Will the real Higgs Boson please stand up?

August 11, 2011 By Lori Ann White, SLAC National Accelerator Laboratory
Manuel Franco Sevilla is only one of the the BaBar collaboration members who gave talks at the International Europhysics Conference on High-energy Physics last month (from left): Manuel Franco Sevilla, Allesandro Gaz, Elisa Guido, Eugenia Puccio, Denis Derkach, Maurizio Martinelli and Andreas Hafner. Credit: Manuel Sevilla.

Although physicists from two experiments at CERN's Large Hadron Collider and from Fermilab’s Tevatron collider recently reported at the Europhysics Conference on High Energy Physics that they didn't find the Higgs boson, they're continuing to home in on the elusive particle, prompting Rolf-Dieter Heuer, the Director General of CERN, to go on record that he believes a neutral Higgs boson will be found by the LHC by the end of 2012.

Meanwhile, at the same conference but during a different session, BaBar collaboration member and SLACer Manuel Franco Sevilla delivered his own report touching on the Higgs. In its own way, Sevilla's contribution was even more curious than the reports from the LHC, because the that the BaBar collaboration didn't find is not the same Higgs boson that the CMS and ATLAS experiments at the LHC could not find in their data.

Wait a minute!  In both cases the Higgs is that mysterious particle responsible for bestowing mass upon its subatomic brethren, right? But – as it happens – not all Higgs bosons are created alike.

"The ATLAS and CMS results refer to a neutral Higgs boson," said SLAC’s Steve Robertson, the current physics analysis coordinator for BaBar. The neutral, or uncharged Higgs boson is the only member of the Standard Model's rogues' gallery of subatomic particles to remain at large after decades of searching.

Or – the neutral Higgs boson could be a member of a family of Higgs bosons, including electrically-charged versions, mandated by supersymmetry. Supersymmetry is the theory that says every particle in the Standard Model has a much heavier partner particle that also hasn't been found yet.

The Higgs boson BaBar didn't find must have a charge. That means it’s not just a Higgs, but a non-Standard Model Higgs.

Which leads one to wonder – how can a low-energy experiment like SLAC’s PEP II B Factory, originally built to investigate differences between matter and antimatter and no longer even taking data, compete with a monster matter masher like the LHC that was built, in a large part, to find the Higgs?

"It turns out we're actually very sensitive to the indirect effects of charged Higgs particles," Robertson explained, "but finding them is hard work for the LHC."

PEP II, like the LHC – and indeed like every other particle collider ever built – turns the energy released by collisions into new particles that decay almost as fast as they're created. Experiments examine the decay products for hints of new physics. The BaBar detector was built to detect B and anti-B mesons, short-lived particles consisting of bottom quarks and anti-bottom quarks, and search for differences in their creation or decay – and to look for an odd phenomenon that might explain why the universe is made of matter rather than antimatter.

Sevilla's study focused on one particular set of decays sensitive to charged Higgs particles – the decay of a B meson to a D meson, a heavy cousin of the electron called a tau lepton, and its partner the tau neutrino. This decay normally proceeds via the W boson, by now a well-known particle. But in general, Higgs particles affect processes involving heavy particles more strongly. Since the B and D mesons and the tau lepton are relatively heavy, if a charged Higgs exists, it could also contribute to this decay. To conduct this study, The BaBar researchers had to make precise measurements of how frequently the decay of the B boson to a D boson and tau lepton-neutrino pair takes place.

It was not an easy job.

One big problem is that pesky tau neutrino, as well as two other neutrinos originating from the subsequent decay of the tau lepton – multiplied by millions of possible events. Neutrinos have almost no interaction with matter, and zip through a detector without leaving a trace. To account for the neutrinos produced in a collision, scientists must subtract the total amount of energy and momentum coming out of the collision from the total mass and energy that went into it. The balance may account for the energy and momentum carried by the neutrinos, but whether it actually does is another question – missing energy and momentum can also be the result of more mundane processes, such as improperly reconstructed particles or electronic noise.

"Accounting for one neutrino is pretty hard," Sevilla said, "but accounting for all three per decay is a nightmare." He's confident they've done it. "We have computer algorithms that we've been working on for the last few years that are super efficient" at distinguishing these decays, he said. Thanks to the sophisticated analysis, the BaBar result is the most precise measurement of this particular decay rate to date. Sevilla has more work to do to improve the precision of his results.

So what precisely did Sevilla and his teammates find?

They found slightly more of the B mesons decaying into D mesons and tau leptons than expected – more than the Standard Model predicts. In more technical terms, the new BaBar results favor the existence of a charged Higgs boson with a significance of about 1.8 – "not considered particularly compelling," Robertson emphasized, "but interesting." Even more interesting, this small discrepancy with respect to the Standard Model prediction matches the results of another process, where the B meson decays into a tau lepton and a tau neutrino without creating a D meson, as measured by BaBar – and by Belle, a Japanese experiment that also looks at B meson decay.

Unfortunately, none of this means the BaBar collaboration is going to scoop the LHC on the charged Higgs. As Robertson explained, BaBar simply doesn't have enough data to make a definitive statement about the charged Higgs one way or another. "This will really be the territory of 'super-B factories'" – upgraded versions of PEP II and KEKB, the Japanese collider that's the home of Belle. Super-B factories planned for Italy and Japan will generate about a hundred times more data, placing a charged Higgs, within reach. But until the new super-B factories come on line, the LHC will continue to generate record-setting numbers of proton-proton collisions and gather ever more data in order to make the director-general's deadline of the end of 2012.

But whether it's a neutral Higgs or a neutral supersymmetric Higgs will still be the question, and the answer will involve the existence – or non-existence – of a charged Higgs boson.

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1 / 5 (3) Aug 11, 2011
The Higgs boson does not exist. Evidence of it is actually brief glimpses of the entangled vacuum structure which comprises matter, in the fleeting moments before it resumes its original shape or stabilizes into an intermediate particle. Since it is part of the vacuum structure in which we reside it can only be glimpsed when it is disturbed, and cannot be observed in its normal state, nor can it be isolated as a particle, which is it not.
1 / 5 (3) Aug 11, 2011
It will never stand up out of the theory pages. It's as fictional a character as a tachyon. Let us accept. There are reasons for the discrepancy, however.There are unexplored regions in explaining space which STR cannot take care of. Even the eV terminology for the mass of a particle needs corrections as space and c gets a clearer understanding. I had been conducting research and have been able to find the basics of gravity. Deciphering space is more challenging but there are promising observations.
2 / 5 (4) Aug 12, 2011
From my high level perspective the case of Higgs boson is dual version of search for gravitational waves at low energy density spectrum. For the phenomena distant from human observer scale a two approaches always exist. The one is, this artefact is real and/or it was already observed. The second one is, that this artefact is of singular nature and it can be never observed.

Before some time I realized, the same dilepton decay channel has been used for both top quark detection, both Higgs boson detection at LHC. If you check the graph of estimated Higgs boson mass spectrum, you will see, the excluded regions are separated into two gaps: one wide and narrow one at ~ 83 GeV.

If you check the top quark mass (172.0±2.2 GeV/c2), you'll realize, it's exactly the twice of the value of the gap. It's another indicia, (at least one of) the Higgs particle(s) is hiding right there...

1 / 5 (3) Aug 12, 2011
It means, the physicists developed some ways, how to detect Higgs with observation of symmetric decay of particles and I'm just saying, this way was already observed for dilepton decay of top quarks.

Does it mean, the Higgs particle is really formed with top quarks? Actually not, because its different concept. The top quarks are just most heavy & dense existing particle, so that all its inner structures are indistinguishable, so it behaves like scalar boson. Analogously black holes are so dense, they lack inner structure from our perspective and we can consider them as a dense cluster of Higgs bosons.

Does it mean, the Higgs boson exists as a distinct particle? IMO not, because these density fluctuations are of fractal nature. The black hole appears homogeneous for us, nevertheless for creatures which could live inside it it would appear like normal extension of our Universe, full of stars and galaxies. And these objects would be indeed formed with another generations of Higgs boson
not rated yet Aug 12, 2011
I like the part where he states that a fermion behaves as a boson.
... (sarcasm)
1 / 5 (2) Aug 12, 2011
..I like the part where he states that a fermion behaves as a boson..

"According to one theoretical interpretation, a top quark bound by to its anti-matter partner, the antitop, would act as a version of the elusive Higgs boson, conferring mass on other particles."


I just predicted it before three years - so I'm explaining it by now.


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