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Interview with Ajeeta Khatiwada: Particle Physicist at CERN

Please tell us about your current research. What do you find most exciting about your research?

I am an experimental particle physicist working on the CMS Experiment at the Large Hadron Collider (LHC), which is the world’s largest and most powerful particle accelerator to date. At the LHC, we collide beams of high energy protons and ions at speeds very close to the speed of light in order to replicate conditions that existed right after the Big Bang. I work on proton-proton collisions, where the speed of the protons before a collision can reach up to 0.999999991 times the speed of light. In proton-proton collisions, the quarks and gluons inside the two protons interact to create many different kinds of particles. Detectors like the CMS are placed around the interaction point to measure the position and energy of the particle spray, which are used to reconstruct the initial interaction. Reconstructing the interactions and studying their properties at the CMS allows us to probe the particles and forces that brought the Universe into existence in the form we see today.

I study interactions that create a pair of top quark and its anti-quark. Top quark is the most massive of the 17 fundamental particles that scientists have discovered to exist. Its heavy mass and other special properties has led physicists to predict that it is more special than the other 5 quarks. All elementary particles have a fundamental property called “spin”, which is a quantum mechanical concept. The particles aren’t exactly spinning but the term came into use due to its similarity with the magnetic properties exhibited by charged spinning objects in the classical physics. Particle spin is a vector quantity, which means it has both magnitude and direction. The amount by which the spin is aligned to a given direction gives you the polarization of a particle. Specifically, my current research measures the polarization of the top quarks, and the correlation between top quark spin and top anti-quark spin when they are produced in a pair at the LHC.

Studying the spin properties of the top quark precisely and checking if it agrees with our current understanding of the Universe is key to validating the Standard Model (theory that describes the fundamental particles and their interactions). Though the Standard Model is quite robust, we also have hints that it is not adequate to describe every phenomenon in nature. Other than validating Standard Model, my research also allows us to look for evidences of new physics beyond the Standard Model.
To me the most exciting thing about my job is being able to contribute in shaping our understanding of the universe.


What is a typical day in an experimental particle physicist’s life like?

There is no one type of schedule for an experimental particle physicist, not even at the CMS. CMS has over 5000 active people, a large fraction of whom are physicists at various stages of their career. Based on the educational institute that hired them, their seniority, country of their educational institution, expertise, and other factors they may have a very different work day from mine. Even I have wildly varying days based on the kind of projects I’m involved in. Since I work from Fermilab in the US, quite often I have to attend early morning video meetings, which are typically organized during office hours in Geneva, Switzerland. If it is very early, I attend the meetings from home and drive to work after that. I may attend more meetings/seminars locally during the day. I usually do all my research work on my laptop, but I connect remotely to machines at CERN, or Fermilab or my home institution (Purdue University). I play with a large amount of data on a regular basis and use programming languages such as C++, ROOT and python to analyze this data.

Besides my research, I am also involved in many activities geared towards the upgrade, maintenance and operation of our detector. Just recently I took some remote shifts from Fermilab to monitor the quality of data collected by the tracking detectors at the CMS. During these shifts, I was at the Remote Operations Center at Fermilab the whole day checking the quality of data taken just a few hours earlier by the CMS. Usually, I leave work anywhere from 5:30 pm to 7:00 pm. If I have any important deadlines coming up, a presentation in one of our regular meetings, or something else I will adjust my schedule accordingly and sometimes I am even up until 3-4 am in the morning trying to cram in work from my laptop at home. I think a typical physicist, especially someone at the early stages of their career, works way more than 8 hours a day but when and where you do your work can be quite flexible depending on the institution or collaboration.


Tell us about your physics journey.

My fascination with physics started when I was in 5th or 6th grade, perhaps even before I really knew what physics was. Growing up in Nepal in the 90s, we were encouraged to do well in school especially since my parents endured a lot of socio-economic hardship to get their higher education, but we didn’t have many resources available outside of the school in order to support science learning. Back then, asking philosophical questions and coming up with random hypothesis while gazing at the stars from our rooftop was a favorite pastime for me and my sister. After I finished high school in Nepal, I applied for scholarships to pursue an undergraduate degree in the US, and I quite naturally chose physics as a major. During the course of my undergraduate studies, I did three physics internships and got a chance to meet many excellent physicists and physics professors that left a lasting impression on me. One of the internships was at Fermilab in 2009, which back then had the world’s largest particle accelerator. Though I did my summer internship with the astrophysics department, I was more enthused by the particle physics research that some of my friends were involved in. Then, after finishing my undergraduate degree in 2010, I joined Florida State University for graduate school in physics. I worked on a particle physics data from the CMS experiment for my thesis and graduated with a PhD in physics on June 2016. Since my graduation, I am continuing to work on CMS through a postdoctoral research associate appointment at Purdue University.


 Tell us about a time you made an exciting breakthrough — or any other highlight in your physics journey.

Experimental particle physics research is becoming more and more of a collaborative endeavor these days and very rarely can a single person solely claim a scientific breakthrough. I joined CMS in 2013. CMS had already discovered the Higgs boson, often touted as the final piece of the puzzle that is the standard model, a year earlier. So, I was on the other side of the aisle when CMS scientists got all the international media attention. To me personally, the highlight of my physics journey was getting to be involved in assembly of the CMS silicon pixel detector, often referred to as the heart of CMS, during Phase I upgrade in late 2016. Until then, I had only been involved in physics analyses and software activities. Though it is equally true for other software contributions as well, this experience gave me a feeling of having contributed to every research done through CMS collaboration.


Tell us about a time you had serious doubts about your own ability in this field. How did you overcome that?

My conversation with my colleagues and other members of my family, who are in similar fields, tells me that almost everyone in physics has doubts about their ability once in a while. It is a very competitive field. Most of us were top of the class while growing up or when in college. When you are in this field very often you are discussing with, disagreeing with, and competing for positions with other scientists who are quite intelligent and smart. So, it’s natural to have some feeling of inadequacy, but often the doubts can be unfounded (described as impostor syndrome). Social studies have shown that minorities and women are more susceptible to suffering from impostor syndrome. Being aware of these facts helps to overcome some of that feeling. I also try not to compare myself with others because all of us have had different journey to get to where we are. Thinking of the humble life my grandparents lived in small villages of Nepal, my parents’ struggle to get their education, and my own struggles to get educated in a foreign country allows me to reflect on my accomplishments and strive to be better rather than indulge in self-doubt.


There are very few women in physical sciences compared to biological sciences. Why do you think it is so?

There are several theories regarding why there are less women in sciences in general. Social scientists have considered explicit gender biases in developing countries, implicit gender biases even in many industrialized societies, lack of mentoring and role models etc. as possible causes. The answer as to why there are very few women in physical sciences as compared to biological sciences, I believe, is more nuanced.

Fields like physics, mathematics, computer sciences and engineering are often associated with inherent intelligence, and people often believe that mere hard-work is not enough to excel in these fields. On the other hand, biological science arguably does not have the same reputation. Most societies have negative stereotypes regarding women’s inherent intelligence. The other side of the same coin are positive stereotypes regarding women’s natural proclivity to nurture, and care. From very early age, women in most societies are taught to adhere to and are shaped by these gender roles and expectations. Perhaps that is why, many women that have ability to choose, go to biological sciences rather than physical sciences. This theory can also explain why many women in less developed countries or middle eastern countries, often accompanied by lesser rights and choices for women, have larger percentage of women in physical sciences than their counterparts in the western countries.

Even when women have the same opportunities to excel academically and professionally, many continue to have responsibilities distinct from men in their private lives. Pursuing physical sciences often demands many days of sleepless nights, and frequent long trips away from home, which are often not compatible with the role that most society demand of adult women. This is why even in the cases where equal number of men and women start out in the field, the percentage of women gets lower and lower as you go higher in the education or profession. Academic institutes and workplaces are not yet fully amicable to these changing realities. So, women have to navigate more roadblocks as compared to men to reach to the same place in their career.


Please tell us about your experience as a woman in physics.

I grew up in Nepal very aware of various kinds of gender discriminations in the society. Most classrooms I was in had less than 30% female students. However, academically speaking there were no significant deterrent for me personally. When I came to the US for my undergraduate program, I continued to be a minority in my physics classes and in my graduate program, women only made up approximately 10% of the class. Though working with male colleagues and hanging out with male friends wasn’t too new for me, some incidences often made me realize that the academic environment, particularly in the male dominated fields, are not very encouraging and friendly towards women. One time, a few of my male colleagues were gathered around discussing if women are as good as men in anything. Graduate school is often very taxing on one’s confidence, constant lack of belief in your entire gender from your peers can quite easily wear many women down. In another incident, a colleague of mine, who perhaps meant to compliment me, told me that I was “quite smart for a girl”. Having heard these kinds of sentiment from my colleagues, who are supposed to be a few of the best minds of our generation, was mind boggling to me. It also made me realize the extent to which gender stereotypes have engulfed our society. Occasionally, I also heard of sexual misdemeanors from faculty members experienced by some of my colleagues or graduate students in other universities. Luckily, all of my supervisors that I worked directly with were extremely professional and aware of the obstacles women face in traditionally male dominated fields. They made sure to treat me equal to my male colleagues. I cannot say the same about all of my male colleagues though. Many times, I noticed a particular colleague of mine asking all other male students for help and skipping me altogether if he ever needed help on computing and physics problems. It occurred so often that even his professor noticed on two occasions and told him to first ask the question to me before going to the professor. These incidences made me certain that when some of these male colleagues reach decision making positions, their implicit biases are sure to impact the careers of future female physicists.


What would be your advice to other women who want to pursue a higher career in physics.

The examples I shared in the previous question gives some ideas on the hurdles faced by women from external sources in order to pursue career in physics. External obstacles such as sexual misconduct or anything that shows sexism can and should be reported to the authority. Though lack of belief from colleagues and professors can be a nuisance, those have to be dealt with on a case by case basis.

Many studies have shown that implicit bias against women are harbored by women just as they are by men. A senior colleague of mine once mentioned that she caught herself judging the entire female gender when one of the female students working under her was performing poorly, while she did not do so when a male student was performing subpar. On another occasion, a female friend working at the LHC expressed a belief that women are not good at coding. So, my second advice is to challenge opinions that are unwarranted and undermine the ability of a large group of people, and be vocal when necessary. If discussed logically, chances are that many will appreciate your comment rather than take it negatively.

My third advice is for women to find a senior physicist that they can go to for guidance in their career. Many insecurities and issues one may think she is facing alone, are sometimes not that unique after all. These days many universities also offer programs that are directed especially towards women and minority in STEM (science, technology, engineering, and mathematics) disciplines.

Other than the external obstacles, I have found that many women also have internal barriers. During my engagement in some outreach activities and through my observation of the experiences of my female peers, I have noticed that many women are raised to be polite, shy, and even meek. Outside of academia, these characteristics are often desired in women, but a highly competitive field like physics often requires you to exude confidence, even when you may be doubting yourself from within. So, my final advice to other women wanting to pursue higher career in physics is to be assertive, work towards gaining more confidence, and be proactive in looking for opportunities. In my opinion, the most important recipe for success is to not undermine your own ability and be persistent in your efforts. I am, myself, working hard each day to live by my advice.


If you were in the admissions committee, what qualities would you look for in a prospective graduate candidate in physics?

From my experience of working with graduate and undergraduate students, I have realized that I have zero tolerance for unmotivated students. So, I would definitely prioritize hard work, passion, and motivation over perfect exam scores. The student also needs to believe in his/her ability to succeed without coming off as overconfident. Impressive recommendation letters, record of involvement in research outside of the academic work, and how the student corresponds to me or other members of the admission committee will give some idea on whether or not the student has the above qualities.


How can prospective graduate students prepare themselves for pursuing graduate studies in physics?

The most important thing is to get involved in some research internship experiences, even if they are not in the exact area of physics that you are interested in. They give you some insight into what real life physics research is like, teach you some important skills that can be applied across fields, and also allow you to explore different sub-fields of physics without having to devote many years of your graduate school in an area only to figure out that you don’t really enjoy it.


How is the job scenario for graduates in physics ?

Based on my observation of career paths of my peers and elders, I can say that the computing, statistical and problem-solving skills one learns as a physicist are highly valued across different professions. Data from many sources, including the American Institute of Physics (AIP) Statistical Research Center, also show the same. A physics degree opens up a variety of career opportunities for graduates in universities, national labs, tech industry, government jobs, financial institutes, and medical facilities to name the few. The job scenario within academia is quite competitive, however. Only a small fraction of physics graduates end up working in physics research throughout their lives.


Can you recommend 3 resources for people looking to get into your field ?

Coursera Physics courses


Tell us about the role of mentorship in your professional life.

It is perhaps the most important thing in graduate school and in research career thereafter as well. Many tasks we do in the research cannot be looked up in the books or searched on the internet. So, it is essential to have someone that you can turn to for research, professional or even personal support. The kind of mentor one has, his/her relationship to the mentor, and the mentor’s expertise in a specific area impacts the course of mentee’s career in many ways. When one applies for academic jobs after the completion of PhD, most positions require recommendation letters. So, the relationship with mentors carries on after the completion of a degree or a job position also. Sometimes, despite the goodwill of the supervisor, other factors such as personality clash, their obligations in other areas, difference between the expectations of the supervisor and the student, other practical issues etc. can also make the relationship incompatible. In such cases, someone other than your advisor, perhaps another faculty member, senior collaborators of the experiment or even a senior graduate student, can fulfill the role of a mentor. After almost three years into my PhD, I had to switch experiment. Instead of switching advisors, I started working under the guidance of an additional co-advisor, who became my primary supervisor thereafter. Currently, as a postdoctoral researcher, I am working under the mentorship of many scientists that are technically not my supervisors.


What is the best career advice you have ever received?

My PhD advisor once told me to not let the perfect be the enemy of the good. I think about that advice quite often.


The career advice you wished you received in your twenties.

I am currently 30 years old, and not too far from my twenties. I will be able to answer this question better a few years from now since I am still figuring out which of my decisions were good and which ones not so much.


Final words of advice for someone who wants to pursue their interest in physics?

Pursue physics if you are the kind of person that gets intrigued by the inner workings of nature. There are very few obstacles that cannot be overcome with willpower.

Ajeeta Khatiwada

Ajeeta Khatiwada is a physicist on the CMS experiment at CERN’s Large Hadron Collider. Her research focuses on the measurement of spin correlation and polarization in top quark pair production at the LHC.

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Sujhaab Chautaari

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