Dennis V. Perepelitsa 🇺🇦🇺🇲

Folks, I'm pleased to be promoted to Associate Professor with Tenure at @CUBoulder, just days before my 36th birthday! An immeasurable thank you to my colleague Jamie Nagle, and to our post-docs, grad students, and undergrads for taking a chance on a new junior faculty!

Great news - we are expecting another boy! 👶💙 For our physics friends, please consult the helpful Feynman diagram below (my wife and I are the fermion lines). 😁

Some (probably overly personal) thoughts on the end of operations at the Relativistic Heavy Ion Collider, America’s only working hadron collider. We watched the last beam dump from the sPHENIX experiment control room. ⚛️ The most precious currency that any of us have is the time and energy of our youth. Thousands of graduate students, post-docs, and junior professors spent this currency in the construction, operation, and analysis of collider data. These were (and are) smart and hard-working people who had many options for how to spend their time. They believed in the scientific mission of RHIC - they gambled and they won big. ⚛️ I first sat on data-taking shift on the (now long decommissioned) PHENIX experiment 16 or 17 years ago, even before I met my wife. To say that this facility has played a dominant role in the trajectory of my scientific career would be an understatement. That practical aspect of my life is over now, although it persists in some form at LHC, test beams, and future facilities. ⚛️ RHIC arose serendipitously (c.f. the partially-built and ultimately cancelled SSC and ISABELLE colliders) but also strategically. A long time ago, before I was born, people had a vision, set it in motion, and doggedly pursued it for years. A society grows great when scientists design and build instruments whose data they will never analyze. We are greatly indebted to these past generations. ⚛️ We now enter a very unusual period, with more than half a decade between LHC heavy-ion runs after this summer, and something like a decade until the first Electron Ion Collider data. I hope our community will see our way through it.

I'm watching the NFL playoffs with my 4-year old son, but the ads are really killing me. He knows, in a general sense, that ads are "people trying to get you to buy something" - fine, whatever. I don't love it, but that's market capitalism. But what can I even say about the predatory and insistent gambling ads - "These are very bad people trying to sell you poison because they think you are stupid" ? How have Americans come to tolerate this in front of their children? How do the people involved in producing these sleep at night?

@Chives_Dylan Indeed I am hoping this becomes a Core Memory for my son. 🐢

@profdvp The Galapagos are so pretty! I went there when I was younger and it was one of the coolest experiences I have ever done.

We spent the start of 2026 🎆 in Quito and the Galápagos Islands, which Charles Darwin surveyed almost 200 years ago and which were a major driver in coming to the correct description of evolution through natural selection. (Ecuador 🇪🇨 is the 48th and 9th country for me and my son, respectively.) A very unique experience. I am sure it is a cliché to say it, but I felt strongly: (1) the urgent responsibility to preserve the remaining biodiversity of this planet, and (2) a great respect for Darwin and all the scientists and thinkers of the past who made such powerful inferences with much more limited data and tools.

I'm here at @CERN for the opening day of this week's Light Ion Collisions at the LHC 2025 workshop, which I am helping organize. We are starting with an overview of @ALICEexperiment flow results! Full program: cern.ch/lightions2025

Fall 2025 🍁🐶🚲🎃💀

A neat paper on using generative AI (CycleGAN) for jet measurements in heavy-ion collisions -- in collaboration with my @BrookhavenLab colleagues Yeonju Go, Jin Huang, and others! Here is our first author Yeonju giving a presentation to 🇰🇷 South Korea's Minister of Science (!) while on the sPHENIX Experiment hall floor. Preprint: arxiv.org/abs/2510.23717 - my own contribution is very modest. 😊

BREAKING NEWS The Royal Swedish Academy of Sciences has decided to award the 2025 #NobelPrize in Physics to John Clarke, Michel H. Devoret and John M. Martinis “for the discovery of macroscopic quantum mechanical tunnelling and energy quantisation in an electric circuit.”

Meet our new puppy, Maxwell 😊 Maxwell is a three-month old Coton de Tuléar, named after the great Scottish physicist who unified the theories of electricity and magnetism.

Friends, apologies for posting so personally and politically — I feel completely radicalized by the killing of Iryna Zarutska. She was an immigrant (like me) seeking a better life. She was beautiful, but she was decidedly not above working - she was coming home from her job at a local pizza restaurant in her dorky uniform (also my first job in high school, complete with dorky uniform). She could, in a literal sense actually, have been a Ukrainian cousin or niece of mine. I feel ashamed, essentially on a personal level. I feel ashamed at how spectacularly we failed in our duty of hospitium - the ancient (pre-Christian, even) duty of the host to protect his guest. Iryna believed that America was a place of stability and opportunity, far from the wave of torture and murder brought by Russian invaders. Even in death, her parents declined to repatriate her body to Ukraine, saying she would have wanted to be buried in the country she loved. If I had known Iryna, I would have told her what I tell other immigrants I encounter in my life - that I am proud of her, that I am impressed by her courage and ambition, that I know it can be tough in the beginning, that America’s super-power is hard-working and well-behaved immigrants just like her, and that she will live to be extraordinarily happy with her choice. But I would have been wrong. Instead, Iryna was killed by a criminal who was allowed, again and again and again and again, to escape the consequences of his actions and prey on people like her. He was allowed to do this, again and again and again and again, for what were — as best as I can determine — purely ideological reasons. We have let the public spaces of this great country be held hostage by its most deranged and criminal elements, rather than kept safe for model “citizens” like Iryna. I am ashamed that I have tolerated it up until now, but I will tolerate it no longer in my neighborhood, city, and country. It is not “fascist” or “authoritarian” to do so — it is the most basic requirement of a free and prosperous society. Let me lay down my marker. Public order will be a top priority for me in 2026, 2028, etc. Which political movement will commit to aggressively defending it? Who will speak for Iryna, and for me?

🚨 BREAKING: Iryna Zarutska's family DECLINED to have her body sent back to Ukraine, despite an offer from the Ukrainian Embassy - because they want her to be buried in AMERICA instead. Stunning. "After Iryna's death, the Embassy in Ukraine called and said, 'We'll help you bring her home.' Her family said, 'no, she loved America, we're gonna bury her here.' I think we can give her an America to be proud of. Something here's broken, and we're here to fix it."

ONE MINUTE, 35 SECONDS. That is how long it was between Iryna Zarutska being stabbed in the neck by an evil and crazed psychopath and anyone -- ANYONE -- doing anything. Many people stood by and looked apathetically at their phones.

The horror of the Charlotte murder is somehow compounded by watching everyone on the train ignore her crying and bleeding to death. Monstrous in so many ways.

It’s bizarre how “psychos with 14 priors shouldn’t be on public transport murdering random women” is right wing coded in the US now. How is it not a universal position? Who wants to campaign on “just tolerate a certain level of random killings”

Imagine thinking that a woman being brutally murdered in public is just a niche issue for MAGA influencers

Of all the terrible things in this tragedy, one detail really stands out to me as Labor Commissioner: this young woman was murdered on her way home from work. If you look closely, she’s wearing her work uniform — a T-shirt and hat from a pizza restaurant. She came to this country for a better life and took a job in the service industry to support herself. At the end of a Friday night shift, she sat down, tired, on a train and tried to relax by scrolling on her phone — something mindless most of us do each day. Then a monster crept up behind her and took her life. This madness must end.