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Ian Hinchliffe Answers Your Higgs Boson Questions

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Ian Hinchliffe, a theoretical physicist who heads Berkeley Lab’s sizable contingent with the ATLAS experiment at CERN, answers many of your questions about the Higgs boson. Ian invited viewers to send in questions about the Higgs via email, Twitter, Facebook, or YouTube in an “Ask a Scientist” video posted July 3: http://youtu.be/xhuA3wCg06s
CERN’s July 4 announcement that the ATLAS and CMS experiments at the Large Hadron Collider have discovered a particle “consistent with the Higgs boson” has raised questions about what scientists have found and what still remains to be found — and what it all means.


http://youtu.be/1BkpD1IS62g

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July 6, 2012 at 2:16 pm

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Higgs decays at 125 GeV

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July 6, 2012 at 7:48 am

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Is the resonance at 125 GeV the Higgs boson?

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Left: assuming mh = 125.5 GeV, we show the measured Higgs boson rates at ATLAS, CMS, CDF, D0 and their average (horizontal gray band at ±1σ). Here 0 (red line) corresponds to no Higgs boson, 1 (green line) to the SM Higgs boson. Right: The Higgs boson rate favored at 1σ (dark blue) and 2σ (light blue) in a global SM fit as function of the Higgs boson mass.


Pier Paolo Giardino, Kristjan Kannike, Martti Raidal, Alessandro Strumia

The recently discovered resonance at 125 GeV has properties remarkably close to those of the Standard Model Higgs boson. We perform model-independent fits of all presently available data. The non-standard best-fits found in our previous analyses remain favored with respect to the SM fit, mainly but not only because the γγ rate remains above the SM prediction.

(……………)

Conclusions
The new particle with mass 125.5 ± 0.5 GeV discovered at the LHC looks like the Higgs boson. We performed a fit to all available collider data in order to test its couplings. We find that the couplings to the W and the Z are in reasonable agreement with the SM Higgs boson expectations, suggesting that the discovered state is, indeed, the Higgs boson. However, the excess in  indicates potential non-standard physics in the loop level process h→γγ (see e.g. [25]). Combining all  channels and all experiments, this enhancement is at the 2.5σ level.

As long as this excess persists, it can be fitted by a non-standard (possibly negative) Yukawa couplings of the Higgs boson to the top quark, or explained by new particles contributions to the loop level process h→γγ  and maybe gg→h. Indeed, allowing for a reduction of gg → h further improves the global fit.
We will update this paper on arXiv (http://arxiv.org/abs/1207.1347) when new data will be presented
Read more: http://arxiv.org/pdf/1207.1347v1.pdf

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July 6, 2012 at 7:40 am

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Le boson de Higgs a deux «papas» belges

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Le physicien Peter Higgs reconnaît lui-même devoir partager la paternité de « sa » particule avec plusieurs collègues, aux premiers rangs desquels deux Belges, Richard Brout et François Englert.

Le Belge François Englert, à gauche, assis à côté de Peter Higgs, mercredi au Cern. Crédits photo : FABRICE COFFRINI/AFP

François Englert et Richard Brout sont victimes d’une grande injustice. Bien que les deux physiciens belges aient coécrit le premier papier publié sur le boson scalaire en août 1964 dans la Physical Review Letters, c’est leur collègue écossais Peter Higgs qui a donné son nom à la particule, grâce à un article publié trois mois plus tard dans la même revue. Pour la petite histoire, une version préalable des travaux du théoricien britannique avait auparavant été refusée par le comité de lecture, qui n’avait manifestement pas bien compris leur intérêt…

«C’est un autre physicien, japonais, Yoichiro Nanbu, Prix Nobel en 2008 et dont les trois hommes se sont ouvertement inspirés, qui a signalé à Peter Higgs les similitudes entre ses travaux et ceux publiés peu auparavant par les chercheurs belges», raconte Étienne Klein, directeur du laboratoire de recherches sur les sciences de la matière du CEA. «Aucun de ces papiers n’évoque d’ailleurs explicitement une particule. Il est plutôt question d’un champ. Ce dernier permet d’apporter une réponse satisfaisante à un problème théorique profond, celui de la masse d’une particule appelée boson intermédiaire.»

Preuve que l’idée était dans l’air du temps, trois autres chercheurs, Gerald Guralnik, Carl Hagen et Tom Kibble, ont eux aussi publié un papier très similaire avant la fin de l’année 1964, toujours dans le même journal. Certains manuels de physique appellent d’ailleurs le mécanisme décortiqué indépendamment par les six chercheurs, mécanisme de Brout-Englert-Higgs-Hagen-Guralnik-Kibble (ou BEHHGK).

Un prix Nobel pour François Englert et Peter Higgs?

«Il faut attendre 1972 pour qu’un autre physicien, Gerard ‘t Hooft, Prix Nobel en 1999, formalise l’existence d’une particule associée au champ scalaire», explique Étienne Klein. C’est d’ailleurs à cette époque que l’idée commence à s’installer dans la communauté scientifique. «Alors qu’on dénombre moins de dix citations par an du papier de Higgs jusque-là, le nombre décolle à 20 puis à 50 pendant les années 1970», rapporte le chercheur. Peu à peu, la nouvelle particule prend alors une place de plus en plus essentielle dans le modèle standard de la physique, dont elle vient combler les lacunes.

Il serait tentant de penser que Peter Higgs a cherché à tirer la couverture à lui en tentant d’imposer son nom au boson éponyme, mais il n’en est rien. L’homme, aujourd’hui âgé de 82 ans, n’a eu de cesse de répéter aux médias qui ont bien voulu l’interroger à ce sujet que cette «découverte» théorique ne lui appartenait pas et qu’il y associait bien volontiers ses collègues. François Englert répète quant à lui à l’envi qu’il ne souhaite pas que son nom soit accolé à celui de Higgs. Il aimerait en revanche qu’on retienne l’appellation de «boson scalaire», qui, selon lui, décrit mieux ce qu’il représente.

Les deux hommes pourraient obtenir un prix Nobel conjoint pour leurs travaux dès cette année. Leur collègue Richard Brout, décédé en mai 2011, n’aura malheureusement pas cette chance, la prestigieuse récompense ne pouvant être décernée à titre posthume.

www.lefigaro.fr

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July 6, 2012 at 7:19 am

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Unofficial Higgs Combinations

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July 5, 2012 at 10:17 pm

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Live: Latest update in the search for the Higgs boson

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press here: CERN webcast

(update)
CERN experiments observe particle consistent with long-sought Higgs boson

Geneva, 4 July 2012. At a seminar held at CERN today as a curtain raiser to the year’s major particle physics conference, ICHEP2012 in Melbourne, the ATLAS and CMS experiments presented their latest preliminary results in the search for the long sought Higgs particle. Both experiments observe a new particle in the mass region around 125-126 GeV.

“We observe in our data clear signs of a new particle, at the level of 5 sigma, in the mass region around 126 GeV. The outstanding performance of the LHC and ATLAS and the huge efforts of many people have brought us to this exciting stage,” said ATLAS experiment spokesperson Fabiola Gianotti, “but a little more time is needed to prepare these results for publication.”

“The results are preliminary but the 5 sigma signal at around 125 GeV we’re seeing is dramatic. This is indeed a new particle. We know it must be a boson and it’s the heaviest boson ever found,” said CMS experiment spokesperson Joe Incandela. “The implications are very significant and it is precisely for this reason that we must be extremely diligent in all of our studies and cross-checks.”

“It’s hard not to get excited by these results,” said CERN Research Director Sergio Bertolucci. “ We stated last year that in 2012 we would either find a new Higgs-like particle or exclude the existence of the Standard Model Higgs. With all the necessary caution, it looks to me that we are at a branching point: the observation of this new particle indicates the path for the future towards a more detailed understanding of what we’re seeing in the data.”

The results presented today are labelled preliminary. They are based on data collected in 2011 and 2012, with the 2012 data still under analysis.  Publication of the analyses shown today is expected around the end of July. A more complete picture of today’s observations will emerge later this year after the LHC provides the experiments with more data.

The next step will be to determine the precise nature of the particle and its significance for our understanding of the universe. Are its properties as expected for the long-sought Higgs boson, the final missing ingredient in the Standard Model of particle physics? Or is it something more exotic? The Standard Model describes the fundamental particles from which we, and every visible thing in the universe, are made, and the forces acting between them. All the matter that we can see, however, appears to be no more than about 4% of the total. A more exotic version of the Higgs particle could be a bridge to understanding the 96% of the universe that remains obscure.

“We have reached a milestone in our understanding of nature,” said CERN Director General Rolf Heuer. “The discovery of a particle consistent with the Higgs boson opens the way to more detailed studies, requiring larger statistics, which will pin down the new particle’s properties, and is likely to shed light on other mysteries of our universe.”

Positive identification of the new particle’s characteristics will take considerable time and data. But whatever form the Higgs particle takes, our knowledge of the fundamental structure of matter is about to take a major step forward.

press.web.cern

Written by physicsgg

July 3, 2012 at 11:21 pm

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A brief history of a boson: Timeline of Higgs

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We seek him here, we seek him there… (Image: Caroline Morley)

by Jacob Aron

It’s turned into science’s worst-kept secret. Tomorrow, physicists at CERN near Geneva in Switzerland are expected to announce the discovery of the Higgs boson, the culmination of a 50-year quest to find the elusive particle that gives others their mass. Here’s how they got there.

1964

Peter Higgs is the first to explicitly predict the particle that would eventually acquire his name in October, but other physicists can also lay claim to the idea of a mass-generating boson. In August, Robert Brout and François Englert independently detail how the mass-generation mechanism could work. Another group – Dick Hagen, Gerald Guralnik and Tom Kibble – also produce similar ideas independently, publishing shortly after Higgs in November.

Identifying exactly who came up with the Higgs could be problematic for the Nobel committee, as the prize can only be shared between a maximum of three people.

1995

Even without the discovery of the Higgs boson we still have evidence for the Higgs mechanism, as it allowed the Standard Model to make a number of successful predictions, including the discovery of the heaviest known particle, the top quark. In 1995, CERN’s Chicago rival, Fermilab, finds the top quark using its Tevatron particle accelerator at around 176 gigaelectronvolts (GeV) – just as predicted.

2001

Before the Large Hadron Collider, CERN had the Large Electron-Positron (LEP) Collider, which spent five years looking for a Higgs with a mass of around 80 GeV before closing in 2000. Conclusive analysis the following year rules out a Higgs with a mass below 115 GeV.

2004

During a gap between the closure of the LEP and the switch-on of the LHC, Chicago was the most likely place to find the Higgs. Data from the Tevatron places the Higgs above 117 GeV, just above LEP’s reach, with an upper limit of 251 GeV.

2007

The LHC is capable of colliding particles at higher energies than any previous accelerator, so experiments pointing to a lighter Higgs increased the Tevatron’s chances of discovery. With pressure from CERN mounting,Fermilab reduces the upper limit to 153 GeV.

2008

One billion people watch as proton beams circulate the Large Hadron Collider for the first time, amid unfounded fears that it could produce a world-destroying black hole. The Higgs hunt is back on at CERN, but only briefly,as a gas leak shuts the accelerator down until the following year.

2009

With the LHC out of action until November, Tevatron researchers say – somewhat hopefully – that they have a 50 per cent chance of finding the Higgs by end of 2010.

2010

Physics blogs buzz with rumours of a Higgs signal at the Tevatron thatultimately prove false.

2011

April sees another round of rumours flourish after an unreviewed LHC study is leaked online, while in September the Tevatron shuts down, having failed to find the Higgs. As the year draws to a close, the LHC’s ATLAS and CMS experiments both show hints of the Higgs at around 125 GeV, the first signal at nearly the same mass.

2012

In February, the LHC boosts collision energy from 7 to 8 teraelectronvolts (TeV), improving its Higgs sensitivity by 30 to 40 per cent. Then in March, data from the Tevatron’s last gasp places the Higgs between 115 and 152 GeV.

4 July

This Wednesday, CERN is due to deliver an update on the search for the Higgs, and researchers are widely expected to announce its discovery. Stick with New Scientist for all the latest developments and follow @newscientist for up-to-the minute news on the biggest physics story of the decade.

 Read more: www.newscientist.com

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July 3, 2012 at 1:22 pm

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Origins of Mass

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Stylized Feynman graph illustrating the production of a Higgs particle through gluon fusion and its decay through photon fission. Time advances upwards

Frank Wilczek
Newtonian mechanics posited mass as a primary quality of matter, incapable of further elucidation. We now see Newtonian mass as an emergent property. Most of the mass of standard matter, by far, arises dynamically, from back-reaction of the color gluon fields of quantum chromodynamics (QCD). The equations for massless particles support extra symmetries – specifically scale, chiral, and gauge symmetries. The consistency of the standard model relies on a high degree of underlying gauge and chiral symmetry, so the observed non-zero masses of many elementary particles (W and Z bosons, quarks, and leptons) requires spontaneous symmetry breaking. Superconductivity is a prototype for spontaneous symmetry breaking and for mass-generation, since photons acquire mass inside superconductors. A conceptually similar but more intricate form of all-pervasive (i.e. cosmic) superconductivity, in the context of the electroweak standard model, gives us a successful, economical account of W and Z boson masses. It also allows a phenomenologically successful, though profligate, accommodation of quark and lepton masses. The new cosmic superconductivity, when implemented in a straightforward, minimal way, suggests the existence of a remarkable new particle, the so-called Higgs particle. The mass of the Higgs particle itself is not explained in the theory, but appears as a free parameter. Earlier results suggested, and recent observations at the Large Hadron Collider (LHC) may indicate, the actual existence of the Higgs particle, with mass mH = 125 GeV GeV. In addition to consolidating our understanding of the origin of mass, a Higgs particle with mH = 125 GeV could provide an important clue to the future, as it is consistent with expectations from supersymmetry.
Read more: http://arxiv.org/pdf/1206.7114v1.pdf

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July 2, 2012 at 3:04 pm

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