Sunday, January 29, 2012

ATLAS sees some multilepton excess, too

In recent months, many TRF articles were dedicated to the CMS' search for multilepton (and multijet) signatures of supersymmetry or similarly behaving new physics. Quite many of them reported some excesses.

See e.g.
TRF: CMS sees SUSY-like trilepton excesses

TRF: Trijet and nonajet excesses

TRF: Multileptons are only "mostly consistent" with SM (CMS)

TRF: Searches for \(R\)-parity violating multileptons at CMS
Finally, five days ago, CMS' friends and foes at ATLAS published a preprint about the same question based on a reasonable amount of data, about 2.1/fb:
ATLAS: Search for Anomalous Production of Multilepton Events and \(R\)-Parity-Violating Supersymmetry in \(\sqrt{s}=7\,\,{\rm TeV}\) \(pp\) Collisions
What did they find?

They looked at events with at least four leptons (electrons and muons) and some missing transverse momentum. In the inclusive selection, they observed 4 events while the expectation was 1.7 ± 0.9 events; that's roughly a 2.5-sigma excess although one should include the non-Gaussianity of the distribution to get a more accurate figure.

When the Z veto was imposed, they got no events while the expectation was 0.7 ± 0.8 events which is OK within 1-sigma error. So only the veto-free figure is intriguing.

It's plausible that one could combine the number with a CMS figure from one of these three CMS papers:
CMS: Search for Physics Beyond the Standard Model Using Multilepton Signatures in \(pp\) Collisions at \(\sqrt{s}=7 \,\,{\rm TeV}\) (tiny 2010 sample)

CMS: Searches for Supersymmetry using Multilepton Signatures in \(pp\) Collisions at 7 TeV

CMS: Search for Anomalous Production of Multilepton Events and \(R\)-Parity-Violating Supersymmetry in \(\sqrt{s} = 7\,\,{\rm TeV}\) \(pp\) Collisions
and get an excess with a local significance above 3.5 sigma. Who knows. At any rate, it's plausible that once CMS and ATLAS analyze their 5/fb of data (which have already been collected), instead of 2.1/fb or so used in all the papers, they could have some pretty tantalizing signals above 3 sigma (per detector) which, in combination, could reach the local significance approaching 5 sigma.

Of course, that assumes that the excesses above are more than just flukes. ;-) At any rate, the multiparticle final states have given us a sufficient number of hints that something interesting could be going on over there. Jester who previously co-authored several SUSY phenomenology papers decided to throw away SUSY because he thinks that She doesn't love him. So he's made a bet $10,000 against your humble correspondent (I will only pay $100 if I lose because I am no fanatic) and wrote a rant claiming that SUSY predicts a Higgs up to 160 GeV and lots of other nonsense. You must agree: this guy has to pay those $10,000, right? He's a villain who behaves to his superbeautiful ex-GF as if She were trash just because he realized he's a f*g, if I use some advanced physics terminology. ;-) The judgment/payment day may even arrive in 2012.

Thanks to Phil Gibbs who reminded me that I wanted to write about the new ATLAS SUSY preprint five days ago. Incidentally, it's more likely than not that the LHC will be restarted at 8 TeV rather than 7 TeV at the beginning of April 2012.

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