Anomalous Like-sign Dimuon Charge Asymmetry Research Articles

Bmeson mixing in effective theories of supersymmetric Higgs bosons

We study a minimal flavor violating extension of the MSSM, where higher dimensional operators in the Kahler potential induce tree level non-holomorphic Higgs couplings that are controlled by the scale of the physics beyond the MSSM, and analyze their possible impact on CP violation in Bs and Bd mixing. We consider results on the time dependent CP asymmetries in Bs --> psi phi and Bs --> psi f_0 from LHCb, in Bs --> psi phi from CDF and D0 and in B --> psi K_S from the B factories as well as the measurement of an anomalous like-sign dimuon charge asymmetry at D0. Taking into account the stringent bounds on the branching ratio of the rare Bs --> mu+mu- decay, we investigate to which extent the framework allows to address the observed (2-3)sigma discrepancies in fits of the unitarity triangle. We find that a non-standard Bd mixing phase, that is in agreement with the current bounds on CP violation in Bs mixing, requires the presence of higher dimensional operators both in the Kahler potential and the superpotential. The corresponding region of parameter space is characterized by small tan(beta)~5, a light Higgs spectrum with masses below ~400 GeV and will be probed by future measurements at LHCb.

THE MEASUREMENTS OF THE ANOMALOUS LIKE-SIGN DIMUON CHARGE ASYMMETRY IN $p\bar{p}$ COLLISIONS BY THE DØ COLLABORATION

In this short review we present the history, an overview of the analysis, and some personal comments on the anomalous like-sign dimuon charge asymmetry measurements by the DØ collaboration.

Measurement of the anomalous like-sign dimuon charge asymmetry with9 fb−1ofpp¯collisions

We present an updated measurement of the anomalous like-sign dimuon charge asymmetry Aslb for semi-leptonic $b$-hadron decays in 9.0 fb^-1 of p pbar collisions recorded with the D0 detector at a center-of-mass energy of sqrt{s} = 1.96 TeV at the Fermilab Tevatron collider. We obtain Aslb = (-0.787 +- 0.172(stat) +- 0.093 (syst))%. This result differs by 3.9 standard deviations from the prediction of the standard model and provides evidence for anomalously large CP violation in semi-leptonic neutral B decay. The dependence of the asymmetry on the muon impact parameter is consistent with the hypothesis that it originates from semi-leptonic b-hadron decays.

A fourth generation, anomalous like-sign dimuon charge asymmetry and the LHC

A fourth chiral generation, with m t′ in the range ∼ (300–500) GeV and a moderate value of the CP-violating phase, can explain the anomalous like-sign dimuon charge asymmetry observed recently by the D0 collaboration. The required parameters are found to be consistent with constraints from other B and K decays. The presence of such quarks, apart from being detectable in the early stages of the LHC, would also have important consequences in the electroweak symmetry breaking sector.

Formula omitted] mixing, lifetime difference [formula omitted] and the Physics Beyond Standard Model

The analysis of tagged B s → J / ψ ϕ decays determines the CP phase ϕ s J / ψ ϕ in B s – B ¯ s mixing with a two–fold ambiguity. The solutions differ in the sign of cos ϕ s J / ψ ϕ which equals the sign of the width difference Δ Γ s among the two B s mass eigenstates. In this talk, I discuss the removal of this sign ambiguity with the help of B s → D s K decays. In addition, I discuss the new physics models that contribute to the absorptive part of B s – B ¯ s mixing through the decay b → s τ + τ − which may enhance Δ Γ s all the way up to its current experimental bound. It can also help to understand the recent data on anomalous like-sign dimuon charge asymmetry observed by DO. A measurement of B R ( B s → τ + τ − ) is thus crucial for a better understanding of new physics involved in B s – B ¯ s mixing.

Implications of large CP violation in B mixing for Supersymmetric Standard Models

Following the anomalous like-sign dimuon charge asymmetry measured by the D0 collaboration at the Tevatron collider we discuss the implications of large CP violation in $B_{d,s}$ mixing for Supersymmetric (SUSY) Standard Models, focussing on those models which allow a family symmetry and unification. For the Minimal Supersymmetric Standard Model (MSSM) we show that it is only possible to account for $B_{s}$ mixing and CP violation at the expense of large squark mixing which would require a new approach to family symmetry models. In order to describe both $B_{s}$ and $B_{d}$ mixing and CP violation we are led to consider SUSY models with Higgs fields transforming as triplets under a family symmetry. We describe a realistic such model based on $\Delta_{27}$ family symmetry in which tree-level exchange of the second Higgs family predicts $B_{s}$ and $B_{d}$ mixing and CP violation in good agreement with a recent global fit, while naturally suppressing flavour and CP violation involving the first and second quark and lepton families.

EnhancedBs–B¯slifetime difference and anomalous like-sign dimuon charge asymmetry from new physics inBs→τ+τ−

New physics models that increase the decay rate of $B_s \to \tau^+ \tau^-$ contribute to the absorptive part of $B_s$--$\bar{B}_s$ mixing, and may enhance $\Delta\Gamma_s$ all the way up to its current experimental bound. In particular, the model with a scalar leptoquark can lead to a significant violation of the expectation $\Delta\Gamma_s \leq \Delta\Gamma_s$ (SM). It can even allow regions in the $\Delta\Gamma_s$-$\beta_s$ parameter space that are close to the best fit obtained by CDF and D\{O} through $B_s \to J/\psi \phi$. In addition, it can help explain the anomalous like-sign dimuon charge asymmetry observed recently by D\O. A measurement of $BR(B_s \to \tau^+ \tau^-)$ is thus crucial for a better understanding of new physics involved in $B_s$--$\bar{B}_s$ mixing.

Evidence for an Anomalous Like-Sign Dimuon Charge Asymmetry

We measure the charge asymmetry A ≡ (N++ - N--)/(N++ + N--) of like-sign dimuon events in 6.1 fb-1 of pp collisions recorded with the D0 detector at a center-of-mass energy square root(s) = 1.96 TeV at the Fermilab Tevatron collider. From A we extract the like-sign dimuon charge asymmetry in semileptonic b-hadron decays: A(sl)(b) = -0.009 57 ± 0.002 51(stat) ± 0.001 46(sys). It differs by 3.2 standard deviations from the standard model prediction A(sl)(b)(SM) = (-2.3(-0.6)(+0.5)) × 10(-4), and provides first evidence of anomalous CP violation in the mixing of neutral B mesons.