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    Critical Thought

    Critical thoughts on quantum technologies

    Unveiling the Quantum Secrets: Unconventional Methods for Probing the Quantum World

    BySam Figg

    Nov 21, 2023
    Unveiling the Quantum Secrets: Unconventional Methods for Probing the Quantum World

    Scientists and researchers at CERN’s Large Hadron Collider in Geneva, Switzerland, constantly seek new ways to unlock the mysteries of the universe. Traditionally, this has involved smashing particles together and observing the resulting debris. However, the limitations of these destructive experiments have prompted physicists to explore alternative methods.

    In a groundbreaking study recently published in Physical Review Letters, a team of nuclear and particle physicists, in collaboration with international scientists, discovered a remarkable technique hidden within the data from previous experiments. Unlike previous approaches that focused on head-on collisions, this novel method involved analyzing the interactions of particles as they whizzed past each other in the accelerator.

    This new technique allowed for significantly more accurate measurements of a particle known as the tau’s wobble, specifically its magnetic moment. The tau, one of the heavier cousins of the electron and muon, exists only for extremely brief periods. When placed in a magnetic field, these particles exhibit a wobbling motion, similar to a spinning top on a table.

    Precisely measuring this wobble provides invaluable insights into the quantum world. Quantum physics suggests that particles and antiparticles constantly appear and disappear, creating fluctuations that subtly influence the wobbling behavior of electrons, muons, and taus. By meticulously measuring these wobbles, scientists can potentially uncover evidence of yet-undiscovered particles.

    Experimental physicists have been captivated by the prospect of measuring magnetic moments since the 1940s. The renowned theoretical physicist Julian Schwinger initially calculated how quantum fluctuations affect the electron’s magnetic moment. Subsequent experiments have successfully measured the speed of the electron’s wobbling motion to an extraordinary 13 decimal places.

    However, due to their lighter mass, electrons are less sensitive to the presence of new particles. Muons and taus, on the other hand, are much heavier but also considerably more short-lived. Their fleeting existence poses a challenge, requiring innovative approaches to measure their magnetic moments accurately.

    A recent breakthrough at Fermilab near Chicago involved measuring the muon’s magnetic moment to an impressive 10 decimal places. This measurement revealed that muons wobbled faster than the predictions of the Standard Model, hinting at the existence of unknown particles within the muon’s quantum cloud.

    The tau, being the heaviest sibling among these particles, offers greater sensitivity to previously undiscovered particles present in its quantum cloud. However, the tau is also much more elusive, with an existence spanning merely a millionth of the time that a muon does. Previous attempts to measure the tau’s magnetic moment had limited success, only achieving a precision of two decimal places.

    To overcome these challenges, scientists turned their attention to near-miss collisions involving lead ions. When lead ions collide, their accompanying photons can collide and generate various particles, including taus. Unlike the chaotic fireworks produced during head-on collisions, these near-miss events create a quieter environment, ideal for studying the elusive tau.

    Researchers initially utilized lead ion experiments from 2015 to 2018 to study exotic hot matter resulting from head-on collisions. However, it wasn’t until 2019 that the potential for measuring the tau’s magnetic moment using the same data was realized. Lead ion collisions often resulted in the ions missing each other but passing in close proximity. During these near-miss events, photons associated with the ions could still collide while the ions continued on their paths.

    Upon analyzing the data from 2018, scientists made an astonishing discovery – these lead ion near misses were creating tau particles. What was once considered mere noise turned out to be a treasure trove of valuable information, hidden in plain sight.

    In April 2022, the CERN team officially announced their breakthrough, providing direct evidence of tau particles produced during lead ion near misses. Furthermore, they successfully measured the tau’s magnetic moment, marking the first such measurement in nearly two decades. The results of this groundbreaking experiment were published on October 12, 2023.

    This unconventional approach to studying particles offers a fresh perspective on unraveling the enigmas of the quantum world. By exploiting near-miss particle collisions, scientists have gained unique insights into the behavior of the tau and potential deviations from the Standard Model. These findings not only expand our understanding of particle physics but also open doors to further experimentation and the possibility of discovering new particles that lie beyond our current knowledge.


    Q: Why do physicists smash particles together in experiments?
    A: Physicists smash particles together to study the resulting debris and gain insights into the fundamental nature of matter and the universe.

    Q: What is the wobble of particles?
    A: The wobble refers to the oscillating motion exhibited by particles, such as electrons, muons, and taus, when placed in a magnetic field.

    Q: How can measuring the wobble of particles help uncover new physics?
    A: By precisely measuring the wobbling motion of particles, scientists can detect deviations from theoretical predictions, potentially indicating the presence of undiscovered particles and phenomena.

    Q: What are lead ions, and how are they used in the study?
    A: Lead ions are electrically charged atoms that are stripped of their electrons. In this study, scientists utilized near-miss collisions involving lead ions to create a quieter environment for measuring the tau’s magnetic moment.

    Q: What is the significance of measuring the tau’s magnetic moment?
    A: Measuring the tau’s magnetic moment provides crucial insights into the behavior of this elusive particle. It can help scientists test the accuracy of existing theories, such as the Standard Model, and potentially reveal the existence of new particles beyond our current understanding.

    – CERN: https://home.cern/