“In a nutshell, we proposed a completely new way to study spin properties of particles and their interactions, something which has never been tried experimentally and never thought possible”. This is how Igor Ivanov, researcher at the Centre for Theoretical Particle Physics – CFTP/IST, describes his co-authored article titled “Doing Spin Physics with Unpolarized Particles” recently published in Physical Review Letters.
“There exists a rich world of hadrons, subatomic particles such as protons and neutrons. Hundreds of hadrons are known, and all of them are made of smaller building blocks called quarks or antiquarks bound together by the strong interactions. But how exactly the quarks organize together to produce what we perceive as hadrons remains elusive”, explains the Técnico researcher. “There is a significant, world-wide experimental effort to investigate spin physics, but many issues are still far from being clear”, he stresses. “Any new method to look at the problem from a different angle is always welcome”.
“Up to now, spin properties are explored through accurate measurements of polarized particle collisions. Typically, one adjusts initial particle polarization, measures the angular distribution of the collision products, and checks how it responds to the polarization change”, explains Igor Ivanov.
The research group propose a different, previously unnoticed handle on spin properties of hadrons. Instead of polarizing initial particles, we suggested to “twist” them, that is, to prepare them in an unusual quantum-mechanical wave packet in which they, in a sense, rotate on the fly”, says the researcher. “We demonstrated that this twist would offer access to spin-sensitive quantities even for unpolarized initial particles and without the need to look at angular distributions. No one thought that spin properties can be studied this way”, he adds.
“I must add that our paper is just a proposal of a new idea, not a resolution of concrete puzzles”, says the Técnico researcher. In the future, the researchers plan to apply this idea “to specific collision processes and show what sort of information can be extracted. We anticipate a long and dynamic research program ahead”, says Igor Ivanov.
This research work started when the Técnico researcher visited the Institute of Modern Physics in Lanzhou, China, last year, where the other three co-authors work. “When we came up with the idea, it struck us as something unexpected. We realized that no-one had thought that nature would allow us to look at spin phenomena from this perspective”, explains Igor Ivanov. The researchers tried to share their excitement in the paper and, “as far as we can judge, it impressed the referees and PRL editors”.
The results achieved open a new direction for research not only in particle physics but possibly in nuclear and atomic physics. “Producing twisted particles with energies suitable for hadronic physics is a serious experimental challenge, which will require dedicated efforts”, assures the Técnico researcher. “We hope that our on-going collaboration with Jorge Vieira and his group at GoLP will show how it can be done”, says the Técnico researcher. Jorge Vieira, Técnico professor – Department of Physics (DF) adds “we are developing computational tools that allow us to simulate the acceleration of this new type of particles up to the energy needed for hadronic physics ”.
“As a proof-of-principle experiment, checking this idea will be a new demonstration of various quantum mechanical effects, such as spin-orbital interaction of freely propagating particles or Young’s two-slit experiment realized in momentum space”, says Igor Ivanov, who considers that it may lead to a new spectroscopic technique. “It remains to be seen what we can learn about the structure of atoms and, possibly, nuclei. In particle physics, when such experiments become feasible, this tool will allow us to probe structure of hadrons in a new way, using, literally, a new dimension available for the final state kinematics”, says the Técnico researcher. “All these novelties will eventually help us sharpen our picture of how the subatomic world is built and how it functions”.
Read the full article here.
