Highlighted Papers

January 2012

EPJ C - "Spooky action at distance" in particle physics?!

Physicists have developed the first conclusive test to better understand high-energy particles correlations.
Researchers have devised a proposal for the first conclusive experimental test of a phenomenon known as "Bell’s nonlocality". This test is designed to reveal correlations that are stronger than any classical correlations, and do so between high-energy particles that do not consist of ordinary matter and light. These results are relevant to the so-called "CP violation" principle, which is used to explain the dominance of matter over antimatter. These findings by Beatrix Hiesmayr, a theoretical physicist at the University of Vienna, and her colleagues, a team of quantum information theory specialists, particle physicists and nuclear physicists, have been published in EPJC.
According to the famous Einstein-Podolsky-Rosen Gedanken-Experiment, two particles that are measured independently obey the principle of locality, implying that an external influence on the first particle, such as measurement, has no direct influence on the second – in other words there is no "spooky action at distance", as Einstein would have described it. In an experimental setup, however, measurement results for one particle revealed a correlated measurement result for the other particle. Initially, these correlations could only be explained by referring to hidden parameters. In 1964, John Bell found that so-called local realistic hidden parameter theories imply that the relations between these correlations could be experimentally tested through so-called Bell tests. Since then many experiments have proven that local, realistic hidden parameters cannot be used as an explanation for these correlations.
In this study, the authors have succeeded in devising a new Bell test, taking into account the decay property of high-energy particles systems, called kaon-antikaon systems. This procedure ensures that the test is conclusive – a goal that has never before been achieved – and simultaneously guarantees its experimental testability. Experimental testing requires equipment such as the KLOE detector at the accelerator facility DAPHNE in Italy.
Revealing “spooky action at distance” for kaon-antikaon pairs has fundamental implications for our understanding of such particles’ correlations and could ultimately allow us to determine whether symmetries in particle physics and manifestations of particles correlations are linked.

Revealing Bell’s Nonlocality for Unstable Systems in High Energy Physics. B.C. Hiesmayr et al., Eur. Phys. J. C (2012) 72: 1856 DOI: 10.1140/epjc/s10052-012-1856-X

October 2011

No sign of supersymmetry - most stringent limits ever set by ATLAS

"Supersymmetry - to be or not to be?" remains a still unanswered question - it is a traditionally difficult business to demonstrate a zero result in experimental physics - yet the ATLAS collaboration has just set new and very stringent limitations on the "viability space" of a class of new physics models incorporating gauge-mediated supersymmetry breaking.
To this end, the collaboration analyzed all channels where W or Z bosons decay into two photons and at least one neutrino while featuring a large missing transverse energy (i.e. measured in all directions perpendicular to the beam axis), these channels being particularly sensitive to new physics in these models.
No deviations from standard model predictions were observed, putting upper limits to the cross-sections for new physics and thus raising significantly the lower mass limits for postulated supersymmetric particles - e.g. to 560 GeV for the gluino mass at a 95% confidence level (see figure).

As an added "bonus" the same results also contributed to ruling out easily observable extra dimensions - the inverse value of the compactification radius of specific models with one universal extra dimension was estimated to be at least 961 GeV with a 95% confidence level.

Search for diphoton events with large missing transverse energy with 36 pb⁻¹ of 7 TeV proton–proton collision data with the ATLAS detector The ATLAS Collaboration, Eur. Phys. J. C (2011) 71: 1744, DOI 10.1140/epjc/s10052-011-1744-9

December 2009

First proton–proton collisions at the LHC as observed with the ALICE detector

On 23rd November 2009, during the early commissioning of the CERN Large Hadron Collider (LHC), two counter-rotating proton bunches were circulated for the first time concurrently in the machine, at the LHC injection energy of 450 GeV per beam, allowing all LHC experiments to report first collision candidates.

284 such candidates were recorded by the ALICE experiment, allowing the events to be immediately reconstructed and analyzed. The results obtained by measuring the spatial distribution (specifically, the pseudorapidity density) of charged primary particles in the central region, were found to be consistent with previous measurements in proton-antiproton interactions at the same centre-of-mass energy at the CERN SppS collider (UA5 Collaboration, G.J. Alner et al., Z Phys. C 33 (1986), DOI 10.1007/BF01410446). To read this paper click here

Fig. 1 shows the first pp collision candidate by the event display in the ALICE counting room (3D view).

J Schukraft, the ALICE spokesman, said: This important benchmark test illustrates also the excellent functioning and rapid progress of the LHC accelerator, and of both the hardware and software of the ALICE experiment, in this early start-up phase.

The paper is published open access on SpringerLink.com and distributed under the Creative Commons Attribution Noncommercial License.

[The ALICE collaboration, Eur. Phys. J. C (2009)]