Test Of Chiral Perturbation Theory Research Articles

The physics potential of the electron-positron collider daφne

The physics to be pursued at the electron‐positron collider DANE in Frascati with the detectors DEAR, FINUDA and KLOE is addressed, with particular emphasis on the test of discrete symmetries in the neutral kaon system, measurements of cross sections of hadron production following electron‐positron annihilation and tests of chiral perturbation theory to be carried out with KLOE and DEAR.

Coherent and incoherent atomic scattering: formalism and application to pionium interacting with matter

The experimental determination of the lifetime of pionium provides avery important test of chiral perturbation theory. This quantity isdetermined in the DIRAC experiment at CERN. In the analysis of thisexperiment, the breakup probabilities of pionium in matter are neededto high accuracy as a theoretical input. We study in detail theinfluence of the target electrons.They contribute through screening and incoherent effects. We useDirac-Hartree-Fock-Slaterwavefunctions in order to determine the corresponding form factors.We find that the inner-shell electrons contribute less thanthe weakly bound outer electrons. Furthermore, we establish a morerigorous estimate for the magnitude of the contribution from thetransverse current (magnetic terms thus far neglected in thecalculations).

γγ → πππ to one loop in chiral perturbation theory

The γγ → π 0 π 0 π 0 and γγ → π + π − π 0 amplitudes are discussed in the general context of Chiral Perturbation Theory (ChPT) to O( p 6). Chiral loops are found to play a major role. This makes these processes a good test of ChPT, mainly in its anomalous sector. We correct earlier numerical results at tree level and determine the one-loop results as well.

Threshold π0 electroproduction at the Mainz 3-spectrometer facility

We investigated the threshold H(e,e′p) π 0 reaction at q 2 = −0.1 (GeV/c) 2 as a test of chiral perturbation theory (ChPT), a low energy approximation to QCD. The longitudinal and transverse structure functions were determined by a Rosenbluth separation. The results differ significantly from recent predictions of ChPT.

A test of chiral perturbation theory from the measurement of the decay K S → γγ

Data from NA31 experiment at CERN have been used to measure the decay K S → γγ. From 69 candidate events of the type K 0 → γγ, 52 events can be attributed to K L → γγ and one event is expected from background processes. The ratio of the relative decay widths R = Γ( K S → γγ) Γ( K L → γγ) is measured to be R = 2.2 ± 1.0(stat.) ± 0.3(syst.) ± 0.2(ext.) where the external systematic error is due to the experimental uncertainty in the branching ratio of the decay K L → γγ. This translates into a branching ratio of BR(K S → γγ) = (2.2 ± 1.1) × 10 −6. If these data are combined with the published data from an earlier data taking period with the same experiment, the ratio R is determined to be R = 2.35 ± 0.75( stat.) ± 0.4( syst.) + 7.5 · (1 − BR(K L → γγ) 5.86 × 10 −4 ) where the last term accounts for the dependence on the measured K L → γγ branching ratio. The corresponding branching ratio for K S → γγ is BR(K S → γγ) = (2.4 ± 0.9) × 10 −6. The measurement is a sensitive test of chiral perturbation theory and in good agreement with theoretical predictions.

Test of chiral perturbation theory in η decays

The decay of the η-meson into three pions plays an important role as a test of low-energy QCD calculations in the framework of chiral perturbation theory. Previous experiments show results that are inconclusive or even contradictory. The Crystal Barrel experiment at LEAR has determined the braching ratiosΓ(η→3π0)/Γ(η→π+π−π0)=1.47±0.09±0.15 andΓ(η→γγ)/Γ(η→π+π−π0)=1.88±0.10±0.17 using its unique features to detect charged particles as well as neutral particles. The value for the first ratio agrees nicely with the theoretical predictions and solves previous experimental uncertainties. The second value, which yields a partial width ofΓ(η→π+π−π0)=(0.24±0.03) keV, shows that the same next-to-leading order chiral perturbation theory calculations still have some problems.

Hadrons at DAΦNE

The Frascati ϕ-factory and its two planned detectors are introduced. Physics items of interest in hadron physics like chiral perturbation theory tests, vector-meson dominance, two-photon physics, radiative ϕ decays and the nature of scalar particles are discussed.

KLOE at DAΦNE

Construction of a ø-factory has begun in 1991 at the Frascati National Laboratory (LNF) of INFN in Italy. A major general purpose detector KLOE has been designed, approved and funded. Its construction begins in 1994. The principal aim of KLOE is a definitive measurement of ϵ′/ϵ. Studying a well prepared quantum state such as the one in ø → K S 0 K L 0, one can make the complete determination of 16 independent parameters which describe the K S 0- K L 0 system, mostly through precision interferometry between pairs of same, different, and one versus sum of the other (inclusive) final states. These measurements allow independent determinations of the five (CPT) violating parameters, as well as high precision determinations of three (CP) violation parameters, which include R (ϵ′/ϵ) and I (ϵ′/ϵ). R (ϵ′/ϵ) can also be determined to an equivalent accuracy using the “double ratio” method, and ϵ from precision measurements of asymmetries in K L 0 semileptonic decays. Furthermore, we can make the first observation of CP violation in the K S 0 system by seeing K S 0→ π 0 π 0 π 0 events, and asymmetries in rates of K S 0 semileptonic decays and searches for other direct CP violating effects in asymmetries in neutral and charged K→3 π decay distributions and in K ±→ π ± π 0 γ decay rates. Other physics topics investigatable with KLOE include precision measurements of the form factors in K semileptonic decays and tests of Chiral Perturbation Theory, and studies of radiative ø decays to resolve puzzles in light meson spectroscopy.

KLOE at DAΦNE

Construction of a ø-factory has begun in 1991 at the Frascati National Laboratory (LNF) of INFN in Italy. A major general purpose detector KLOE has been designed, approved and funded. Its construction begins in 1994. The principal aim of KLOE is a definitive measurement of ϵ′/ϵ. Studying a well prepared quantum state such as the one in ø → KS0KL0, one can make the complete determination of 16 independent parameters which describe the KS0-KL0 system, mostly through precision interferometry between pairs of same, different, and one versus sum of the other (inclusive) final states. These measurements allow independent determinations of the five (CPT) violating parameters, as well as high precision determinations of three (CP) violation parameters, which include R(ϵ′/ϵ) and I(ϵ′/ϵ). R(ϵ′/ϵ) can also be determined to an equivalent accuracy using the “double ratio” method, and ϵ from precision measurements of asymmetries in KL0 semileptonic decays. Furthermore, we can make the first observation of CP violation in the KS0 system by seeing KS0→π0π0π0 events, and asymmetries in rates of KS0 semileptonic decays and searches for other direct CP violating effects in asymmetries in neutral and charged K→3π decay distributions and in K±→π±π0γ decay rates. Other physics topics investigatable with KLOE include precision measurements of the form factors in K semileptonic decays and tests of Chiral Perturbation Theory, and studies of radiative ø decays to resolve puzzles in light meson spectroscopy.

Quark physics at a phi-meson factory

The physics objectives other than tests of CP and CPT of a phi factory are discussed. They include: (1) better measurements of the down-up quark mass difference using ϱ° − ω and π° − η mixing studies; (2) the detailed investigation of the validity of the OZI rule and of the quark structure of the φ meson via e +e − → π + π −, π 2 γ, and 3 π measurements; (3) the extraction of important information on the structure of the 0 ++ meson which can be learned from measurements of radiative decays, in particular of φ → ππγ and φ → K Kγ . A phi factory is really a factory of tagged, monochromatic K 5 and K L mesons allowing precision measurements of various neutral K-decay modes. This enables one to make a precision measurement of the V us element of the K-M matrix based on K μ3 ° decay and to perform critical tests of chiral perturbation theory, in particular through the acurate determination of the K π3 , K μ3 , and K → π° γγ decay spectra. Also of interest are the ππ lengths which are obtained from K μ4 decays.

Two-pion production in photon-photon collisions

We calculate within chiral perturbation theory the cross section for γγ→π0π0 and γγ→π+π− to next-to-leading order. The first process only depends on the one-loop contributions and forms a test of chiral perturbation theory. We also calculate the pion electromagnetic form factor and compare it to recent data.