Wekelijks weblog masterstudent Heleen Mulder vanuit Seattle

22 mei 2023

Heleen Mulder, masterstudent theoretische natuurkunde aan de UvA en Nikhef, verblijft momenteel in Seattle op het Institute for Nuclear Theory. Haar reis is mogelijk door een beurs van het Volkert van Willigen fonds, die ze vorig jaar ontving. De komende weken houdt Heleen (in het engels) een weblog bij over haar werk en haar ervaringen.

Scroll naar beneden voor week 1, 2 en 3

Week 4 in Seattle: an interesting fit result, cool neighborhoods and sunny hikes
Dear reader,
I am writing this final post about my wonderful month in Seattle from Amsterdam, having traveled back home earlier this week. Funny coincidence: when I was walking through Schiphol airport, I saw that they have an exhibition of Dale Chihuly’s art! A little bit of Seattle in the Netherlands… Anyway, I hope this post will be coherent, because I feel pretty jet lagged. I also have to get used to colder weather again, after the (highly unusual) heat wave in Seattle!
My last week at the INT was again filled with interesting talks: it was the ‘intensive’ week of the month-long conference on precision physics, which meant there were 5-6 talks each day, about all three of the conference topics – beta decays, neutrinoless double beta decay and EDMs. I will work on a SMEFT framework for EDMs during my PhD at the Van Swinderen Institute in Groningen, starting in the fall, so attending some experimental and theoretical talks on EDMs was a nice opportunity to start building up my knowledge about this field. From a couple of the other talks, I also got a useful overview of BSM models related to the CKM unitarity anomaly: this is the anomaly that I am working on in my master’s thesis, so it helped put my own research into context. Since one of the models I am looking at is adding sterile neutrinos to the SM, it was also valuable to learn about a different aspect of neutrino physics, in the talks about neutrinoless double beta decay.
Speaking of the sterile neutrino model, I have made some progress on that this week! I worked out all the lower mass ranges for the fourth sterile neutrino I add to the SM. This involved some changes to my code which did not go off without a hitch, so Wouter and I spent quite some time trying to understand what the results meant. The preliminary conclusion seems to be that only neutrinos in the lightest mass range I am looking at (between ~ 1 and 30 MeV) give a better fit to the data than the Standard Model. It’s pretty cool to start arriving at the final results of my research, after working on these topics for months!
On the weekend, I got to see some pretty cool parts of Seattle. We went to lively Capitol Hill on Friday evening, saw a spontaneous brass street band performance and had a beer in the grungy bar Linda’s Tavern – the last place where Kurt Cobain was seen before his death. On Saturday, I hiked in Discovery Park: this is Seattle’s biggest park, full of lovely meadows, forests and beaches. We had lunch in Ballard, another really cool neighborhood with lots of nice restaurants. And as a final trip, I took the ferry to Vashon Island on Sunday! A really beautiful place, we had a great hike through the forest and emerged onto cliffs with a stunning view of the sea (actually the Puget Sound, as I’m sure locals would want me to specify) and Mount Rainier. A seal also bobbed up while we were having lunch on the beach!
Looking back on this month, physics-wise, I feel that being around nuclear physicists a lot has given me a nice introduction to their field and research topics – especially those that were treated in the conference talks. Apart from the new physics topics I heard about, the conferences also gave me the opportunity to present my own work, which I really appreciated and enjoyed. It was also nice to meet people from so many different universities, mostly in the US & Canada but also some from Europe: even though I only visited one small part of this huge continent, I feel like I learned more about the rest of it too, through all the people I spoke to. Hearing about people’s lives & experiences in this part of the world and in academia in general has given me more tools to think about how I would like my own career to be. But for now, I don’t have any big decisions to make anymore: my plan is to write and present my master’s thesis before the summer, and continue my research on low-energy precision tests of BSM in October, with my current supervisor Jordy de Vries.
So see you at Nikhef!


Week 3 in Seattle: beta decays, sterile neutrinos and a weekend in Portland

At the start of my last week in Seattle (sadly), let me tell you about the interesting talks I’ve attended in the past week! The first week of the month-long conference on ‘New Physics Searches at the Precision Frontier’, organized at the INT, was focused on beta decays. Many of the speakers and participants were experts in this field, so I found the level to be quite high. Nevertheless, it was very instructive to get an overview of the many aspects of this high-precision research field – especially because I use |Vud| as determined from both superallowed nuclear & neutron beta decays in my own project, on the CKM anomaly.

Roughly, the first part of the week was about theoretical research on various SM corrections to beta decay rates. On Thursday, the talks were more on the experimental side: both of the speakers presented detection methods I hadn’t heard of before, so this was an enlightening day for me. What I especially liked was the possibility of using one of these methods to detect sterile neutrinos. This specific method measures the recoil of the nucleus undergoing beta decay, and the emission of a heavier neutrino mass state would have a measurable impact on this recoil. Sterile neutrinos with masses in the keV range could be probed in this way, which ties in nicely to my own research on the effect of sterile neutrinos on the CKM anomaly (see my first post): ‘my’ neutrinos have masses in the MeV range.

The talks on Friday focused on BSM research: Wouter presented a SMEFT analysis of low-energy measurements and EW precision observables (a.o. the W boson mass and CKM unitarity), Vincenzo’s graduate student Maria spoke about describing BSM tree & loop level effects on beta decays using SMEFT, and I also gave a talk about my thesis research! I discussed the CKM anomaly and the three NP models I have investigated so far: right-handed currents, pseudoscalar currents and a fourth sterile neutrino. Giving this talk was a very fun and useful experience, and it led to lots of interesting discussions on sterile neutrinos during the rest of the day.

Apart from the scientific programme, the conference is also giving me the opportunity to explore some of the innumerable cafes and restaurants in Seattle, at lunch or dinner with other conference participants. In the past week, I’ve had Thai, Indian, Mexican and even El Salvadorian food!

After this busy week, I visited another part of the Pacific Northwest: I took the train from Seattle to Portland and stayed with friends for the weekend. On Saturday, we went hiking in an absolutely stunning place: Multnomah falls – the biggest waterfall in the state of Oregon! I had actually never seen a waterfall before, so it was an amazing experience for me. We explored Portland on Sunday: we went to the famous and huge bookstore Powell’s, had lunch at one of Portland’s many food cart pods, went for one of the crazy donuts at Voodoo’s, and visited the Chinese garden, a wonderful oasis of calm in the city. I liked Portland a lot, it’s smaller than Seattle and has less of a big-city feel, and I enjoyed the artistic, funky atmosphere.

A week from now, I’ll be on the plane back home… I plan to make the most of this last week, by attending talks at the conference, working on my new neutrino masses, and visiting parts of Seattle I haven’t been to yet!


Week 2 in Seattle: correlations, hiking and a trip downtown

Dear reader,
Once again, greetings from Seattle, where the sun surprised us all in the past week by shining most of the time! Spring is really in the air now, and my walks around the city are often accompanied by fresh smells of flowers in bloom and trees blossoming. And I have been doing quite a bit of walking in this second week of my stay: I’ve explored the rest of the campus grounds (with Simon and Garfunkel’s line stroll around the grounds until you feel at home stuck in my head…), visited the Union Bay Natural Area – wetlands tended by the university that house beavers and many types of birds – and gone for a run with the Husky Running Club! This club, named after the University of Washington mascot, meets every weekday for a group run or track workout. The students in the group were very nice, and we ran a route of about 8 km over the 520 bridge: great views over the water and of the mountains beyond!
But this was just the start of the amazing views this week had in store for me: on Saturday, I went for a hike at Oyster Dome (about 1.5 hours north of Seattle, on the coast) with Wouter, Vincenzo and Vincenzo’s wife Elena. Right at the beginning, we already had an amazing view over the sea and the islands just off the coast. Then we hiked through the woods filled with pretty streams and waterfalls to the highest point – about 300 m in elevation. We had a great time and the view from the top was absolutely spectacular!

On Sunday, I took the metro to the downtown area to visit Seattle’s most famous hotspots. I walked around Pike Place Market, a famous indoor market with stalls selling local products, everything from fish and honey to jewelry, glass ornaments and tulips – there are actually a lot of tulip fields north of Seattle, it’s like a tiny slice of the Netherlands!

The first Starbucks in the world is also located here, established in 1971. From Pike Place Market, I walked along the nice little parks and beaches on the waterfront towards the huge and beautiful artworks in Olympic Sculpture Park, part of the Seattle Art Museum.

Lastly, I explored the area called Seattle Center, where the famous Chihuly Garden and Glass exposition and the prominent Space Needle (185 m high tower) can be found. The former of these is a museum showcasing work by the glass artist Dale Chihuly, who is originally from Tacoma (very close to Seattle) and learned the art of glass-blowing in Venice. His enormous and colorful glass artworks really blew my mind!

The week ended with a trip up the Space Needle: I timed my visit so I could see the view over the city and sea with daylight, at sunset and by night. I took way too many pictures to include here, but I hope these two give you an idea of how impressive the panorama was!

You might be wondering if I’ve given up on my thesis and become a full-time tourist, but I have also been doing some physics. I’ve been learning a lot about how to quantize and include the correlations between the different parameters in my fit, both in the input and output. This has involved a lot of tweaking in my code, and maybe a bit less fundamental physics work, but I’m happy I am doing this: it feels like my project is becoming more and more ‘professional’.

I am writing this on Monday afternoon, so we have just kicked off the month-long conference on ‘New Physics Searches at the Precision Frontier’ that the INT is organizing. I will be here for the first two weeks of this conference, and I will also give a talk on Friday! And that brings me to the end of this post, because I should really start working on my slides…



Week 1 in Seattle: cherry blossoms, a coyote and neutrinos

Dear reader,

I am writing this from my Airbnb in the University District in Seattle, surrounded by fraternity and sorority houses and very close to the beautiful, green campus. I am here on a month-long visit to the Institute for Nuclear Theory (INT), thanks to the Volkert van der Willigen grant which I received for my master’s project.

Since September, I have been conducting my thesis research under supervision of Jordy de Vries in the Nikhef Theory Group, on (nu-)SMEFT solutions to the CKM anomaly – this is the deviation of the first row of the CKM matrix from the unitarity relation predicted by the SM, as well as the disagreement between various measurements of this relation.

Last year, prof. Vincenzo Cirigliano and collaborators wrote an article on this topic, which has been the starting point and an important inspiration for my project (2208.11707, for those interested). In my project, I have been investigating the effects of various New Physics models on this anomaly, some of which – BSM right-handed and pseudoscalar currents – were proposed in prof. Cirigliano’s article.

However, I am also working on another model: adding sterile, right-handed neutrinos to the SM. What’s especially exciting about this, is that I am looking at so far unexplored parts of the possible mass range of these neutrinos! Here in Seattle, there is plenty of expertise on this topic: both prof. Cirigliano and INT fellow Wouter Dekens are experienced specialists, with whom I will be working during my visit.

In this past week, we have already had fruitful discussions, and I also had the chance to attend interesting talks at a conference organized by the INT (on nuclear, neutrino and BSM physics at low energies). Moreover, the INT has provided me with a spacious office with a lovely view towards downtown Seattle, so I’m all set to make great progress in my time here!

But enough about physics: the title of this post promised way more exciting things. Before this trip, I had only been to the US when I was very young, so this past week has been a constant amazement at how American everything is.

So many students walking around in purple University of Washington merchandise, fraternities and sororities with Greek letters as their names, their members playing beer pong with red solo cups, suburban neighborhoods with huge houses and yards full of pretty flowers and trees, the enormous amount of cars…

I’m sure it sounds very silly to anyone who’s been to the US before, but I keep feeling like I’m walking around in a movie. I was completely blown away by how beautiful the university campus is, especially because I was lucky enough to catch the last of the cherry blossom season. Today, I even got a squirrel to pose between the pretty pink blossoms!

Aside from the university area, I have also explored other parts of Seattle. On Tuesday, I walked to the Arboretum, a huge park (I’m pretty sure we would call it a forest in the Netherlands) in central Seattle. I even saw a coyote in this park! As a sign at the entrance advised, I waved my arms to scare it, and it ran away.

Yesterday, I went to a running event in another of the city’s parks, and because it was Earth Day (which seems like quite a big deal here!) you could plant your own tree! You were allowed to take it with you, but since I don’t have one of these lovely suburban yards (yet), I donated it to Seattle Parks & Recreation.

Today I went to yet another park: Gas Works Park, located on the shore of the lake, which offers an amazing view of the downtown area. I plan to visit that part of the city next, so perhaps you’ll read about it next week: I will keep you updated on my time here with a weekly blog!