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CERN | Geneva | Switzerland

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Getting closer to finding out if the Higgs exists

CERN has been in effervescence for the last few weeks, with rumors running wild and hopes flying even higher. In fact, for the past few weeks, the physicists from ATLAS and CMS, the two collaborations looking for the Higgs boson at the Large Hadron Collider (LHC), have known half the answer. The problem is that the truth lies in knowing the other half, which will only be known officially at a special seminar organized by CERN director general on tomorrow December 13 at 14:00.

What can we expect to find out next Tuesday? Already, in November, the first combined results from the two experiments were released based on 40% of all collected data, excluding large values of the Higgs boson mass. This means, we now know better where to concentrate our efforts.

Looking for the Higgs has kept physicists on their toes for decades. In this case, the theory predicts the existence of this particle. Finding it would be one more confirmation, and a very strong one, that the theoretical description we currently have, the Standard Model, is correct.

At this point, the region at low mass, between 114 and 141 GeV, is where we expect to see something. The Standard Model predicts how many Higgs bosons should be produced at a given mass, and how many of them will decay in a specific way, but it does not tell us its mass. So CMS and ATLAS are searching blindly, not knowing exactly where to look, but also searching using all possible decay modes.

In the low mass range, three different decay channels contribute the most, namely when a Higgs boson decays into two photons, two Z bosons going into four leptons, or two W bosons decaying into two leptons and two neutrinos.

How and when will we know if we have indications from the Higgs boson? If one experiment sees hints of the Higgs boson not only from one channel, but two or even three of these channels, then it’s encouraging. Even better, if not one but both experiments see such signs, and both see them at the same mass, it’s time to call your mother.

This is very much like trying to catch a faint radio signal. We suspect this hidden radio station exists but nobody knows at which frequency it broadcasts. If one search team hears a weak signal using a crystal radio at a given frequency, this is one thing. But say another group also catches something independently at the same frequency using a digital radio, it gets more interesting.

For the Higgs boson, each decay channel represents one different type of detecting technology. Since CMS and ATLAS are looking without telling the other group what they have, if the results that will be presented tomorrow are similar, it could be an indication on the presence of the Higgs boson. But caution will be exerted until we have the irrefutable proof of its presence.

So, stay tuned on December 13 to find out what we have so far…. I will be tweeting live like a little bird from the seminar so you can follow the action as it unfolds from the @CERN account. My colleague Aidan Randle-Conde will be blogging live on the Quantum Diaries site. The seminar will also be broadcasted live from the CERN home page. I will also report the results here towards the end of the afternoon.

Pauline Gagnon

To be alerted of new postings, follow me on Twitter: @GagnonPauline or sign-up on this mailing list to receive and e-mail notification.

 


 

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