$W_R$ Gauge Boson in an Asymmetric Left-Right Model

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Date/Time:Wednesday, 24 Oct 2012 from 4:10 pm to 5:10 pm
Location:A401, Zaffarano Hall
Contact:Chunhui Chen
Channel:High Energy Physics
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Dr. Alper Hayreter, Iowa State University

We studied the Left Right Symmetric Model as an alternative to the Standard Model of particle physics. Motivated by recently observed disagreements with the Standard Model predictions in $B$ decays, we first focus on $b to d, s$ transitions in an asymmetric class of $SU(2)_L times SU(2)_R times U(1)_{B-L}$ models, with a simple one-parameter structure of the right handed mixing matrix for the quarks, which obeys the constraints from Kaon physics. We use experimental constraints on the branching ratios of $b to s gamma$, and $B_{d,s}^0-bar{B}^0_{d,s}$ mixing to restrict the parameters of the model: $displaystyle {g_R}/{g_L}, M_{W_R}, M_{H^pm},tanbeta$ as well as the elements of the right-handed quark mixing matrix $V^R_{CKM}$. We present a comparison with the more commonly used (manifest) left-right symmetric model. Our analysis exposes the parameters most sensitive to $b$ transitions and reveals a large parameter space where left- and right-handed quarks mix differently, opening the possibility of observing marked differences in behavior between the standard model and the left-right

Then we analyze the single $W_R$ boson production in the asymmetric left-right model, where the left and right quark mixing matrices are not constrained to be equal. We investigate the cross sections as well as branching ratios of $W_R$ bosons at the LHC, including constraints from low energy phenomenology. We then look for most likely signals in $pp to W_R tto t ~(dijet)$ production. Including the background, we find that LHC could show significant signals for the new charged bosons. We compare our results throughout with the manifest left-right symmetric model and comment on similarities and differences.

Finally, in light of the recent measurements of the top quark forward-backward asymmetry at the Fermilab Tevatron experiment, which in some regions of the parameter space shows a discrepancy of 3$sigma$ compared to the SM prediction, we analyze top quark pair production and asymmetry in the context of left-right models both at the Tevatron and LHC. We use the minimal manifest left-right model and an asymmetric left-right model where gauge couplings and flavor mixing in the right-handed sector are allowed to differ from those in the left-handed sector. We explore the consequences of including effects from $W_R$ and $Z_R$ gauge bosons, consistent with phenomenological constraints from meson mixing and new bounds from ATLAS and CMS, for the $t bar{t}$ cross section, invariant mass distribution and forward-backward asymmetry at the Tevatron, and predict their values at the LHC. We show that, varying the parameters of the model while preserving agreement with collider, electroweak precision, and flavor violation data, the generic left-right model cannot account for the large deviations of the observed asymmetry at the Tevatron and also that it predicts very small charge asymmetries at the LHC.