The main building of the University of Ljubljana

Lepton Photon 2015

28th August 2015This was my first time in Ljubljana, the capital city of Slovenia – a nation rich with forests and lakes, and the only country that connects the Alps, the Mediterranean and the Pannonian Plain. The slight rain was not an ideal welcome, but knowing that such an important conference that was to be held there - together with a beautiful evening stroll - relaxed my mind.

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Dragon sculpture in Ljubljana

Getting ready for the next discovery

25th August 2015I’m just on my way back home after a great week spent in Ljubljana where I joined (and enjoyed!) the XXVII edition of the Lepton-Photon conference. During the Lepton-Photon conference many topics were discussed, including particle physics at colliders, neutrino physics, astroparticle physics as well as cosmology.

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the density of allowed supersymmetric models before and after the ATLAS Run-1 searches

Devouring dark matter theories

24th August 2015Most of the matter in the Universe is made not of stuff we understand, but of invisible “dark matter” particles. We have yet to observe these mysterious particles on Earth, presumably because they interact so weakly with normal matter. The high energy collisions in the Large Hadron Collider provide our best current hope of making dark matter particles, and thus giving us a better understanding what most of the Universe is made of.

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Ratio of W+ to W- boson production fiducial cross sections

Probing inside the proton

17th August 2015W and Z bosons are the massive carriers of the weak force, responsible for radioactive decays. These bosons also couple closely to the Higgs boson. W and Z bosons are produced at a large rate in proton-proton collisions at the LHC, where ATLAS physicists have now measured the rates for W and Z boson production using 13 TeV proton-proton collisions

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The inelastic cross section, as measured in this work, versus the collision energy

Measuring the way protons interact at 13 TeV

17th August 2015One of the most basic quantities in particle physics, the rate at which protons scatter off of one another (the cross section), cannot be calculated from the theory of strong interactions, quantum chromodynamics. It must instead be measured, and those measurements can then be used to tune the numerical models of LHC proton–proton collisions. 

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Particle Fever

BOOST Outreach and Particle Fever

15th August 2015 – Conferences like BOOST are designed to bring physicists to think about the latest results in the field. When you put 100 experts from around the world together into a room for a week, you get a fantastic picture of the state of the art in searches for new physics and measurements of the Standard Model.

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Chicago at night

A boost for the next discovery

14th August 2015I arrived in Chicago for my first conference after the first long LHC shutdown, where new results from the two big experiments ATLAS and CMS were to be shown. Before the beginning of the conference on Monday, I had one day to fight against jetlag and see the city – certainly not enough time to see everything!

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Rejection of quark and gluon jets for a 50% W boson selection efficiency

ATLAS ready to “boost” Run 2 physics

12th August 2015A new set of techniques is being used to identify highly energetic top quarks, W and Z bosons, and Higgs bosons decaying to quarks and, ultimately, to hadrons measured in ATLAS. Signatures of these “boosted” Standard Model particles are particularly useful when searching for massive new particles and measuring processes at high energies.

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Boost and never look back!

Boost and never look back

12th August 2015When I arrived in Chicago this last Sunday for the BOOST conference I had a pretty good idea what new results we were going to show from ATLAS. I also had some rough ideas of what our friends from the other experiments and theory groups would be up to. What I didn’t expect was to see an ad that would fit the conference so nicely!

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Q&A with EPS Outreach Award-Winner Kate Shaw

12th August 2015 – ATLAS Outreach Co-coordinator Kate Shaw has been awarded the 2015 European Physical Society (EPS) Outreach prize "for her contributions to the International Masterclasses and for her pioneering role in bringing them to countries with no strong tradition in particle physics".

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New Neighbour for ATLAS Tilecal Prototypes

6th August 2015 – There's a new resident in ATLAS' Tile Hadronic Calorimeter (Tilecal) development laboratory: the last surviving UA2 central calorimeter module. After years at CERN's Microcosm exhibition, the module has found a new home next to prototype ATLAS Tilecals. Side-by-side, they illustrate the progress in sampling organic scintillator calorimeters over the past 35 years.

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ATLAS control room

A summer evening in the ATLAS control room

4th August 2015The sun has already set over Geneva when I finally walk out from the ATLAS control room. We have been waiting for beams to be injected into the machine since the early hours of the afternoon, but without much success so far. Just a regular day for the most ambitious particle accelerator mankind has ever built, but a pretty boring afternoon for our entire shift crew.

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ATLAS Overview Week in Marrakech in 2013

From ATLAS Around the World: Brief history of Morocco in ATLAS

31st July 2015In 1996, Morocco officially became a member of the ATLAS collaboration. The eagerly awaited day had finally arrived, and the first Arabic and African country signed a collaborative agreement with CERN to participate in the great scientific adventure of particle physics.

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Average ATLAS charged-particle multiplicity

Physics and Performance With 13 TeV Proton Collisions

30th July 2015 – After a shutdown of more than two years, Run 2 of the Large Hadron Collider (LHC) has restarted with proton–proton collisions at a centre-of-mass energy of 13 TeV. This new phase will allow the LHC experiments to explore nature and probe the physical laws governing it at scales never reached before.

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This new result at 13 TeV (red circle) is compared to previous results from ATLAS

Top quarks in Run 2 are spot on

27th July 2015With a precision of just under 14% − currently dominated by our ability to understand how many proton-proton collisions have occurred at ATLAS (i.e. luminosity) − this measurement is able to confirm that quantum chromodynamics, the theory of the strong interaction, still seems to be going strong! 

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Murrough Landon and Manuel discussing results from the beam splashes

From ATLAS Around the World: Triggers (and dark) matter

27th July 2015To the best of our knowledge, it took the Universe about 13.798 billion years to allow funny looking condensates of mostly oxygen, carbon and hydrogen to ponder on their own existence. Some particularly curious specimens became scientists, founded CERN, dug several rings into the ground near Geneva, Switzerland, built the Large Hadron Collider, and also installed a handful of large detectors along the way.

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Lepton transverse momentum distribution from the W→ μν selection

Of mesons and bosons

24th July 2015ATLAS is ready for detailed physics studies. The experiment used early data collected from the LHC’s Run 2 to calibrate its detectors. Measurements of the production and leptonic decay of certain particle resonances have shown that the detectors and software are working as expected. 

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Inclusive-jet cross sections as a function of the jet pT

First measurements set the stage for early searches of new physics

24th July 2015Jets are collimated sprays of hadrons generated from quarks and gluons, produced either directly in the proton-proton collision or as a part of the decay of W bosons, Z bosons, Higgs bosons, top quarks or new particles yet to be discovered. In fact, all W, Z and Higgs bosons decay most often to quarks which form jets. 

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Two-particle correlations

ATLAS measurements of the ridge in proton-proton collisions at 13TeV

24th July 2015Previous studies of two-particle angular correlations in proton-proton, proton-lead, and lead-lead collisions at the LHC have provided important insight on the physics of the particle production process. On 24 July, Atlas presented new preliminary measurements of two-particle correlations...

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The average charged-particle multiplicity as a function of the centre-of-mass energy

Early Run 2 results test event generator energy extrapolation

22nd July 2015On 23 July 2015, ATLAS presented its first measurements of soft strong interaction processes using charged particles produced in proton–proton collisions at 13 TeV centre-of-mass energy delivered by the Large Hadron Collider at CERN. These measurements were performed with a dataset collected beginning of June under special low-luminosity conditions.

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