20th November 2014 – The winner of the four-month long Higgs Machine Learning Challenge, launched on 12 May, is Gábor Melis from Hungary, followed closely by Tim Salimans from The Netherlands and Pierre Courtiol from France. They will receive cash prizes, sponsored by Paris-Saclay Centre for Data Science and Google, of $7000, $4000, and $2000 respectively. The three winners have been invited to participate at the Neural Information Processing Systems conference on 13 December in Canada.
13th November 2014 – The Large Hadron Collider is known to collide protons, but for one month a year, beams of lead ions are circulated in the 27-km tunnel and made to collide in the centre of the experiments. The ATLAS experiment has made new precise measurements of the suppression of jets as they blast through the dense matter created by the lead ion collisions.
28th October 2014 – This is the last part of my attempt to explain our simulation software. You can read Part 1, about event generators, and Part 2, about detector simulation, if you want to catch up. Just as a reminder, we’re trying to help our theorist friend by searching for his proposed “meons” in our data.
21st October 2014 – The ATLAS Outstanding Achievement Awards 2014 were given on 9 October to five individuals or teams of physicists and engineers for their contributions during the Large Hadron Collider's first run in all areas of ATLAS except physics analyses.
15th October 2014 – The ATLAS and CMS experiments hosted a virtual visit together with the IceCube Experiment in the South Pole for students from five different European schools on 2 October. The visit allowed the students to interact with researchers in both the LHC experiments and the IceCube experiment. The virtual visit was a second event in the Open Discovery Space project series' 'Bringing Frontier Science to Schools'.
7th October 2014 – The Standard Model makes many different predictions regarding the production and decay properties of the Higgs boson, most of which can be tested at the Large Hadron Collider (LHC). Since the discovery, experimentalists from the ATLAS collaboration have analysed the complete dataset recorded in 2011 and 2012, have improved the calibration of the detector, and have increased substantially the sensitivity of their analyses.
6th October 2014 – One of the perks of working in our field is the opportunities we get to go to exotic places for conferences. I always felt the HEP-MAD conference in Madagascar would top this list, but the one some of us went to in Vietnam can't be too far behind. The Rencontres du Vietnam conference series has been organised in the coastal town of Quy Nhon since 2011, covering different physics topics. This year, one of them was titled Physics at the LHC and Beyond, where I had the privilege of presenting ATLAS soft QCD results.
5th October 2014 – Having spent many hours working on the simulation software in ATLAS, I thought this would be a good place to explain what on earth that is (H/T to Al Brooks for the title). Our experiment wouldn’t run without the simulation, and yet there are few people who really understand it.
22nd September 2014 – Theories, such as supersymmetry, propose the existence of new types of particles to explain important questions about the universe, such as the nature of dark matter. ATLAS has performed a search for one such type – exotic heavy particles that have lifetimes long enough that they travel partway through the detector before decaying, at what is called a displaced vertex.
10th September 2014 – The Standard Model of particle physics has been extremely successful in predicting a vast variety of phenomena – so successful, that it is easy to forget that some of its predictions have not yet been verified. A very important one, related intimately to electroweak symmetry breaking, is that the gauge bosons (γ, W and Z) can interact with each other through quartic interactions.
10th September 2014 – The fusion of two weak bosons is an important process that can be used to probe the electroweak sector of the Standard Model. Measurements of Higgs production via weak-boson fusion are crucial for precise extraction of the Higgs-boson couplings and have the potential to help pin down the charge conjugation and parity of the Higgs boson. A similar process, weak-boson scattering, is sensitive to alternative electroweak symmetry-breaking models and to anomalous weak-boson gauge couplings. These processes are extremely rare and the experimental observation of the production of heavy bosons via weak-boson fusion has become possible only recently with the large centre-of-mass energy and luminosity provided by the LHC. Extracting the signals from the huge backgrounds in the high pile-up conditions at the LHC is a major challenge.
10th September 2014 – The discovery of the Higgs boson by the ATLAS and CMS collaborations in 2012 marked a new era in particle physics because it completed the Standard Model and gave us another tool to explore territories beyond. The Standard Model predicts precisely the interactions of the Higgs boson to all other elementary particles once its mass is measured.
21st August 2014 – For her contribution toward the discovery of the Higgs boson, Kerstin Tackmann was awarded the Young Scientist Prize in Particle Physics 2014 by the International Union of Pure and Applied Physics.
17th July 2014 – ATLAS has measured properties of events likely to contain a Higgs boson, in order to get a better understanding of the frequency and manner in which they are produced. The study specifically examines the fiducial and differential cross sections for Higgs bosons that decay into two photons or into two Z bosons, using proton-proton collisions recorded by ATLAS in 2012.
14th July 2014 – ATLAS physicists have studied the “shadow” of the Higgs boson far above its mass peak in an analysis of the full sample of 8 TeV proton-proton collisions delivered by the LHC in 2012. The study involves Higgs boson decays into two Z bosons, which themselves decay into four charged leptons or two charged leptons plus two neutrinos. Among other interesting properties, it provides new insight into the lifetime, or natural width, of the Higgs boson.
8th July 2014 – The production of pairs of heavy bosons, such as two Z bosons, a Z and a W boson, or the more challenging pair of W bosons (WW), are processes that particle physicists are passionate about because they cover a rich spectrum of phenomena. The WW channel, in particular, represents a substantial experimental challenge. In the events considered for this measurement, each W boson decays into an electron or a muon plus a neutrino that remains undetected and is reconstructed through the presence of missing energy in the event.
6th July 2014 – From decades of discoveries made at particle colliders, we know that protons are composed of quarks bound together by gluons. We also know that there are six kinds of quarks, each one with its associated antiparticle. But are quarks fundamental? ATLAS searched for signs that quarks may have substructure in its most recent data, collected from the LHC’s proton-proton collisions in 2012.
5th July 2014 – ATLAS has observed a particle state of mass and decay properties consistent with expectations for an excited state of the Bc meson. The discovery follows analysis of the full 7 TeV and 8 TeV proton-proton collision data sets from the LHC’s first run.
5th July 2014 – Data from a special run of the LHC using dedicated beam optics at 7 TeV have been analysed to measure the total cross-section of proton-proton collisions in ATLAS. Using the Absolute Luminosity For ATLAS (ALFA), a Roman Pot sub-detector located 240 metres from the collision point, ATLAS has determined the cross-section with unprecedented precision to be σtot (pp → X) = 95.4 ± 1.4 millibarn.