Broadest set of results to date about theproperties of the Higgs boson27 January 2015, by Andr David

New results from the CMS collaboration are pinningdown the properties of the Higgs boson Credit:Maximilien Brice/CERN

With the Large Hadron Collider (LHC) preparing torestart in a few months, data from its first run hasalready been bearing fruit.

A recent publication by the CMS collaborationbrings together the broadest set of results to dateabout the properties of the Higgs boson. The paper, submitted to The European Physical Journal Cshowcases what CMS physicists have learnt aboutthe particle using data taken between 2011 and2012 Together with another paper on the spin andparity of the boson, the results draw a picture of aparticle that for the moment cannot bedistinguished from the Standard Model predictionsfor the Higgs boson.

The Standard Model of particle physics is atheoretical framework that explains how the basicbuilding blocks of matter interact, governed by fourfundamental forces. Developed in the early 1970s,it has successfully explained almost allexperimental results and precisely predicted a widevariety of phenomena including the mass of theHiggs boson.

The CMS experiment recently combinedmeasurements from different decays of the Higgsto extract the most precise measurement of itsmass to date: 125.020.30 GeV, with a relativeuncertainty of 0.2%. This uncertainty can be splitinto a systematic component (0.15 GeV) and astatistical component (0.26 GeV), which providesexcellent prospects for Run 2 to yield an even moreprecise mass measurement, as more data willreduce the statistical component.

The Higgs boson is the final piece of the StandardModel when it was discovered by the CMS andATLAS experiments in 2012, it was the last particlepredicted by the Model to be verifiedexperimentally. But with all parameters nowexperimentally constrained, physicists can use theModel to make even more specific predictions. Forexample, having measured the mass of the Higgsboson, the Standard Model makes unambiguouspredictions as to what the Higgs boson's otherproperties should be. Some, such as the boson'sspin (zero), parity (positive), and electric charge(neutral) stem directly from the symmetries of theStandard Model. But others, such as the strengthwith which the Higgs boson interacts (or couples)with other Standard Model particles are harder tocheck.

The Higgs boson decays to many differentparticles, including photons, Z bosons, W bosons,tau leptons, b quarks and muons. Checking howthe Higgs decays into these particles, and withwhat probabilities, will allow physicists to completethe picture and gain a better understanding of theHiggs.

Finding no significant deviations with the StandardModel has set the bar high for the LHC's Run 2.Theorists and experimentalists will continueworking together to find a small wrinkle in the so far

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smooth Higgs boson picture. That small wrinkle thatmay point the way out of the Standard Model oasis,across the desert, and the as-yet unknown physicsbeyond. It's going to be an exciting Run 2.

More information: "Precise determination of themass of the Higgs boson and tests of compatibilityof its couplings with the standard model predictionsusing proton collisions at 7 and 8 TeV. " arXiv:1412.8662 [hep-ex] arxiv.org/abs/1412.8662

"Constraints on the spin-parity and anomalous HVVcouplings of the Higgs boson in proton collisions at7 and 8 TeV." arXiv:1411.3441 [hep-ex] arxiv.org/abs/1411.3441

Provided by CERN

APA citation: Broadest set of results to date about the properties of the Higgs boson (2015, January 27)retrieved 15 May 2015 from http://phys.org/news/2015-01-broadest-results-date-properties-higgs.html

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