Search results for " Perturbation theory"

Running of the Charm-Quark Mass from HERA Deep-Inelastic Scattering Data

2017

Physics letters / B 775, 233 - 238 (2017). doi:10.1016/j.physletb.2017.11.002

Precision measurement of the ratio of the charged kaon leptonic decay rates

2013

A precision measurement of the ratio RK of the rates of kaon leptonic decays K+- --> e nu and K+- --> mu nu with the full data sample collected by the NA62 experiment at CERN in 2007-2008 is reported. The result, obtained by analysing ~150000 reconstructed K+- --> e nu candidates with 11% background contamination, is RK = (2.488+-0.010)*10^{-5}, in agreement with the Standard Model expectation.

Compton scattering off pions and electromagnetic polarizabilities

2019

The electric ($\alpha_\pi$) and magnetic ($\beta_\pi$) Compton polarizabilities of both the charged and the neutral pion are of fundamental interest in the low-energy sector of quantum chromodynamics (QCD). Pion polarizabilities affect the shape of the $\gamma\pi\to\gamma\pi$ Compton scattering angular distribution at back scattering angles and $\gamma\gamma\to\pi\pi$ absolute cross sections. Theory derivations are given of the $\gamma\pi\to\gamma\pi$ Compton scattering differential cross section, dispersion relations, and sum rules in terms of the polarizabilities. We review experimental charged and neutral polarizability studies and theoretical predictions. The $\pi^0$ polarizabilities we…

Experiments at the electron accelerator MAMI

2008

Measurement of ππ Scattering Lengths from and Decays

2011

In the last few years it has become possible to study low energy ππ scattering with high precision in kaon decays, thanks to the high statistics measurements of K ± → π ± π 0 π 0 ( K 3 π ) and K ± → π + π − e ± ν ( K e 4 ) decays performed by the NA48/2 experiment at the CERN SPS. In K ± → π ± π 0 π 0 , at the π + π − threshold, the π 0 π 0 mass spectrum exhibits a Wigner-cusp, from which the scattering lengths a 0 and a 2 are extracted. From the study of K e 4 decays a similar precision, but quite independent measurement of a 0 and a 2 can be obtained. The combination of both measurements provides one of the most stringent tests of Chiral Perturbation Theory.

The longitudinal muon polarization in KL → μ+μ-

1991

17 páginas, 3 figuras, 1 tabla.-- CERN-TH-6035-91 ; UWTHPH-1991-9.

A new measurement of the K±→π±γγ decay at the NA48/2 experiment

2014

Abstract The NA48/2 experiment at CERN collected two data samples with minimum bias trigger conditions in 2003 and 2004. A measurement of the rate and dynamic properties of the rare decay K ± → π ± γ γ from these data sets based on 149 decay candidates with an estimated background of 15.5 ± 0.7 events is reported. The model-independent branching ratio in the kinematic range z = ( m γ γ / m K ) 2 > 0.2 is measured to be B MI ( z > 0.2 ) = ( 0.877 ± 0.089 ) × 10 − 6 , and the branching ratio in the full kinematic range assuming a particular Chiral Perturbation Theory description to be B ( K π γ γ ) = ( 0.910 ± 0.075 ) × 10 − 6 .

Kaon Physics at CERN – Recent Results from the NA48/2 and NA62 Experiments

2012

This letter presents recent results from the kaon experiments NA48/2 and its successor NA62 at CERN. With samples of 2.5 × 106 K µ 3 ± and 4.0 × 106 K e 3 ± events collected by NA48/2 in 2004, precise measurements of the form factors were performed. The Chiral Perturbation Theory was tested through a new study of K ± → π± γγ decays based on data taken with minimal trigger conditions. Using the beam line and detector of NA48/2 in the years 2007-2008, NA62 performed a precison measurement of the helicitysuppressed ratio of the charged kaon leptonic decay rates K ± → e+ ν and K ± → μ + ν Using the full data set, which is about ten times larger than the previous world data sample, the total unc…

Experiments on threshold pion electroproduction

2008

Experimental techniques to access the reactions p(e, e′ p)π0 and d(e, e′ d)π0 at low four momentum transfer and close to threshold are presented. For p(e, e′ p)π0 results at Q 2=0.1 GeV2/c 2 are given and compared to chiral perturbation theory. A new experimental program on d(e, e′ d)π0 is presented.

Linear and nonlinear optical properties of some organoxenon derivatives

2007

We employ a series of state-of-the-art computational techniques to study the effect of inserting one or more Xe atoms in HC2H and HC4H, on the linear and nonlinear optical (L&NLO) properties of the resulting compounds. It has been found that the inserted Xe has a great effect on the L&NLO properties of the organoxenon derivatives. We analyze the bonding in HXeC2H, and the change of the electronic structure, which is induced by inserting Xe, in order to rationalize the observed extraordinary L&NLO properties. The derivatives, which are of interest in this work, have been synthesized in a Xe matrix. Thus the effect of the local field (LF), due to the Xe environment, on the properties of HXeC2…