Saturday, July 05, 2014

W boson excess at LHC and ATLAS: explanations?

Tommaso Dorigo told about diboson excess (W boson pairs) reported both by ATLAS and CMS in 7 - and 8-TeV collision data. ATLAS measure the cross section to be 71.4+/- 7.5 pb, which is higher than the theory prediction 57.3 pb. Two sigma excess is the technical term. 2 sigma is not convincing but both ATLAS and CMS have measured the excess forces to consider the situation more seriously.

A rather simple SUSY model has been proposed to explain the deviations and the mathematical measure allowing to compare explanations favors SUSY model over standard model. The model involves stop as the lightest squark, neutralino and chargino and bino as spartners of weak bosons. Bino is assumed to be the lightest supersymmetric particle. W pairs are produced in a decay chain initiated by the production of stop pair. Stop then decays to b quark and chargino and chargino to neutralino plus W boson. Same happens for antistop so that one obtains W pair. The model has as parameters M(stop) and M(neutralino). The model produces the values M(stop)= 200 GeV for stop mass and M(neu)=150 GeV for neutralino mass, which are not in already excluded region of the parameter space. Also the production of neutralino pairs is predicted and might serve as a test for the model.

This is certainly not the only model that one can imagine. Especially so in TGD framework which predicts a lot of new physics about which part might be already visible.

  1. M89 hadron physics (see this) could explain the findings about heavy ion and proton heavy ion collisions at RHIC and LHC in terms of mesonlike states of M89 - string like objects for low energy M89 hadron physics - decaying to ordinary hadrons.

  2. TGD predicts a version of SUSY based with covariantly constat right-handed neutrinos generating the SUSY is consistent with the separate conservation of B and L (see this and also this). p-Adic thermodynamics provides an elegant mechanism predicting the masses of spartners: the mass formula is the same as for partners but p-adic length scale can be different. Unfortunately it is not possible to predict the p-adic length scale associated with the right-handed neutrino.

  3. TGD predicts also higher generations of gauge bosons, which could form effectively SU(3) octet whereas fermion generations would effectively form SU(3) triplets (see this).
The decays of the new particles predicted by these scenarios could generate excess of W bosons. W bosons are favored over Z bosons for any production mechanism involving a decay chain of pair of new particles producing quark pairs whose members, which are U or D type quarks, decay to lighter D or U type quarks by the emission of W boson. That decay to lighter quarks can involve W boson emission but no Z emission is due to the basic properties of CKM mixing.

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