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M. Ciuchini

Publications and source records attributed to M. Ciuchini.

At least 37 records · Page 2Linked to original sources
arXiv2009

Status of the Unitarity Triangle Analysis

We present an update of the Unitarity Triangle (UT) analysis, within the Standard Model (SM) and beyond. Within the SM the main novelties are the inclusion in epsilon_K of the contributions of xi and phi_epsilon \neq π/4 pointed out by A.J. Buras and D. Guadagnoli, and an accurate prediction of BR(B -> tau nu), by using the indirect determination of |V_ub| from the UT fit, which can be compared to the present experimental result. In the generalization of the UT analysis to investigate New Physics (NP) effects, the estimate of xi is more delicate and only the effect of phi_epsilon \neq π/4 has been included. We confirm an hint of NP in the B_s-\bar B_s mixing at the 2.9 sigma level, which makes a comparison with new experimental data certainly desired.

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arXiv2009

New Physics from Flavour

The UT{\it{fit}} Collaboration has produced several analyses in the context of flavour physics both within and beyond the Standard Model. In this paper we present updated results for the Standard Model analysis of the Unitarity Triangle using the latest experimental and lattice QCD inputs, as well as an update of the Unitarity Triangle analysis in a scenario beyond the Standard Model. Combining all available experimental and theoretical information on $ΔF=2$ processes and using a model-independent parameterization, we extract the allowed New Physics contributions in the $K^0$, $D^0$, $B_d$, and $B_s$ sectors. We observe a departure of the $B_s$ mixing phase from the Standard Model expectation with a significance of about $3σ$.

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arXiv2009

Searching For New Physics With B to K pi Decays

We propose a method to quantify the Standard Model uncertainty in B to K pi decays using the experimental data, assuming that power counting provides a reasonable estimate of the subleading terms in the 1/mb expansion. Using this method, we show that present B to K pi data are compatible with the Standard Model. We analyze the pattern of subleading terms required to reproduce the B to K pi data and argue that anomalously large subleading terms are not needed. Finally, we find that S(KS pi0) is fairly insensitive to hadronic uncertainties and obtain the Standard Model estimate S(KS pi0)=0.74 +- 0.04.

hep-ph↗
arXiv2008

Proceedings of SuperB Workshop VI: New Physics at the Super Flavor Factory

The sixth SuperB Workshop was convened in response to questions posed by the INFN Review Committee, evaluating the SuperB project at the request of INFN. The working groups addressed the capability of a high-luminosity flavor factory that can gather a data sample of 50 to 75 /ab in five years to elucidate New Physics phenomena unearthed at the LHC. This report summarizes the results of the Workshop.

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arXiv2008

Model-independent constraints on Delta F=2 operators and the scale of New Physics

We update the constraints on new-physics contributions to Delta F=2 processes from the generalized unitarity triangle analysis, including the most recent experimental developments. Based on these constraints, we derive upper bounds on the coefficients of the most general Delta F=2 effective Hamiltonian. These upper bounds can be translated into lower bounds on the scale of new physics that contributes to these low-energy effective interactions. We point out that, due to the enhancement in the renormalization group evolution and in the matrix elements, the coefficients of non-standard operators are much more constrained than the coefficient of the operator present in the Standard Model. Therefore, the scale of new physics in models that generate new Delta F=2 operators, such as next-to-minimal flavour violation, has to be much higher than the scale of minimal flavour violation, and it most probably lies beyond the reach of direct searches at the LHC.

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arXiv2008

B, D and K decays

With the advent of the LHC, we will be able to probe New Physics (NP) up to energy scales almost one order of magnitude larger than it has been possible with present accelerator facilities. While direct detection of new particles will be the main avenue to establish the presence of NP at the LHC, indirect searches will provide precious complementary information, since most probably it will not be possible to measure the full spectrum of new particles and their couplings through direct production. In particular, precision measurements and computations in the realm of flavour physics are expected to play a key role in constraining the unknown parameters of the Lagrangian of any NP model emerging from direct searches at the LHC. The aim of Working Group 2 was twofold: on one hand, to provide a coherent, up-to-date picture of the status of flavour physics before the start of the LHC; on the other hand, to initiate activities on the path towards integrating information on NP from high-pT and flavour data.

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arXiv2007

B_s to K^(*)0 \bar K^(*)0 decays: the golden channels for new physics searches

We point out that time-dependent CP asymmetries in B_s to K^{*0} \bar K^{*0} decays probe the presence of new physics in b to s transitions with an unprecedented theoretical accuracy. We show that, contrary to the case of B_d to phi K_S, it is possible to obtain a model-independent prediction for the coefficient S(B_s to K^{*0} \bar K^{*0}) in the Standard Model. We give an estimate of the experimental precision achievable with the next generation of B physics experiments. We also discuss how this approach can be extended to the case of B_s to \bar K^{*0} K^0, B_s to K^{*0} \bar K^0 and B_s to K^0 \bar K^0 decays and the different experimental challenges for these channels.

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arXiv2007

On the Physics Case of a Super Flavour Factory

We summarize the physics case of a high-luminosity e+e- flavour factory collecting an integrated luminosity of 50-75 ab^(-1). Many New Physics sensitive measurements involving B and D mesons and tau leptons, unique to a Super Flavour Factory, can be performed with excellent sensitivity to new particles with masses up to ~100 (or even ~1000 TeV). Flavour- and CP-violating couplings of new particles that may be discovered at the LHC can be measured in most scenarios, even in unfavourable cases assuming minimal flavour violation. Together with the LHC, a Super Flavour Factory, following either the SuperKEKB or the SuperB proposal, could be soon starting the project of reconstructing the New Physics Lagrangian.

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arXiv2007

D-Dbar mixing and new physics: general considerations and constraints on the MSSM

Combining the recently available experimental evidence of D-Dbar mixing, we extract model-independent information on the mixing amplitude and on its CP-violating phase. Using this information, we present new constraints on the flavour structure of up-type squark mass matrices in supersymmetric extensions of the Standard Model.

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arXiv2007

Investigating The Physics Case of Running a B-Factory at the Y(5S) Resonance

We discuss the physics case of a high luminosity B-Factory running at the Y(5S) resonance. We show that the coherence of the B meson pairs is preserved at this resonance, and that Bs can be well distinguished from Bd and charged B mesons. These facts allow to cover the physics program of a traditional B-Factory and, at the same time, to perform complementary measurements which are not accessible at the Y(4S). In particular we show how, despite the experimental limitations in performing time-dependent measurements of Bs decays, the same experimental information can be extracted, in several cases, from the determination of time-integrated observables. In addition, a few examples of the potentiality in measuring rare Bs decays are given. Finally, we discuss how the study of Bs meson will improve the constraints on New Physics parameters in the Bs sector, in the context of the generalized Unitarity Triangle analysis.

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arXiv2007

Soft SUSY Breaking Grand Unification: Leptons vs Quarks on the Flavor Playground

We systematically analyze the correlations between the various leptonic and hadronic flavor violating processes arising in SUSY Grand Unified Theories. Using the GUT-symmetric relations between the soft SUSY breaking parameters, we assess the impact of hadronic and leptonic flavor observables on the SUSY sources of flavor violation.

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arXiv2007

Improved Determination of the CKM Angle alpha from B to pi pi decays

Motivated by a recent paper that compares the results of the analysis of the CKM angle alpha in the frequentist and in the Bayesian approaches, we have reconsidered the information on the hadronic amplitudes, which helps constraining the value of alpha in the Standard Model. We find that the Bayesian method gives consistent results irrespective of the parametrisation of the hadronic amplitudes and that the results of the frequentist and Bayesian approaches are equivalent when comparing meaningful probability ranges or confidence levels. We also find that from B to pi pi decays alone the 95% probability region for alpha is the interval [80^o,170^o], well consistent with recent analyses of the unitarity triangle where, by using all the available experimental and theoretical information, one gets alpha = (93 +- 4)^o. Last but not least, by using simple arguments on the hadronic matrix elements, we show that the unphysical region alpha ~ 0, present in several experimental analyses, can be eliminated.

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arXiv2006

Constraints on new physics from the quark mixing unitarity triangle

The status of the Unitarity Triangle beyond the Standard Model including the most recent results on Delta m_s, on dilepton asymmetries and on width differences is presented. Even allowing for general New Physics loop contributions the Unitarity Triangle must be very close to the Standard Model result. With the new measurements from the Tevatron, we obtain for the first time a significant constraint on New Physics in the B_s sector. We present the allowed ranges of New Physics contributions to Delta F=2 processes, and of the time-dependent CP asymmetry in B_s to J/Psi phi decays.

hep-ph↗
arXiv2006

The Unitarity Triangle Fit in the Standard Model and Hadronic Parameters from Lattice QCD: A Reappraisal after the Measurements of Delta m_s and BR(B to tau nu)

The recent measurements of the B_s meson mixing amplitude by CDF and of the leptonic branching fraction BR(B to tau nu) by Belle call for an upgraded analysis of the Unitarity Triangle in the Standard Model. Besides improving the previous constraints on the parameters of the CKM matrix, these new measurements, combined with the recent determinations of the angles alpha, beta and gamma from non-leptonic decays, allow, in the Standard Model, a quite accurate extraction of the values of the hadronic matrix elements relevant for K-Kbar and B_{s,d}-B_{s,d}bar mixing and of the leptonic decay constant f_B. These values, obtained ``experimentally'', can then be compared with the theoretical predictions, mainly from lattice QCD. In this paper we upgrade the UT fit, we determine from the data the kaon B-parameter B_Khat, the B^0 mixing amplitude parameters f_Bs B^{1/2}_Bs and xi, the decay constant f_B, and make a comparison of the obtained values with lattice predictions. We also discuss the different determinations of V_ub and show that current data do not favour the value measured in inclusive decays.

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arXiv2006

New Bounds On The CKM Matrix From B -> K pi pi Dalitz Plot Analyses

We present a new technique to extract information on the Unitarity Triangle from the study of B -> K pi pi Dalitz plots. Using the sensitivity of Dalitz analyses to the absolute values and the phases of decay amplitudes and isospin symmetry, we obtain a new constraint on the elements of the CKM matrix. We discuss in detail the role of electroweak penguins and outline future prospects.

hep-ph↗
arXiv2006

Next-to-leading order strong interaction corrections to the Delta F=2 effective Hamiltonian in the MSSM

We compute the next-to-leading order strong interaction corrections to gluino-mediated Delta F=2 box diagrams in the Minimal Supersymmetric Standard Model. These corrections are given by two loop diagrams which we have calculated in three different regularization schemes in the mass insertion approximation. We obtain the next-to-leading order Wilson coefficients of the Delta F=2 effective Hamiltonian relevant for neutral meson mixings. We find that the matching scale uncertainty is largely reduced at the next-to-leading order, typically from about 10-15% to few percent.

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arXiv2006

Upper bounds on SUSY contributions to b to s transitions from B_s - B_sbar mixing

We study the constraints on supersymmetric contributions to b to s transitions from the recent allowed range and measurement of Bs-Bsbar mixing obtained by the D0 and CDF collaborations at the Tevatron. We compute the upper bounds on the relevant off-diagonal squark mass terms and compare them with the bounds coming from Delta F=1 decays. We find that the constraints on chirality-flipping mass insertions are unaffected. Conversely, the measurement of Bs-Bsbar mixing is effective in constraining chirality-conserving mass insertions, and it has striking effects in the case in which left- and right-handed insertions have similar size. Finally, we discuss the phase of the Bs-Bsbar mixing amplitude in the presence of SUSY contributions.

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