Updates tagged: “Standard Model”
In a paper published today in the European Physical Journal C, the ATLAS Collaboration reports the first high-precision measurement at the Large Hadron Collider (LHC) of the mass of the W boson. This is one of two elementary particles that mediate the weak interaction – one of the forces that govern the behaviour of matter in our universe. The reported result gives a value of 80370±19 MeV for the W mass, which is consistent with the expectation from the Standard Model of Particle Physics, the theory that describes known particles and their interactions.
With the huge amount of proton–proton collisions delivered by the LHC in 2015 and 2016 at the increased collision energy of 13 TeV, ATLAS has entered a new era of Higgs boson property measurements. The new data allowed ATLAS to perform measurements of inclusive and differential cross sections using the “golden” H->ZZ*->4l decay.
Ever since the LHC collided its first protons in 2009, the ATLAS Collaboration has been persistently studying their interactions with increasing precision. To this day, it has always observed them to be as expected by the Standard Model. Though it remains unrefuted, physicists are convinced that a better theory must exist to explain certain fundamental questions: What is the nature of the dark matter? Why is the gravitational force so weak compared to the other forces?
High-energy photon pairs at the LHC are famous for two things. First, as a clean decay channel of the Higgs boson. Second, for triggering some lively discussions in the scientific community in late 2015, when a modest excess above Standard Model predictions was observed by the ATLAS and CMS collaborations.
What precision measurement of the inclusive W+, W− and Z/γ∗ production cross sections can tell us about the true nature of the proton.
For the first time, ATLAS has measured the kinematics of the top quark and of the tt̅ system in 13 TeV events containing two charged leptons, two neutrinos and two jets (called “dilepton” events).
The strong force is one of the four fundamental interactions of Nature. It governs the interactions between quarks and gluons, and is thus responsible for the stability of ordinary matter. In the proton-proton collisions at the Large Hadron Collider, the strong force is seen in the production of collimated sprays of mesons and baryons, known as hadron jets. The ATLAS Collaboration has released the measurement of the inclusive jet production cross sections at the new 13 TeV energy frontier.
ATLAS has performed measurements of boson-pair production using data from 13 TeV proton-proton collisions that began in 2015. The cross-section (a measure of the production frequency) of the WW boson pair production was measured and was compared to a previous measurement in 8 TeV collisions.
The LHC’s jump in energy to 13 TeV in Run 2, together with the copious amount of collisions delivered over the last 12 months, has allowed the ATLAS experiment to collect a data sample that is more than equivalent to the one collected during Run 1.
The ATLAS experiment has been searching for the process in which a pair of top quarks is produced, where one is a “virtual” particle that emits a Higgs boson on the way to becoming a “real” particle. This process is referred to as ttH production after the particles that are produced.