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Alexander Lenz

Alexander Lenz appears in the imported research catalog. Authorship, coauthor and topic links are available while profile ownership is still unclaimed.

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hep-phhep-exhep-latArtificial Intelligencenucl-exnucl-thphysics.class-phphysics.pop-phSoftware Engineering

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Published work

43 published item(s)

preprint2026arXiv

A Pattern Language for Resilient Visual Agents

Integrating multimodal foundation models into enterprise ecosystems presents a fundamental software architecture challenge. Architects must balance competing quality attributes: the high latency and non-determinism of vision language action (VLA) models versus the strict determinism and real-time performance required by enterprise control loops. In this study, we propose an architectural pattern language for visual agents that separates fast, deterministic reflexes from slow, probabilistic supervision. It consists of four architectural design patterns: (1) Hybrid Affordance Integration, (2) Adaptive Visual Anchoring, (3) Visual Hierarchy Synthesis, and (4) Semantic Scene Graph.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

Cornering the Two Higgs Doublet Model Type II

We perform a comprehensive study of the allowed parameter space of the Two Higgs Doublet Model of Type II (2HDM-II). Using the theoretical framework flavio we combine the most recent flavour, collider and electroweak precision observables with theoretical constraints to obtain bounds on the mass spectrum of the theory. In particular we find that the 2HDM-II fits the data slightly better than the Standard Model (SM) with best fit values of the heavy Higgs masses around 2 TeV and a value of $\tan β\approx 4$. Moreover, we conclude that the wrong-sign limit is disfavoured by Higgs signal strengths and excluded by the global fit by more than five standard deviations and potential deviations from the alignment limit can only be tiny. Finally we test the consequences of our study on electroweak baryogenesis via the program package BSMPT and we find that the allowed parameter space strongly discourages a strong first order phase transition within the 2HDM-II.

0 citations0 reviewsNo code linkedOpen access
preprint2022arXiv

MUonE, muon $g-2$ and electroweak precision constraints within 2HDMs

Two Higgs doublet models are attractive scenarios for physics beyond the Standard Model. In particular, lepton-specific manifestations remain contenders to explain the observed discrepancy between the anomalous magnetic moment of the muon $a_μ$ predicted within the Standard Model and recent observations at Fermilab and BNL. Dominant uncertainties that affect $a_μ$ have motivated the MUonE experiment to access the hadronic vacuum polarisation contribution that impacts $a_μ$ via elastic muon-electron scattering. In this work, we contrast the high precision that is achievable within the MUonE context with constraints from flavour physics, precision electroweak constraints and LHC searches as well as their extrapolations for a range of two Higgs doublet models with a softly broken $\mathbb{Z}_2$ symmetry. We find that the sensitivity of MUonE does not extend beyond the parameter regions that are already excluded by other constraints. MUonE will therefore provide a detailed measurement of the hadronic vacuum polarisation contribution which then transparently informs $a_μ$ interpretations in 2HDMs without modifications of correlations from beyond the Standard Model interactions. In passing we extend earlier results of LHC and flavour projections to lepton-specific 2HDM (Types X and Y) scenarios, and comment on the possibility of modifying the value of the W-boson mass; we briefly discuss the implications for a strong first-order electroweak phase transition for these models.

0 citations0 reviewsNo code linkedOpen access
preprint2021arXiv

$SU(3)$ breaking effects in $B$ and $D$ meson lifetimes

In the heavy quark expansion (HQE) of the total decay rates of $B_s$ and $D_s^+$ mesons non-perturbative matrix elements of four quark operators are arising as phase space enhanced contributions. We present the first determination of $m_s$ effects to the dimension six matrix elements of these four quark operators via a heavy quark effective theory (HQET) sum rule analysis. In addition we calculate for the first time eye contractions of the four quark operators as well as matrix elements of penguin operators. For the perturbative part we solve the 3-loop contribution to the sum rule and we evaluate condensate contributions. In this study we work in the strict HQET limit and our results can also be used to estimate the size of the matrix element of the Darwin operator via equations of motion.

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preprint2021arXiv

Contribution of the Darwin operator to non-leptonic decays of heavy quarks

We compute the Darwin operator contribution ($1/m_b^3$ correction) to the width of the inclusive non-leptonic decay of a $B$ meson ($B^+$, $B_d$ or $B_s$), stemming from the quark flavour-changing transition $b \to q_1 \bar q_2 q_3$, where $q_1,q_2 = u, c$ and $q_3 = d, s$. The key ideas of the computation are the local expansion of the quark propagator in the external gluon field including terms with covariant derivative of the gluon field strength tensor and the standard technique of the Heavy Quark Expansion (HQE). We confirm the previously known expressions of the $1/m_b^3$ contributions to the semi-leptonic decay $b \to q_1 \ell \bar ν_\ell$, with $\ell = e, μ, τ$ and of the $1/m_b^2$ contributions to the non-leptonic modes. We find that this new term can give a sizeable correction of about $- 4 \, \%$ to the non-leptonic decay width of a $B$ meson. For $B_d$ and $B_s$ mesons this turns out to be the dominant correction to the free b-quark decay, while for the $B^+$ meson the Darwin term gives the second most important correction - roughly 1/2 to 1/3 of the phase space enhanced Pauli interference contribution. Due to the tiny experimental uncertainties in lifetime measurements the incorporation of the Darwin term contribution is crucial for precision tests of the Standard Model.

0 citations0 reviewsNo code linkedOpen access
preprint2021arXiv

Revisiting Inclusive Decay Widths of Charmed Mesons

Determining for the first time the Darwin operator contribution for the non-leptonic charm-quark decays and using new non-perturbative results for the matrix elements of $ΔC=0$ four-quark operators, including eye-contractions, we present a comprehensive study of the lifetimes of charmed mesons and inclusive semileptonic decay rates as well as the ratios, within the framework of the Heavy Quark Expansion (HQE). We find good agreement with experiment for the ratio $τ(D^+)/τ(D^0)$, for the total $D_s^+$-meson decay rate, for the semileptonic rates of all three mesons $D^0$, $D^+$ and $D_s^+$, and for the semileptonic ratio $Γ_{sl}^{D^+}/Γ_{sl}^{D^0}$. The total decay rates of the $D^0$ and $D^+$ mesons are underestimated in our HQE approach and we suspect that this is due to missing higher-order QCD corrections to the free charm quark decay and the Pauli interference contribution. For the $SU(3)_F$ breaking ratios $τ(D_s^+) / τ(D^0) $ and $Γ_{sl}^{D_s^+}/Γ_{sl}^{D^0} $ our predictions lie closer to one than experiment. This might originate from the poor knowledge of the non-perturbative parameters $μ_G^2$, $μ_π^2$ and $ρ_D^3$ in the $D^0$ and $D_s^+$ systems. These parameters could be determined by experimental studies of the moments of inclusive semileptonic $D$ meson decays.

0 citations0 reviewsNo code linkedOpen access
preprint2021arXiv

Testing the Standard Model with CP-asymmetries in flavour-specific non-leptonic decays

Motivated by recent indications that the rates of colour-allowed non-leptonic channels are not in agreement with their Standard Model expectations based on QCD factorisation, we investigate the potential to study CP asymmetries with these decays. In the Standard Model, these flavour-specific decays are sensitive to CP violation in $B^0_{(s)}$--$\bar{B}^0_{(s)}$ mixing, which is predicted with low uncertainties and can be measured precisely with semileptonic decays. If there are beyond Standard Model contributions to the non-leptonic decay amplitudes, there could be significant enhancements to the CP asymmetries. Measurements of these quantities therefore have potential to identify BSM effects without relying on Standard Model predictions that might be affected by hadronic effects. We discuss the experimental prospects, and note the excellent potential for a precise determination of the CP asymmetry in $\bar{B}_s \to D_s^+ π^-$ decays by the LHCb experiment.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

$|V_{cb}|$ and $γ$ from $B$-mixing -- Addendum to "$B_s$ mixing observables and $|V_{td}/V_{ts}|$ from sum rules"

In this addendum to "$B_s$ mixing observables and $|V_{td}/V_{ts}|$ from sum rules" \cite{King:2019lal} we study the impact of the recent improvements in the theoretical precision of $B$ meson mixing onto CKM unitarity fits. Our key results are the most precise determination of the angle $γ= \left(63.4\pm0.9\right)^\circ$ in the unitarity triangle and a new value for the CKM element $|V_{cb}|=(41.6\pm0.7)\cdot10^{-3}$.

0 citations0 reviewsNo code linkedOpen access
preprint2020arXiv

Model-independent bounds on new physics effects in non-leptonic tree-level decays of B-mesons

We present a considerably improved analysis of model-independent bounds on new physics effects in non-leptonic tree-level decays of B-mesons. Our main finding is that contributions of about $\pm 0.1 $ to the Wilson coefficient of the colour-singlet operator $Q_2$ of the effective weak Hamiltonian and contributions in the range of $\pm 0.5$ (both for real and imaginary part) to $Q_1$ can currently not be excluded at the $90\%$ C.L.. Effects of such a size can modify the direct experimental extraction of the CKM angle $γ$ by up to $10^{\circ}$ and they could lead to an enhancement of the decay rate difference $ΔΓ_d$ of up to a factor of 5 over its SM value - a size that could explain the D0 dimuon asymmetry. Future more precise measurements of the semi-leptonic asymmetries $a_{sl}^q$ and the lifetime ratio $τ(B_s) / τ(B_d)$ will allow to shrink the bounds on tree-level new physics effects considerably. Due to significant improvements in the precision of the non-perturbative input we update all SM predictions for the mixing obervables in the course of this analysis, obtaining: $ΔM_s = (18.77 \pm 0.86 ) \, \mbox{ps}^{-1}$, $ΔM_d = (0.543 \pm 0.029) \, \mbox{ps}^{-1}$, $ΔΓ_s = (9.1 \pm 1.3 ) \cdot 10^{-2} \, \mbox{ps}^{-1}$, $ΔΓ_d = (2.6 \pm 0.4 ) \cdot 10^{-3} \, \mbox{ps}^{-1}$, $a_{sl}^s = (2.06 \pm 0.18) \cdot 10^{-5}$ and $a_{sl}^d = (-4.73 \pm 0.42) \cdot 10^{-4}$.

0 citations0 reviewsNo code linkedOpen access
preprint2015arXiv

On new physics in $ΔΓ_d$

Motivated by the recent measurement of the dimuon asymmetry by the DØ collaboration, which could be interpreted as an enhanced decay rate difference in the neutral $B_d$-meson system, we investigate the possible size of new-physics contributions to $ΔΓ_d$. In particular, we perform model-independent studies of non-standard effects associated to the dimension-six current-current operators $(\bar{d} p)(\bar p^{\hspace{0.25mm}\prime} b)$ with $p,p^\prime= u,c$ as well as $(\bar{d}b) (\barττ)$. In both cases we find that for certain flavour or Lorentz structures of the operators sizable deviations of $ΔΓ_d$ away from the Standard Model expectation cannot be excluded in a model-independent fashion.

0 citations0 reviewsNo code linkedOpen access
preprint2014arXiv

$B$-mixing in and beyond the Standard model

We review the status of mixing of neutral $B$-mesons, including a discussion of the current precision of Standard Model (SM) predictions as well as the space that is left for effects of new physics. In that respect we present several observables, which are particularly sensitive to the remaining new physics (NP) parameter space. $B$-mixing can also be used to test the fundaments of quantum mechanics, here we suggest a new measurement of the ratio of like-sign dilepton events to opposite-sign dilepton events. Finally we summarise briefly the status of lifetimes of heavy hadrons. The corresponding theory predictions rely on the same tool - the Heavy Quark Expansion (HQE) - as some of the mixing quantities. New experimental data has recently proven the validity of the HQE to a high accuracy. However, the theoretical precision of lifetime predictions is strongly limited by a lack of non-perturbative evaluations of matrix elements of dimension-six operators.

0 citations0 reviewsNo code linkedOpen access
preprint2014arXiv

Investigating bounds on decoherence in quantum mechanics via B and D-mixing

We investigate bounds on decoherence in quantum mechanics by studying $B$ and $D$-mixing observables, making use of many precise new measurements, particularly from the LHC and B factories. In that respect we show that the stringent bounds obtained by a different group in 2013 rely on unjustified assumptions. Finally, we point out which experimental measurements could improve the decoherence bounds considerably.

0 citations0 reviewsNo code linkedOpen access
preprint2014arXiv

New physics effects in tree-level decays

We critically review the assumption that no new physics is acting in tree-level $B$-meson decays and study the consequences for the ultimate precision in the direct determination of the CKM angle $γ$. In our exploratory study we find that sizable universal new physics contributions, $ΔC_{1,2}$, to the tree-level Wilson coefficients $C_{1,2}$ of the effective Hamiltonian describing weak decays of the $b$ quark are currently not excluded by experimental data. In particular we find that Im $ΔC_1 $ and Im $ΔC_2 $ can easily be of order $\pm 10%$ without violating any constraints from data. Such a size of new physics effects in $C_1$ and $C_2$ corresponds to an intrinsic uncertainty in the CKM angle $γ$ of the order of $|δγ| \approx 4^\circ$, which is slightly below the current experimental precision. The accuracy in the determination of $γ$ can be improved by putting stronger constraints on the tree-level Wilson coefficients, in particular $C_1$. To this end we suggest a more refined theoretical study as well as a more precise measurements of the observables that currently provide the strongest bounds on hypothetical new weak phases in $C_1$ and $C_2$. We note that the semi-leptonic CP asymmetries seem to have the best prospect for improving the bound on the weak phase in $C_1$.

0 citations0 reviewsNo code linkedOpen access
preprint2014arXiv

Selected Topics in Heavy Flavour Physics

We review the status of flavour physics in spring 2014. The numerous accurate new measurements of flavour experiments have enabled us to test our theoretical understanding of flavour processes with an unprecedented precision. At first sight the dominant amount of measurements seems to be standard model like. Having a closer look one finds, however, that in most of the observables there is still some considerable space for new effects. In addition many discrepancies are still not settled yet. For further investigations and definite conclusions an improvement of the theoretical precision as well as the experimental one is mandatory.

0 citations0 reviewsNo code linkedOpen access
preprint2013arXiv

D-meson lifetimes within the heavy quark expansion

Even if new data indicate that direct CP violation in D-meson decays is compatible with the standard model expectation, it has triggered a lot of interest, and charm phenomenology will remain an essential part of new physics searches due to its unique role as a probe for flavor-changing neutral currents among up-type quarks. Charm physics poses considerable theoretical challenges, because the charm mass is neither light nor truly heavy. The heavy quark expansion (HQE) provides a perturbative expansion in the inverse heavy quark mass for inclusive rates. It has proved to be very successful in the B sector, yet its validity for charm decays has often been questioned. We present results of a HQE study of D-meson lifetimes including NLO QCD and subleading 1/m_c corrections. We find good agreement with experimental data, but with huge hadronic uncertainties due to missing lattice input for hadronic matrix elements.

0 citations0 reviewsNo code linkedOpen access
preprint2013arXiv

Short distance D-Dbar mixing

We review the status of Standard Model predictions for lifetimes and mixing rates of charmed mesons. It is shown that the short distance approach is able to reproduce tau(D^+)/tau(D^0) at leading order in the 1/m_c expansion. SU(3) violating effects from interactions with the soft hadronic background are identified as the dominant contribution to the D-Dbar mixing rate. We discuss the contribution from operators of dimension nine, which is able to enhance the neutral charm width splitting by a factor of order ten and comment on possible CP violation in mixing.

0 citations0 reviewsNo code linkedOpen access
preprint2013arXiv

The inclusive decay b to ccs revisited

The inclusive decay rate b to ccs is enhanced considerably due to perturbative QCD corrections. We recalculate the dominant part of the NLO-QCD corrections, because they cannot be reconstructed from the literature and we give the full expressions in this paper. Further we include some previously neglected corrections originating from penguin diagrams. Combined with the impressive progress in the accurate determination of input parameters like charm quark mass, bottom quark mass and CKM parameters, this enables us to make a very precise prediction of the corresponding branching ratio Br (b to ccs) = (23 pm 2)%. This result is an essential ingredient for a model and even decay channel independent search for new physics effects in B decays.

0 citations0 reviewsNo code linkedOpen access
preprint2013arXiv

What did we learn in theory from the $ΔA_{CP}$-saga?

The measurement of CP violation in the charm sector triggered a lot of theoretical activities and re-considerations. Nevertheless currently neither theory nor experiment have reached definite conclusions about the origin of a large CP violating effect in hadronic $D$ decays. We review briefly (part of) the current theory literature and present as the most important outcome of the many investigations initial steps in a long journey to understand the standard model contribution to hadronic $D$ meson decays from first principles as well as various control channels, that can be studied by experiment.

0 citations0 reviewsNo code linkedOpen access
preprint2012arXiv

A simple relation for B_s-mixing

We reinvestigate a simple relation between the semileptonic CP asymmetry a_{sl}^s, the decay rate difference ΔΓ_s, the mass difference ΔM_s and S_{ψϕ} extracted from the angular analysis of the decay B_s \to ψϕ, which is regularly used in the literature. We find that this relation is not suited to eliminate the theory prediction for Γ_{12}, it can, however be used to determine the size of the penguin contributions to the decay B_s \to ψϕ. Moreover we comment on the current precision of the theory prediction for Γ_{12}.

0 citations0 reviewsNo code linkedOpen access
preprint2012arXiv

Fourth Generation Majorana Neutrinos

We investigate the possibility of a fourth sequential generation in the lepton sector. Assuming neutrinos to be Majorana particles and starting from a recent - albeit weak - evidence for a non-zero admixture of a fourth generation neutrino from fits to weak lepton and meson decays we discuss constraints from neutrinoless double beta decay, radiative lepton decay and like-sign dilepton production at hadron colliders. Also an idea for fourth generation neutrino mass model building is briefly outlined. Here we soften the large hierarchy of the neutrino masses within an extradimensional model that locates each generation on different lepton number violating branes without large hierarchies.

0 citations0 reviewsNo code linkedOpen access
preprint2012arXiv

Impact of a Higgs boson at a mass of 126 GeV on the standard model with three and four fermion generations

We perform a comprehensive statistical analysis of the standard model (SM) with three and four generations using the latest Higgs search results from LHC and Tevatron, the electroweak precision observables (EWPOs) measured at LEP and SLD and the latest determinations of M_W, m_t and alpha_s. For the three-generation case we analyse the tensions in the electroweak fit by removing individual observables from the fit and comparing their predicted values with the measured ones. In particular, we discuss the impact of the Higgs search results on the deviations of the EWPOs from their best-fit values. Our indirect prediction of the top mass is m_t=175.7(+3.0)(-2.2) GeV at 68.3% CL, in good agreement with the direct measurement. We also plot the preferred area in the M_W - m_t plane. The best-fit Higgs mass is 126.0 GeV. For the case of the SM with a perturbative sequential fourth fermion generation (SM4) we discuss the deviations of the Higgs signal strengths from their best-fit values. The H -> gamma gamma signal strength now disagrees with its best-fit SM4 value at more than 4 sigma. We perform a likelihood-ratio test to compare the SM and SM4 and show that the SM4 is excluded at 5.3 sigma. Without the Tevatron data on H -> b bbar the significance drops to 4.8 sigma.

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preprint2012arXiv

Joint analysis of Higgs decays and electroweak precision observables in the Standard Model with a sequential fourth generation

We analyse the impact of LHC and Tevatron Higgs data on the viability of the Standard Model with a sequential fourth generation (SM4), assuming Dirac neutrinos and a Higgs mass of 125 GeV. To this end we perform a combined fit to the signal cross sections of pp -> H -> gamma gamma,ZZ*,WW* at the LHC, to p pbar -> VH -> V b bbar (V = W, Z) at the Tevatron and to the electroweak precision observables. Fixing the mass of the fourth generation down-type quark b' to 600 GeV we find best-fit values of m_t' = 632 GeV, m_l4 = 113.6 GeV and m_nu4 = 58.0 GeV for the other fourth-generation fermion masses. We compare the chi-square values and pulls of the different observables in the three and four-generation case and show that the data is better described by the three-generation Standard Model. We also investigate the effects of mixing between the third and fourth-generation quarks and of a future increased lower bound on the fourth-generation charged lepton mass of 250 GeV.

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preprint2012arXiv

Sealing the fate of a fourth generation of fermions

The search for the effects of heavy fermions in the extension of the Standard Model with a fourth generation is part of the experimental program of the Tevatron and LHC experiments. Besides being directly produced, these states affect drastically the production and decay properties of the Higgs boson. In this note, we first reemphasize the known fact that in the case of a light and long-lived fourth neutrino, the present collider searches do not permit to exclude a Higgs boson with a mass below the WW threshold. In a second step, we show that the recent results from the ATLAS and CMS collaborations which observe an excess in the $γγ$ and $4\ell^\pm$ search channels corresponding to a Higgs boson with a mass $M_H \approx 125$ GeV, cannot rule out the fourth generation possibility if the $H \to γγ$ decay rate is evaluated when naively implementing the leading ${\cal O}(G_F m_{f'}^2)$ electroweak corrections. Including the exact next-to-leading order electroweak corrections leads to a strong suppression of the $H \to γγ$ rate and makes this channel unobservable with present data. Finally, we point out that the observation by the Tevatron collaborations of a $\gsim 2σ$ excess in the mass range $M_H = 115$-135 GeV in the channel $q\bar q \to WH \to Wb\bar b$ can definitely not be accommodated by the fourth generation fermion scenario. All in all, if the excesses observed at the LHC and the Tevatron are indeed due to a Higgs boson, they unambiguously exclude the perturbative fermionic fourth generation case. In passing, we also point out that the Tevatron excess definitely rules out the fermiophobic Higgs scenario as well as scenarios in which the Higgs couplings to gauge bosons and bottom quarks are significantly reduced.

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preprint2012arXiv

Status of the fourth fermion generation before ICHEP2012: Higgs data and electroweak precision observables

We perform a global fit of the parameters of the Standard Model with a sequential fourth generation (SM4) to LHC and Tevatron Higgs data and electroweak precision data. Using several likelihood ratio tests we compare the performance of the SM4 and SM3 at describing the measured data. Since the SM3 and SM4 are not nested (i.e. the SM3 can not be considered as a special case of the SM4 with some parameters fixed) the usual analytical formulae for p-values in likelihood ratio tests do not hold. We thus apply a new method to compute these p-values. For a Higgs mass of 126.5 GeV and fourth-generation quark masses above 600 GeV we find that the SM4 is excluded at 3.1 sigma.

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preprint2012arXiv

Theoretical status of $B_s$-mixing and lifetimes of heavy hadrons

We review the theoretical status of the lifetime ratios $τ_{B^+} / τ_{B_d}$, $τ_{B_s} / τ_{B_d}$, $τ_{Λ_b} / τ_{B_d}$ and $τ_{B_c}$ and of the mixing quantities $ΔM_s$, $ΔΓ_s$ and $ϕ_s$. $ΔM_s$ and $ΔΓ_s$ suffer from large uncertainties due to the badly known decay constants, while the ratio $ΔΓ_s / ΔM_s$ can be determined with almost no non-perturbative uncertainties, therefore it can be used perfectly to find possible new physics contributions in the mixing parameters. We suggest a very clear method of visualizing the bounds on new physics and demonstrate this by combining the latest experimental numbers on the mixing quantities quantities with theory - one already gets some hints for new physics contributions, but more precise experimental numbers are needed to draw some definite conclusions. We conclude with a ranking list of all the discussed quantities according to their current theoretical uncertainties and point out possible improvements.

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preprint2012arXiv

Theoretical update of $B$-Mixing and Lifetimes

We review the current status of theoretical predictions for mixing quantities and lifetimes in the $B$-sector. In particular, due to the first non-zero measurement of the decay rate difference in the neutral $B_s$-system, $ΔΓ_s/ Γ_s = 17.6 % \pm 2.9 %$ by the LHCb collaboration and very precise data for $τ_{B_s}$ from TeVatron and LHCb our theoretical tools can now be rigorously tested and it turns out that the Heavy Quark Expansion works in the $B$-system to an accuracy of at least 30% for quantities like $Γ_{12}$, which is most sensitive to hypothetical violations of quark hadron duality. This issue that gave rise in the past to numerous theoretical papers, has now been settled experimentally. Further data will even allow to shrink this bound. For total inclusive quantities like lifetimes the compliance is even more astonishing: $τ_{B_s}^{\rm LHCb}/ τ_{B_d}^{\rm HFAG} = 1.001 \pm 0.014$ is in perfect agreement with the theory expectation of $τ_{B_s}/τ_{B_d} = 0.996 ... 1.000$. Despite the fact that the new data show no deviations from the standard model expectations, there is still some sizable room for new physics effects. Model-independent search strategies for these effects are presented with an emphasis on the interconnection with many different observables that have to be taken into account. In that respect a special emphasis is given to the large value of the di-muon asymmetry measured by the D0 collaboration.

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preprint2011arXiv

Numerical updates of lifetimes and mixing parameters of B mesons

We update the Standard-Model predictions for several quantities related to $B_s - \bar B_s$ and $B_d - \bar B_d$ mixing. The mass and width differences in the $B_s$ system read $ ΔM_s^{\rm SM} = (17.3 \pm 2.6) ps^{-1}$ and $ΔΓ_s^{\rm SM}= (0.087 \pm 0.021) ps^{-1}$, respectively. The CP asymmetries in flavour-specific decays are $a_{\rm fs}^{s,\rm SM} = (1.9 \pm 0.3) \cdot 10^{-5}$ and $a_{\rm fs}^{d,\rm SM} = - (4.1 \pm 0.6) \cdot 10^{-4}$. We further critically discuss the sensitivity of $ΔΓ_d$ to new physics and the uncertainties in the relation between $ΔΓ_s$ and the branching fraction of $B_s \to D_s^{(*)}{}^+ D_s^{(*)}{}^-$. Then we present a numerical update of the average width $Γ_s$ in the $B_s$ system and correlate $Γ_s$ with the $B^+$-$B_d$ lifetime ratio. Finally we summarise the key results of our recent global analysis with the CKMfitter collaboration addressing new physics in $B - \bar B$-mixing. In an appropriately defined scenario parametrising new physics in $B - \bar B$-mixing by two complex parameters $Δ_d$ and $Δ_s$ the Standard-Model point {$Δ_d=Δ_s=1$} is disfavoured by 3.6 standard deviations.

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preprint2011arXiv

Summary of WG4: "Lifetime, mixing and weak mixing phase in charm and beauty, including direct determination of V_{tx}

We present the summary of the Working Group on lifetimes, mixing and weak mixing phases in charm and beauty mesons at the CKM 2010 workshop. In the past year or so good progress was achieved on both experimental and theoretical sides. While this yields improvement in our understanding of neutral meson mixing, further work is necessary to achieve the highest possible precision in order to investigate current hints for deviations between experiment and standard model predictions. With the recent LHC startup we see bright prospects for the near term future for huge improvements.

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preprint2010arXiv

Charm mixing in the Standard Model

In this talk we report on a study on the mixing of neutral charmed mesons and argue that, at the present stage, a CP violating weak phase of the order of some per mille can not be excluded in the Standard Model. It is shown how some, seemingly reasonable, simplifying assumptions about CKM couplings lead to the wrong conclusion that CP violation of this amount is an unambiguous indication of new physics. The presented results rely on a recent short-distance analysis of the Delta C=2 transition, which confirms the expectation that the dominant contribution is due to effects of flavour symmetry breaking appearing in higher orders of the Heavy Quark Expansion. We investigate meson-antimeson transitions with an intermediate state coupling to the meson's sea quark background, present in dimension 10 and 12, using a factorisation approach to simplify the operator basis. On account of a lifting of GIM suppression by one power of m_s/m_c, the contribution to y=Delta Gamma/2 Gamma is found to exceed that of the formally leading dimension six by a factor close to ten.

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preprint2010arXiv

Constraints on fourth generation Majorana neutrinos

We investigate the possibility of a fourth sequential generation in the lepton sector. Assuming neutrinos to be Majorana particles and starting from a recent - albeit weak - evidence for a non-zero admixture of a fourth generation neutrino from fits to weak lepton and meson decays we discuss constraints from neutrinoless double beta decay, radiative lepton decay and like-sign di-lepton production at hadron colliders.

0 citations0 reviewsNo code linkedOpen access
preprint2010arXiv

Large loop effects of extra SUSY Higgs doublets to CP violation in B^0 mixing

We consider more than one pair of SU(2)_L doublet Higgs supermultiplets in a generic supersymmetric extension of the standard model, and calculate their one-loop contributions to the soft mass insertions delta_{LL} etc. We find that if large supersymmetry breaking in this sector is realized, the loop effects can give rise to large contributions to the soft mass insertions, meaning that they We apply our result to a recently proposed model based on the discrete Q_6 family group, and calculate the non-diagonal matrix element M_{12} of the neutral meson systems. We focus our attention on the extra phases phi_{d,s}^Delta in B_{d,s}-mixing and flavor-specific CP-asymmetries a_{sl}^{d,s} in neutral B decays and obtain values that can be about one order of magnitude larger than the standard model predictions. Our final results are comparable with the recent experimental observations at D0 and CDF, but they are still about a factor of 5 smaller than the recently measured dimuon asymmetry from D0.

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preprint2010arXiv

Less space for a new family of fermions

We investigate the experimentally allowed parameter space of an extension of the standard model (SM3) by one additional family of fermions. Therefore we extend our previous study of the CKM like mixing constraints of a fourth generation of quarks. In addition to the bounds from tree-level determinations of the 3$\times$3 CKM elements and FCNC processes ($K$-, $D$-, $B_d$-, $B_s$-mixing and the decay $b \to s γ$) we also investigate the electroweak $S$, $T$, $U$ parameters, the angle $γ$ of the unitarity triangle and the rare decay $B_s \to μ^+ μ^-$. Moreover we improve our treatment of the QCD corrections compared to our previous analysis. We also take leptonic contributions into account, but we neglect the mixing among leptons. As a result we find that typically small mixing with the fourth family is favored, but still some sizeable deviations from the SM3 results are not yet excluded. The minimal possible value of $V_{tb}$ is 0.93. Also very large CP-violating effects in $B_s$ mixing seem to be impossible within an extension of the SM3 that consists of an additional fermion family alone. We find a delicate interplay of electroweak and flavor observables, which strongly suggests that a separate treatment of the two sectors is not feasible. In particular we show that the inclusion of the full CKM dependence of the $S$ and $T$ parameters in principle allows the existence of a degenerate fourth generation of quarks.

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preprint2010arXiv

The optimal angle of Release in Shot Put

We determine the optimal angle of release in shot put. The simplest model - mostly used in textbooks - gives a value of $45^\circ$, while measurements of top athletes cluster around $37 - 38^\circ$. Including simply the height of the athlete the theory prediction goes down to about $42^\circ$ for typical parameters of top athletes. Taking further the correlations of the initial velocity of the shot, the angle of release and the height of release into account we predict values around $37 - 38^\circ$, which coincide perfectly with the measurements.

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preprint2010arXiv

Triangle Relation of Dark Matter, EDM and CP Violation in B0 Mixing in a Supersymmetric Q6 Model

We consider a recently proposed supersymmetric model based on the discrete Q6 family group.Because of the family symmetry and spontaneous CP violation the electric dipole moment (EDM), the CP violation in the mixing of the neural mesons and the dark matter mass m_DM are closely related. This triangle relation is controlled by the size of the mu parameters. Loop effects can give rise to large contributions to the soft mass insertions, and we find that the model allows a large CP violation in the B0 system. Its size is comparable with the recent experimental observations at D0 and CDF, and it could be observed at LHCb in the first years. If the parameter space is constrained by the neutron EDM, and flavor changing neutral currents and CP violations in K0 as well as B0 mixing, the triangle relation yields the following bound on the dark matter candidate: 0.12 TeV < m_DM < 0.33 TeV, which is directly observable at LHC. We also compute a_sl^s - a_sl^d, which is observable at LHCb, where a_sl^s(d) is the semi-leptonic CP asymmetryfor the B_s(d) system.

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preprint2009arXiv

How much space is left for a new family?

We perform an exploratory study of the allowed parameter range for the CKM-like mixing of hypothetical quarks of a fourth generation. As experimental constraints we use the tree-level determinations of the 3 $\times$ 3 CKM elements and FCNC processes ($K$-, $D$-, $B_d$-, $B_s$-mixing and the decay $b \to s γ$) under the assumption that the 4 $\times$ 4 CKM matrix is unitary. For the FCNCs we use some simplifying assumptions concerning the QCD corrections. Typically small mixing with the fourth family is favoured, but contrary to expectation we find that also a quite large mixing with the 4th family is not yet excluded.

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preprint2009arXiv

Testing the new CP phase in a Supersymmetric Model with Q6 Family Symmetry by Bs Mixing

The new contribution to the non-diagonal matrix element M_12 of the neutral B_s meson system is investigated in a supersymmetric extension of the standard model based on the discrete Q6 family symmetry. We assume that CP is explicitly, but softly broken only by the b terms in the soft supersymmetry breaking sector. We find that the new contributions to M_12 are real, and that nevertheless there exists an observable difference in the CP phase compared with the standard model. We focus our attention on the flavor-specific CP asymmetry a_fs^s, and find that a_fs^s of the model is mostly negative and its size can be one order of magnitude larger the standard model value. This prediction is consistent with the current experimental value, and can be experimentally tested in the near future.

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preprint2007arXiv

Theoretical update of Bs-Bs-bar mixing

We update the theory predictions for the mass difference $\dm_s$, the width difference $\dg_s$ and the CP asymmetry in flavour-specific decays, $a_{\rm fs}^{s}$, for the \bbs system. In particular we present a new expression for the element $Γ_{12}^s$ of the decay matrix, which enters the predictions of $\dg_s$ and $a_{\rm fs}^{s}$. To this end we introduce a new operator basis, which reduces the troublesome sizes of the $1/m_b$ and $α_s$ corrections and diminishes the hadronic uncertainty in $\dg_s/\dm_s$ considerably. Logarithms of the charm quark mass are summed to all orders. We find $\dg_s/\dm_s= (49.7 \pm 9.4) \cdot 10^{-4}$ and $\dg_s =(f_{B_s}/240 {\rm MeV})^2 [(0.105 \pm 0.016) B + (0.024 \pm 0.004) \tilde{B}_S' - 0.027 \pm 0.015] {ps}^{-1}$ in terms of the bag parameters $B$, $\tilde{B}_S'$ in the NDR scheme and the decay constant $f_{B_s}$. The improved result for $Γ_{12}^s$ also permits the extraction of the CP-violating \bbms phase from $a_{\rm fs}^{s}$ with better accuracy. We show how the measurements of $ΔM_s$, $ΔΓ_s$, $a_{\rm fs}^{s}$, $A_{\rm CP}^{\rm mix}(B_s\to J/ψϕ)$ and other observables can be efficiently combined to constrain new physics. Applying our new formulae to data from the DØexperiment, we find a 2$σ$ deviation of the \bbms phase from its Standard Model value. We also briefly update the theory predictions for the \bbd system and find $\dg_d/\dm_d = \lt(52.6 \epm{11.5}{12.8} \rt) \cdot 10^{-4}$ and $a_{\rm fs}^d = \lt(-4.8\epm{1.0}{1.2} \rt) \cdot 10^{-4}$ in the Standard Model.

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preprint2003arXiv

Improved Light-Cone Sum Rules for the Electromagnetic Form Factors of the Nucleon

We calculate the electromagnetic form factors of the nucleon within the light-cone sum rule approach. In comparison to previous work (hep-ph/0112085) we suggest to use a pure isospin-1/2 interpolating field for the nucleon, since the Chernyak-Zhitnitsky current leads to numerically large, unphysical, isospin violating contributions. The leading-order sum rules are derived for the form factors and the results are confronted with the experimental data. Our approach tends to favor the nucleon distribution amplitudes that are not far from the asymptotic shape.

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preprint1997arXiv

Penguin Diagrams, Charmless B-Decays and the ``Missing Charm Puzzle''

We calculate the contributions of penguin diagrams with internal u or c quarks to various inclusive charmless B-decay rates. Further we analyze the influence of the chromomagnetic dipole operator Q_8 on these rates. We find that the rates corresponding to B-bar --> X_{u u-bar s}, B-bar --> X_{d d-bar s}, B-bar --> X_{s s-bar s}, B-bar --> X_{s s-bar d} and B --> X_{d d-bar d} are dominated by the new penguin contributions. The contributions of Q_8 sizably diminish these rates. Despite of an increase of the total charmless decay rate by 36 % the new contributions are not large enough to explain the charm deficit observed by ARGUS and CLEO. We predict n_c=1.33 +/- 0.06 for the average number of charmed particles per B-decay in the Standard Model. Then the hypothesis of an enhancement of the chromomagnetic dipole coefficient C_8 by new physics contributions is analyzed. We perform a model independent fit of C_8 to the experimental data. If the CKM structure of the new physics contribution is the same as in the Standard Model, |C_8(M_W)| must be enhanced by a factor of 9 to 16 in order to explain the observed charm deficit.

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