In the depths of the French-Swiss border, the world’s largest scientific instrument fell silent. After years of smashing proton particles together at nearly the speed of light, Cern’s Large Hadron Collider (LHC) has shut down and has been idle for a long time.
No particle collisions occur LHCthousands of scientists, engineers, and technicians disassemble machine parts, install new technologies, and develop one of the most ambitious improvements ever attempted in experimental physics.
When it reboots, around 2030, it will High Luminosity Large Hadron Collider (HL-LHC)It is capable of transmitting about seven times more information than the collider that discovered the Higgs boson.
For me, this closure marks another milestone in a project that has shaped much of my scientific life. I first got involved in the High Luminosity collider long before I got involved Higgs boson particle was It was discovered in 2012. For nearly two decades, I have had the privilege of contributing to the program on both sides of the Atlantic.
In the United States, I worked as a program development coordinator Compact Muon Solenoid (CMS)A key experiment at the LHC. CMS is built at one of the points of the Large Hadron Collider, where separate beams of proton particles collide. CMS then receives data from these collisions so that it can be analyzed by CERN physicists. I helped lead the international effort developing the CMS for the HL-collider cycle.
Today I am working on another LHC experiment in Oxford Atlas. Atlas and CMS work in very similar ways, but having two similar machines allows important discoveries in one experiment to be cross-checked by a separate team of scientists. Here, my colleagues and I build silicon pixel detector modules for its improved internal tracker. This will form an important part of the HL-LHC upgrade.
A few months ago I looked at the first full pixel ring assembled in Oxford. It was stunningly beautiful: a delicate arrangement of silicon sensors, electronics and support structures whose elegance reflected years of painstaking engineering.
Through countless design reviews, prototypes, and production meetings, the detector we imagined became a reality for the first time.
Our contribution is just one part of the detector being built by teams around the world. Thousands of components must come together before the High Luminosity Collider is ready to explore a new frontier in particle physics.
The LHC has already changed our understanding of nature. His discovery of the Higgs boson confirmed the mechanism that gives elementary particles their mass. The Higgs was the last missing piece in the film standard model of particle physics. It is the best theory to explain elementary particles and the three fundamental forces that govern their interactions. But as is often the case in science, answering one question answered many.
Investigating the Higgs
Many of the most important questions now are no longer whether the Higgs exists, but whether it behaves as predicted. Small deviations from the standard model may point to entirely new particles or forces. Such discoveries will help us understand mysteries like dark matter, or why the universe contains more matter than antimatter.
The problem is that these clues are incredibly subtle. Instead of requiring higher collision energies, they require more collisions. The HL-LHC will increase the collider’s luminosity — the number of proton collisions it produces — by about seven times over its lifetime.
Imagine replacing a camera that takes one photo per second with a camera that takes seven photos. Each image looks roughly the same, but together they reveal details that otherwise remain invisible.
For Higgs physics, this extra information will be game-changing. The Higgs boson seems quite elusive. Some of its most interesting decays into other particles are so rare that they are beyond the reach of today’s LHC. Others have only recently emerged as compelling hints.
An example is the decay of the Higgs boson becomes two muons (a muon is an unstable, subatomic particle). This decay a rare process It tests whether the Higgs pairs with the second generation of lepton particles. Another is the Higgs decay attractive quark particles. This is one of the most challenging Higgs measurements because it must be subtracted from the large background of ordinary particle collisions.
These processes test one of the most fundamental properties of the Higgs boson: whether it interacts with lighter particles as predicted by the standard model. Any deviation from these predictions, even small ones, could prove that new particles or forces are affecting the Higgs behind the scenes.
And perhaps the most ambitious goal of all is to observe Higgs boson pairs, which will allow us to measure them for the first time. Higgs self-associator— The interaction strength of the Higgs field with itself. This interaction determines the shape of the Higgs field, which fills the entire cosmos and is thought to play a key role in the evolution of the universe moments after the Big Bang.
These are the dimensions that drove the design of the improved LHC. Achieving them requires a revolution not only in the accelerator itself, but also in the detectors that register the collisions.
Particle network
Each crossing of proton beams at the High Brightness LHC will produce up to 200 simultaneous proton-proton interactions, several times more than today. Unraveling this dense network of particles requires detectors that are faster, more precise, and more resistant to radiation than anything previously built.
Brand new silicon tracking detectors replace existing ones at the heart of the Atlas and CMS experiments. They must survive radiation levels that would quickly destroy previous generations of sensors while measuring particle trajectories with extraordinary precision. Achieving this requires years of advances in silicon sensor technology, ultra-fast electronics, cooling systems and lightweight mechanical structures.
One of the most innovative features of the improved detectors is the addition of precise timing. The new timing detectors—the High Granularity Timing Detector at Atlas and a similar system at CMS—will measure particle arrival times with an accuracy of only a few tens of trillionths of a second. Although hundreds of collisions occur almost simultaneously, they do not occur exactly at the same time.
By adding time as a fourth dimension to particle tracking, these detectors will allow physicists to associate each particle with the correct collision, allowing them to reconstruct rare Higgs events hidden in the large background of overlapping interactions.
One of the greatest rewards of working on these detectors is seeing the next generation of physicists prepare to use them. Students who help assemble today’s detectors will spend much of their careers analyzing the data they eventually collect.
When the HL-LHC becomes operational, it will not just expand the science program of the Large Hadron Collider. It will usher in a new era of exact Higgs physics. Whether it reveals subtle cracks in the Standard Model or confirms our current understanding with unprecedented precision, it will shape particle physics for decades to come.
Daniela Bortoletto is a professor and the head of the department of particle physics University of Oxford. This article is being republished Conversation Under Creative Commons license. read it original article. 
