CERN experiments report new Higgs boson measurements

Monday, Jun 23, 2014

 CERN)In a paper published in the journal Nature Physics today, the CMS experiment at CERN reports new results on an important property of the Higgs particle, whose discovery was announced by the ATLAS and CMS experiments on 4 July 2012. The CMS result follows preliminary results from both experiments, which both reported strong evidence for the fermionic decay late in 2013.

Princeton University scientists have been deeply involved in the recent experiments at CERN.

Professor of Physics James Olsen is the 2013-14 co-leader of the Higgs analysis group of the Compact Muon Solenoid (CMS) experiment and has worked at the LHC since 2007. The discovery of the Higgs boson also included significant contributions from the research groups of Professor of Physics Christopher Tully; professional specialist Valerie Halyo; and Daniel Marlow, the Evans Crawford 1911 Professor of Physics.

“Since the initial discovery of the Higgs particle in 2012, the program has been focused on establishing that what we’ve seen is really the Higgs,” said Daniel Marlow, Princeton’s Evans Crawford 1911 Professor of Physics. “This is very important evidence that the particle detected in July 2012 is acting as the Higgs is predicted to act.”

The Higgs boson is associated with a mechanism first put forward in 1964 by Robert Brout, François Englert and Peter Higgs to account for the different ranges of two fundamental forces of nature. Now referred to as BEH, this mechanism is postulated to give rise to the masses of all the fundamental particles. In order to test that idea fully, it is necessary to measure the direct decay of the Higgs boson into all kinds of particles.

When the Higgs boson discovery was announced in 2012, it was based on measurements of the decay of the Higgs to other bosons, the carriers of nature’s forces. The results reported by ATLAS and CMS discuss the decay of Higgs bosons directly to fermions, the particles that make up matter.

The measurements from both have given substantial evidence that the Higgs boson decays directly to fermions at a rate consistent with that predicted by the Standard Model of particle physics, the theory that accounts for the fundamental particles of visible matter and the interactions that work between them, giving structure to matter.

“With our on-going analyses, we are really starting to understand the BEH mechanism in depth,” said CMS Spokesperson, Tiziano Camporesi. “So far, it is behaving exactly as predicted by theory.”

“These results show the power of the detectors in allowing us to do precision Higgs physics,” said ATLAS Spokesperson, Dave Charlton. “We’re coming close to achieving all we can on the Higgs analysis with run 1 data, and are all looking forward to new data when the LHC restarts in 2015.”

The Large Hadron Collider, CERN’s flagship research facility, has been off-line for maintenance and upgrading in last 18 months. Preparations are now underway for it to restart early in 2015.

More information will be available as results are announced at the International Conference on High Energy Physics, ICHEP, which starts in Valencia, Spain, on 2 July.

Links to relevant ATLAS and CMS papers/notes:

CMS Collaboration, "Evidence for the direct decay of the 125 GeV Higgs boson to fermions”, Nature Physics (2014):

CMS Collaboration, “Search for the standard model Higgs boson produced in association with a W or a Z boson and decaying to bottom quarks”:

CMS Collaboration, “Evidence for the 125 GeV Higgs boson decaying to a pair of tau leptons”:

ATLAS Collaboration, “Evidence for Higgs Boson Decays to the tau+tau- Final State with the ATLAS Detector” - 28 November 2013:

ATLAS Collaboration, “Updated coupling measurements of the Higgs boson with the ATLAS detector using up to 25/fb of proton-proton collision data” - 20 March 2014:

This article was adapted from a press release by CERN.