arXiv subjects

Y. Nir

Publications and source records attributed to Y. Nir.

13 recordsLinked to original sources

arXiv2016

Flavour Physics and CP Violation

We explain the many reasons for the interest in flavor physics. We describe flavor physics and the related CP violation within the Standard Model, and explain how the B-factories proved that the Kobayashi-Maskawa mechanism dominates the CP violation that is observed in meson decays. We explain the implications of flavor physics for new physics, with emphasis on the "new physics flavor puzzle", and present the idea of minimal flavor violation as a possible solution. We explain why the values flavor parameters of the Standard Model are puzzling, present the Froggatt-Nielsen mechanism as a possible solution, and describe how measurements of neutrino parameters are interpreted in the context of this puzzle. We show that the recently discovered Higgslike boson may provide new opportunities for making progress on the various flavor puzzles.

hep-ph↗

arXiv2013

Implications of LHCb measurements and future prospects

During 2011 the LHCb experiment at CERN collected 1.0 fb-1 of sqrt{s} = 7 TeV pp collisions. Due to the large heavy quark production cross-sections, these data provide unprecedented samples of heavy flavoured hadrons. The first results from LHCb have made a significant impact on the flavour physics landscape and have definitively proved the concept of a dedicated experiment in the forward region at a hadron collider. This document discusses the implications of these first measurements on classes of extensions to the Standard Model, bearing in mind the interplay with the results of searches for on-shell production of new particles at ATLAS and CMS. The physics potential of an upgrade to the LHCb detector, which would allow an order of magnitude more data to be collected, is emphasised.

hep-ex↗

arXiv2010

Flavour physics and CP violation

This is a written version of a series of lectures aimed at graduate students in particle theory/string theory/particle experiment familiar with the basics of the Standard Model. We explain the many reasons for the interest in flavour physics. We describe flavour physics and the related CP violation within the Standard Model, and explain how the B-factories proved that the Kobayashi-Maskawa mechanism dominates the CP violation that is observed in meson decays. We explain the implications of flavour physics for new physics. We emphasize the "new physics flavour puzzle". As an explicit example, we explain how the recent measurements of D0-D0 mixing constrain the supersymmetric flavour structure. We explain how the ATLAS and CMS experiments can solve the new physics flavour puzzle and perhaps shed light on the standard model flavour puzzle. Finally, we describe various interpretations of the neutrino flavour data and their impact on flavour models.

hep-ph↗

arXiv2004

Working Group Report: Neutrino and Astroparticle Physics

This is the report of neutrino and astroparticle physics working group at WHEPP-8. We present the discussions carried out during the workshop on selected topics in the above fields and also indicate progress made subsequently. The neutrino physics subgroup studied the possibilites of constraining neutrino masses, mixing and CPT violation in lepton sector from future experiments. Neutrino mass models in the context of abelian horizontal symmetries, warped extra dimensions and in presence of triplet Higgs were studied. Effect of threshold corrections on radiative magnification of mixing angles was investigated. The astroparticle physics subgroup focused on how various particle physics inputs affect the CMBR fluctuation spectrum, and on brane cosmology. This report also contains an introduction on how to use the publicly available code CMBFAST to calculate the CMBR fluctuations.

hep-ph↗

arXiv2003

Neutrino Masses and Mixing: Evidence and Implications

Measurements of various features of the fluxes of atmospheric and solar neutrinos have provided evidence for neutrino oscillations and therefore for neutrino masses and mixing. We review the phenomenology of neutrino oscillations in vacuum and in matter. We present the existing evidence from solar and atmospheric neutrinos as well as the results from laboratory searches, including the final status of the LSND experiment. We describe the theoretical inputs that are used to interpret the experimental results in terms of neutrino oscillations. We derive the allowed ranges for the mass and mixing parameters in three frameworks: First, each set of observations is analyzed separately in a two-neutrino framework; Second, the data from solar and atmospheric neutrinos are analyzed in a three active neutrino framework; Third, the LSND results are added, and the status of accommodating all three signals in the framework of three active and one sterile light neutrinos is presented. We review the theoretical implications of these results: the existence of new physics, the estimate of the scale of this new physics and the lessons for grand unified theories, for supersymmetric models with R-parity violation, for models of extra dimensions and singlet fermions in the bulk, and for flavor models.

hep-ph↗

arXiv2002

B Physics at the Tevatron: Run II and Beyond

This report provides a comprehensive overview of the prospects for B physics at the Tevatron. The work was carried out during a series of workshops starting in September 1999. There were four working groups: 1) CP Violation, 2) Rare and Semileptonic Decays, 3) Mixing and Lifetimes, 4) Production, Fragmentation and Spectroscopy. The report also includes introductory chapters on theoretical and experimental tools emphasizing aspects of B physics specific to hadron colliders, as well as overviews of the CDF, D0, and BTeV detectors, and a Summary.

hep-ph↗

arXiv2002

New CP Violation in Neutrino Oscillations

Measurements of CP--violating observables in neutrino oscillation experiments have been studied in the literature as a way to determine the CP--violating phase in the mixing matrix for leptons. Here we show that such observables also probe new neutrino interactions in the production or detection processes. Genuine CP violation and fake CP violation due to matter effects are sensitive to the imaginary and real parts of new couplings. The dependence of the CP asymmetry on source--detector distance is different from the standard one and, in particular, enhanced at short distances. We estimate that future neutrino factories will be able to probe in this way new interactions that are up to four orders of magnitude weaker than the weak interactions. We discuss the possible implications for models of new physics.

hep-ph↗

arXiv2000

Phenomenology of Maximal and Near-Maximal Lepton Mixing

We study the phenomenological consequences of maximal and near-maximal mixing of the electron neutrino with other ($x$=tau and/or muon) neutrinos. We describe the deviations from maximal mixing in terms of a parameter $ε\equiv1-2\sin^2θ_{ex}$ and quantify the present experimental status for $|ε|<0.3$. We find that the global analysis of solar neutrino data allows maximal mixing with confidence level better than 99% for $10^{-8}$ eV$^2\lsimΔm^2\lsim2\times10^{-7}$ eV$^2$. In the mass ranges $Δm^2\gsim 1.5\times10^{-5}$ eV$^2$ and $4\times10^{-10}$ eV$^2\lsimΔm^2\lsim2\times10^{-7}$ eV$^2$ the full interval $|ε|<0.3$ is allowed within 4$σ$(99.995 % CL). We suggest ways to measure $ε$ in future experiments. The observable that is most sensitive to $ε$ is the rate [NC]/[CC] in combination with the Day-Night asymmetry in the SNO detector. With theoretical and statistical uncertainties, the expected accuracy after 5 years is $Δε\sim 0.07$. We also discuss the effects of maximal and near-maximal $ν_e$-mixing in atmospheric neutrinos, supernova neutrinos, and neutrinoless double beta decay.

hep-ph↗

arXiv1999

Probing Supersymmetric Flavor Models with $ε'/ε$

We discuss the supersymmetric contribution to $ε'/ε$ in various supersymmetric flavor models. We find that in alignment models the supersymmetric contribution could be significant while in heavy squark models it is expected to be small. The situation is particularly interesting in models that solve the flavor problems by either of the above mechanisms and the remaining CP problems by means of approximate CP, that is, all CP violating phases are small. In such models, the standard model contributions cannot account for $ε'/ε$ and a failure of the supersymmetric contributions to do so would exclude the model. In models of alignment and approximate CP, the supersymmetric contributions can account for $ε'/ε$ only if both the supersymmetric model parameters and the hadronic parameters assume rather extreme values. Such models are then strongly disfavored by the $ε'/ε$ measurements. Models of heavy squarks and approximate CP are excluded.

hep-ph↗

arXiv1995

The Role of CP violation in D0 anti-D0 Mixing

In current searches for D0 anti-D0 mixing, the time evolution of ``wrong-sign'' decays is used to distinguish between a potential mixing signal and the dominant background from doubly-Cabibbo-suppressed decays. A term proportional to $ΔMt$ in the expression for the time evolution is often neglected in theoretical discussions and experimental analyses of these processes. We emphasize that, in general, this term does not vanish even in the case of CP invariance. Furthermore, CP invariance is likely to be violated if the rate of D0 anti-D0 mixing is close to the experimental bound. The consequence of either of these two facts is that the strongest existing measured bound is not applicable for constraining New Physics.

hep-ph↗

arXiv1993

The Subleading Isgur-Wise Form Factor $ξ_3(v\cdot v')$ and its Implications for the Decays $\bar B\to D^{(*)}\ell\,\barν$

We calculate, in the framework of QCD sum rules and to next-to-leading order in perturbation theory, the universal function $ξ_3(v\cdot v')$ which appears at order $1/m_Q$ in the heavy quark expansion of meson weak decay form factors. We find that radiative corrections of order $α_s$ are very important. Over the kinematic range accessible in semileptonic decays, $ξ_3(v\cdot v')$ is proportional to the leading-order Isgur-Wise function $ξ(v\cdot v')$ to very good accuracy. Taking into account all sources of uncertainty, we estimate $ξ_3/ξ=(0.6\pm 0.2)$. This reduces the theoretical uncertainty in the extraction of $|\,V_{cb}|$ from $\bar B\to D\,\ell\, \barν$ transitions. A measurement of the form factor ratio $A_2/A_1$ in $\bar B\to D^*\ell\,\barν$ decays can be used to test our prediction.

hep-ph↗

arXiv1992

The Subleading Isgur-Wise Form Factor $χ_3(v\cdot v')$ to Order $α_s$ in QCD Sum Rules

We calculate the contributions arising at order $α_s$ in the QCD sum rule for the spin-symmetry violating universal function $χ_3(v\cdot v')$, which appears at order $1/m_Q$ in the heavy quark expansion of meson form factors. In particular, we derive the two-loop perturbative contribution to the sum rule. Over the kinematic range accessible in $B\to D^{(*)}\ell\,ν$ decays, we find that $χ_3(v\cdot v')$ does not exceed the level of $\sim 1\%$, indicating that power corrections induced by the chromo-magnetic operator in the heavy quark expansion are small.

hep-ph↗

arXiv1992

QCD Sum Rule Analysis of the Subleading Isgur-Wise Form Factor $χ_2(v\cdot v')$

We present a QCD sum rule calculation of the spin-symmetry violating universal function $χ_2(v\cdot v')$, which appears at order $1/m_Q$ in the heavy quark expansion of meson form factors. This function vanishes in the standard approximation, where radiative effects are neglected. For the first time, the complete set of diagrams arising at order $α_s$ is evaluated. In particular, we find $χ_2(1) = -(3.8\pm 0.4)\%$ at zero recoil, indicating that $1/m_Q$ corrections induced by the chromo-magnetic moment operator are small.

hep-ph↗