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I. Bigi

Publications and source records attributed to I. Bigi.

At least 19 recordsLinked to original sources
arXiv2011

η- η' Mixing -- From Electromagnetic Transitions to Weak Decays of Charm and Beauty Hadrons (presented at Hadron 2011)

It has been realized for a long time that knowing the ηand η' wave functions in terms of quark and gluon components probes our understanding of non-perturbative QCD dynamics. Great effort has been given to this challenge -- yet no clear picture has emerged even with the most recent KLOE data. We point out which measurements would be most helpful in arriving at a more definite conclusion. A better knowledge of these wave functions will significantly help to disentangle the weight of different decay subprocesses in semi-leptonic decays of D^+, D_s^+ and B^+ mesons. The resulting insights will be instrumental in treating even non-leptonic B transitions involving $η$ and $η^{\prime}$ and their CP asymmetries; thus they can sharpen the case for or against New Physics intervening there.

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.

hep-ph↗
arXiv2008

Flavour physics of leptons and dipole moments

This chapter of the report of the ``Flavour in the era of the LHC'' Workshop discusses the theoretical, phenomenological and experimental issues related to flavour phenomena in the charged lepton sector and in flavour-conserving CP-violating processes. We review the current experimental limits and the main theoretical models for the flavour structure of fundamental particles. We analyze the phenomenological consequences of the available data, setting constraints on explicit models beyond the Standard Model, presenting benchmarks for the discovery potential of forthcoming measurements both at the LHC and at low energy, and exploring options for possible future experiments.

hep-ph↗
arXiv2005

Four-Quark Mesons in Non-leptonic B Decays--Could They Resolve Some Old Puzzles?

We point out that non-leptonic B decays driven by b-->ccbar s should provide a favourable environment for the production of hidden charm diquark-antidiquark bound states that have been suggested to explain the resonances with masses around 4 GeV recently observed by BaBar and BELLE. Studying their relative abundances in non-leptonic B decays can teach us novel lessons about their structure and the strong interactions. Through their decay into psi they can provide a natural explanation of the excess of B-->psi X observed for p_psi < 1 GeV. Other phenomenological consequences are mentioned as well.

hep-ph↗
arXiv2005

The Discovery Potential of a Super B Factory

The Proceedings of the 2003 SLAC Workshops on flavor physics with a high luminosity asymmetric e+e- collider. The sensitivity of flavor physics to physics beyond the Standard Model is addressed in detail, in the context of the improvement of experimental measurements and theoretical calculations.

hep-ph↗
arXiv2003

The CKM Matrix and the Unitarity Triangle

This report contains the results of the Workshop on the CKM Unitarity Triangle, held at CERN on 13-16 February 2002 to study the determination of the CKM matrix from the available data of K, D, and B physics. This is a coherent document with chapters covering the determination of CKM elements from tree level decays and K and B meson mixing and the global fits of the unitarity triangle parameters. The impact of future measurements is also discussed.

hep-ph↗
arXiv2003

A Cicerone for the physics of charm, Part I: production, spectroscopy, lifetimes

This is part I of a two-part review of charm physics. After briefly recapitulating the history of the charm quantum number we sketch the experimental environments and instruments employed to study the behaviour of charm hadrons and then describe the theoretical tools for treating charm dynamics. After discussing a wide range of inclusive production processes we analyze the spectroscopy of hadrons with hidden and open charm and the weak lifetimes of charm mesons and baryons. In part II we shall address exclusive charm decays, $D^0 - \bar D^0$ oscillations and CP violation. This review is meant to be both a pedagogical introduction for the young scholar and a useful reference for the experienced researcher. We aim for a complete description of the fundamental features while providing a guide through the literature for purely technical issues.

hep-ex↗
arXiv2003

A Cicerone for the Physics of Charm

After briefly recapitulating the history of the charm quantum number we sketch the experimental environments and instruments employed to study the behaviour of charm hadrons and then describe the theoretical tools for treating charm dynamics. We discuss a wide range of inclusive production processes before analyzing the spectroscopy of hadrons with hidden and open charm and the weak lifetimes of charm mesons and baryons. Then we address leptonic, exclusive semileptonic and nonleptonic charm decays. Finally we treat $D^0 - \bar D^0$ oscillations and CP (and CPT) violation before concluding with some comments on charm and the quark-gluon plasma. We will make the case that future studies of charm dynamics -- in particular of CP violation -- can reveal the presence of New Physics. The experimental sensitivity has only recently reached a level where this could reasonably happen, yet only as the result of dedicated efforts. This review is meant to be both a pedagogical introduction for the young scholar and a useful reference for the experienced researcher. We aim for a self-contained description of the fundamental features while providing a guide through the literature for more technical issues.

hep-ex↗
arXiv2001

The Potential for Neutrino Physics at Muon Colliders and Dedicated High Current Muon Storage Rings

Conceptual design studies are underway for muon colliders and other high-current muon storage rings that have the potential to become the first true ``neutrino factories''. Muon decays in long straight sections of the storage rings would produce precisely characterized beams of electron and muon type neutrinos of unprecedented intensity. This article reviews the prospects for these facilities to greatly extend our capabilities for neutrino experiments, largely emphasizing the physics of neutrino interactions.

hep-ph↗
arXiv2000

b Quark Physics with 2 .10^9 Z Bosons

It has been suggested to realize a factory for 10^9 Z^0 through a linear e^+e^- collider with polarized beams. Very likely the relevant CP studies for B mesons will already have been performed at the B factories by that time, hence GIGA-Z will be a third generation b physics experiment. Yet such a facility would provide us with unique opportunities in the domain of beauty physics that would be of essential significance even in 2010: (1) Production and decay of polarized beauty baryons; (2) searching for and probing transitions driven by b --> q ν\barν; (3) detailed and comprehensive studies of inclusive semileptonic B_s decays.

hep-ph↗
arXiv1999

CP Violation and Beauty Decays -- A Case Study of High Impact, High Sensitivity and Even High Precision Physics

The narrative of these lectures contains three main threads: (i) CP violation despite having so far been observed only in the decays of neutral kaons has been recognized as a phenomenon of truly fundamental importance. The KM ansatz constitutes the minimal implementation of CP violation: without requiring unknown degrees of freedom it can reproduce the known CP phenomenology in a nontrivial way. (ii) The physics of beauty hadrons -- in particular their weak decays -- opens a novel window onto fundamental dynamics: they usher in a new quark family (presumably the last one); they allow us to determine fundamental quantities of the Standard Model like the $b$ quark mass and the CKM parameters $V(cb)$, $V(ub)$, $V(ts)$ and $V(td)$; they exhibit speedy or even rapid $B^0 - \bar B^0$J oscillations. (iii) Heavy Quark Expansions allow us to treat $B$ decays with an accuracy that would not have been thought possible a mere decade ago. These three threads are joined together in the following manner: (a) Huge CP asymmetries are {\em pre}dicted in $B$ decays, which represents a decisive test of the KM paradigm for CP violation. (b) Some of these predictions are made with high {\em parametric} reliability, which (c) can be translated into {\em numerical} precision through the judicious employment of novel theoretical technologies. (d) Beauty decays thus provide us with a rich and promising field to search for New Physics and even study some of its salient features. At the end of it there might quite possibly be a New Paradigm for High Energy Physics. There will be some other threads woven into this tapistry: electric dipole moments, and CP violation in other strange and in charm decays.

hep-ph↗
arXiv1998

Heavy flavor decays, OPE and duality in two-Dimensional 't Hooft model

The 't Hooft model (two-dimensional QCD in the limit of large number of colors) is used as a laboratory for exploring various aspects of the heavy quark expansions in the nonleptonic and semileptonic decays of heavy flavors. We perform a complete operator analysis and construct the operator product expansion (OPE) up to terms O(1/m_Q^4), inclusively. The OPE-based predictions for the inclusive widths are then confronted with the "phenomenological" results, obtained by summation of all open exclusive decay channels, one by one. The summation is carried out analytically, by virtue of the 't Hooft equation. The two alternative expressions for the total widths match. We comment on the recent claim in the literature of a 1/m_Q correction to the total width which would be in clear conflict with the OPE result. The issue of duality violations both in the simplified setting of the 't Hooft model and in actual QCD is discussed. The amplitude of oscillating terms is estimated.

hep-ph↗
arXiv1997

CP Violation -- An Essential Mystery in Nature's Grand Design

CP violation has so far been observed in one system only, namely in the decays of neutral kaons, and it can still be described by a single real quantity corresponding to a superweak scenario. In these lectures I describe why limitations on CP invariance are a particularly fundamental phenomenon and what experimental information is available. The KM ansatz constitutes the minimal implementation of CP violation: without requiring unknown degrees of freedom it can reproduce the known CP phenomenology. It unequivocally predicts large or even huge CP asymmetries of various kinds in the decays of beauty hadrons. New theoretical technologies will enable us in the foreseeable future to express at least some of these predictions in a quantitatively reliable fashion. There is tremendous potential for discovering New Physics in beauty transitions. Continuing efforts in strange decays and further dedicated searches for electric dipole moments and for CP asymmetries in charm decays are likewise essential for discovering crucial elements that still are missing in the puzzle that is Nature's Grand Design.

hep-ph↗
arXiv1997

Aspects Of Heavy Quark Theory

Recent achievements in the heavy quark theory are critically reviewed. The emphasis is put on those aspects which either did not attract enough attention or cause heated debates in the current literature. Among other topics we discuss (i) basic parameters of the heavy quark theory; (ii) a class of exact QCD inequalities; (iii) new heavy quark sum rules; (iv) virial theorem; (v) applications (|V_cb| from the total semileptonic width and from the B->D* transition at zero recoil). In some instances new derivations of the previously known results are given, or new aspects addressed. In particular, we dwell on the exact QCD inequalities. Furthermore, a toy model is considered that may shed light on the controversy regarding the value of the kinetic energy of heavy quarks obtained by different methods.

hep-ph↗
arXiv1997

The Hadronic Recoil Mass Spectrum in Semileptonic B Decays and Extracting |V_{ub}| in a Model-Insensitive Way

We present an extended discussion of the previously noted possibility to extract |V_{ub}| from an analysis of the hadronic recoil mass spectrum in B->X_u l nu decays. Invariant mass spectra containing perturbative as well as nonperturbative corrections are given; their shape is manifestly sensitive to the three basic quantities mu_pi^2, m_b, and alpha_s$, whereas the total integrated rate is much less so. Only a small fraction of b->u transitions generates a recoil mass M_X of at least M_D. We find that the fraction of events with M_X < 1.5 GeV (to reject leakage from b->c) exhibits fairly little dependence on mu_pi^2, m_b and alpha_s; |V_{ub}| can then be extracted in a largely model-insensitive way. This conclusion is based on the applicability of the OPE to actual semileptonic B decays. A direct cross-check of this assumption and a determination of the required basic parameters of the heavy quark expansion will be possible in the future with more experimental data.

hep-ph↗
arXiv1997

High Power n of m_b in Beauty Widths and n=5 -> oo Limit

The leading term in the semileptonic width of heavy flavor hadrons depends on the fifth power of the heavy quark mass. We present an analysis where this power can be self-consistently treated as a free parameter n and the width can be studied in the limit n -> oo. The resulting expansion elucidates why the small velocity (SV) treatment is relevant for the inclusive semileptonic b->c transition. The extended SV limit (ESV limit) is introduced. The leading terms in the perturbative alpha_s expansion enhanced by powers of n are automatically resummed by using the low-scale Euclidean mass. The large-n treatment explains why the scales of order m_b/n are appropriate. On the other hand, the scale cannot be too small since the factorially divergent perturbative corrections associated with running of alpha_s show up. Both requirements are met if we use the short-distance mass normalized at a scale around m_b/n \sim 1 GeV. A convenient definition of such low-scale OPE-compatible masses is briefly discussed.

hep-ph↗
arXiv1994

How to Measure Kinetic Energy of the Heavy Quark Inside B Mesons?

We discuss how one can determine the average kinetic energy of the heavy quark inside heavy mesons from differential distributions in $B$ decays. A new, so-called third, sum rule for the $b\rightarrow c$ transition is derived in the small velocity (SV) limit. Using this sum rule and the existing data on the momentum dependence in the $B\rightarrow D^*$ transition (the slope of the Isgur-Wise function) we obtain a new lower bound on the parameter $μ_π^2 = (2M_B)^{-1}\langle B |\bar b (i\vec{D})^2 b |B\rangle $ proportional to the average kinetic energy of $b$ quark inside $B$ meson. The existing data suggest $μ_π^2 > 0.4$~GeV$^2$ and (from the ``optical'' sum rule) $\overlineΛ > 500$ MeV, albeit with some numerical uncertainties.

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