共查询到20条相似文献,搜索用时 484 毫秒
1.
First measurements of
mesons production properties and their spin alignment in
charged current (CC) and neutral current (NC) interactions are presented. The analysis of the full data sample of the NOMAD
experiment is performed in different kinematic regions. For
and
mesons produced in
CC interactions and decaying into
we have found the following yields per event:
and
respectively, while for the
and
mesons produced in
interactions the corresponding yields per event are:
and
. The results obtained for the
parameter,
and
for
and
produced in
CC interactions, are compared to theoretical predictions tuned on LEP measurements in
annihilation at the
pole. For
mesons produced in
interactions the measured
parameter is
.
PACS 13.15.+g, 13.60.Le, 13.87.Fh, 13.88.+e, 14.40.Ev 相似文献
2.
3.
E. Accomando A. Denner C. Meier 《The European Physical Journal C - Particles and Fields》2006,47(1):125-146
We have calculated the electroweak
corrections to the processes
,
, and
at the LHC, with l=e,μ and
. The virtual corrections are evaluated in leading-pole approximation, whereas the real corrections are taken into account
exactly. These corrections are implemented into a Monte Carlo generator which includes both phase-space slicing and subtraction
to deal with soft and collinear singularities. We present numerical results for total cross sections as well as for experimentally
interesting distributions. Applying typical LHC cuts, the electroweak corrections are of the order of -5% for the total cross
sections and exceed -20% for observables dominated by high center-of-mass energies of the partonic processes. 相似文献
4.
C.A. Nelson J.J. Berger J.R. Wickman 《The European Physical Journal C - Particles and Fields》2006,46(2):385-402
This continuation of the derivation of general beam-referenced stage-two spin-correlation functions is for the analysis of
top–antitop pair-production at the Tevatron and at the Large Hadron Collider. Both the gluon-production and the quark-production
contributions are included for the charged-lepton-plus-jets reaction pp or
. There is a simple 4-angle beam-referenced spin-correlation function for determination of the relative sign of or for measurement
of a possible non-trivial phase between the two dominant
helicity amplitudes for the
decay mode. There is an analogous function and tests for
decay. This signature requires use of the
energy of the hadronically decaying W-boson, or the kinematically equivalent cosine of the polar angle of
emission in the antitop (top) decay frame. Spinors and their outer-products are constructed so that the helicity-amplitude
phase convention of Jacob and Wick can be used throughout for the fixing of the signs associated with this large W-boson longitudinal–transverse
interference effect. 相似文献
5.
A search for lepton-flavor-violating interactions
and
has been performed with the ZEUS detector using the entire HERA I data sample, corresponding to an integrated luminosity
of
. The data were taken at center-of-mass energies,
, of 300 and
. No evidence of lepton-flavor violation was found, and constraints were derived on leptoquarks (LQs) that could mediate such
interactions. For LQ masses below
, limits were set on
, where
is the coupling of the LQ to an electron and a first-generation quark q1, and
is the branching ratio of the LQ to the final-state lepton
(μ or
) and a quark q. For LQ masses much larger than
, limits were set on the four-fermion interaction term
for LQs that couple to an electron and a quark
and to a lepton
and a quark
, where
and
are quark generation indices. Some of the limits are also applicable to lepton-flavor-violating processes mediated by squarks
in R-Parity-violating supersymmetric models. In some cases, especially when a higher-generation quark is involved and for the
process
, the ZEUS limits are the most stringent to date.
Received: 1 April 2005, Revised: 13 July 2005, Published online: 18 October 2005 相似文献
6.
Twist-3 distribution amplitudes of the pion and kaon are studied in this paper. We calculate the first several moments for the twist-3 distribution amplitudes (
and
) of the pion and kaon by applying the QCD sum rules. Our results show that (i) the first three moments of
and the first two moments of
and
of the pion and kaon can be obtained with 30
uncertainty; (ii) the fourth moment of the
and the second moment of the
can be obtained when the uncertainty are relaxed to 35
; (iii) the fourth moment of the
can be obtained only when the uncertainty are relaxed to 40
; (iv) we have
and
after including the
-corrections to the perturbative part. These moments will be helpful for constructing the twist-3 wave functions of the pion and kaon.Received: 6 January 2005, Revised: 29 March 2005, Published online: 22 June 2005PACS:
13.20.He, 11.55.Hx 相似文献
7.
M. Chaichian A. Kobakhidze A. Tureanu 《The European Physical Journal C - Particles and Fields》2006,47(1):241-245
We propose a mechanism for the spontaneous (gauge-invariant) reduction of noncommutative
gauge theories down to SU(n). This can be achieved through the condensation of composite
gauge invariant fields that involve half-infinite Wilson lines in the trace-U(1) noninvariant and SU(n) preserving direction.
Based on this mechanism, we discuss an anomaly-free fully gauge invariant noncommutative standard model based on the minimal
gauge group
, previously proposed, and show how it can be consistently reduced to the standard model with the usual particle spectrum.
Charge quantization for quarks and leptons naturally follows from the model. 相似文献
8.
We present a superfield Lax formalism of the superspace sigma model based on the target space
and show that a one-parameter family of flat superfield connections exists if the target space
is a symmetric space. The formalism has been related to the existence of an infinite family of local and non-local superfield
conserved quantities. A few examples have been given to illustrate the results. 相似文献
9.
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
10.
Upper limits on the cross-section of the pair-production process
, assuming 100
branching fraction to hadrons, are derived from a new search for the
hadrons final state, independently of the hadronic flavour of the decay products. This study, combined with previously published searches for the neutral Higgs bosons h0 and A0, is used to constrain the Type II Two Higgs Doublet Model (2HDM(II)) with no CP violation in the Higgs sector and no additional non-Standard Model particles besides the five Higgs bosons. The analysis combines LEP1 and LEP2 data collected with the OPAL detector up to the highest available centre-of-mass energies. The searches are sensitive to the
and
decay modes of the Higgs bosons. A benchmark scan of the 2HDM(II) parameter space is performed. Large regions of the 2HDM(II) parameter space explored are excluded at the 95% CL in the (
and
planes, using both direct neutral Higgs boson searches and indirect limits derived from Standard Model high precision measurements. The region
GeV and
GeV is excluded at 95 % CL, independently of
and for selected values of
which are representative of a complete
-scan.Received: 28 July 2004, Revised: 4 January 2005, Published online: 3 March 2005 相似文献
11.
A. Mischke 《The European Physical Journal C - Particles and Fields》2005,43(1-4):311-316
In this paper, preliminary results are presented on high
inclusive neutral pion measurements in d-Au collisions at
GeV in the pseudo-rapidity range
. Photons from the decay
are detected in the Barrel Electromagnetic Calorimeter of the STAR experiment at RHIC. The analysis of this first BEMC hadron
measurement is described in detail. The results are compared to earlier RHIC findings. Furthermore, the obtained
invariant differential cross sections show good agreement with next-to-leading order (NLO) perturbative QCD calculations.
Arrival of the final proofs: 4 July 2005
PACS:
25.75.-q 相似文献
12.
M. Neubert 《The European Physical Journal C - Particles and Fields》2005,40(2):165-186
Using results on soft-collinear factorization for inclusive B-meson decay distributions, a systematic study of the partial
decay rate with a cut
on photon energy is performed. For values of E
0 below about 1.9 GeV, the rate can be calculated without reference to shape functions using a multi-scale operator product expansion (MSOPE). The transition from the shape-function region to the MSOPE region is studied analytically. The resulting prediction for the
branching ratio depends on three large scales: m
b
,
, and
. Logarithms associated with these scales are resummed at next-to-next-to-leading logarithmic order. While power corrections in
turn out to be small, the sensitivity to the scale
GeV (for
GeV) introduces significant perturbative uncertainties, which so far have been ignored. The new theoretical prediction for the
branching ratio with
GeV is
, where the first error is an estimate of perturbative uncertainties and the second one reflects uncertainties in input parameters. With this cut
of all events are contained. When this fraction is combined with the previously best prediction for the total decay rate, one obtains
, with a somewhat less conservative estimate of parametric uncertainties. The implications of larger theory uncertainties for new physics searches are briefly explored with the example of the type-II two-Higgs-doublet model, for which the lower bound on the charged-Higgs mass is reduced compared with previous estimates to approximately 200 GeV at 95% confidence level.Received: 18 September 2004, Revised: 18 January 2005, Published online: 21 February 2005 相似文献
13.
14.
The Standard Model constraints on
which can be derived from the
decays are revisited in some depth. As experimental inputs, the
,
decays complemented by the
decays, the CP parameters
and
, and/or the value of
as determined by the global CKM fit are used. The constraints discussed here are model independent in the sense that they rely only on Isospin symmetry, following the Gronau-London proposal. A new bound on
and the function
are introduced. While another bound applied to BABAR results is shown to imply that
is negative. The Grossman-Quinn bound is rediscussed. A close form expression is given for
as a function of the measurements. Various scenarios for the future of the isospin analysis are explored. To probe the Standard Model the
plane is introduced.Received: 17 December 2004, Published online: 25 January 2005 相似文献
15.
A study of Z-boson pair production in e + e- annihilation at center-of-mass energies between 190 GeV and 209 GeV is reported. Final states containing only leptons, (
and
), quark and lepton pairs, (
,
) and only hadrons (
) are considered. In all states with at least one Z boson decaying hadronically, lifetime, lepton and event-shape tags are used to separate
pairs from
final states. Limits on anomalous ZZ
and ZZZ couplings are derived from the measured cross sections and from event kinematics using an optimal observable method. Limits on low scale gravity with large extra dimensions are derived from the cross sections and their dependence on polar angle.Received: 14 July 2003, Published online: 18 December 2003 相似文献
16.
A resonance search has been made in the
invariant-mass spectrum with the ZEUS detector at HERA using an integrated luminosity of
. The decay channels
and
(and the corresponding antiparticle decays) were used to identify
mesons. No resonance structure was observed in the
mass spectrum from more than 60 000 reconstructed
mesons. The results are not compatible with a report of the H1 Collaboration of a charmed pentaquark,
.Received: 14 September 2004, Revised: 29 September 2004, Published online: 9 November 2004 相似文献
17.
production in
interactions has been detected via its decays into
,K
+
K
-
K
+
K
- and
in the data taken with the DELPHI detector at LEP1 and LEP2 energies. The two-photon radiative width averaged over all observed decay channels is
= 13.9
2.0 (stat.)
1.4(syst.)
2.7 (BR) keV. No direct decay channel
has been observed. An upper limit
< 5.5 keV at 95% confidence level has been evaluated for this decay mode.Received: 3 July 2003, Published online: 7 November 2003 相似文献
18.
In the SUSY SO(10) GUT context, we study the exclusive processes
. Using the Wilson coefficients of the relevant operators including the new operators
which are induced by neutral Higgs boson (NHB) penguins, we evaluate some possible observables associated with these processes like the invariant mass spectrum (IMS), lepton pair forward-backward asymmetry (FBA), lepton polarization asymmetries etc. In this model the contributions from Wilson coefficients
, among new contributions, are dominant. Our results show that the NHB effects are sensitive to the FBA,
, and
of
decay, which are expected to be measured in B factories, the deviation of
in
can reach 0.1 from SM, which could be seen in B factories, and the average of the normal polarization
can reach several percent for
and it is 0.05 or so for
, which could be measured in the future super B factories and provide useful information to probe new physics and discriminate different models.Received: 30 October 2004, Published online: 9 March 2005 相似文献
19.
20.
We compute the one-loop
-functions describing the renormalisation of the coupling constant
and the frequency parameter
for the real four-dimensional duality-covariant non-commutative
-model, which is renormalisable to all orders. The contribution from the one-loop four-point function is reduced by the one-loop wavefunction renormalisation, but the
-function remains non-negative. Both
and
vanish at the one-loop level for the duality-invariant model characterised by
. Moreover,
also vanishes in the limit
, which defines the standard non-commutative
-quantum field theory. Thus, the limit
exists at least at the one-loop level.Received: 19 March 2004, Published online: 5 May 2004 相似文献