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1.
We study the decay K
+→ π
+
π
0
e
+
e
−, currently under analysis by the NA62 Collaboration at CERN. In particular, we provide a detailed analysis of the Dalitz
plot for the long-distance, γ
∗-mediated, contributions (Bremsstrahlung, direct emission and its interference). We also examine a set of asymmetries to isolate
genuine short-distance effects. While we show that charge asymmetries are not required to test short distances, they provide
the best environment for its detection. This constitutes by itself a strong motivation for NA62 to study K
− decays in the future. We therefore provide a detailed study of different charge asymmetries and the corresponding estimated
signals. Whenever possible, we make contact with the related processes K
+→ π
+
π
0
γ and K
L
→ π
+
π
−
e
+
e
− and discuss the advantages of K
+→ π
+
π
0
e
+
e
− over them. 相似文献
2.
We present measurements of the hadronic photon structure function F
2
( x), in two Q
2 ranges with mean values of 5.9 GeV 2 and 14.7 GeV 2. The data were taken by the OPAL experiment at LEP, with
close to the Z
0 mass and correspond to an integrated e
+
e
– luminosity of 44.8 pb –1. In the context of a QCD-based model we find the quark transverse momentum cutoff separating the vector meson dominance (VMD) and perturbative QCD regions to be 0.27±0.10 GeV. We confirm that there is a significant pointlike component of the photon when the probe photon has Q
2>4 GeV 2. Our measurements extend to lower values of x than any previous experiment, and no increase of F
2
( x) is observed. 相似文献
3.
A model-independent analysis of anomalous gauge coupling constants of W
± bosons is presented and the corresponding restrictions on them and on the electromagnetic characteristics of W
± bosons following from the experiments on measuring the e+ e- ? W+ W- ? ( e | / |
m, [`(v)] ) ?( q,[`(q)] ) {e^{+} }{e^{-} } \to {W^{+} }{W^{-} } \to \left( {{{e} \left/ {{\mu, \bar{v}}} \right.}} \right) \oplus \left( {q,\bar{q}} \right) process on the e
+
e
− International Linear Collider are obtained. The method of obtaining the model-independent restrictions on the anomalous gauge
constants is based on the use of the polarization scattering cross sections for different initial and final polarization states. 相似文献
4.
CLEO-c measurements of the timelike form factors F
π
, F
K
at ? s=3.671\sqrt{s}=3.671 GeV provide a direct probe of power corrections (PC’s) at energies near m
B
. PC’s in F
π,K
and B→ Kπ, ππ are separated into perturbative and soft parts. In F
π,K
the latter are ≥ O(10) larger. A PC fit to the B→ Kπ, ππ data also yields a ≥ O(10) soft-to-perturbative hierarchy for the QCD penguin PC’s. Hence, both can be attributed to dominance of the soft-overlap
between energetic (approximately) back-to-back collinear partons, and consistency of the B→ Kπ, ππ fit with the Standard Model appears to be naturally realized. The CP asymmetries SKs p0S_{K_{s} \pi^{0}}, CKs p0C_{K_{s} \pi^{0}} are well determined, providing a clean test for new physics. 相似文献
5.
Monte-Carlo generator with photon jets radiation in collinear regions for the process e
+
e
−→ γγ is described in detail. Radiative corrections in the first order of α are treated exactly. Large leading logarithmic corrections coming from collinear regions are taken into account in all orders
of α by applying the Structure Function approach. Theoretical precision of the cross section with radiative corrections is estimated
to be 0.2%. This process is considered as an additional tool to measure luminosity in forthcoming experiments with the CMD-3
detector at the e
+
e
− collider VEPP-2000. 相似文献
6.
A search for minimal standard model (MSM) and minimal supersymmetric model (MSSM), Higgs bosons with masses larger than 3 GeV/c 2 has been performed by the OPAL collaboration on e
+
e
– data from LEP corresponding to an integrated luminosity of 1.24 pb –1. The limits for MSM Higgs bosons have been obtained using the channels Z
0Z
0*
H
0, Z
0*( v
or e
+
e
– or µ +, µ –. The search for MSSM Higgs bosons has been performed using the channels Z
0Z
0*
H
0, v
or e
+
e
– or µ +µ –), h
0 q
and Z
0h
0
A
0, h
0
A
0(4 jet or
+
– or 4), where h
0 and A
0 are the two lightest neutral MSSM Higgs bosons. No Higgs boson signal has been observed. The MSM Higgs boson is excluded in the mass range 3 GeV
<25.3>25.3> 2 at the 95% confidence level; limits on the masses of the two lightest neutral MSSM Higgs bosons are obtained for h
0 mases up to 40.5 GeV/c 2.Now at Applied Silicon Inc. 相似文献
7.
An analysis of effects induced by new neutral gauge Z′ bosons was performed on the basis of data from the OPAL, DELPHI, ALEPH, and L3 experiments devoted to measuring differential
cross sections for the process of the annihilation production of pairs of charged gauge W
± bosons at the LEP2 collider. By using these experimental data, constraints on the Z′-boson mass and on the angle of Z-Z′ mixing were obtained for a number of extended gauge models. 相似文献
9.
This paper describes a study of Bose-Einstein correlations made using the ALEPH detector at LEP. The correlations are found to enhance the two particle differential cross section for pairs of identical pions by a factor which can be roughly parametrized by R(Q)=1+ exp(-Q 22), where Q is the difference in the 3-momenta of the two pions in their centre of mass frame, =0.51±0.04±0.11 and =3.3±0.2±0.8 GeV –1, which corresponds to a source size of 0.65±0.04±0.16 fm. The large systematic errors on these results reflect their strong dependence on the choice of the reference sample used in the analysis. This problem is believed to occur primarily because of uncertainties in the rates of resonance production and a lack of knowledge about the pion-pion strong interaction. No significant correlations are seen amongst like-charged pion-kaon pairs.Supported by CAICYT, Spain 相似文献
10.
Light gravitino productions in association with a neutralino (selectron) in e
+
e
− ( e
−
γ) collisions are restudied in a scenario that the lightest supersymmetric particle is a gravitino and the produced neutralino
(selectron) promptly decays into a photon (electron) and a gravitino. We explicitly give the helicity amplitudes for the production
processes by using the effective goldstino interaction Lagrangian, and present the cross sections with different collision
energies and mass spectra. We also examine selection efficiencies by kinematical cuts and beam polarizations for the signal
and background processes, and show that the energy and angular distributions of the photon (electron) can explore the mass
of the t-channel exchange particle as well as the mass of the decaying particle at a future e
+
e
− ( e
−
γ) collider. 相似文献
12.
Spin correlations of e
+
e
− pair productions of two colliding photons are investigated and explicit expressions for their corresponding probabilities
are derived and found to be energy (speed) dependent, for initially linearly and circularly polarized photons, different from those obtained by simply combining the spins of the relevant particles, for initially polarized photons. These expressions also depend on the angles of spin of e
+ (and/or of e
−), for initially linearly polarized photons, but not for circularly polarized photons, as a function of the energy. It is remarkable that these explicit results obtained from quantum field theory show
a clear violation of Bell’s inequality of Local Hidden Variables theories at all energies beyond that of the threshold one for particle production, in support of quantum field theory in the relativistic regime.
We hope that our explicit expression will lead to experiments, of the type described in the bulk of this paper, which can
monitor energy (and speed) in polarization correlation experiments. 相似文献
13.
The associated production of a dark particle and photon, represented as a mono- γ event, is a promising channel to probe particle content and dynamics in the dark sector. In this study, we investigate the properties of the mono- γ production of vector dark matter at future \begin{document}$ e^+e^- $\end{document}![]() ![]() colliders. Photon-like and Pauli operators as well as triple gauge boson interactions involving dark matter are considered in the framework of effective field theory. We show that, in comparison with the Pauli operator, the triple gauge boson couplings are significantly more interesting in high energy colliders. Beam polarization effects are also analyzed, and we show that the experimental sensitivities cannot be significantly enhanced because of the smaller luminosity. 相似文献
14.
On the basis of perturbative QCD and the relativistic quark model we calculate relativistic and bound state corrections in
the production processes of a pair of S-wave and P-wave charmonium states. Relativistic factors in the production amplitude connected with the relative motion of heavy quarks
and the transformation law of the bound state wave function to the reference frame of the moving S- and Pwave mesons are taken into account. For the gluon and quark propagators entering the production vertex function we use a truncated
expansion in the ratio of the relative quark momenta to the center-of-mass energy $
\sqrt s
$
\sqrt s
up to the second order. Relativistic corrections to the quark bound state wave functions in the rest frame are considered
by means of the Breit-like potential. It turns out that the examined effects change essentially the nonrelativistic results
of the cross section for the considered reactions at the center-of-mass energy $
\sqrt s
$
\sqrt s
= 10.6 GeV. 相似文献
15.
The axial coupling and the magnetic moment of D
∗-meson or, more specifically, the couplings gD*Dpg_{D^{\ast}D\pi} and gD*Dgg_{D^{\ast}D\gamma }, encode the non-perturbative QCD effects describing the decays D
∗→ Dπ and D
∗→ Dγ. We compute these quantities by means of lattice QCD with N
f=2 dynamical quarks, by employing the Wilson (“ clover”) action. On our finer lattice ( a≈0.065 fm) we obtain gD*Dp+=20±2g_{D^{\ast}D\pi^{+}}=20\pm2, and gD*0 D0g=2.0±0.6 GeV -1g_{D^{\ast0} D^{0}\gamma}=2.0\pm 0.6~{\rm GeV}^{-1}. This is the first determination of gD*0 D0gg_{D^{\ast0} D^{0}\gamma} on the lattice. We also provide a short phenomenological discussion and the comparison of our result with experiment and
with the results quoted in the literature. 相似文献
16.
By studying the scattering process of scalar particle pion on the noncommutative scalar quantum electrodynamics, the non-commutative amendment of differential scattering cross-section is found, which is dependent of polar-angle and the results are significantly different from that in the commutative scalar quantum electrodynamics, particularly when cos θ∼±1. The non-commutativity of space is expected to be explored at around Λ NC∼TeV. 相似文献
17.
Due to its sensitivity to New Physics contributions, the branching ratio of the very rare decay B
s
0 → μ
+
μ
− is one of the most interesting measurements using the first data from the LHC accelerator. The analysis strategy for the
study of this channel in the LHCb experiment is presented, as well as a review of the potential of the experiment in such
study, using the latest simulations. With four months of nominal data taking, any enhancement from the Standard Model prediction
can be excluded. 相似文献
18.
Heavy quarks, such as charm, are produced in hard scatterings in the early stages of high energy nucleus-nucleus collisions
and are expected to be a powerful tool to investigate the properties of the quark gluon plasma (QGP). The tracking detectors
of the ALICE apparatus will allow to track and identify particles in central rapidity range down to low P
t
. Among D mesons it would be particularly interesting to measure D
s
yield via an exclusive hadronic decay channel because it could help to disentangle different hadronization mechanisms. The
possibility of reconstructing the D
s
meson through its D
s
+→ K
+
K
−
π
+ decay channel in the central barrel was studied. The problem considered is characterized by the comparatively low yield of
the D
s
mesons against the huge amount of combinatorial background. Different kinematic and topological cuts have been studied in
order to increase the signal-to-background ratio and the statistical significance. In addition, D
s
mesons preferentially decay through intermediate resonant states and this fact can improve the separation of signal from
background. Results of cut parameters tuning and values of significance for an analysis performed on simulated data are presented. 相似文献
19.
Prospects for discovering heavy graviton resonances in decays to an electron-positron pair and for identifying the nature
of these resonances in the ATLAS experiment at the Large Hadron Collider (LHC) are investigated. Gravitons in the Randall-Sundrum
model, which features extra spatial dimensions, are considered by way of example. A comparative analysis of effects of new
different-spin heavy resonances, scalar [supersymmetric neutrino (sneutrino)], vector (new gauge Z′ boson), and tensor (graviton) ones, is performed in order to identify the graviton spin. An identification of gravitons
is performed by using the integrated center-edge asymmetry. For LHC, the graviton discovery (identification) reach is found
to be 2.1 TeV (1.2 TeV) and 3.9 TeV (2.9 TeV) at a confidence level of 5 δ (95%) for the graviton coupling constants of k/$
\bar M
$
\bar M
Pl = 0.01 and 0.1, respectively. This analysis is the most general, since, for the first time, it takes into account the possible
existence of scalar resonances, which affects substantially quantitative estimates of the identification reach. 相似文献
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