My name is Palma Bejarano, I’m 16 years old and I live in a small village in southern Spain, surrounded by the wonderful Los Alcornocales Natural Park: a place full of beauty, but with very few STEM opportunities. This summer, I had the incredible chance to take part in a Job-Shadowing Internship at CERN. It has truly been the greatest dream of my life come true.
Tuesday - Sept. 16, 2025
My week began at Point 5 (P5) in Cessy, France, where the CMS experiment is located. Pablo guided me through the experimental site to inspect some equipment. The ride there took around 20 minutes from the main CERN campus in Meyrin, and I would later realise that we were crossing through part of the circumference of the LHC, heading toward one of the far ends of the ring where CMS is located, opposite to ATLAS.
After visiting the control room, we descended a hundred metres below ground in a massive elevator into a vast cavern that hosts the CMS data servers and the CMSinfrastructure. The experiment itself was running during our visit, yet we could feel its power without even standing directly beside the detector. The magnet is so strong that if you hang a few paper clips, they are drawn toward the nearby concrete wall by its magnetic pull. Surrounded by cables and the hum of machinery, you realise that physics isn’t abstract down here; it’s alive and tangible in every sense.
After this incredible visit, I met Amina and Dimitra, who welcomed me into the High-Granularity Calorimeter (HGCAL) clean room at P5. They explained their work assembling the cassettes that will soon become part of the new CMS calorimeter. I even helped label the stands where the boxes full of materials will be placed once they arrive.
Wednesday - Sept. 17, 2025
The next day moved at the rhythm of precision. Inside the clean rooms with Dimitra and Amina, every movement was deliberate, every surface spotless. Each piece held months of work and collaboration from people around the world. I continued organising shelves for the incoming materials, what might seem a small task to some, but one that made me realise how even the tiniest detail is part of something monumental. I learned that an entire wall would need to be dismantled to move the full structure once it’s complete, and then rebuilt to continue the process.
Later that day, I had the pleasure of visiting the CLOUD experiment with Dr. Álvaro De Rújula, theoretical physicist, and learning all about its role in studying how cosmic rays influence our atmosphere. It is an experiment of great importance in the current setting.
Thursday - Sept. 18, 2025
On Thursday, the day started with Gizem who took me to the HGCAL lab where her team tests and assembles the individual pieces that later form the cassettes. I learned about silicon sensors, hexaboards, and how their design varies depending on the radiation levels they must withstand. I watched the cassettes come together layer by layer, slowly resembling what I had seen the previous day in the clean room.
Then, we entered what felt like the heart of the process and where the ‘magic’ occurs: the beam area. I saw the huge space, filled with machinery and cables, and the specific place where the beam would go through for testing. Later, we went into another clean room where silicon sensors were being prepared and examined under microscopes. Gizem taught me how to look for any minimal dust particle on the surface. These sensors are the eyes of CMS, impossibly delicate, but capable of recording collisions that 
happen in less than a trillionth of a second. As I leaned over the microscope, watching a tiny defect sparkle under the light, I thought: this is how you see the invisible. That afternoon, I met again with Dr. De Rújula to visit the building where the magnets for the LHC are built. It was fascinating to see the installations, the precision of the work, and to hear stories about the early days of CERN. Before leaving that day, Dr. De Rújula introduced me to Dr. Michelangelo Mangano, with whom I had an inspiring conversation about his work and the future of particle physics.
Friday - Sept. 19, 2025
Friday, my last day at CERN, is a day I’ll never forget. I will always remember this day because it started with a conversation with David, who decided it was unacceptable for me to leave without visiting the Antimatter Factory. Right after, he took me to one of the first accelerators that CERN has hosted, and answered all the million questions I had about it. Standing there felt like stepping inside the memory of science itself. I think that enormous, chaotic, and filled with cables hall where the accelerator lies, in that exact moment became my new favourite place on planet Earth.
Later that morning, I met Olena, who showed me her work with both diamond and silicon sensors. These materials can survive the intense radiation inside the CMS detector. After lunch, I joined Cristina, a brilliant engineer working on putting everything together inside the upgraded detector. Along with Pablo and Diego (Pablo’s student), we visited the area where the cooling system is being redesigned. Cristina explained how the cabling must be restructured to accommodate far more components in the same limited space. She showed me the prototypes her team is developing, a convoluted wall of metal and tubing that somehow represents the future of high-energy physics.
She also took me to the Computing Centre, where – as David had told me earlier – enormous wall-sized computers once handled long calculations. Later that afternoon, I had the opportunity to meet Adi, a researcher from Caltech, who shared how his work ties to CMS. Finally, I met with Nefeli and Lorenzo from the Communications team. They explained how CERN translates complex science into stories the world can understand. Together, we made a post about the work happening in the clean rooms, my first small contribution to CERN’s outreach.
Each morning throughout the week, I had spoken with David, whose mentorship tied everything together. A good team works because of a good mentor, and David is the living proof of that. By the end of the week, I realised that CERN is not only a place where particles collide, it’s a place where people, ideas, and generations meet. It’s an alphabet with all its letters. Every wire, every equation, every perfectly aligned sensor tells the same story: curiosity is the strongest tool we know to help us understand the world around us.
As I stood in front of the exit door on my last day, the air filled with the sound of innovation. I felt that same pull as the paper clips underground close to the CMS detector, an invisible force drawing me toward the heart of discovery.
I know I will be back very soon.
Disclaimer: The views expressed in CMS blogs are personal views of the authors and do not necessarily represent official views of the CMS collaboration.