共查询到20条相似文献,搜索用时 15 毫秒
1.
《Physics letters. [Part B]》1987,189(3):363-368
The decays KL,S → π0γγ are calculated within the framework of chiral perturbation theory. The amplitude for KL → π0γγ is found to be finite at the one-loop level yielding a branching ratio of 6.8 × 10−7. The decay spectra of both decays are very characteristic and provide good tests of the effective chiral symmetry realization of the standard model. 相似文献
2.
《Physics letters. [Part B]》1997,415(4):395-401
The short distance QCD corrections to b→sγγ are calculated in the leading logarithmic approximation. The equivalence of operator basis reduction for S-matrix elements by using the equations of motion or by proving a low energy theorem is discussed. We apply the above results to the exclusive Bs→γγ decay. The branching ratio of this decay is found to be 5×10−7 in the Standard Model. We also found that QCD corrections modify considerably the ratio between CP-even and CP-odd two-photon amplitudes. 相似文献
3.
《Physics letters. [Part B]》2004,578(3-4):276-284
Using the NA48 detector at the CERN SPS, 31 KS→π0γγ candidates with an estimated background of 13.7±3.2 events have been observed. This first observation leads to a branching ratio of BR(KS→π0γγ)z>0.2=(4.9±1.6stat±0.9syst)×10−8 in agreement with Chiral Perturbation Theory predictions. 相似文献
4.
It is shown that the contribution of diagrams with intermediate state vector mesons to the KL 0
amplitude, intensively discussed in literature in recent years, is close to zero provided that theSU(3) group breaking is taken into account. At the same time, the contribution of scalar mesons in the intermediate state is essential. The obtained estimates for Br(KL 0) conform with the recent experimental data Br(KL
0
)=(2·1 ± 0·6)×10–6.Dedicated to the memory of our friend Prof. M. Gmitro.We wish to thank S. B. Gerasimov and A. B. Govorkov for useful discussions. 相似文献
5.
Contributions of fermion loops, W-boson loops and their sum to the high energy γγ -- γγ scatteringtotal cross sections (1 cosθ< cos30) are calculated by analytical expressions of γγ - γγ scattering amplitude. Thesecontributions may be observed in the future photon linear collider and may be uscd to test standard model. Thecontribution of fermions' loops is a half of that in R.K. Arphlus and M. Neuuman's paper (Phys. Rev. 80 (1950) 380;83 (1951) 776). 相似文献
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7.
《Nuclear Physics B》2001,600(1):3-20
The η→π0γγ decay was investigated by the SND detector at VEPP-2M e+e− collider in the reaction e+e−→φ→ηγ. Here we present the results and some details of this study. We report an upper limit (90% c.l.) Br(η→π0γγ)<8.4×10−4 as our final result. Our upper limit does not contradict the earlier measurement by GAMS spectrometer. To facilitate future studies a rather detailed review of the problem is also given. 相似文献
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9.
We perform a comparative study for the LHC di-photon Higgs signal in three different littlest Higgs models with T-parity (named LHT-Ⅰ, LHT-Ⅱ and LHT-Ⅲ). We find that compared with the Standard Model prediction, the di-photon rate is always suppressed and the suppression extent can be different for different models. The LHC will soon give a solid judgement whether the di-photon rate is larger than the SM prediction, which can be utilized as a sensitive probe for the three models. 相似文献
10.
In this paper we calculate the contributions to the branching ratio of Bs→γγ from charged pseudo-Goldstone bosons appearing in the one generation Technicolor model. We find that the theoretical value of the branching ratio, BR(Bs→γγ), including the contributions of PGBs, P± and P±8, is very different from the standard model (SM) prediction. The new physical effects can provide a one to two order of magnitude enhancement of the SM results. It is shown that the decay Bs→γγ can test new physical signals from the technicolor model. 相似文献
11.
《Nuclear Physics B》1996,474(1):32-56
In the minimal supersymmetric standard model the decay h0 → A0A0 of the light neutral scalar h0 is kinematically allowed for low values of tan β when radiative corrections to the neutral Higgs masses are taken into account. The width of this decay mode is revisited on the basis of a complete one-loop diagrammatic calculation. We give the analytical expressions and numerical results and compare them with the corresponding ones from the simpler and compact approximations of the effective potential method and the renormalization group approach. 相似文献
12.
A.V. Anisovich V.V. Anisovich V.A. Nikonov L. Montanet 《The European Physical Journal A - Hadrons and Nuclei》1999,6(3):247-249
We discuss γγ partial widths of pseudoscalar/isoscalar mesons η:(M) in the mass region M∼ 1000–1500 MeV. The transition amplitudes η:(1295) →γγ and η:(1440) →γγ are studied within an assumption that the decaying
mesons are the members of the first radial excitation nonet 21
S
0qˉq. The calculations show that partial widths being of the order of 0.1 keV are dominantly due to the nˉn meson component
while the contribution of the sˉs component is small.
Received: 24 September 1999 相似文献
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15.
Precise measurements of the ft-values for superallowed nuclear β-decay yield results that support conservation of the weak vector current but violate the
unitarity of the Cabibbo-Kobayashi-Maskawa matrix by more than two standard deviations. This apparent violation of the Standard
Model has led to considerable theoretical and experimental activity largely focussed on reducing uncertainties in the small
correction terms that account for charge-dependent nuclear effects. This activity is outlined and the prospects for future
sharpening of the unitarity test are assessed.
Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002
RID="a"
ID="a"e-mail: hardy@comp.tamu.edu 相似文献
16.
《Nuclear Physics B》1995,452(3):626-645
Within the Extended Nambu Jona-Lasinio model, we calculate the O(π6) counterterms entering the low-energy expansion of the ψψ → π0π0 and the η → π0ψψ amplitudes in Chiral Perturbation Theory. For ψψ → π0π0 our results are compatible with both the experimental data and the two-loop calculation using meson resonance saturation. For the η decay we find Φ(η → π0ψψ) = 0.58 ± 0.3 eV which is in agreement with experiment within one standard deviation. We also give predictions for the neutral pion polarizabilities and compare them with the results obtained from resonance saturation. 相似文献
17.
We describe the analytic and numerical evaluation of the γγ → γZ process cross section and the Z → γγγ decay rate within the SANC system multi-channel approach at the one-loop accuracy level with all masses taken into account. The corresponding package for numeric calculations is presented. For checking of the results’ correctness we make a comparison with the other independent calculations. 相似文献
18.
Federico Nguyen 《中国物理 C》2010,34(6):795-800
Studies of γγ interactions are performed with the KLOE detector, without tagging of the outgoing e^+e^-. The data sample is from an integrated luminosity of 240 pb^-1. It was collected at the φ-factory DAONE with e^+e^- beams colliding at √s ≌1 GeV, below the φ resonance peak. We present preliminary results concerning the observation of the γγ→η process and the evidence for γγ→π^0π^0 production at low π^0π^0 invariant masses. 相似文献
19.
Federico Nguyen 《中国物理C(英文版)》2010,34(6):795-800
Studies of γγ interactions are performed with the KLOE detector,without tagging of the outgoing e+e-.The data sample is from an integrated luminosity of 240 pb-1.It was collected at the φ-factory DAΦNE with e+e-beams colliding at s~(1/2) 1 GeV,below the φ resonance peak.We present preliminary results concerning the observation of the γγ→η process and the evidence for γγ→π0π0 production at low π0π0 invariant masses. 相似文献
20.
We study the CP-averaged branching fractions and the CP-violating asymmetries in the pure annihilation decays ofB _s~0→a_0~+a _0~-andB _d~0→K_0~(*+)K_0~(*-),where a_0[K_0~*]denotes the scalar a_0(980) and a_0(1450)[K_0~*(800)(ork)and K_0~*(1430)],with the perturbative QCD factorization approach under the assumption of two-quark structure for the a_0and K_0~*states.The numerical results show that the branching ratios of theB _d~0→K_0~(*+)K_0~(*-)decays are in the order of 10~(-6),while the decay rates of theB_s~0→a_0~+a _0~-modes are in the order of 10~(-5).In light of the measured modes with the same quark components in the pseudoscalar sector,namely,B _d~0→K~+K~-and B_s~0→p p~(+-),the predictions for the considered decay modes in this work are expected to be measured at the Large Hadron Collider beauty and/or Belle-Ⅱ experiments in the (near) future.Meanwhile,it is of great interest to find that the twist-3 distribution amplitudes φ~S and φ~T with inclusion of the Gegenbauer polynomials for the scalar a_0(1450) and K_0~*(1430)states in scenario2 contribute slightly to the branching ratios while significantly to the CP violations in the B_d~0→K_0~*(14 30)~+K_0*(14 30)~-and B_s~0→a_0(1450)~+a_0(1450)~-decays,which indicates that,compared to the asymptotic φ~Sand φ~T,these Gegenbauer polynomials could change the strong phases evidently in these pure annihilation decay channels.These predictions await for the future confirmation experimentally,which could further provide useful information to help explore the inner structure of the scalars and shed light on the annihilation decay mechanism. 相似文献