arXiv subjects

Gudrun Hiller

Publications and source records attributed to Gudrun Hiller.

103 records · Page 6Linked to original sources

arXiv2007

Angular Distributions of B -> K ll Decays

We model-independently analyze the angular distributions of B -> K ll decays, l = e, mu, for low dilepton mass using QCD factorization. Besides the decay rate, we study the forward-backward asymmetry A_FB^l and a further observable, F_H^l, which gives rise to a flat term in the angular distribution. We find that in the Standard Model F_H^l ~ m_l^2, hence vanishing F_H^e and F_H^mu of around 2% (exact value depends on cuts) with a very small theoretical uncertainty of a few percent. We also give predictions for R_K, the ratio of B -> K mu mu to B -> K ee decay rates. We analytically show using large recoil symmetry relations that in the Standard Model R_K equals one up to lepton mass corrections of the order 10^(-4). The New Physics reach of the observables from the B -> K ll angular analysis is explored together with R_K and the B_s -> ll and B -> X_s ll branching ratios for both l = e and l = mu. We find substantial room for signals from (pseudo-) scalar and tensor interactions beyond the Standard Model. Experimental investigations of the B -> K mu mu angular distributions are suitable for the LHC environment and high luminosity B factories, where also studies of the electron modes are promising.

hep-ph↗

arXiv2005

Phenomenological study of the double radiative decay $B ->Kγγ$

Using the operator product expansion (OPE) technique, we study the rare double radiative decay $B\to K γγ$ in the Standard Model (SM) and beyond. We estimate the short-distance (SD) contribution to the decay amplitude in a region of the phase space which is around the point where all decay products have energy $\sim m_b/3$ in the rest frame of the $B$-meson. At lowest order in $1/m_b$, the $B\to K γγ$ matrix element is then expressed in terms of the usual $B\to K$ form factors known from semileptonic rare decays. The integrated SD branching ratio in the SM in the OPE region turns out to be $Δ{\cal{B}}(B \to K γγ)_{SM}^{OPE} \simeq 1 \times 10^{-9}$. We work out the di-photon invariant mass distribution with and without the resonant background through $B\to K \{η_c,χ_{c0}\}\to Kγγ$. In the SM, the resonance contribution is dominant in the region of phase space where the OPE is valid. On the other hand, the present experimental upper limit on $B_s \to τ^+ τ^-$ decays, leaves considerable room for New Physics (NP) in the one-particle-irreducible contribution to $B\to K γγ$ decays. In this case, we find that the SD $B\to K γγ$ branching ratio can be enhanced by one order of magnitude with respect to its SM value and the SD contribution can lie outside of the resonance peaks.

hep-ph↗

arXiv2005

The Pattern of CP Asymmetries in $b\to s$ Transitions

New CP violating physics in $b\to s$ transitions will modify the CP asymmetries in B decays into final CP eigenstates ($ϕK_S$, $η^\prime K_S$, $π^0 K_S$, $ωK_S$, $ρ^0 K_S$ and $ηK_S$) from their Standard Model values. In a model independent analysis, the pattern of deviations can be used to probe which Wilson coefficients get a significant contribution from the new physics. We demonstrate this idea using several well-motivated models of new physics, and apply it to current data.

hep-ph↗

arXiv2004

Implications of Non-Standard CP Violation in Hadronic $B$-Decays

We investigate a class of models for new physics which could produce a large difference in sin 2 beta between B0-> J/ψK(S) and the ``pure penguin'' mode B0-> phi K(S). In such models, the dominant effect is through a Z-penguin and therefore a pattern of deviation in sin 2beta as measured in B0-> chi(1) K(S); eta(c) K(S); J/ψK(S) and psi-prime K(S) is predicted. If the preliminary data concerning the discrepancy between J/ψK(S) and phi K(S) proves correct in magnitude, discrepancies in these other modes would likely be observable. We also consider the effects such new physics could have on the B(s) system and the isospin analysis of B-> Kπ. We compare this scenario with a scenario where contributions to sin 2beta in various modes is produced by gluino loops and down squark mixing.

hep-ph↗

arXiv2004

b-physics signals of the lightest CP-odd Higgs in the NMSSM at large tan beta

We investigate the low energy phenomenology of the lighter pseudoscalar $A_1^0$ in the NMSSM. The $A_1^0$ mass can naturally be small due to a global $U(1)_R$ symmetry of the Higgs potential, which is only broken by trilinear soft terms. The $A_1^0$ mass is further protected from renormalization group effects in the large $\tan β$ limit. We calculate the $b \to s A_1^0$ amplitude at leading order in $\tan β$ and work out the contributions to rare $K$, $B$ and radiative $Υ$-decays and $B -\bar B$ mixing. We obtain constraints on the $A_1^0$ mass and couplings and show that masses down to ${\cal{O}}(10)$ MeV are allowed. The $b$-physics phenomenology of the NMSSM differs from the MSSM in the appearance of sizeable renormalization effects from neutral Higgses to the photon and gluon dipole operators and the breakdown of the MSSM correlation between the $B_s \to μ^+ μ^-$ branching ratio and $B_s - \bar B_s$ mixing. For $A_1^0$ masses above the tau threshold the $A_1^0$ can be searched for in $b \to s τ^+ τ^-$ processes with branching ratios $\lsim 10^{-3}$.

hep-ph↗

arXiv2003

Phenomenology of New Physics

I review the phenomenology of new physics in low energy processes using the notion of minimal flavor violation (vs. non-minimal flavor violation). I compare the predictions of beyond-the-standard models and show that among certain observables in rare $b$-decays pattern arise, which allow to distinguish between extensions of the Standard Model. I discuss the status and future of the model independent analysis of $b \to s$ processes.

hep-ph↗

arXiv2002

First hint of non-standard CP violation from B --> Phi K_S decay

We comment on the implications of the recently measured CP asymmetry in B --> Phi K_S decay. The data disfavor the Standard Model at 2.7 sigma and -if the trend persists in the future with higher statistics - require the existence of CP violation beyond that in the CKM matrix. In particular, the b --> s bar{s} s decay amplitude would require new contributions of comparable size to the Standard Model ones with an order one phase. While not every model can deliver such a large amount of CP and flavor violation, those with substantial FCNC couplings to the Z can reproduce the experimental findings.

hep-ph↗

arXiv2002

Physics reach of rare b-decays

I discuss the theoretical and empirical status of $b \to s γ$, $b \to s \ell^+ \ell^-$ decays, as well as their future prospects. I emphasize those observables in rare $b$-decays which can potentially establish new physics and distinguish between extensions of the Standard Model. I briefly review current models of electroweak symmetry breaking, all of which can carry interesting flavor characteristics accessible with $b$-physics experiments.

hep-ph↗

arXiv2002

Strong-weak CP hierarchy from non-renormalization theorems

We point out that the hierarchy between the measured values of the CKM phase and the strong CP phase has a natural origin in supersymmetry with spontaneous CP violation and low energy supersymmetry breaking. The underlying reason is simple and elegant: in supersymmetry the strong CP phase is protected by an exact non-renormalization theorem while the CKM phase is not. We present explicit examples of models which exploit this fact and discuss corrections to the non-renormalization theorem in the presence of supersymmetry breaking. This framework for solving the strong CP problem has generic predictions for the superpartner spectrum, for CP and flavor violation, and predicts a preferred range of values for electric dipole moments.

hep-ph↗

arXiv2001

Testing factorization

We briefly review the status of factorization in $b$-decays. We discuss several experimental tests of its nature and stress their importance. We show that decays into mesons which have small decay constants or spin greater than one (`designer mesons') offer a variety of new opportunities.

hep-ph↗

arXiv2000

Semileptonic Form-factors from B-> K* gamma Decays in the Large Energy Limit

Making use of the measurement of the $B\to K^*γ$ branching ratio together with the relations following from the limit of high recoil energy, we obtain stringent constraints on the values of the form-factors entering in heavy-to-light $B\to V\ell\ell'$ processes such as $B\to K^*\ell^+\ell^-$, $B\to K^*ν\barν$ and $B\to ρ\ellν$ decays. We show that the symmetry predictions, when combined with the experimental information on radiative decays, specify a severely restricted set of values for the vector and axial-vector form-factors evaluated at zero momentum transfer, $q^2=0$. These constraints can be used to test model calculations and to improve our understanding of the $q^2$-dependence of semileptonic form-factors. We stress that the constraints remain stringent even when corrections are taken into account.

hep-ph↗

arXiv1999

The CP-conserving contribution to the transverse muon polarization in K+ -> mu+ nu gamma

We present a detailed estimate of the transverse muon polarization (P_T) due to electromagnetic final-state interactions in the decay $K^+ \to μ^+ νγ$. This CP-conserving effect represents the dominant contribution to P_T within the Standard Model. As a result of an explicit calculation, we find that the CP-conserving contribution to P_T is quite small, typically of $\cO(10^{-4})$, essentially due to the suppression factor $α/4π^2$. This enforces the sensitivity of P_T in probing extensions of the Standard Model with new sources of time-reversal violations. A brief discussion about possible CP-violating contributions to P_T in the framework of supersymmetric models with unbroken R-parity is also presented.

hep-ph↗

arXiv1998

Improved QCD perturbative contributions and power corrections in radiative and semileptonic rare B decays

We calculate the leading power corrections to the decay rates, distributions and hadronic spectral moments in rare inclusive \bxsll decays in the standard model, using heavy quark expansion (HQE) in $(1/m_b)$ and a phenomenological model implementing the Fermi motion effects of the b-quark bound in the B-hadron. We include next-to-leading order perturbative QCD corrections and work out the dependences of the spectra, decay rates and hadronic moments on the model parameters in either HQE and the Fermi motion model. In the latter, we take into account long-distance effects via $B \to X_s +(J/ψ, ψ^\prime,...) \to X_s \ell^+ \ell^- $ with a vector meson dominance ansatz and study the influence of kinematical cuts in the dilepton and hadronic invariant masses on branching ratios, hadron spectra and hadronic moments. We present leading logarithmic QCD corrections to the $b \to s γγ$ amplitude. The QCD perturbative improved $B_{s}\toγγ$ branching ratio is given in the standard model including our estimate of long-distance effects via $B_s \to ϕγ\to γγ$ and $B_s \to ϕψ\to ϕγ\to γγ$ decays. The uncertainties due to the renormalization scale and the parameters of the HQE inspired bound state model are worked out.

hep-ph↗