CERN Courier October 2013 EPS-HEP 2013 Verify and optimize your designs with COMSOL Multiphysics.® Conference time in RF COUPLER: This model computes the transmission probability through an RF coupler using both the angular coefficient method Stockholm available in the Free Molecular Flow interface and a Monte Carlo method using the Mathematical Particle Tracing interface. Multiphysics tools let you build simulations that accurately replicate the important characteristics of your designs. The key is the ability to include all physical effects that exist in the real world. To learn more about COMSOL Multiphysics, visit www.comsol.com/introvideo © Copyright 2013 COMSOL The Higgs boson, dark matter and rare The city of Stockholm provided a beautiful setting for the 2013 edition of EPS-HEP, one of the major international summer processes were among the highlights of the conferences in particle physics. (Image credit: Marina 2013 International Europhysics Conference on Lukashova/Dreamstime.com.) 0.5% precision – better than for any quark – and several tests by thermodynamicscompetent High-Energy Physics. P www.reuter-technologie.de ATLAS and CMS show that its spin-parity, J , is compatible with the 0+ expected for a Standard Model Higgs boson. These results exclude other models to greater than 95% confi dence level (CL), while a new When the Swedish warship Vasa capsized in Stockholm harbour result from DØ rejects a graviton-like 2+ at >99.2% CL. Your Expert for Vacuum Brazing and UHV Systems on her maiden voyage in 1628, many hearts must have also sunk The new boson’s couplings provide a crucial test of whether it is metaphorically, as they did at CERN in September 2008 when the the particle responsible for electroweak-symmetry breaking in the UHV compatible joining of LHC’s start-up came to an abrupt end. Now, the raised and pre- Standard Model. A useful parameterization for this test is the ratio Ceramic to Stainless Steel served Vasa is the pride of Stockholm and the LHc – following a of the observed signal strength to the Standard Model prediction, Low and high temperature successful restart in 2009 – is leading research in particle physics μ = (σ × BR)/(σ × BR) , where σ is the cross-section and BR the technologies SM Waveguide structures at the high-energy frontier. This year the two icons crossed paths branching fraction. The results for the fi ve major decay channels Development and design when the International Europhysics Conference on High-Energy measured so far (γγ, WW*, ZZ*, bb and ττ) are consistent with the of complex systems Physics, EPS-HEP 2013, took place in Stockholm on 18–24 July, expectations for a Standard Model Higgs boson, i.e. μ = 1, to 15% hosted by the KTH (Royal Institute of Technology) and Stockholm accuracy. Although it is too light to decay to the heaviest quark University. Latest results from the LHC experiments featured in – top, t – and its antiquark, the new boson can in principle be pro- many of the parallel, plenary and poster sessions – and the 750 or duced together with a tt- pair, so yielding a sixth coupling. While so participants had the opportunity to see the Vasa for themselves this is a challenging channel, new results from CMS and ATLAS at the conference dinner. There was, of course, much more and this are starting to approach the level of sensitivity for the Standard report can only touch on some of the highlights. Model Higgs boson, which bodes well for its future use. Coming a year after the fi rst announcement of the discovery of a The mass of the top quark is in fact so large – 173 GeV/c2 – that it Vacuum brazing of “Higgs-like” boson on 4 July 2012, the conference was the perfect decays before forming particles, making it possible to study the Diamond to Copper occasion for a birthday celebration for the new particle. Not only has “bare” quark. At the conference, the CMS collaboration announced its identity been more fi rmly established in the intervening time – it the fi rst observation, at 6.0σ, of the associated production of a top Clean room assembly and particle-free cleaning almost certainly is a Higgs boson – but many of its attributes have quark and a W boson, in line with the Standard Model’s prediction. been measured by the ATLAS and CMS experiments at the LHC, Both ATLAS and CMS had previously found evidence for this as well as by the CDF and DØ collaborations using data collected process but not to this significance. The DØ collaboration REUTER TECHNOLOGIE GmbH Roentgenstr. 1 63755 Alzenau Germany E-Mail: [email protected] Tel.: +49 (0)6023 / 5044 - 0 ▲ at Fermilab’s Tevatron. At 125.5 GeV/c2, its mass is known to within presented latest results on the lepton-based forward–backward 37 p36.indd 1 09/09/2013 16:28 CERNCOURIER www. V OLUME 5 3 N UMBER 8 O CTOBER 2 0 1 3 CERN Courier October 2013 CERN Courier October 2013 EPS-HEP 2013 EPS-HEP 2013 lepton asymmetry in tt- production, which had previously indicated constitute dark matter, which is becoming a worldwide effort. Indeed, some deviation from theory. The new measurement, based on the although the Higgs boson may have been top of the bill for hadron- full data set of 9.7 fb–1 of proton–antiproton collisions at the collider physics, more generally, the number of papers with dark mat- +1.1 Tevatron, gives an asymmetry of (4.7±2.3 stat. –1.4 syst.)%, which is ter in the title is growing faster than those on the Higgs boson. consistent with predictions from the Standard Model to next-to- While experiments at the LHC look for the production of new leading order. kinds of particles with the correct properties to make dark mat- The study of B hadrons, which contain the next heaviest quark, b, ter, “direct” searches seek evidence of interactions of dark-matter is one of the aspects of fl avour physics that could yield hints of new particles in the local galaxy as they pass through highly sensitive physics. One of the highlights of the conference was the announce- detectors on Earth. Such experiments are showing an impressive 0 ment of the observation of the rare decay mode Bs → μμ by both the evolution with time, increasing in sensitivity by about a factor of 10 LHCb and CMS collaborations, at 4.0 and 4.3σ, respectively (CERN every two years and now reaching cross-sections down to 10–8 pb. Courier September 2013 p19). While there had been hopes that Among the many results presented, an analysis of 140.2-kg days of this decay channel might open a window on new physics, the long- data in the silicon detectors of the CDMS II experiment revealed awaited results align with the predictions of the Standard Model. The three WIMP-candidate events with an expected background of BaBar and Belle collaborations also reported on their precise meas- The museum that now houses the 17th century Swedish warship 0.7. A likelihood analysis gives a 0.19% probability for the known Plenary sessions took place in the magnifi cent Aula Magna (*) urements of the decay B → D τντ at SLAC and KEK, respectively, Vasa provided a fascinating venue for the conference dinner. background-only hypothesis. lecture theatre on the Stockholm University campus. (Image which together disagree with the Standard Model at the 4.3σ level. (Image credit: Bluesunphoto/Dreamstime.com.) “indirect” searches, by contrast, involve in particular the search credit: T Pritchard.) The results rule out one model that adds a second Higgs doublet to from signals from dark-matter annihilation in the cosmos. In the Standard Model (2HDM type II) but are consistent with a differ- results come from the analysis of proton–lead collisions and reveal 2012, an analysis of publically available data from 43 months of terrestrial origin (CERN Courier July/August 2013 p5). ent variant, 2HDM type IIi – a reminder that the highest energies are features that previously were seen only in lead–lead collisions, where the Fermi Large Area Telescope (LAT) indicated a puzzling sig- not the only place where new physics could emerge. the hot dense matter that was created appears to behave like a perfect nal at 130 GeV, with the interesting possibility that these γ rays Towards the future liquid. The new results could indicate that similar effects occur in could originate from the annihilation of dark-matter particles. A In addition to the sessions on the latest results, others looked to the Precision, precision proton–lead collisions, even though far fewer protons and neutrons new analysis by the Fermi LAT team of four years’ worth of data continuing health of the fi eld with presentations of studies on novel Precise measurements require precise predictions for comparison are involved. Other results from ALICE included the observation of gives preliminary indications of an effect with a local signifi cance ideas for future particle accelerators and detection techniques. and here theoretical physics has seen a revolution in calculating higher yields of J/ψ particles in heavy-ion collisions at the LHC than of 3.35σ but the global signifi cance is less than 2σ. The HESS II These topics also featured in the special session for the European next-to-leading order (NLO) effects, involving a single loop in the at Brookhaven’s Relativistic Heavy-Ion Collider, although the den- experiment is currently accumulating data and might soon be able Committee for Future Accelerators, which looked at future devel- related Feynman diagrams. Rapid progress during the past few sities are much higher at the LHC (CERN Courier September 2013 to cross-check these results.