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In the scenario with four quark generations, we perform a fit using flavor-physics data and determine the allowed values-preferred central values and errors-of all of the elements of the 4×4 quark-mixing matrix. In addition to the direct measurements of some of the elements, we include in the fit the present measurements of several flavor-changing observables in the K and B systems that have small hadronic uncertainties, and also consider the constraints from the vertex corrections to Z→bb̄. The values taken for the masses of the fourth-generation quarks are consistent with the measurements of the oblique parameters and perturbativity of the Yukawa couplings. We find that |Vtb|0.98 at 3σ, so that a fourth generation cannot account for any large deviation of |Vtb| from unity. The fit also indicates that all the new-physics parameters are consistent with zero, and the mixing of the fourth generation with the other three is constrained to be small: we obtain |Vub′|&lt;0.06, |Vcb′|&lt;0.027, and |Vtb′|&lt;0.31 at 3σ. Still, this does allow for the possibility of new-physics signals in Bd, Bs and rare K decays. © 2011 American Physical Society.

Department of Physics

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Physical Review D - Particles, Fields, Gravitation and Cosmology

Constraints on the four-generation quark mixing matrix from a fit to flavor-physics data

Recently, the DØ Collaboration measured the CP-violating like-sign dimuon charge asymmetry in neutral B decays, finding a 3.2ν difference from the standard-model (SM) prediction. A non-SMcharge asymmetry as s1 suggests a new-physics (NP) contribution to Bs-Bs mixing. In this case, in order to explain the measured value of as s1 within its 1s range, NP must be present in Γss 12, the absorptive part of the mixing. In this paper, we examine whether such an explanation is possible in models with flavor-changing Z″ (ZFCNC) or Z″ (Z″FCNC) gauge bosons. The models must also reproduce the measured values of the indirect CP asymmetry Sψφ in Bs → J/ψφ, and δΓs, the Bs-Bs width difference. We find that the ZFCNC model cannot reproduce the present measured values of Sψφ and as s1 within their 1s ranges. On the other hand, in the Z″FCNC model, the values of all three observables can be simultaneously reproduced. © SISSA 2011.

Journal of High Energy Physics

Neutral gauge boson contributions to the dimuon charge asymmetry in B decays

We perform a comprehensive study of the impact of new-physics operators with different Lorentz structures on decays involving the b → sμ + μ - transition. We examine the effects of new vector-axial vector (VA), scalar-pseudoscalar (SP) " and tensor (T) interactions on the differential branching ratios and forward-backward asymmetries (A FB 's) of B o s → μ + μ - , B o d X s + μ - , B o s → μ + μ - γ, B o d → Kμ + μ - , and B o d → K*μ + μ - , taking the new-physics couplings to be real. In B o d → K*μ + μ - , we further explore the polarization fraction f L , the angular asymmetry A (2) T , and the longitudinaltransverse asymmetry A LT . We identify the Lorentz structures that would significantly impact these observables, providing analytical arguments in terms of the contributions from the individual operators and their interference terms. In particular, we show that while the new VA operators can significantly enhance most of the asymmetries beyond the Standard Model predictions, the SP and T operators can do this only for A FB in B o d → Kμ + μ - . © SISSA 2011.

New physics in b → sμ + μ - : CP-conserving observables

We perform a comprehensive study of the impact of new-physics operators with different Lorentz structures on CP-violating observables involving the b → sμ+μ- transition. We examine the effects of new vector-axial vector (VA), scalar-pseudoscalar (SP) and tensor (T) interactions on the CP asymmetries in the branching ratios and forwardbackward asymmetries of Bo s → μ+μ -, Bo d Xs +μ -, Bo s → μ+μ -γ, Bo d → Kμ+μ -, and Bo d → K*μ+μ -. In Bo d → K*μ+μ -, we also explore the direct CP asymmetries in the longitudinal polarization fraction fL and the angular asymmetries A (2) T and ALT, as well as the triple-product CP asymmetries A(im) T and A(im) LT. We find that, in almost all cases, the CP-violating observables are sensitive only to new physics which involves VA operators. The VA new physics may therefore be unambiguously identified by a combined analysis of future measurements of these CP-violating observables. © SISSA 2011.

New physics in b → sμ+μ-: CP-violating observables

We extend our recent work and study implications of the standard model with four generations (SM4) for rare B and K decays. We again take seriously the several 2-3σ anomalies seen in B, Bs decays and interpret them in the context of this simple extension of the SM. SM4 is also of course of considerable interest for its potential relevance to dynamical electroweak symmetry breaking and to baryogenesis. Using experimental information from processes such as B→Xsγ, Bd and Bs mixings, indirect CP-violation from KL→ππ etc. along with oblique corrections, we constrain the relevant parameter space of the SM4, and find mt′ of about 400-600 GeV with a mixing angle |Vt′b*Vt ′s| in the range of about 0.05-1.4×10-2 and with an appreciable CP-odd associated phase, are favored by the current data. Given the unique role of the CP asymmetry in Bs→ψ due to its gold-plated nature, correlation of that with many other interesting observables, including the semileptonic asymmetry (ASL) are studied in SM4. We also identify several processes, such as B→Xsνν̄, KL→π0νν̄ etc., that are significantly different in SM4 from the SM. Experimentally the very distinctive process Bs→μ+μ- is also discussed; the branching ratio can be larger or smaller than in SM, (3.2→4.2)×10-9, by a factor of O(3). © 2010 The American Physical Society.

Standard model with four generations: Selected implications for rare B and K decays

We show that a fourth family of quarks with mt′ in the range of (400-600) GeV provides a rather simple explanation for the several indications of new physics that have been observed involving CP asymmetries of the b-quark. The built-in hierarchy of the 4 × 4 mixing matrix is such that the t′ readily provides a needed perturbation (≈ 15 %) to sin 2 β as measured in B → ψ Ks and simultaneously is the dominant source of CP asymmetry in Bs → ψ φ{symbol}. The correlation between CP asymmetries in Bs → ψ φ{symbol} and Bd → φ{symbol} Ks suggests mt′ ≈ (400 - 600) GeV. Such heavy masses point to the tantalizing possibility that the 4th family plays an important role in the electroweak symmetry breaking. © 2009 Elsevier B.V.

Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

The fourth family: A simple explanation for the observed pattern of anomalies in B - CP asymmetries

We study the forward-backward asymmetry (AFB) and the differential branching ratio (DBR) in B → K*μ+μ- in the presence of new physics (NP) with different Lorentz structures. We consider NP contributions from vector-axial vector (VA), scalarpseudoscalar (SP), and tensor (T) operators, as well as their combinations. We calculate the effects of these new Lorentz structures in the low-q2 and high-q2 regions, and explain their features through analytic approximations. We find two mechanisms that can give a significant deviation from the standard-model predictions, in the direction indicated by the recent measurement of AFB by the Belle experiment. They involve the addition of the following NP operators: (i) VA, or (ii) a combination of SP and T (slightly better than T alone). These two mechanisms can be distinguished through measurements of DBR in B → K*μ+μ- and AFB in B → Kμ+μ-. © 2010 SISSA.

New-physics contributions to the forward-backward asymmetry in B → K*μ+μ-

We study Bs→μ+μ- in the context of the R-parity violating minimal supergravity in the high-tan β regime. We find that the lowest value of the branching ratio can go well below the present LHCb sensitivity and hence Bs→μ+μ- can even be invisible to the LHC. We also find that the present upper bound on Br (Bs→μ+μ-) puts strong constraint on the minimal supergravity parameter space. The constraints become more severe if the upper bound is close to its standard model prediction. © Springer-Verlag / Società Italiana di Fisica 2009.

European Physical Journal C

Bs→μ+μ- decay in the R-parity violating minimal supergravity

New physics in the form of scalar/pseudoscalar operators cannot lower the semileptonic branching ratio Br(B → K μ+μ-) below its standard model value. In addition, we show that the upper bound on the leptonic branching ratio Br(Bs → μ+μ -) sets a strong constraint on the maximum value of Br(B → K μ+μ-) in models with multiple Higgs doublets: with the current bound, Br(B → K μ+μ-) cannot exceed the standard model prediction by more than 2.5%. The conclusions hold true even if the new physics couplings are complex. However, these constraints can be used to restrict new physics couplings only if the theoretical and experimental errors in Br(B → K μ+μ-) are reduced to a few per cent. The constraints become relaxed in a general class of models with scalar/pesudoscalar operators. © 2010 World Scientific Publishing Company.

Modern Physics Letters A

Tension between scalar/pseudoscalar new physics contribution to B s → μ+μ- and B → K μ+μ-

We estimate the CP asymmetry ACP(q2) in the decays B→Xsμ+μ- and B→Xdμ+μ- in the standard model (SM) with an additional fourth generation. We use a parametrization that allows us to explore the complete parameter space of the 4×4 quark mixing matrix, and constrain these parameters from the current data on B decays. We find that the enhancement in ACP(q2) depends strongly on the mass of the t′, the up-type quark in the fourth generation. For mt′ around 400 GeV, the CP asymmetry in the high-q2 region (q2>14.4GeV2) can be enhanced by more than an order of magnitude for B→Xsμ+μ- and up to a factor of 6 for B→Xdμ+μ-. There is no enhancement in the low-q2 region (1<q2<6GeV2). With increasing mt′, ACP(q2) in the high-q2 (low-q2) region first decreases (increases) and then saturates at a value a few times the SM prediction. In the high-q2 region of B→Xsμ+μ-, this saturation value may be up to 25 times the SM expectation. © 2009 The American Physical Society.

CP asymmetry in the decays B→(Xs,Xd)μ+μ- with four generations

We study the constraints on possible new physics contributions to the forward-backward asymmetry of muons, AFB(q2), in B→Kμ+μ-. New physics in the form of vector/axial-vector operators does not contribute to AFB(q2), whereas new physics in the form of scalar/pseudoscalar operators can enhance AFB(q2) only by a few percent. However, new physics in the form of tensor operators can take the peak value of AFB(q2) to as high as 40% near the high-q2 end point. In addition, if both scalar/pseudoscalar and tensor operators are present, then AFB(q2) can be more than 15% for the entire high-q2 region q2>15GeV2. The observation of significant AFB would imply the presence of new physics tensor operators, whereas its q2 dependence could further indicate the presence of new scalar/pseudoscalar physics. © 2008 The American Physical Society.

Large forward-backward asymmetry in B→Kμ+μ- from new physics tensor operators

We study the constraints on the contribution of new physics in the form of scalar/pseudoscalar operators to the average forward-backward asymmetry AFB of muons in B→Kμ+μ- and the longitudinal polarization asymmetry ALP of muons in Bs→μ+μ-. We find that the maximum possible value of AFB allowed by the present upper bound on B(Bs→μ+μ-) is about 1% at 95% C.L. and hence will be very difficult to measure. On the other hand, the present bound on B(Bs→μ+μ-) fails to put any constraints on ALP, which can be as high as 100% even if B(Bs→μ+μ-) is close to its standard model prediction. The measurement of ALP will be a direct evidence for an extended Higgs sector, and combined with the branching ratio B(Bs→μ+μ-) it can even separate the new physics scalar and pseudoscalar contributions. © 2008 The American Physical Society.

Probing the extended Higgs sector through rare b→sμ+μ- transitions

We consider the effect of new physics on the branching ratio of B s → l+l-γ where l = e, μ. If the new physics is of the form scalar/pseudoscalar, then it makes no contribution to Bs → l+l-γ, unlike in the case of Bs → l+l-, where it can potentially make a very large contribution. If the new physics is in the form of vector/axial-vector operators, then the present data on B → (K, K*)l+l- does not allow a large enhancement for B(Bs → l+l-γ). If the new physics is in the form of tensor/pseudotensor operators, then the data on B → (K, K*)l+l- gives no useful constraint but the data on B → K*γ does. Here again, a large enhancement of B(Bs → l+l-γ), much beyond the Standard Model expectation, is not possible. Hence, we conclude that the present data on b → s transitions allow a large boost in B(Bs → l +l-) but not in B(Bs → l+l -γ). © World Scientific Publishing Company.

New physics upper bound on the branching ratio of Bs → l+l-γ

We consider the most general new physics effective Lagrangian for b → s l+ l-. We derive the upper limit on the branching ratio for the processes Bs → l+ l- where l = e, μ, subject to the current experimental bounds on related processes, B → (K, K*) l+ l-. If the new physics interactions are of vector/axial-vector form, the present measured rates for B → (K, K*) l+ l- constrain B (Bs → l+ l-) to be of the same order of magnitude as their respective Standard Model (SM) predictions. On the other hand, if the new physics interactions are of scalar/pseudoscalar form, B → (K, K*) l+ l- rates do not impose any useful constraint on B (Bs → l+ l-) and the branching ratios of these decays can be as large as present experimental upper bounds. If future experiments measure B (Bs → l+ l-) to be ≥ 10-8 then the new physics giving rise to these decays has to be of the scalar/pseudoscalar form. We also consider the effect of new physics on B (Bs → l+ l- γ) subject to the present experimental constraints on B → (K, K*) l+ l- and B → K* γ. New physics in form scalar/pseudoscalar, which makes a very large contribution to Bs → l+ l-, makes no contribution at all to Bs → l+ l- γ due to angular momentum conservation. New Physics in the form of vector/axial-vector operators is constrained by the data on B → (K, K*) l+ l- and new physics in the form of tensor/pseudo-tensor is constrained by the data on B → K* γ. In both cases, enhancement of B (Bs → l+ l- γ) much beyond the SM expectation is impossible. In conclusion, present data on B → (K, K*) transitions allow for large B (Bs → l+ l-) but do not allow B (Bs → l+ l- γ) to be much larger than its SM expectation. © 2007 Elsevier B.V. All rights reserved.

Nuclear Physics B - Proceedings Supplements

New physics upper bound on the branching ratio of Bs → l+ l- and Bs → l+ l- γ

This is the report of flavor physics and model building working group at WHEPP-9. While activities in flavor physics have been mainly focused on B-physics, those in model building have been primarily devoted to neutrino physics. We present summary of working group discussions carried out during the workshop in the above fields, and also briefly review the progress made in some projects subsequently. © Indian Academy of Sciences.

Pramana - Journal of Physics

Working group report: Flavor physics and model building

We consider the most general new physics effective Lagrangian for b→sl+l-. We derive the upper limit on the branching ratio for the processes Bs→l+l- where l=e,μ, subject to the current experimental bounds on related processes, B→Kl+l- and B→K*l+l -. If the new physics interactions are of vector/axial-vector form, the present measured rates for B→(K,K*;)l+l- constrain B(Bs→l+l-) to be of the same order of magnitude as their respective Standard Model predictions. On the other hand, if the new physics interactions are of scalar/pseudoscalar form, B→(K,K*)l+l- rates do not impose any constraint on Bs→l+l- and the branching ratios of these decays can be as large as present experimental upper bounds. If future experiments measure B(Bs→l+l-) to be ≥10-8 then the new physics giving rise to these decays has to be of the scalar/pseudoscalar form.