共查询到20条相似文献,搜索用时 687 毫秒
1.
R. Barate et al. 《The European Physical Journal C - Particles and Fields》1999,7(4):553-569
A search for oscillations is performed using a sample of semileptonic b-hadron decays collected by the ALEPH experiment during 1991–95.
Compared to previous inclusive lepton analyses, the proper time resolution and b-flavour mistag rate are significantly improved.
Additional sensitivity to mixing is obtained by identifying subsamples of events having a purity which is higher than the average for the whole data sample. Unbinned maximum likelihood amplitude fits are performed
to derive a lower limit of at the 95% confidence limit (95% CL). Combining with the ALEPH -based analyses yields at 95% CL.
Received: 20 July 1998 / Published online: 19 February 1999 相似文献
2.
《Zeitschrift fur Physik C Particles and Fields》1997,76(3):417-423
This paper reports a study of B meson oscillations using hadronic Z0 decays with two identified leptons, and updates a previous publication by including data collected in 1994. Decay times are reconstructed for each of the semileptonic B decays by forming vertices which include the lepton and by estimating the B meson momentum. The mass difference, Δm d, between the two mass eigenstates in the B0d system is measured to be 0.430 ± 0.043 +0.028 ?0.030 ps.1, where the first error is statistical and the second error is systematic. For the B0 s system, a lower limit of Δms < 2.2 ps.1 is obtained at 95% C.L. 相似文献
3.
《Zeitschrift fur Physik C Particles and Fields》1997,76(3):401-415
An event sample enriched in semileptonic decays of b hadrons is selected using an inclusive lepton selection from approximately 3.0 million hadronic Z0 decays collected with the OPAL detector. This sample is used to investigate B meson oscillations by reconstructing a proper decay time for the parent of each lepton, using a jet charge method to estimate the production flavour of this parent, and using the lepton charge to tag the decay flavour. We measure the mass difference between the two B0 d mass eigenstates 相似文献
4.
Alexander Yu. Korchin Vladimir A. Kovalchuk 《The European Physical Journal C - Particles and Fields》2012,72(9):1-11
The fully differential angular distribution for the rare flavor-changing neutral current decay $\bar{B}_{d}^{0} \to\bar{K}^{*0} (\to K^{-} \pi^{+}) \mu^{+}\mu^{-} $ is studied. The emphasis is placed on accurate treatment of the contribution from the processes $\bar{B}_{d}^{0} \to\bar{K}^{*0} (\to K^{-} \pi^{+}) V $ with intermediate vector resonances V=??(770),??(782),?(1020),J/??,??(2S),?? decaying into the ?? + ?? ? pair. The dilepton invariant-mass dependence of the branching ratio, longitudinal polarization fraction f L of the $\bar{K}^{*0}$ meson, and forward?Cbackward asymmetry A FB is calculated and compared with data from Belle, CDF and LHCb. It is shown that inclusion of the resonance contribution may considerably modify the branching ratio, calculated in the SM without resonances, even in the invariant-mass region far from the so-called charmonia cuts applied in the experimental analyses. This conclusion crucially depends on values of the unknown phases of the B 0??K ?0 J/?? and B 0??K ?0 ??(2S) decay amplitudes with zero helicity. 相似文献
5.
S. G. Zemlyanoi D. V. Karaivanov Yu. P. Gangrsky K. P. Marinova B. N. Markov J. Badamsambuu 《Hyperfine Interactions》2010,196(1-3):107-113
Using the method of laser-induced fluorescence in an atomic beam we have measured the hyperfine splitting constants, A and B, of the ground and excited states of the optical transition 4f 76s 2 8S $_{1/2}\to 4f^{7}$ 6s6p 6P5/2 (564.58 nm) for 151???155Eu isotopes. For all isotopes, the magnetic dipole constants of the 6P5/2 atomic level are determined to a precision better than 0.04%. The A and B constants for the ground state 8S7/2 of the radioactive 152,154,155Eu were obtained for the first time with a precision better than 0.5%. Our data along with previous ground state hyperfine structure measurements for the stable europium isotopes allow us to determine the hyperfine anomaly for mentioned Eu isotopes. 相似文献
6.
Alakabha Datta David London Joaquim Matias Makiko Nagashima Alejandro Szynkman 《The European Physical Journal C - Particles and Fields》2009,60(2):279-284
Certain B
s
0→V
1
V
2 decays (V
i
is a vector meson) can be related by flavor SU(3) symmetry to corresponding B
d
0→V
3
V
4 decays. In this paper, we show that the final-state polarization can be predicted in the B
s
0 decay, assuming polarization measurements of the B
d
0 decay. This can be done within the scenario of penguin annihilation (PA), which has been suggested as an explanation of the
unexpectedly large transverse polarization in B→φ
K
*. PA is used to estimate the breaking of flavor SU(3) symmetry in pairs of decays. Two of these for which PA makes a reasonably
precise prediction of the size of SU(3) breaking are (B
s
0→φ
φ,B
d
0→φ
K
0*) and (
). The polarization measurement in the B
d
0 decay can be used to predict the transverse polarization in the B
s
0 decay and will allow for testing of PA as well as the other assumptions in the analysis. 相似文献
7.
Cong-Feng Qiao Li-Ping Sun De-Shan Yang Rui-Lin Zhu 《The European Physical Journal C - Particles and Fields》2011,71(10):1766
In this paper, the production rates of quarkonia η
c
, J/ψ, η
b
, ϒ and Bc(*)B_{c}^{(*)} mesons through W
+ boson decay at the LHC are calculated, at the leading order in both the QCD coupling α
s
and in v, the typical velocity of the heavy quark inside mesons. It shows that a sizable number of quarkonia and Bc(*)B_{c}^{(*)} mesons from W
+ boson decay will be produced at the LHC. Comparison with the predictions by using quark fragmentation mechanism is also discussed.
Results show that, for the charmonium production through W
+ decay, the difference between predictions by the fragmentation mechanism and complete leading order calculation is around
3%, and it is insensitive to the uncertainties of theoretical parameters; however, for the bottomonium and Bc(*)B_{c}^{(*)} productions, the difference cannot be ignored as the fragmentation mechanism is less applicable here due to the relatively
large ratio m
b
/m
w
. 相似文献
8.
G. Abbiendi et al. The OPAL Collaboration 《The European Physical Journal C - Particles and Fields》2001,20(3):445-454
A sample of 3.73 million hadronic Z decays, recorded with the OPAL detector at LEP in the years 1991–95, has been used to
search for a narrow resonance corresponding to the decay of the meson into . The mesons are reconstructed in the decay channel with . No evidence for a narrow resonance is found. A limit on the production of narrow in hadronic Z decays is derived:
Received: 16 January 2001 / Published online: 28 May 2001 相似文献
9.
Andrzej J. Buras Jennifer Girrbach Diego Guadagnoli Gino Isidori 《The European Physical Journal C - Particles and Fields》2012,72(10):1-10
The decay B s →μ + μ ? is one of the milestones of the flavor program at the LHC. We reappraise its Standard Model prediction. First, by analyzing the theoretical rate in the light of its main parametric dependence, we highlight the importance of a complete evaluation of higher-order electroweak corrections, at present known only in the large-m t limit, and leaving sizable dependence on the definition of electroweak parameters. Using insights from a complete calculation of such corrections for $K\to\pi\nu\bar{\nu}We present O(?? s ) results on the decays of polarized W ± and Z bosons into massive quark pairs. The NLO QCD corrections to the polarized decay functions are given up to the second order in the quark mass expansion. We find a surprisingly strong dependence of the NLO polarized decay functions on finite quark mass effects even at the relatively large mass scale of the W ± and Z bosons. As a main application we consider the decay t??b+W + involving the helicity fractions ?? mm of the W + boson followed by the polarized decay $W^{+}(\uparrow)\to q_{1}\bar{q}_{2}$ for which we determine the O(?? s ) polar angle decay distribution. We also discuss NLO polarization effects in the production/decay process $e^{+}e^{-}\to Z(\uparrow)\to q\bar{q}$ . 相似文献
10.
Dmitri Melikhov 《EPJ direct》2002,4(1):1-154
The dispersion approach based on the constituent quark picture and its applications to weak decays of heavy mesons are reviewed. Meson interaction amplitudes are represented within this approach as relativistic spectral integrals over the mass variables in terms of the meson wave functions and spectral densities of the corresponding Feynman diagrams. Various applications of this approach are discussed:Relativistic spectral representations for meson elastic and transition form factors at spacelike momentum transfers are constructed. Form factors at q2 > 0 are obtained by the analytical continuation. As a result of this procedure, form factors are given in the full q2 range of the weak decay in terms of the wave functions of the participating mesons.The 1/mQ expansion of the obtained spectral representations for the form factors for the particular limits of the heavy-to-heavy and heavy-to-light transitions are analysed. Their full consistency with the constraints provided by QCD for these limits is demonstrated.Predictions for form factors for B(s) and D(s) decays to light mesons are given.The B → γℓν decay and the weak annihilation in rare radiative decays are considered. Nonfactorizable corrections to the B0
mixing are calculated.Inclusive weak B decays are analysed and the differential distributions are obtained in terms of the B meson wave function. 相似文献
11.
12.
Harpreet Kaur 《Pramana》1999,52(4):389-393
The beauty-conserving strangeness-changing decays ofB
s meson are examined. In the charm sector, charm-conserving strangeness changing (Δc = 0, Δs ≠ 0) decays are Cabibbo suppressed and are governed by the CKM elementV
us which is much smaller than the CKM diagonal elementV
cs, so may be of little interest. On the other hand, in theb-sector, beauty-conserving strangeness changing (Δb = 0, Δs ≠ 0) decays are CKM allowed as the CKM matrix elementV
us governing such decays is much larger thanV
bc orV
bu which govern respectively theb →c orb →u transitions. The phase space available, however, is too small for the decays considered here. The numerical estimates for
the decay widths of two such modes ofB
s meson are presented. 相似文献
13.
D. Wang J. Qi M. F. Stone O. Nikolayeva B. Hattaway S. D. Gensemer H. Wang W. T. Zemke P. L. Gould E. E. Eyler W. C. Stwalley 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2004,31(2):165-177
We have observed the photoassociative spectra of colliding ultracold 39K and 85Rb atoms to produce KRb* in all eight bound electronic states correlating with the 39K (4s) + 85Rb(5p
1/2 and 5p
3/2) asymptotes. These electronically excited KRb* ultracold molecules are detected after their radiative decay to the metastable triplet (a
state and (in some cases) the singlet (X
ground state. The triplet (a
ultracold molecules are detected by two-photon ionization at 602.5 nm to form KRb + , followed by time-of-flight mass spectroscopy. We are able to assign a majority of the spectrum to three states (2(0 + ), 2(0-), 2(1)) in a lower triad of states with similar C
6 values correlating to the K(4s) + Rb (5p
1/2) asymptote; and to five states in an upper triad of three states (3(0 + ), 3(0-), 3(1)) and a dyad of two states (4(1), 1(2)), with one set of similar C
6 values within the upper triad and a different set of similar C
6 values within the dyad. We are also able to make connection with the short-range spectra of Kasahara et al. [J. Chem. Phys. 111, 8857 (1999)], identifying three of our levels as v = 61, 62 and 63 of the 1
4(1) state they observed. We also argue that ultracold photoassociation to levels between the K(4s) + Rb (5p
3/2) and K(4s) + Rb (5p
1/2) asymptotes may be weakly or strongly predissociated and therefore difficult to observe by ionization of a
(or X
molecules; we do know from Kasahara et al. that levels of the 1
4(1) and 2
5(1) states in the intra-asymptote region are predissociated. A small fraction (
1/3) of the triplet (a
ultracold molecules formed are trapped in the weak magnetic field of our magneto-optical trap (MOT).Received: 22 September 2004, Published online: 23 November 2004PACS:
33.20.Fb Raman and Rayleigh spectra (including optical scattering) - 34.20.Cf Interatomic potentials and forces - 33.80.Ps Optical cooling of molecules; trapping 相似文献
14.
K. Azizi R. Khosravi V. Bashiry 《The European Physical Journal C - Particles and Fields》2008,56(3):357-370
Taking into account the gluon correction contributions to the correlation function, the form factors relevant to the rare
decays are calculated in the framework of the three-point QCD sum rules, where X stands for axial vector particle, AV(D
s1), and vector particles, V(D
*,D
s
*). The total decay width as well as the branching ratio of these decays are evaluated using the q
2 dependent expressions of the form factors. A comparison of our results with the predictions of the relativistic constituent
quark model is presented. 相似文献
15.
We investigate the physics potential of the annihilation decays
in the standard model and beyond. In a naive factorization approach, the branching ratios are estimated to be
and
. In the framework of QCD factorization, we compute the non-factorizable corrections and get
,
. Future measurements of these decays would be useful for testing the factorization frameworks. The smallness of these decays in the SM makes them sensitive probes of new physics. As an example, we will consider the possible admixture of the (V + A) charge current to the standard (V-A) current. This admixture will give a significant contribution to the decays.Received: 29 August 2003, Revised: 17 January 2004, Published online: 19 March 2004Corresponding author: Y.D. Yang 相似文献
16.
Recent experimental results onD-,D s - andB-decays are interpreted on the basis of the valence quark model. For nonleptonic decays generally good results are obtained using factorization with little direct annihilation. Final state interaction causes corrections, however: small bare amplitudes can be fed by stronger amplitudes through channel mixing. This effect can simulate or enhance weak annihilation processes in particular if high lying resonances contribute. A comparison of \(D^0 \to \bar K^0 \phi \) withD s →?π decays will clarify this issue. The effective QCD coefficients obtained in the analysis are discussed and used to estimate the contribution of two-body decays to the total widths. The result reflects already the lifetime differences betweenD 0 andD + mesons. Predictions for numerousB-decay branching rations allow for further tests and for a determination of so far unknown decay constants. A first bound on |V ub | from nonleptonic decays is found from the experimental limit on \(\bar B^0 \to \pi ^ + \pi ^ - \) . 相似文献
17.
Laser-microwave double resonance techniques applied to a cloud of a natural mixture of Eu
+ isotopes confined in a Penning trap has been used to induce and detect nuclear Zeeman transitions. In spite of the complex level structure of Eu
+ and overlapping spectra from the two isotopes five different
transitions could be observed from which the nuclear magnetic moment can be derived. We obtain for 151
Eu
+
g
I
= 1.377 34(6) demonstrating the potential for high accuracy of the technique. The experiment can be considered as a feasibility test that precise spectroscopy data using the ion storage technique can be obtained of very complex ions and under unfavourable conditions.Received: 13 June 2003, Published online: 12 August 2003PACS:
32.60. + i Zeeman and Stark effects - 32.10.Dk Electric and magnetic moments, polarizability 相似文献
18.
《Zeitschrift fur Physik C Particles and Fields》1997,74(3):413-423
The process B*→Bγ has been observed in a sample of approximately 4.1 million hadronic Z0 decays collected by the OPAL detector at LEP in the years 1991–1995. Inclusively reconstructed B mesons have been combined with converted photons to reconstruct approximately 1900 B* mesons. The B*–B mass difference is found to be ΔM(B* ?B) = 46.2 ± 0.3 ± 0.8 MeV/c 2, and the rate of B* meson production relative to that of B mesons is found to be σ B*/σ B = 0.760 ± 0.036 ± 0.083, where the first errors are statistical and the second systematic. The angular distribution of the transition photon in the B* rest frame has been measured and the relative contribution of longitudinal B* polarization states found to be σ l/(σ l + σ t ) = 0.36 ± 0.06 ± 0.07, consistent with a simple spin counting picture. These results average over B0, B± and B s 0 mesons. 相似文献
19.
D. Ebert R. N. Faustov V. O. Galkin 《The European Physical Journal C - Particles and Fields》2003,32(1):29-43
Semileptonic and non-leptonic decays of the B
c
meson to B
s
and B mesons, caused by the
quark transitions, are studied in the framework of the relativistic quark model. The heavy quark expansion in inverse powers of the active c and spectator
quark is used to simplify calculations while the final s and d quarks in the B
s
and B mesons are treated relativistically. The decay form factors are explicitly expressed through the overlap integrals of the meson wave functions in the whole accessible kinematical range. The obtained results are compared with the predictions of other approaches.Received: 14 August 2003, Revised: 3 September 2003, Published online: 7 November 2003 相似文献