first direct observation of a fundamental effect in particle physics

A charmed quark (c) in a shower of partons loses energy by emitting radiation in the form of gluons (g). The sheaf has a dead cone: an absence of radiation (Radiation, synonymous with radiation in physics, designates the process of emission or…) around (Autour is the name that the avian nomenclature in the French language (update) gives…) of quark (Quarks are fermions which the Standard Model theory describes, along with…) for angles less than the ratio of the mass (The term mass is used to designate two quantities attached to one…) (m) on theenergy (In common sense, energy designates everything that allows you to do work, make energy, etc.) (E). The energy decreases with each stage of the sheaf. (Picture: CERN)

« It was really not easy to observe the dead cone directlyexplains Luciano Musa, spokesperson for ALICE. But by exploiting three years of data from proton-proton collisions at the LHC coupled with sophisticated data analysis techniques, we were finally able to bring it to light. day (The day or the day is the interval which separates the sunrise from the sunset; it is the…).« 

Quarks and gluons, generically called « partons », are produced during collisions of particles such as those which take place at the LHC. Once produced, the partons undergo cascade transformations (one speaks of a « sheaf of partons »): they lose energy by emitting radiation in the form of gluons, which in turn emit gluons. The configuration of the radiation of this shower depends on the mass of the leave (In particle physics, the parton model was proposed by Richard…) emitting gluons and has a region around the flight direction of the parton in which the emission of gluons is attenuated: this is the dead cone¹.

Predicted thirty years ago from the first principles of theory (The word theory comes from the Greek word theorein, which means « to contemplate, to observe,…) of the strength (The word force can designate a mechanical power over things, and also, metaphorically, a…) strong, the dead cone has been observed indirectly in particle colliders. However, it has always been difficult to observe it directly from the radiation profile of the shower of partons, mainly because the dead cone can be filled by particles emitted by the original parton and because it is difficult to determine the changing direction of the parton everything (The whole understood as the whole of what exists is often interpreted as the world or…) throughout the sheaf production process.

The ALICE collaboration overcame these challenges by applying state-of-the-art analytical techniques to a sample (Generally speaking, a sample is a small amount of material, information, or…) large number of proton-proton collisions at the LHC. These techniques make it possible to go back to the sheaf of partons from its final products, namely the signals left in the detector (A detector is a technical device (instrument, substance, matter) that changes…) ALICE in the form of a « jet » of particles. By analyzing the jets that included a particle containing a charmed quark, the researchers were able to identify a jet created by this type of quark and trace the entire history of the gluons emitted by this quark. Comparison of the gluon emission profile of the charmed quark with that of gluons and nearly zero-mass quarks then revealed a dead cone in the profile of the charmed quark.

Furthermore, the result directly highlights the mass of the charmed quark, since the theory predicts that zero-mass particles do not have a corresponding dead cone.

« Quark masses are fundamental quantities in particle physics, but it is not possible to observe and measure them directly in experiments because, with the exception of the top quark (The top quark (often abbreviated as top quark) is a quark, a particle…)the quarks are confined inside composite particlesexplains Andrea Dainese, coordinator of the physical (Physics (from the Greek φυσις, nature) is etymologically the…) from ALICE. Our technique allowed us to directly observe the dead cone of a sheaf of partons; it could give us a way to measure the mass of quarks.« 

As the parton shower progresses, gluons are emitted at smaller angles and the quark energy decreases, creating larger dead cones, where gluon emission is attenuated. (Picture: CERN)

To know more:

– Additional graphics
– ALICE Image Gallery
– Gallery of videos (The video brings together all the techniques, technology, allowing the recording as well as the…) ALICE
– ALICE Collaboration: https://alice.cern/

Note:
¹Technical precision: for an emitting particle of mass m and energy E, the emission of gluons is attenuated at angles less than the ratio m/E with respect to the sense (SENS (Strategies for Engineered Negligible Senescence) is a scientific project which aims to…) of shift (In geometry, a displacement is a similarity that preserves distances and angles…) of the emitting particle.