The most wanted particle after 4 fb-1 of data at LHC Run 2 : a Z' ?

A handful of new particles for Higgsmas? May be...
What have we learned from the LHC this year, our first year of data-taking at 13 TeV, the highest collision energies we have ever achieved, and the highest we might hope to have for years to come?

We will get our first answers to this question at a CERN seminar scheduled for Tuesday, December 15, where ATLAS and CMS will be presenting physics results from this year’s run. The current situation is reminiscent of December 2011, when the experiments had recorded their first significant datasets from LHC Run 1, and we saw what turned out to be the first hints of the evidence for the Higgs boson that was discovered in 2012.
Quantum Diaries blog 12/05/2015

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Event display of a candidate electron-positron pair with an invariant mass of 2.9 TeV reported by the CMS collaboration for an integrated luminosity of 65 pb-1 at LHC13 that could be interpreted as a Z' resonance in in a model with SU(3)C×SU(2)L×SU(2)R×U(1)B−L gauge structure, a Higgs sector with only a bidoublet and an SU(2)R doublet, and a flavor symmetry that controls the masses of the right-handed neutrinos.

The Z' production cross section at the 13 TeV LHC, computed at leading order with MadGraph and multiplied by K(Z') = 1.16 is shown in Figure 5 {below}. For MZ' = 2.9 TeV (corresponding to gR = 0.48 for MW' = 1.9 TeV) the production cross section is ∼ 19 fb. Assuming similar acceptance-times-efficiency at Run 2 as at Run 1, we predict approximately 5 dilepton Z' events after 5 fb-1. Intriguingly, after 65 pb-1 CMS has already observed a dielectron event with invariant mass of 2.9 TeV; the probablity for this event to be due to the SM background is ∼ 10-3 [43]. The scattering angle of the electron, in the Collins-Soper frame, for this event is negative, as expected for the Z' in this model. Note also that the Z' resonance is narrow in this model. For a Z' mass of 2.9 TeV (corresponding to gR = 0.48) the total width is ΓZ' ≈ 38 GeV; for MZ' = 4.5 TeV (gR = 0.4) we find ΓZ' ≈ 130 GeV. 
 Figure 5: Production cross section, including a K-factor of 1.16, for a Z' boson of mass 2.9, 3.5, 4, and 4.5 TeV at the LHC with √s=13 TeV. The thicker region of each curve denotes the range of gR for which 2 ≥ MW' ≥ 1.8 TeV, with the marked point at MW'=1.9 TeV. 

Bogdan A. Dobrescu, Patrick J. Fox (Submitted on 6 Nov 2015)

A bunch of Geminid meteors? For sure!

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The two nights before the December 15 meeting at CERN are expected to be peak nights for observing the 2015 Geminid meteor shower. Then why not wishing upon a shooting star for future experimental evidence of new particles beyond the Higgs completed standard model? Of course it requires less efforts than an educated guess from a few anomalies but it is worth a bet on one event in a large hadron collider... 

//last edition December 9 2015.


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