arXiv subjects
Publications and source records attributed to G. Colangelo.
The mini-proceedings of the MesonNet 2013 International Workshop held in Prague from June 17th to 19th, 2013, are presented. MesonNet is a research network within EU HadronPhysics3 project (1/2012 -- 12/2014). The web page of the conference, which contains all talks, can be found at http://ipnp.mff.cuni.cz/mesonnet13
We describe a measurement-and-feedback technique to deterministically prepare low-entropy states of atomic spin ensembles. Using quantum non-demolition measurement and incoherent optical feedback, we drive arbitrary states in the spin-orientation space toward the origin of the spin space. We observe 12 dB of spin noise reduction, or a factor of 63 reduction in phase-space volume. We find optimal feedback conditions and show that multi-stage feedback is advantageous. An input-output calculation of quantum noise incorporating realistic quantum noise sources and experimental limitations agrees well with the observations. The method may have application to generation of exotic phases of ultracold gases, for example macroscopic singlet states and valence-bond solids.
Quantum non-demolition (QND) measurements improve sensitivity by evading measurement back-action. The technique was first proposed to detect mechanical oscillations in gravity wave detectors,and demonstrated in the measurement of optical fields, leading to the development of rigorous criteria to distinguish QND from similar non-classical measurements. Recent QND measurements of macroscopic material systems such as atomic ensembles, and mechanical oscillators, show some QND features, but not full QND character. Here we demonstrate certified QND measurement of the collective spin of an atomic ensemble. We observe quantum state preparation (QSP) and information-damage trade-off (IDT) beyond their classical limits by seven and twelve standard deviations, respectively. Our techniques complement recent work with microscopic systems, and can be used for quantum metrology and memory, the preparation and detection of non-gaussian states, and proposed quantum simulation and information protocols. They should enable QND measurements of dynamical quantum variables and the realization of QND-based quantum information protocols.
These are the proceedings of the workshop "HadAtom05", held at the University of Bern, Switzerland, February 15 and 16, 2005. The main topics of the workshop concerned the physics of hadronic atoms, and in this context recent results from experiments and theory were presented. These proceedings contain the list of participants, the scientific program and a short contribution from each speaker.
The scalar radius of the pion plays an important role in CHPT, because it is related to one of the basic effective coupling constants, viz. the one which controls the quark mass dependence of F_pi at one loop. In a recent paper, Yndurain derives a {\it robust lower bound} for this radius, which disagrees with earlier determinations. We show that such a bound does not exist: the "derivation" relies on an incorrect claim. Moreover, we discuss the physics of the form factors associated with the operators \ubar u, \dbar d and \sbar s and show that their structure in the vicinity of the K \Kbar threshold is quite different. Finally, we draw attention to the fact that the new data on the slope of the scalar K_l3 form factor confirm a recent, remarkably sharp theoretical prediction.
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.
In a recent paper, Pelaez and Yndurain evaluate some of the low energy observables of pi pi scattering and obtain flat disagreement with our earlier results. The authors work with unsubtracted dispersion relations, so that their results are very sensitive to the poorly known high energy behaviour of the scattering amplitude. They claim that the asymptotic representation we used is incorrect and propose an alternative one. We repeat their calculations on the basis of the standard, subtracted fixed-t dispersion relations, using their asymptotics. The outcome fully confirms our earlier findings. Moreover, we show that the Regge parametrization proposed by these authors for the region above 1.4 GeV violates crossing symmetry: Their ansatz is not consistent with the behaviour observed at low energies.
We present a determination of the shift $M_π(L)-M_π$ due to the finite spatial box size $L$ by means of $N_f=2$ Chiral Perturbation Theory and Lüscher's formula. The range of applicability of the chiral prediction is discussed.
We propose a new method to obtain the K -> pi pi amplitude from K -> pi which allows one to fully account for the effects of final state interactions. The method is based on a set of dispersion relations for the K -> pi pi amplitude in which the weak Hamiltonian carries momentum. The soft pion theorem, which relates this amplitude to the K -> pi amplitude, can be used to determine one of the two subtraction constants - the second constant is at present known only to leading order in chiral perturbation theory. We solve the dispersion relations numerically and express the result in terms of the unknown higher order corrections to this subtraction constant.
It has been recently suggested that it is possible to calculate the effect of final state interactions in K -> pi pi amplitudes by applying dispersive methods to the amplitude with the kaon off-shell. We critically reexamine the procedure, and point out the effects of the arbitrariness in the choice of the off-shell field for the kaon.
We demonstrate that, together with the available experimental information, chiral symmetry determines the low energy behaviour of the $ππ$ scattering amplitude to within very small uncertainties. In particular, the threshold parameters of the S-, P-, D- and F-waves are predicted, as well as the mass and width of the $ρ$ and of the broad bump in the S-wave. The implications for the coupling constants that occur in the effective Lagrangian beyond leading order and also show up in other processes, are discussed. Also, we analyze the dependence of various observables on the mass of the two lightest quarks in some detail, in view of the extrapolations required to reach the small physical masses on the lattice. The analysis relies on the standard hypothesis, according to which the quark condensate is the leading order parameter of the spontaneously broken symmetry. Our results provide the basis for an experimental test of this hypothesis, in particular in the framework of the ongoing DIRAC experiment: The prediction for the lifetime of the ground state of a $π^+π^-$ atom reads $τ=(2.90\pm 0.10)10^{-15} sec$.
We show that, independently of the size of the quark condensate, chiral symmetry correlates the two S-wave ππscattering lengths. In view of this constraint, the new precision data on K_{e_4} decay allow a remarkably accurate determination of these quantities. The result confirms the hypothesis that the quark condensate is the leading order parameter.
We match the known chiral perturbation theory representation of the pi pi scattering amplitude to two loops with a phenomenological description that relies on the Roy equations. On this basis, the corrections to Weinberg's low energy theorems for the S-wave scattering lengths are worked out to second order in the expansion in powers of the quark masses. The resulting predictions, a00=0.220 \pm 0.005, a20=-0.0444 \pm 0.0010, contain remarkably small uncertainties and thus allow a very sensitive experimental test of the hypothesis that the quark condensate is the leading order parameter of the spontaneously broken chiral symmetry.
We analyze the Roy equations for the lowest partial waves of elastic pi pi scattering and demonstrate that the two S-wave scattering lengths a_0^0 and a_0^2 are the essential parameters in the low energy region: Once these are known, the available experimental information determines the behaviour near threshold to within remarkably small uncertainties. An explicit numerical representation for the energy dependence of the S- and P-waves is given and it is shown that the threshold parameters of the D- and F-waves are also fixed very sharply in terms of a_0^0 and a^2_0. In agreement with earlier work, which is reviewed in some detail, we find that the Roy equations admit physically acceptable solutions only within a band of the (a_0^0,a_0^2) plane. We show that the data on the reactions e+e- -> pi pi and tau -> pi pi nu reduce the width of this band quite significantly. Furthermore, we discuss the relevance of the decay K -> pi pi e nu in restricting the allowed range of a_0^0, preparing the grounds for an analysis of the forthcoming precision data on this decay and on pionic atoms. We expect these to reduce the uncertainties in the two basic low energy parameters very substantially, so that a meaningful test of the chiral perturbation theory predictions will become possible.
We analyze the supersymmetric contributions to direct-CP-violating observables in $K \to ππγ$ decays induced by gluino-mediated magnetic-penguin operators. We find that $\epsp_{+-γ}$ and the differential width asymmetry of $K^\pm \to π^\pm π^0 γ$ decays could be substantially enhanced with respect to their Standard Model values, especially in the scenario where $\epsp/\eps$ is dominated by supersymmetric contributions. These observables could therefore provide a useful tool to search for New Physics effects in $|ΔS|=1$ transitions, complementary to $\epsp/\eps$ and rare decays.
We analyze the rare kaon decays $K_L \to π^0 ν\bar ν$, $K^+ \to π^+ ν\bar ν$, $K_L \to π^0 e^+ e^-$ and $K_L \to μ^+ μ^-$ in conjunction with the CP violating ratio $ε'/ε$ in a general class of supersymmetric models in which $Z$- and magnetic-penguin contributions can be substantially larger than in the Standard Model. We point out that radiative effects relate the double left-right mass insertion to the single left-left one, and that the phenomenological constraints on the latter reflect into a stringent bound on the supersymmetric contribution to the $Z$ penguin. Using this bound, and those coming from recent data on $ε'/ε$ we find ${\rm BR}(K_L \to π^0 ν\bar ν)\lsim 1.2\cdot 10^{-10}$, ${\rm BR}(K^+ \to π^+ ν\bar ν)\lsim 1.7\cdot 10^{-10}$, ${\rm BR}(K_L \to π^0 e^+ e^-)_{\rm dir}\lsim 2.0\cdot 10^{-11}$, assuming the usual determination of the CKM parameters and neglecting the possibility of cancellations among different supersymmetric effects in $ε'/ε$. Larger values are possible, in principle, but rather unlikely. We stress the importance of a measurement of these three branching ratios, together with improved data and improved theory of $ε'/ε$, in order to shed light on the realization of various supersymmetric scenarios. We reemphasize that the most natural enhancement of $ε'/ε$, within supersymmetric models, comes from chromomagnetic penguins and show that in this case sizable enhancements of $BR(K_L \to π^0 e^+ e^-)_{\rm dir}$ can also be expected.
The renormalization of chiral perturbation theory is carried out to next-to-next-to-leading order in the meson sector. We calculate the divergent part of the generating functional of Green functions of quark currents to O(p^6) for chiral SU(n), involving one- and two-loop diagrams. The renormalization group equations for the renormalized low-energy constants of O(p^6) are derived. We compare our results with previous two-loop calculations in chiral perturbation theory.
We determine the full structure of the leading (double-pole) divergences of O(p^6) in the meson sector of chiral perturbation theory. The field theoretic basis for this calculation is described. We then use an extension of this result to determine the p^6 contributions containing double chiral logarithms (L^2), single logarithms times p^4 constants (L x L_i^r) and products of two p^4 constants (L_i^r x L_j^r) for F_π, F_K/F_π, K_{l3} and K_{e4} form factors. Numerical results are presented for these quantities.