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1.
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
2.
Chong-Xing Yue Wei Wang Zheng-Jun Zong Feng Zhang 《The European Physical Journal C - Particles and Fields》2005,42(3):331-339
In the framework of the littlest Higgs (LH) model, we consider the processes
and
, and we calculate the contributions of new particles to the cross sections of these processes in the future high energy e + e- collider (ILC) with
TeV. We find that, with reasonable values of the free parameters, the deviations of the cross sections for the processes
from their SM values might be comparable to the future ILC measurement precision. The contributions of the light Higgs boson H0 to the process
are significantly large in all of the parameter space preferred by the electroweak precision data, which might be detected in the future ILC experiments. However, the contributions of the new gauge bosons BH and ZH to this process are very small.Received: 22 February 2005, Revised: 27 April 2005, Published online: 6 July 2005PACS:
12.60.Cn, 14.70.Pw, 14.80.Cp 相似文献
3.
We study the effects of heavy Higgs bosons on the
production process at photon linear colliders. The interference patterns between the resonant Higgs production amplitudes and the continuum QED amplitudes are examined. The patterns tell us not only the CP nature of the Higgs bosons but also the phase of the
-Higgs vertex which gives new information about the Higgs couplings to new charged particles. We point out that it is necessary to use circularly polarized photon beams to produce efficiently heavy Higgs bosons whose masses exceed the electron beam energy, and show that the above interference patterns of the production amplitudes can be studied by observing t and
decay angular distributions. Analytic expressions for the helicity amplitudes for the sequential process
are presented in terms of the generic
production amplitudes.Received: 2 June 2003, Published online: 24 October 2003 相似文献
4.
In the context of the littlest Higgs (LH) model, we study the process
. We find that the new gauge bosons Z
H
and B
H
can produce significant correction effects on this process, which can be further enhanced by suitably polarized beams. In most of the parameter space preferred by the electroweak precision data, the absolute value of the relative correction parameter
is larger than 5 %. As long as
and
the absolute value of the relative correction parameter
is larger than
. With reasonable values of the parameters of the LH model, the possible signals of the new gauge bosons B
H
and Z
H
can be detected via the process
in the future LC experiments with the CM energy
. B
H
exchange and Z
H
exchange can generate significantly corrections to the forward-backward asymmetry
only in a small part of the parameter space.Received: 29 October 2004, Revised: 29 November 2004, Published online: 15 February 2005 相似文献
5.
A Monte-Carlo analysis on production and decay of supersymmetric charginos at a future photon-collider is presented. A photon collider offers the possibility of a direct branching-ratio measurement. In this study, the process
has been considered for a specific mSUGRA scenario. Various backgrounds and a parameterised detector simulation have been included. Depending on the centre-of-mass energy, a statistical error for the directly measurable branching ratio BR(
) of up to 3.5% can be reached.Received: 14 March 2005, Revised: 31 May 2005, Published online: 28 June 2005G. Klämke: Now at: Institut für Theoretische Physik, Universität Karlsruhe, Wolfgang-Gaede-Str. 1, 76131 Karlsruhe, Germany 相似文献
6.
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
7.
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
8.
In the CP-violating minimal supersymmetric standard model (MSSM), for certain values of the CP-violating phases associated to the universal trilinear couplings (At, Ab) and the gluino mass
, e.g.,
or
, for
GeV and
-5, the lightest Higgs boson mass (
) is
GeV. This mass interval is still allowed by results of standard LEP Higgs searches because of a strongly suppressed H1ZZ coupling. However, in the same region of parameter space in which these two conditions occur, the
coupling is enhanced because the two mentioned sets of couplings satisfy a sum rule. In this paper we probe such a light Higgs scenario at the Large Hadron Collider (LHC) by studying
associate production, leading to a
signal. We show that the latter is readily accessible at the CERN hadron collider, upon the application of suitable selection cuts against the standard model (SM) backgrounds. Our parton level Monte Carlo (MC) analysis yields
-45 signal events, completely free of SM background, for
- 30 fb-1 of accumulated luminosity, after taking into account the overall efficiency for tagging four b-jets.Received: 21 February 2005, Published online: 6 July 2005 相似文献
9.
We discuss the time-dependent CP asymmetry of the decay
in an extension of the standard model with both a two Higgs doublet and additional fourth-generation quarks. We show that, although the standard model with a two Higgs doublet and the standard model with fourth-generation quarks alone are not likely to largely change the effective
from the decay
, the model with both an additional Higgs doublet and fourth-generation quarks can easily account for the possible large negative value of
without conflicting with other experimental constraints. In this model, additional large CP violating effects may arise from the flavor-changing Yukawa interactions between neutral Higgs bosons and the heavy fourth-generation down type quark, which can modify the QCD penguin contributions. With the constraints obtained from
processes such as
and
, this model can lead to an effective
as large as - 0.4 in the CP asymmetry of
.Received: 25 March 2004, Revised: 20 April 2004, Published online: 18 June 2004 相似文献
10.
11.
We present standard model predictions for the four-fermion reaction
being one of the best detection channels of a low-mass Higgs boson produced through the Higgsstrahlung mechanism at a linear
collider. We include leading virtual and real QED corrections due to initial state radiation and a modification of the Higgs-
Yukawa coupling, caused by the running of the b-quark mass, for
. The complete
electroweak corrections to Z-Higgs production and to the Z-boson decay width, as well as the remaining QCD and EW corrections to the Higgs decay width, as can be calculated with the
program HDECAY, are taken into account in the double-pole approximation.
Received: 17 March 2005, Revised: 30 March 2005, Published online: 30 August 2005
Work supported in part by the Polish State Committee for Scientific Research in years 2004-2006 as a research grant, by the
European Community's Human Potential Program under contracts HPRN-CT-2000-00149 Physics at Colliders and CT-2002-00311 EURIDICE,
and by DFG under Contract SFB/TR 9-03. 相似文献
12.
The decay chain
is identified in a sample of 3.9 million hadronic Z decays collected with the OPAL detector at LEP. The branching ratio BR
is measured to be
for the J
P
=1+ (D0
1) state. For decays into the J
P
=2+ (D2
*0) state, an upper limit of 1.4 x 10-3 is placed on the branching ratio at the 95% confidence level.Received: 20 December 2002, Revised: 15 April 2003, Published online: 12 September 2003 相似文献
13.
M. Bisset N. Kersting J. Li F. Moortgat S. Moretti Q. L. Xie 《The European Physical Journal C - Particles and Fields》2006,45(2):477-492
Processes of the form pp → anything → XiXj →
+
+ notE are studied via a technique that may be viewed as an adaptation of time-honoured Dalitz plot analyses. Xi and Xj are new heavy states (with i, j =1, . . .,n), which may be identical or distinct; and
and
are necessarily distinct standard model (SM) fermion pairs whose invariant masses can be measured. A Dalitz-like plot of
said invariant masses,
versus
, exhibits a topology connected to the masses and specific decay chains of Xi and Xj. Aside from relatively minor details, observed patterns consist of a collection of box and wedge shapes. This collection
is model-dependent: comparison of the observed pattern to the possibilities for a specific model yields information on which
new particle pair combinations are actually being produced, information beyond that extractable from conventional one-dimensional
invariant mass distributions. The technique is illustrated via application to the minimal supersymmetric standard model (MSSM)
process pp →
→ e+e- + μ+μ- notE. Here the heavy states are neutralinos
(i = 2,3,4) - note that
is excluded - which are produced in gluino/squark (
/
) cascade decay chains. Even with fairly modest expectations for the LHC performance during the first few years, this method
still provides substantial insight into the neutralino mass spectrum and couplings if gluino/squark masses are relatively
low (≃ 400 GeV).
Arrival of the final proofs: 29 November 2005 相似文献
14.
K. Ozawa 《The European Physical Journal C - Particles and Fields》2005,43(1-4):421-426
Recent results on low mass dilepton measurements from the PHENIX experiment are reported. Invariant mass spectra of
are measured for the first time in Au-Au collisions at
GeV in Run2. In d-Au collisions, the yields and MT slopes of both
and
are measured. Both results are consistent with each other within errors. In the future, a Hadron Blind Detector will be installed
in PHENIX which will enhance our capabilities of rejecting external photon conversions and Dalitz pairs, that will result
in a significant reduction of the large combinatorial background.
* Deceased
Spokesperson 相似文献
15.
Multijet production rates in neutral current deep inelastic scattering have been measured in the range of exchanged boson
virtualities
. The data were taken at the ep collider HERA with centre-of-mass energy
using the ZEUS detector and correspond to an integrated luminosity of
. Jets were identified in the Breit frame using the kT cluster algorithm in the longitudinally invariant inclusive mode. Measurements of differential dijet and trijet cross sections
are presented as functions of jet transverse energy (
), pseudorapidity (
) and Q2 with
and
. Next-to-leading-order QCD calculations describe the data well. The value of the strong coupling constant
, determined from the ratio of the trijet to dijet cross sections, is
.
Received: 1 April 2005, Revised: 28 June 2005, Published online: 30 August 2005 相似文献
16.
Measurements of on-shell ZZ production are described, using data from the DELPHI experiment at LEP in e
+
e
- collisions at centre-of-mass energies between 183 and 209 GeV, corresponding to an integrated luminosity of about 665 pb-1. Results obtained in each of the final states
,
,
,
,
, l
+
l
-
l
+
l
-, and
(with
) are presented. The measured production cross-sections are consistent with the Standard Model expectations. These results update and supersede those already published at 183 and 189 GeV.Received: 3 March 2002, Revised: 28 May 2003, Published online: 19 September 2003 相似文献
17.
The most precise measurement of the weak mixing angle
at LEP is from the forward-backward asymmetry
at the Z-pole. In this note the QED and electroweak radiative corrections to obtain the pole asymmetry from the measured asymmetry for b- and c-quarks have been calculated using ZFITTER, which has been amended to allow a consistent treatment of partial two-loop corrections for the b-quark final asymmetries. A total correction of
and
has been found, where the remaining theoretical uncertainty is much too small to explain the apparent discrepancy between
obtained from A
FB
b
and from the left-right asymmetry at SLD.Received: 1 December 2004, Published online: 9 March 2005 相似文献
18.
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
19.
The L Collaboration 《The European Physical Journal C - Particles and Fields》2005,40(3):333-341
Data collected at LEP at centre-of-mass energies
GeV are used to study correlations of the spin of W bosons using
events. Spin correlations are favoured by data, and found to agree with the Standard Model predictions. In addition, correlations between the W-boson decay planes are studied in
and
events. Decay-plane correlations are measured to be consistent with the Standard Model predictions.Received: 26 October 2004, Revised: 15 January 2005, Published online: 3 March 2005 相似文献
20.
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