIPP right now, but I recovered slower than anticipated from a minor wrist surgery. This week is my first shift – I had avoided taking the owl shift up to now since I didn’t have daytime experience. With no WIPP trips on the horizon, it became time to bite the bullet. During the day there is a group of people at WIPP and a supervisor at SLAC. During the night there is just one shifter at SLAC. And right now, that is me.

The SLAC surface control center.

The SLAC surface control center.

I was a bit nervous the first night – with 8 screens of data (and hundreds of channels to plot) it was quite overwhelming. I’ve worked very little with the cryogenic systems and xenon systems, so everything was unfamiliar to me. While I would be by myself, it was supposed to be fairly easy (even boring). The evening shift would put the system into a stable state and then I would just have to monitor to make sure nothing goes wrong.

As you can imagine, things went wrong. Around 1:30 AM our pump stopped. I didn’t know at the time what went wrong – I just saw a bunch of the numbers I was watching suddenly change. I called one of our co-coordinators and she had me shut down the pump. Luckily, this is not a problem on the scale of the magnets at CERN quenching. This pump circulates xenon in the system between the condenser and heater. The condenser and heater do the work of keeping our pressure constant by balancing the amount of liquid and gaseous xenon in the system.

This actually ended up being a great experience. I made many plots trying to understand if anything had happened before the pump failed. I looked for evidence that the system was warming up or becoming unstable. I learned a lot about our system! I’ve now had a few quiet nights, and then there really isn’t anything interesting to plot and learn about. The next shift that went into WIPP checked the pump and it had simply been a screw failure – something easy to fix. So in the end, I learned a huge amount about our experiment, the collaboration learned about a mechanical weakness, and we learned that the system could sustain itself without the pump. The xenon levels didn’t drop after the initial failure and later the system started filling itself. Few night shifts are that exciting!

The desk of power

The desk of power


Theory: Women in Physics

Sunday, October 25th, 2009

There are many reasons for the lack of women in physics – all correctable. I’ll highlight some of the arguments below, some coming specifically out of physics, some from science in general, and others coming out of social-psychology studies. While almost all of it is focused on the United States, similar cultures would share these effects. I want to point out that many of these effects also apply to underrepresented racial minorities, whose numbers in physics are far lower than for women [6].

(Unconscious) Bias

We are not too far from an era where female graduate students were asked to double as babysitters or when female physicists had a hard time getting a paid job at CERN[1]. We aren’t far enough for all experimental buildings to have women’s bathrooms. While there are still a few giant jerks left, most of the problems are from people who wouldn’t think they are doing anything to disadvantage women in the field, including women themselves.

We’re scientists, so what can actually be measured? Studies can be done on how decisions are made and what the field actually looks like. Studies have been done (not specific to physics) showing that white names favored over African-American names in otherwise identical CVs for interview callback (3:2), “Brian” was preferred over “Karen” (2:1) using identical resumes, and that women had to be 2.5 times more productive to rate equally in scientific competence as the average male for a postdoc fellowship [4]. The people making these decisions may not be consciously racist or sexist, but have picked up unconscious bias from societal messages [7].

Perhaps you want to believe that these studies – done in labs or outside of physics – don’t actually relate to what we experience. A study was done on members of D0 (an accelerator experiment at Fermilab) to look at male and female post-docs. There was evidence that the female post-docs did more “service work” (40% more) than their male peers and had to work on twice the number of internal physics analyses papers to go to the same number of conferences[3]. In physics, recommendations and supervisors’ support are necessary to advance a career, and women are again disadvantaged. According to Prof. Urry, a physicist who has written about these issues, [2] (and I have certainly witnessed it for years), “Young men are talked about as superstars, while young women are described as “very good”.” There are many ways in which recommendation letters for female students aren’t as impressive as those for males, including shorter length, more gender-stereotypical adjectives, lack of use of title, and more negative language or irrelevant comments that could raise doubts. [8]


Our society socializes men and women to like different things and behave in different ways. This can disadvantage female physicists (or women who could have been physicists otherwise) in many different ways, including

  1. Trained to not have personality traits beneficial to being a physicist
  2. Not encouraged to participate in activities that would foster an interest in the physical sciences
  3. Not encourages to pursue technical careers

I think the first point is often ignored, and perhaps one of the most important. Many physicists (perhaps this is just in the US, but I doubt it) are egotistical, hard-headed jerks. In some groups, meetings seem to be a contest to either talk the most or interrupt each other the most. These are habits that society discourages far more in girls than boys. Urry writes that “To succeed as a physicist, one must not only do good work but also aggressively promote one’s ideas and accomplishments.” and

Men who are highly aggressive, intrusive, peremptory, and obnoxious still enjoy the confidence and respect of their colleagues. Women with even a fraction of the same toughness are characterized as “difficult” (there are other words for this) and demoted or told to play nice.[2]

Obviously there are some ‘nice’ men who have succeeded in physics and numerous women that have. But the majority of the women I have met who entered physics in the 70’s and 80’s are absolutely tough as nails. They didn’t succeed by playing nice.

There is much that could be said about exposure to and encouragement in technical fields, but I don’t think it is a dominant problem. Freshman physics is hard and boring, but you would still expect both male and female students to quit. About 50% of high school physics students are female, while only 22% of bachelor’s degrees are [9]. Much of this can be attributed to the students entering physics culture – with all of it’s problems – and being discouraged by the issues I am discussing.

If socialization and familiarity with technical fields and the physical sciences was simple, we’d expect to see similar gender breakdowns in other sciences, math, and engineering. Not only does physics have fewer female PhD’s than other technical field, but the improvement over time is also slower [9]. One argument is that physics has an ancient history of being tied to the clergy [10], and that particle physics still has much of the same mentality. While it isn’t the whole story, it does provide one reason why particle physics has the smallest percentage of female PhD’s [9].

Stereotype Threat and Solo Status

When a department or field lacks women or minorities, the problem is much deeper than young people not having role models. While it is important for people to have mentors who can give helpful advice, there are extensive psychological challenges for both the minority individual and those belonging to the majority. Some of this relates to bias: “As the ratio of women to men, or racial minorities to Whites, increases, women and racial minorities receive lower evaluations and are less likely to be promoted than White males.”[5]

The idea of “stereotype threat” and “solo status” is that self-perception of being in a disadvantaged group decreases ones own performance. In research discussed in [5], a math test is given to subjects in two different circumstances. If told it measures their ability and given the test, men outperform women. If told beforehand that it is a “special” type of test that has no gender bias, women perform the same as men. This is the same test- the difference is only stereotype threat! Additionally, if a person thinks they are the only member of a marginalized group in an evaluation, the person performs worse than if they are in a group with the same race or gender. Research has shown that women have lower expectations of their performance if they are in a solo situations, and these expectations lower their actual performance [5].

Research into these issues is extensive. Believing that you are representative of your group has been shown to hurt performance in a multitude of ways.

Low-status groups engage in different communication styles when interacting with high-status groups… Women tend to use more tentative language (e.g. weakening the strength of a statement by using phrases such as “sort of” or “maybe”) when interacting with men. Solos … may say only what is neccessary, without elaborating on answers, in order to provide less room for error.[5]

With the culture of physics being what it is, these effects can be debilitating to someone facing stereotype threat and solo status. Urry says that “To succeed as a physicist, one must not only do good work but also aggressively promote one’s ideas and accomplishments.” This is in great conflict with tentative communication and lowered expectations of one’s performance.


Often the “leaky pipeline” – women leaving academia after each stage – is discussed with regards to the lack of women in physics. Pointing to family or child-raising issues is sometimes just a cop-out – many issues apply. This can’t be solved by “fixing” the women. The environment and mentality must be changed. Perhaps you have never experienced these issues in physics – perhaps that explains why you have made it as far as you have. Yes, there are some amazing women in physics- but there are plenty of mediocre men in physics! If some of the women who would be good (but not amazing) physicists could make it, they would still be improving the field.

For an excellent summary, see this excellent APS article written by Prof. Urry. For some interesting stories on the bias female professors face, I recommend reading through the archives at FemaleScienceProfessor

[1] Report On Women In Scientific Careers At Cern Gaillard, M. K. 1980

[2] “Are Photons Gendered: Women in Physics and Astronomy” Urry, C. M. In Gendered Innovations in Science and Engineering.2008

[3] Title: A Case Study of Gender Bias at the Postdoctoral Level in Physics, and its Resulting Impact on the Academic Career Advancement of Females Towers, S. 2008

[4] “Nepotism and Sexism in Peer-Review” Wenneras,C. and Wold,A. Nature 337, pp 341. 1997

[5] “When Being Different is Detrimental: Solo Status and the Performance of Women and Racial Minorities” Thompson, M and Sekaquaptewa, D. Analyses of Social Issues and Public Policy Vol 2 No 1 pp 183-203, 2002

[6] Diversity in Science Association 2007 Report (Nelson Diversity Survey)

[7] Implicit Association Test

[8]”Exploring the Color of Glass: Letters of Recommendation for Female and Male Medical Faculty “, Trix, F, Psenka, C, Discourse & Society, Vol. 14, No. 2, 191-220. 2003


[10] “Pythagoras’ Trousers: God, Physics, and the Gender Wars” Wertheim, M. 1995