In particular, W-boson pairs can be produced from the proton’s constituents. LHC protons can break up into their constituents and fragment into several detectable particles at very low energy. (Image: ATLAS Collaboration/CERN)ĪTLAS physicists had to overcome several unique challenges to observe this process, starting with separating the signal from background. The photon-induced W-boson pair production accumulates at low particle multiplicities (white area). The background process with the largest contribution is the W-boson-pair production from proton constituents its simulation (blue) describes the observed data (black points) very well. As the skimming protons stay intact, the only detectable particles produced in the interaction are the visible decay products of the W bosons – namely, for this measurement, an electron and a muon with opposite electric charge.įigure 3: The distribution of the number of particles reconstructed in the ATLAS inner detector, in addition to the electron and the muon. Quasi-real photons from these fields scatter off one another to produce a pair of W bosons and leave a distinct signature in the ATLAS experiment. This rare process occurs as bunches of high-energy protons skim past each other in “ultra-peripheral collisions”, if only their surrounding electromagnetic fields interact. Although the ATLAS and CMS Collaborations saw first evidence of this process in data recorded during Run 1 of the LHC (2011–2012), its observation required the substantially larger dataset taken during Run 2 (2015–2018). The newly observed process proceeds via a very rare type of phenomenon where two photons collide to directly produce two W bosons of opposite electric charge via a four force-carrier interaction, among others (see Figure 2). Indeed, the Standard Model describes quantum electrodynamics as part of electroweak theory, which not only predicts that force-carrying particles – the W bosons, Z boson and photon – interact with ordinary matter, but also among themselves. This process was first observed by the ATLAS Collaboration in 2019. For a short moment, photons radiated off the incoming proton beams can scatter and transform into a particle–antiparticle pair which appears as light-by-light interactions in the detector. However, at the high energies seen in LHC collisions, effects of quantum electrodynamics become important. In everyday life, two crossing light beams follow the rules of classical electrodynamics and do not deflect, absorb or disrupt one another. The photons are scattered off of two protons which in the process lose energy but remain intact. Figure 2: Feynman diagram depicting the production of a pair of W bosons from two photons in a four force-carrier interaction. The ATLAS Collaboration announces the first observation of two W bosons produced from the scattering of two photons - particles of light - at the International Conference on High-Energy Physics ( ICHEP 2020). Top left corner shows that these particles do not originate from the same interaction and are thus attributed to additional proton–proton interactions. The many particles reconstructed in the Inner Detector are shown in orange. The electron deposits its energy in the electromagnetic calorimeter (yellow blocks). The muon path (red line) and electron path (yellow line) are shown. (The mean lifetime of a Carbon-14 atom is 8267 years.Figure 1: A 2018 ATLAS event display consistent with the production of a pair of W bosons from two photons, where the W bosons decay into a muon and an electron (visible in the detector) and neutrinos (not detected). A carbon-14 nucleus, with 6 protons and 8 neutrons, spontaneously decays into nitrogen-14, with 7 protons and 7 neutrons, with a half-life of 5,730 years, emitting an electron and antineutrino in the process.The ratio of C-14 to C-12 in a fossil can then be used to estimate how long ago the organism died.When the organism dies, however, C-14 is no longer replenished and the ratio of C-14 to C-12 decreases as C-14 atoms decay.The ratio of C-14 to C-12 remains constant as long as the organism is alive, since C-14, though decaying, is constantly replenished.The carbon is passed onto animals when they eat the plants. Through photosynthesis, plants absorb carbon in the form of carbon dioxide.C-14, making up a tiny percent, is radioactive, spontaneously decaying into nitrogen.Carbon has three naturally-occurring isotopes.wiki/Beta_decay Carbon Dating (Electron Emission Beta Decay)
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