Fermilab zooms in on the Higgs boson
August 4, 2008 | 9:01 am
Mass range for Higgs excluded by Fermilab search
Scientists working on the CDF and DZero experiments at the Fermi National Accelerator Laboratory are entering Higgs territory. On Sunday, the two groups reported at a conference in Pennsylvania that for the first time their results directly restrict the allowed mass range for the elusive Higgs boson. The results show that the CDF and DZero experiments are sensitive to Higgs signals that may show up as the two collaborations gather and analyze more data.
“These results mean that the Tevatron experiments are very much in the game for finding the Higgs,” said Fermilab Director Pier Oddone. Fermilab issued a press release with the details of these results.
“We have been working toward this exclusion for many years,” said DZero cospokesperson Darien Wood, of Northeastern University. “Of course, our goal is to find the Higgs boson, not just restrict its mass.”
The Standard Model of particles and forces–the theoretical framework for particle physics–predicts the existence of a particle, the Higgs boson, that interacts with other particles of matter–such as electrons and quarks–to give them mass. The mechanism by which particles acquire different mass values is unknown, and finding evidence for the existence of the Higgs boson would address this fundamental mystery of nature.
Sensitivity of the Fermilab experiments to the Higgs boson at various masses
The CDF and DZero collaborations obtained their result by analyzing hundred trillions of proton-antiproton collisions produced by the Tevatron particle collider. While the current data sample did not reveal the Higgs boson, both groups expect to double their data sets in the next couple of years, improving their chance to observe the particle. According to CDF cospokesperson Rob Roser, Fermilab, the two experiments are close to ruling out a Higgs particle with a mass of 165 GeV/c2 and 175 GeV/c2. (At present, the two experiments look for the Higgs particle in steps of 5 GeV/c2.) This graph (right) shows the current sensitivity of the two experiments to the Higgs boson for various mass values. (Because of the way that the Higgs particle is expected to interact with other subatomic particles, it is easier for the Tevatron experiments to exclude–or to find–a Higgs particle with a mass of 160 GeV/c2 than, say, 120 or 155 GeV/c2.)
The previous constraints on the Higgs mass stem from direct searches at CERN’s Large Electron-Positron (LEP) collider, which operated from 1989-2000, and indirect constraints produced by the LEP and Tevatron experiments. Quantum effects produce indirect constraints. They yield a mathematical relation among the values of the masses of the W boson, the top quark and the Higgs boson. Accordingly, precise measurements of the masses of the W boson and the top quark constrain the Higgs boson mass. Such measurements indicate that the Higgs boson should be lighter than about 200 GeV/c2. Direct searches by the LEP experiments, which analyzed electron-positron collisions, have shown that the Higgs boson is heavier than 114 GeV/c2.
In 2009, the Large Hadron Collider at CERN will begin its hunt for the Higgs boson. The LHC will produce particle collisions with seven times the energy of the Tevatron collider.
Kurt Riesselmann
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August 5th, 2008 at 5:09 am
This is fascinating, even more so in light of the new result showing the bounds on the Higgs mass is between 115 to 135 GeV at 1-sigma http://dorigo.wordpress.com/2008/08/01/new-bounds-for-the-higgs/
Does this mean that the Tevatron will have very little chance of discovering the Higgs if it indeed lies within this range because the decay channels preferred in this range are so rare? The black curves in the above plot would appear to suggest so….. no?
August 5th, 2008 at 11:39 am
This is extremely funny. They ruled out one particular number and it happens to be exactly the number predicted by Alain Connes. Back luck. Alain Connes should start to watch out asteroids, too.
http://motls.blogspot.com/2008/08/tevatron-falsifies-connes-model-of.html
August 5th, 2008 at 12:42 pm
In response to Blake’s comment: The CDF and DZero result reported yesterday is for the high-Higgs-mass scenario (155 to 200 GeV/c^2, see graph above). The two collaborations are working on the corresponding analysis of the “low-mass end” of the Higgs mass range, which would also cover the range that you point out (115 to 135). This analysis is not yet complete.
One should be careful with regard to the significance of the 115-135 GeV/c^2 window for the Higgs mass that you refer to. That range has only a significance of 1 sigma, or 68 percent. That’s not very reliable. If you look at the CDF and DZero graph above, you can see that the two experiments can rule out the entire range from 155 to 185 GeV/c^2 AT THE 68-PERCENT LEVEL (1 sigma). But nobody would take such a claim seriously. To rule out a specific Higgs mass value, scientists require that the result exceeds a 95-percent confidence level. At that level, CDF and DZero exclude only 170 GeV/c^2.
With enough data, the CDF and DZero experiments might become sensitive enough to exclude a Higgs mass of around 115 GeV/c^2. The tough range will be from 120 to 130 GeV/c^2. But both groups of experimenters are still refining their analysis techniques. It will be interesting to see how this all plays out.
August 6th, 2008 at 10:54 am
Russian scientist V.V.Belokurov and D.V.Shirkov in the book http://ru.dleex.com/read/?5565 “Theory of Particles interactions”p.102 illustreted Higgs mechanism trivial: 2+2=1+3.I didn’t see before and after so simple explanation Higgs effect. Discovery of Higgs my be confirm this approach?
August 7th, 2008 at 6:03 am
[...] widely expected that it will discover the Higgs boson, or something very much like it (unless the Tevatron finds it first!). The Higgs is an essential component of the Standard Model of particle physics [...]
August 7th, 2008 at 11:14 am
As a recent follower of this subject, I’m beginning to find it interesting from an anthropological stand point, the debate between the different theoretical schools of thought in particle physics, exactly what these mass/energy constraints actually mean in this street brawl. Can someone please explain to me who SUSY is and what would happen to one street gang if we lost her number? How can you tell who’s winning or losing the fight?
The struggle continues….
August 8th, 2008 at 12:10 am
Kevin:
In paticle physics SUSY is short for ” supersymmetry ”
which is a symmetry that relates elementary particles of on
of one spin to another particle that differs by half unit
a unit of spin and are known as superpartners. In other
words, for every boson there exists a corresponding
fermion.Evidence of supersymmtry might indicate the existnce
of a Grand Unification Theory ( Gut ) of the strong, weak,
and electromagnetic fields, the hierarchy problem, and the
controversial strings of superstring theory.
” Wickipedia “.
October 8th, 2008 at 1:34 pm
In psrticle accelerators particle unite so to speak and actually can give rise to a particle with a greater mass then the combining particles.
In the case of photons they give rise to electrons and positrons that have much more mass than an electron[a photon has an amount of matter measured to 10 to the minus 48 grams which is much less than the mass of an electron.
So where does the mass come from?
A Higgs particle is not suppose to add mass to a photon.
October 8th, 2008 at 3:31 pm
You are correct: A Higgs particle does not add mass to a photon. Nevertheless, photons have energy. If their energy is high enough, photons can produce electron and positrons as energy can transform into mass according to Einstein’s equation E=mc^2.
October 8th, 2008 at 3:55 pm
@Bruce: You are right that the Higgs does not add mass to the photon. It has, as far as we know, zero mass. (The 10^-48 g is presumably an upper limit from an experiment somewhere. It is essentially impossible to “prove” a zero mass, just to get a limit closer and closer to zero.)
Einstein’s concept of mass-energy conversion comes into play here and is the secret to most of this. In a collider, the particles have a certain amount of rest mass. This is small for an electron, positron, or proton. But when they are accelerated, the total mass-energy can be large. Much of this energy can be converted into particles, which can be of a higher mass than the original particles.
So the Higgs would help provide the mass for those massive particles, but not provide mass for photons.
As an extra point, photons are not used as the source of energy in particle collider experiments (although there are some proposals floating around for photon colliders).