共查询到20条相似文献,搜索用时 46 毫秒
1.
Zhi-Qing Zhang Zhen-Jun Xiao 《The European Physical Journal C - Particles and Fields》2009,59(1):49-66
We calculate the important next-to-leading-order (NLO) contributions to the B→KK
* decays from the vertex corrections, the quark loops, and the magnetic penguins in the perturbative QCD (pQCD) factorization
approach. The pQCD predictions for the CP-averaged branching ratios are
,
,
and Br(B
0→K
+
K
*−+K
−
K
*+)≈1.3×10−7, which agree well with both the experimental upper limits and the predictions based on the QCD factorization approach. Furthermore,
the CP violating asymmetries of the considered decay modes are also evaluated. The NLO pQCD predictions for
and
decays are
and
. 相似文献
2.
A. Brandenburg M. Maniatis M. M. Weber P. M. Zerwas 《The European Physical Journal C - Particles and Fields》2008,58(2):291-300
Supersymmetry predicts the identity of Yukawa and gauge couplings in the QCD sector:
. We examine whether the
Yukawa coupling can be determined, by methods complementary to LHC, by analyzing squark–gluino final states at a TeV e
+
e
− collider. 相似文献
3.
Zhi-Gang Wang 《The European Physical Journal C - Particles and Fields》2009,61(2):321-329
We calculate the masses and the pole residues of the
heavy baryons Ω
c
0(css) and Ω
b
−(bss) with the QCD sum rules. The numerical values
GeV (or
GeV) and
GeV (or
GeV) are in good agreement with the experimental data. 相似文献
4.
The production of
, D0, D + , Ds + and
charm hadrons and their antiparticles in e p scattering at HERA was measured with the ZEUS detector using an integrated luminosity of
. The measurement has been performed in the photoproduction regime with the exchanged-photon virtuality
and for photon-proton centre-of-mass energies in the range
. The charm hadrons were reconstructed in the range of transverse momentum
and pseudorapidity
. The production cross sections were used to determine the ratio of neutral and charged D-meson production rates,
, the strangeness-suppression factor,
, and the fraction of charged D mesons produced in a vector state,
. The measured
and
values agree with those obtained in deep inelastic scattering and in e + e- annihilations. The measured
value is smaller than, but consistent with, the previous measurements. The fractions of c quarks hadronising as a particular charm hadron,
, were derived in the given kinematic range. The measured open-charm fragmentation fractions are consistent with previous
results, although the measured
is smaller and
is larger than those obtained in e + e- annihilations. These results generally support the hypothesis that fragmentation proceeds independently of the hard sub-process.
Received: 12 August 2005, Revised: 8 September 2005, Published online: 6 October 2005 相似文献
5.
Camelia Mironov Ramona Vogt Gerd J. Kunde 《The European Physical Journal C - Particles and Fields》2009,61(4):893-898
We propose a new method for identifying and isolating
events through semileptonic decays of the
pair. Employing these decay dileptons to tag the jet in a specific kinematic region provides a clean signature of jets associated
with heavy-quark production. The measurement, in both pp and heavy-ion collisions, is essential for addressing heavy-quark fragmentation in vacuum and in a dense medium. We present
next-to-leading order calculations of
production (leading order in
production) in
TeV pp collisions at the LHC and discuss the feasibility of the measurement in heavy-ion collisions at
TeV. 相似文献
6.
7.
Song Mao Ma Wen-Gan Zhang Ren-You Guo Lei Wang Shao-Ming 《The European Physical Journal C - Particles and Fields》2009,59(4):761-768
Higgs-boson production in association with a W-boson pair at e
+
e
− linear colliders is one of the important processes in probing the coupling between the Higgs boson and vector gauge bosons
and discovering the signature of new physics. We describe the impact of the complete electroweak (EW) radiative corrections
of
to this process in the standard model (SM) at the International Linear Collider (ILC), and investigate the dependence of the
lowest-order (LO) and EW next-to-leading order (NLO) corrected cross sections on the colliding energy
and the Higgs-boson mass. The LO and NLO EW corrected distributions of the invariant mass of the W-boson pair and the transverse
momenta of the final W-boson and Higgs boson are presented. Our numerical results show that the relative EW radiative correction
(δ
ew) varies from −19.4% to 0.2% when m
H=120 GeV and
grows from 300 GeV to 1.2 TeV. 相似文献
8.
A. Dewanto A. H. Chan C. H. Oh R. Chen K. Sitaram 《The European Physical Journal C - Particles and Fields》2008,57(3):515-523
We study the evolution of Lee-Yang zeros structure of generalized multiplicity distribution (GMD) in high energy collision.
Starting our study with electron-positron e
+
e
− scattering data, we extend the study by Chan and Chew (Z. Phys. C 55:503, 1992) on TASSO and AMY multiplicity data for
, 22, 34.8, 43.6 and 57 GeV to the ones from DELPHI and OPAL Collaboration for
, 133, 161, 172, 183 and 189 GeV. We compare the results with the Lee-Yang structure for proton-antiproton
at
, 546 and 900 GeV from UA5 Collaboration. Our preliminary result shows that there is indeed a change in the shape and size
of the Lee-Yang zeros with increasing energy, accompanied by the development of the so-called “ear”-like structure in the
Lee-Yang plot. We expect that the development of this “ear”-like structure is related to the “shoulder” structure in the multiplicity
data, which further indicates an ongoing phase transition from soft to semihard scattering. We also extend our prediction
to LHC’s
TeV. Insert your abstract here. 相似文献
9.
《The European Physical Journal C - Particles and Fields》2007,50(2):269-281
A search for stop production in R-parity-violating supersymmetry has been performed in e+p interactions with the ZEUS detector at HERA, using an integrated luminosity of 65 pb-1. At HERA, the R-parity-violating coupling λ’ allows resonant squark production, . Since the lowest-mass squark state in most supersymmetry models is the light stop, , this search concentrated on production of , followed either by a direct R-parity-violating decay, or by the gauge decay to . No evidence for stop production was found and limits were set on λ’131 as a function of the stop mass in the framework of the minimal supersymmetric standard model. The results have also been
interpreted in terms of constraints on the parameters of the minimal supergravity model. 相似文献
10.
11.
Shao-Long Chen Xiao-Gang He Xue-Peng Hu Yi Liao 《The European Physical Journal C - Particles and Fields》2009,60(2):317-321
An unparticle
with scaling dimension
has peculiar thermal properties due to its unique phase space structure. We find that the equation of state parameter
, the ratio of pressure to energy density, is given by
providing a new form of energy in our universe. In an expanding universe, the unparticle energy density
evolves dramatically differently from that for photons. For
, even if
at a high decoupling temperature T
D is very small, it is possible to have a large relic density
at present photon temperature T
γ
0, large enough to play the role of dark matter. We calculate T
D and
using photon–unparticle interactions for illustration. 相似文献
12.
The ZEUS inclusive differential cross-section data from HERA, for charged and neutral current processes taken with e + and e- beams, together with differential cross-section data on inclusive jet production in e + p scattering and dijet production in
scattering, have been used in a new NLO QCD analysis to extract the parton distribution functions of the proton. The input of jet-production data constrains the gluon and allows an accurate extraction of
at NLO;
An additional uncertainty from the choice of scales is estimated as
. This is the first extraction of
from HERA data alone. 相似文献
13.
A.?Sibirtsev J.?Haidenbauer S.?Krewald U.?-G.?Mei?ner A.?W.?Thomas 《The European Physical Journal A - Hadrons and Nuclei》2009,41(1):71-84
A Regge model with absorptive corrections is employed in a global analysis of the world data on the reactions
p
p and
n
n for photon energies from 3 to 18GeV. In this region resonance contributions are expected to be negligible so that the available
experimental information on differential cross-sections and single and double polarization observables at - t
2 GeV2allows us to determine the reaction amplitude reliably. The model amplitude is then used to predict observables for photon
energies below 3GeV. A detailed comparison with recent data from the CLAS and CB-ELSA Collaborations in that energy region
is presented. Furthermore, the prospects for determining the radiative decay width via the Primakoff effect from the reaction
p
p are explored. 相似文献
14.
A recent investigation of the possibility of having a
-symmetric periodic potential in an optical lattice stimulated the urge to generalize non-hermitian quantum mechanics beyond
the case of commutative space. We thus study non-hermitian quantum systems in non-commutative space as well as a
-symmetric deformation of this space. Specifically, a
-symmetric harmonic oscillator together with an iC(x
1+x
2) interaction are discussed in this space, and solutions are obtained. We show that in the
deformed non-commutative space the Hamiltonian may or may not possess real eigenvalues, depending on the choice of the non-commutative
parameters. However, it is shown that in standard non-commutative space, the iC(x
1+x
2) interaction generates only real eigenvalues despite the fact that the Hamiltonian is not
-symmetric. A complex interacting anisotropic oscillator system also is discussed. 相似文献
15.
We calculate the oblique electroweak corrections and confront them with the experiments in an extension of the standard model.
The new fields added are a vector-like weak doublet and a singlet fermion. After electroweak symmetry breaking there is a
mixing between the components of the new fields, but there is no mixing allowed with the standard fermions. Four electroweak
parameters,
,
, W and Y, are presented in the formalism of Barbieri et al.; these are the generalization of the Peskin–Takeuchi S, T and U. The vector-like extension is slightly constrained.
requires the new neutral fermion masses not to be very far from each other, allowing for higher mass differences for higher
masses and smaller mixing.
, W and Y give practically no constraints on the masses. This extension can give a positive contribution to
, allowing for a heavy Higgs boson in electroweak precision tests of the standard model. 相似文献
16.
A.?Sibirtsev J.?Haidenbauer F.?Huang S.?Krewald U.?-G.?Mei?ner 《The European Physical Journal A - Hadrons and Nuclei》2009,40(1):65-75
We present a systematic analysis of backward pion photoproduction for the reactions
p
p and
p
n . Regge phenomenology is applied at invariant collision energies above 3GeV in order to fix the reaction amplitude. A comparision
with older data on - and -photoproduction at = 180° indicates that the high-energy limit as given by the Regge calculation could be reached possibly at energies of around ≃ 3 GeV. In the energy region of
2.5 GeV, covered by the new measurements of
p
p differential cross-sections at large angles at ELSA, JLab, and LEPS, we see no clear signal for a convergence towards the
Regge results. The baryon trajectories obtained in our analysis are in good agreement with those given by the spectrum of
excited baryons. 相似文献
17.
《The European Physical Journal C - Particles and Fields》2008,54(3):345-364
A determination of the single W spin density matrix (SDM) elements in the reaction e+e-→W+W-→lνqq̄(l=e/μ) is reported at centre-of-mass energies between 189 and 209 GeV. The data sample used corresponds to an integrated
luminosity of 520 pb-1 taken by DELPHI between 1998 and 2000.
The single W SDM elements, ρττ’
W± (τ,τ’=± 1 or 0), are determined as a function of the W- production angle with respect to the e- beam direction and are obtained from measurements of the W decay products by the application of suitable projection operators,
Λττ’, which assume the V-A coupling of the W-boson to fermions.
The measured SDM elements are used to obtain the fraction of longitudinally polarised Ws, with the result: at a mean energy of 198 GeV. The SDM elements are also used to determine the triple gauge couplings Δg1
Z,Δκγ,λγ and g4
Z, and . For the CP-violating couplings the results of single parameter fits are:
The errors are a combination of statistical and systematic errors. All results are consistent with the Standard Model. 相似文献
18.
Xiang Liu Zhi-Gang Luo Yan-Rui Liu Shi-Lin Zhu 《The European Physical Journal C - Particles and Fields》2009,61(3):411-428
We perform a systematic study of the possible molecular states composed of a pair of heavy mesons such as
,
,
in the framework of the meson exchange model. The exchanged mesons include the pseudoscalar, scalar and vector mesons. Through
our investigation, we find the following results. (1) The structure X(3764) is not a molecular state. (2) There exists strong attraction in the range r<1 fm for the
system with J=0,1. If future experiments confirm Z
+(4051) as a loosely bound molecular state, its quantum number is probably J
P
=0+. Its partner state Φ
**0 may be searched for in the π
0
χ
c1 channel. (3) Vector meson exchange provides strong attraction in the
channel together with pion exchange. A bound state solution may exist with a reasonable cutoff parameter Λ∼1.4 GeV. X(3872) may be accommodated as a molecular state dynamically although drawing a very definite conclusion needs further investigation.
(4) The
molecular state may exist. 相似文献
19.
A new evaluation of the hadronic vacuum polarization contribution to the muon magnetic moment is presented. We take into account the reanalysis of the low-energy e
+
e
-annihilation cross section into hadrons by the CMD-2 Collaboration. The agreement between e
+
e
-and
spectral functions in the
channel is found to be much improved. Nevertheless, significant discrepancies remain in the center-of-mass energy range between 0.85 and
, so that we refrain from averaging the two data sets. The values found for the lowest-order hadronic vacuum polarization contributions are
where the errors have been separated according to their sources: experimental, missing radiative corrections in e
+
e
-data, and isospin breaking. The corresponding Standard Model predictions for the muon magnetic anomaly read
where the errors account for the hadronic, light-by-light (LBL) scattering and electroweak contributions. The deviations from the measurement at BNL are found to be
(1.9
) and
(0.7
) for the e
+
e
-- and
-based estimates, respectively, where the second error is from the LBL contribution and the third one from the BNL measurement.Received: 7 September 2003, Published online: 30 October 2003 相似文献
20.
A. Capella L. Bravina E. G. Ferreiro A. B. Kaidalov K. Tywoniuk E. Zabrodin 《The European Physical Journal C - Particles and Fields》2008,58(3):437-444
Charmonium production at heavy-ion colliders is considered within the comovers-interaction model. The formalism is extended
by including possible secondary J/ψ production through recombination and an estimate of recombination effects is made without adjusting the model parameters.
The comovers-interaction model also includes a comprehensive treatment of initial-state nuclear effects, which are discussed
in the context of such high energies. With these tools, the model properly describes the centrality and the rapidity dependence
of experimental data at RHIC energy,
GeV, for both Au+Au and Cu+Cu collisions. Predictions for LHC,
TeV, are presented and the assumptions and extrapolations involved are discussed. 相似文献