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1.
An upper limit for the –neutrino mass has been determined from the decay using data collected with the OPAL detector from 1991 to 1995 in collisions at . A limit of 43.2 MeV at 95% CL is obtained using a two–dimensional method in the invariant mass and energy distribution from 22 selected events. Combining this result with OPAL's previously published measurement
using decays, a new combined limit of MeV (95% CL) is obtained.
Received: 15 April 1998 / Published online: 12 August 1998 相似文献
2.
S. Hesselbach S. Moretti S. Munir P. Poulose 《The European Physical Journal C - Particles and Fields》2008,54(1):129-147
The di-photon decay channel of the lightest Higgs boson is considered as a probe to explore CP violation in the minimal supersymmetric
standard model (MSSM). The scalar/pseudo-scalar mixing is considered along with CP violation entering through the Higgs–sfermion–sfermion
couplings, with and without light sparticles. The impact of a light stop on the decay width and branching ratio (BR) is established
through a detailed study of the amplitude of the process H1→γγ. The other sparticles have little influence even when they are light. With a suitable combination of other MSSM parameters,
a light stop can change the BR by more than 50% with a CP-violating phase φμ∼90°, while the change is almost nil with a heavy stop. 相似文献
3.
S.Y. Choi A. Djouadi H.S. Song P.M. Zerwas 《The European Physical Journal C - Particles and Fields》1999,8(4):669-677
In most supersymmetric theories, charginos , mixtures of charged color-neutral gauginos and higgsinos, belong to the class of the lightest supersymmetric particles.
They are easy to observe at colliders. By measuring the total cross sections and the left–right asymmetries with polarized electron beams in , the chargino masses and the gaugino–higgsino mixing angles can be determined. From these observables the fundamental SUSY
parameters can be derived: the SU(2) gaugino mass , the modulus and of the higgsino mass parameter, and , the ratio of the vacuum expectation values of the two neutral Higgs doublet fields. The solutions are unique; the CP-violating
phase can be determined uniquely by analyzing effects due to the normal polarization of the charginos.
Received: 3 December 1998 / Published online: 27 April 1999 相似文献
4.
S. Bornhauser M. Drees H. Dreiner O. J. P. Éboli J. S. Kim O. Kittel 《The European Physical Journal C - Particles and Fields》2012,72(3):1887
In the CP-violating Minimal Supersymmetric Standard Model, we study the production of a neutralino–chargino pair at the LHC.
For their decays into three leptons, we analyze CP asymmetries which are sensitive to the CP phases of the neutralino and
chargino sector. We present analytical formulas for the entire production and decay process, and identify the CP-violating
contributions in the spin correlation terms. This allows us to define the optimal CP asymmetries. We present a detailed numerical
analysis of the cross sections, branching ratios, and the CP observables. For light neutralinos, charginos, and squarks, the
asymmetries can reach several 10%. We estimate the discovery potential for the LHC to observe CP violation in the trilepton
channel. 相似文献
5.
We present a general parametrization of , and , decays, taking into account both electroweak penguin and rescattering effects. This formalism allows – among other things
– a generalized implementation of the strategies that were recently proposed by Neubert and Rosner to probe the CKM angle
with the help of , decays. In particular, it allows us to investigate the sensitivity of the extracted value of to the basic assumptions of their approach. We find that certain rescattering processes may have an important impact and
emphasize that additional hadronic uncertainties may be due to non-factorizable SU(3)-breaking effects. The former can be controlled by using SU(3) flavour symmetry arguments and additional experimental information provided by modes. We propose a new strategy to probe the angle with the help of the neutral decays , , which is theoretically cleaner than the , approach. Here rescattering processes can be taken into account by just measuring the CP-violating observables of the decay
. Finally, we point out that an experimental analysis of modes would also be very useful to probe the CKM angle , as well as electroweak penguins, and we critically compare the virtues and weaknesses of the various approaches discussed
in this paper. As a by-product, we point out a strategy to include the electroweak penguins in the determination of the CKM
angle from decays.
Received: 14 June 1999 / Published online: 28 September 1999 相似文献
6.
Aubert B Boutigny D De Bonis I Gaillard JM Jeremie A Karyotakis Y Lees JP Robbe P Tisserand V Palano A Chen GP Chen JC Qi ND Rong G Wang P Zhu YS Eigen G Reinertsen PL Stugu B Abbott B Abrams GS Borgland AW Breon AB Brown DN Button-Shafer J Cahn RN Clark AR Dardin S Day C Dow SF Elioff T Fan Q Gaponenko I Gill MS Goozen FR Gowdy SJ Gritsan A Groysman Y Jacobsen RG Jared RC Kadel RW Kadyk J Karcher A Kerth LT Kipnis I Kluth S Kolomensky YG Kral JF Lafever R LeClerc C Levi ME Lewis SA 《Physical review letters》2001,86(12):2515-2522
We present measurements of time-dependent CP-violating asymmetries in neutral B decays to several CP eigenstates. The measurement uses a data sample of 23x10(6) Upsilon(4S)-->BbarB decays collected by the BABAR detector at the PEP-II asymmetric B Factory at SLAC. In this sample, we find events in which one neutral B meson is fully reconstructed in a CP eigenstate containing charmonium and the flavor of the other neutral B meson is determined from its decay products. The amplitude of the CP-violating asymmetry, which in the standard model is proportional to sin2beta, is derived from the decay time distributions in such events. The result is sin2beta = 0.34+/-0.20 (stat)+/-0.05 (syst). 相似文献
7.
Z.J. Xiao W.J. Li L.B. Guo G.R. Lu 《The European Physical Journal C - Particles and Fields》2001,18(4):681-709
Based on the low energy effective Hamiltonian with generalized factorization, we calculate the new physics contributions
to the branching ratios and CP-violating asymmetries of the two-body charmless hadronic decays from the new strong and electroweak penguin diagrams in the topcolor-assisted technicolor (TC2) model. The top-pion penguins
dominate the new physics corrections, and both new gluonic and electroweak penguins contribute effectively to most decay modes.
For tree-dominated decay modes , etc. the new physics corrections are less than 10%. For decays , etc. the new physics enhancements can be rather large (from to ) and are insensitive to the variations of and within reasonable ranges. For the decays and is strongly dependent: varying from to in the range of –. The new physics corrections to the CP-violating asymmetries vary greatly for different B decay channels. For five measured CP asymmetries of the decays, is only about 20% and will be masked by large theoretical uncertainties. The new physics enhancements to interesting decays are significant in size (), insensitive to the variations of the input parameters and hence lead to a plausible interpretation for the unexpectedly
large decay rates. The TC2 model predictions for branching ratios and CP-violating asymmteries of all fifty-seven decay modes are consistent with the available data within one or two standard deviations.
Received: 18 August 2000 / Revised version: 22 October 2000 / Published online: 5 February 2001 相似文献
8.
E.H. Müller B. Kubis U.-G. Meißner 《The European Physical Journal C - Particles and Fields》2006,48(2):427-440
The charged kaon decay channel K+
ℓ3γ allows for studies of direct CP violation, possibly due to non-standard mechanisms, with the help of T-odd correlation variables. In order to be able to extract a CP-violating signal from experiment, it is necessary to understand all possible standard model phases that also produce T-odd asymmetries. We complement earlier studies by considering strong interaction phases in hadronic structure functions that appear at higher orders in chiral perturbation theory, and we compare our findings to other potential sources of asymmetries. PACS 13.20.Eb; 11.30.Er; 12.39.Fe 相似文献
9.
E. Boos M. Dubinin M. Sachwitz H.J. Schreiber 《The European Physical Journal C - Particles and Fields》2000,16(2):269-278
The Wtb vertex can be probed on future colliders in the processes of single top production (LHC, pp mode, NLC, mode) and of top pair production (NLC, mode). We analyze observables sensitive to anomalous Wtb couplings in the top pair production process of collisions. In particular, forward–backward and spin–spin asymmetries of the top decay products and the asymmetry of the
lepton energy spectrum are considered. Possible bounds on anomalous couplings obtained are competitive to those expected from
the upgraded Tevatron and LHC. The validity of the infinitely small width approximation for the three-body top decay is also
studied in detail.
Received: 20 January 2000 / Revised version: 12 April 2000 / Published online: 18 May 2000 相似文献
10.
《The European Physical Journal C - Particles and Fields》2006,47(3):547-587
The four LEP collaborations, ALEPH, DELPHI, L3 and OPAL, have searched for the neutral Higgs bosons which are predicted by
the Minimal Supersymmetric standard model (MSSM). The data of the four collaborations are statistically combined and examined
for their consistency with the background hypothesis and with a possible Higgs boson signal. The combined LEP data show no
significant excess of events which would indicate the production of Higgs bosons. The search results are used to set upper
bounds on the cross-sections of various Higgs-like event topologies. The results are interpreted within the MSSM in a number
of “benchmark” models, including CP-conserving and CP-violating scenarios. These interpretations lead in all cases to large
exclusions in the MSSM parameter space. Absolute limits are set on the parameter cosβ and, in some scenarios, on the masses
of neutral Higgs bosons. 相似文献
11.
Abe K Abe K Abe T Adachi I Ahn BS Aihara H Akatsu M Asano Y Aso T Aulchenko V Aushev T Bakich AM Ban Y Banas E Bedny I Behari S Behera PK Bondar A Bozek A Bracko M Brodzicka J Browder TE Casey BC Chang P Chao Y Cheon BG Chistov R Choi SK Choi Y Danilov M Dong LY Dragic J Drutskoy A Eidelman S Eiges V Enari Y Everton CW Fang F Fujii H Fukunaga C Fukushima M Gabyshev N Garmash A Gershon T Golob B Gordon A Guo R Haba J Hamasaki H Hanagaki K Handa F Hara K Hara T Hastings NC Hayashii H Hazumi M 《Physical review letters》2002,89(7):071801
We present a measurement of CP-violating asymmetries in B0-->pi(+)pi(-) decays based on a 41.8 fb(-1) data sample collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. We fully reconstruct one neutral B meson as a B0-->pi(+)pi(-) CP eigenstate and identify the flavor of the accompanying B meson from its decay products. From the asymmetry in the distribution of the time intervals between the two B meson decay points, we obtain the CP-violating asymmetry parameters S(pipi)=-1.21(+0.38)(-0.27)(stat)+0.16-0.13(syst) and A(pipi)=+0.94(+0.25)(-0.31)(stat)+/-0.09(syst). 相似文献
12.
A. Abele et al. 《The European Physical Journal C - Particles and Fields》2001,21(2):261-269
Two different annihilation modes, and , are used to study the 4–decays of scalar and vector mesons. The data are dominated by 4 scalar isoscalar interactions. At least two states are needed, the and the . The 4–decay width of the is more than 6 times larger than the sum of all observed partial decay widths to two pseudoscalar mesons. The state has important
couplings to and to . The 4-decays of the (1500) represent about half of its total width. The and the are observed in several 4 decay modes. The ratio of the relative to the decay of the is in contradiction to its proposed interpretation as a pure hybrid state but it suggests that it is not a pure –state either. Our results favour the assignment of the as state, its interpretation as -state is less plausible.
Received: 7 December 2000 / Published online: 19 July 2001 相似文献
13.
Saurabh D Rindani 《Pramana》2000,54(6):791-812
We obtain analytic expressions for the energy and polar-angle double differential distributions of a secondary lepton l
+ (l
−) arising from the decay of t(t) in e
+
e
− → tt with an anomalous tbW decay vertex. We also obtain analytic expressions for the various differential cross-sections with the lepton energy integrated
over. In this case, we find that the angular distributions of the secondary lepton do not depend on the anomalous coupling
in the decay, regardless of possible anomalous couplings occurring in the production amplitude for e
+
e
− → tt. Our study includes the effect of longitudinal e
− and e
+ beam polarization. We also study the lepton energy and beam polarization dependence of certain CP-violating lepton angular
asymmetries arising from an anomalous tbW decay vertex and compare them with the asymmetries arising due to CP-violation in the production process due to the top electric
or weak dipole moment. 相似文献
14.
Aubert B Boutigny D Gaillard JM Hicheur A Karyotakis Y Lees JP Robbe P Tisserand V Palano A Chen GP Chen JC Qi ND Rong G Wang P Zhu YS Eigen G Reinertsen PL Stugu B Abbott B Abrams GS Borgland AW Breon AB Brown DN Button-Shafer J Cahn RN Clark AR Gill MS Gritsan AV Groysman Y Jacobsen RG Kadel RW Kadyk J Kerth LT Kluth S Kolomensky YG Kral JF LeClerc C Levi ME Liu T Lynch G Meyer AB Momayezi M Oddone PJ Perazzo A Pripstein M Roe NA Romosan A Ronan MT Shelkov VG Telnov AV Wenzel WA Zisman MS 《Physical review letters》2001,87(9):091801
We present an updated measurement of time-dependent CP-violating asymmetries in neutral B decays with the BABAR detector at the PEP-II asymmetric B Factory at SLAC. This result uses an additional sample of Upsilon(4S) decays collected in 2001, bringing the data available to 32 x 10(6) BB macro pairs. We select events in which one neutral B meson is fully reconstructed in a final state containing charmonium and the flavor of the other neutral B meson is determined from its decay products. The amplitude of the CP-violating asymmetry, which in the standard model is proportional to sin2 beta, is derived from the decay time distributions in such events. The result sin2 beta = 0.59+/-0.14(stat)+/-0.05(syst) establishes CP violation in the B(0) meson system. We also determine absolute value of lambda = 0.93+/-0.09(stat)+/-0.03(syst), consistent with no direct CP violation. 相似文献
15.
Chen S Fast J Hinson JW Lee J Menon N Miller DH Shibata EI Shipsey IP Pavlunin V Cronin-Hennessey D Kwon Y Lyon AL Thorndike EH Jessop CP Marsiske H Perl ML Savinov V Ugolini D Zhou X Coan TE Fadeyev V Maravin Y Narsky I Stroynowski R Ye J Wlodek T Artuso M Ayaad R Boulahouache C Bukin K Dambasuren E Karamnov S Kopp S Majumder G Moneti GC Mountain R Schuh S Skwarnicki T Stone S Viehauser G Wang JC Wolf A Wu J Csorna SE Danko I McLean KW Márka S Xu Z Godang R Shapiro A 《Physical review letters》2000,85(3):525-529
We search for CP-violating charge asymmetries (alpha(CP)) in the B meson decays to K(+/-)pi(-/+), K(+/-)pi(0), K(0)(S)pi(+/-), K(+/-)eta('), and omega pi(+/-). Using 9.66 million upsilon(4S) decays collected with the CLEO detector, the statistical precision on alpha(CP) is in the range of +/-0.12 to +/-0.25 depending on decay mode. While CP-violating asymmetries of up to +/-0.5 are possible within the standard model, the measured asymmetries are consistent with zero in all five decay modes studied. 相似文献
16.
17.
N.G. Stefanis W. Schroers H.-Ch. Kim 《The European Physical Journal C - Particles and Fields》2000,18(1):137-156
We develop and discuss in technical detail an infrared-finite factorization and optimized renormalization scheme for calculating
exclusive processes, which enables the inclusion of transverse degrees of freedom without entailing suppression of calculated
observables, like form factors. This is achieved by employing an analytic, i.e., infrared stable, running strong-coupling
which removes the Landau singularity at by a minimum power-behaved correction. The ensuing contributions to the cusp anomalous dimension – related to the Sudakov
form factor – and to the quark anomalous dimension – which controls evolution – lead to an enhancement at high of the hard part of exclusive amplitudes, calculated in perturbative QCD, while simultaneously improving its scaling behavior.
The phenomenological implications of this framework are analyzed by applying it to the pion's electromagnetic form factor,
including the NLO contribution to the hard-scattering amplitude, and also to the pion–photon transition at LO. For the pion
wave function, an improved ansatz of the Brodsky–Huang–Lepage type is employed, which includes an effective (constituent-like)
quark mass, GeV. Predictions for both form factors are presented and compared to the experimental data, applying Brodsky–Lepage–Mackenzie
commensurate scale setting. We find that the perturbative hard part prevails at momentum transfers above about 20 GeV, while at lower values the pion form factor is dominated by Feynman-type contributions. The theoretical prediction for the form factor indicates that the true pion distribution amplitude may be somewhat broader than the asymptotic one.
Received: 19 May 2000 / Revised version: 16 August 2000 / Published online: 13 November 2000 相似文献
18.
This report summarizes the final results from the OPAL collaboration on searches for neutral Higgs bosons predicted by the Minimal Supersymmetric Standard Model (MSSM). CP-conserving and, for the first time at LEP, CP-violating scenarios are studied. New scenarios are also included, which aim to set the stage for Higgs searches at future colliders. The results are based on the data collected with the OPAL detector at e + e- centre-of-mass energies up to 209 GeV. The data are consistent with the prediction of the Standard Model with no Higgs boson produced. Model-independent limits are derived for the cross-sections of a number of event topologies motivated by predictions of the MSSM. Limits on Higgs boson masses and other MSSM parameters are obtained for a number of representative MSSM benchmark scenarios. For example, in the CP-conserving scenario m
h-max where the MSSM parameters are adjusted to predict the largest range of values for m
h at each
, and for a top quark mass of 174.3 GeV, the domain
is excluded at the 95% confidence level and Higgs boson mass limits of m
h > 84.5 GeV and m
A > 85.0 GeV are obtained. For the CP-violating benchmark scenario CPX which, by construction, enhances the CP-violating effects in the Higgs sector, the domain
is excluded but no universal limit can be set on the Higgs boson masses.Received: 6 April 2004, Revised: 8 June 2004, Published online: 12 August 2004 相似文献
19.
E. Gotsman E. Levin U. Maor E. Naftali 《The European Physical Journal C - Particles and Fields》2000,14(3):511-523
We extend our previous treatment of the p cross section based on Gribov's hypothesis to the case of photon–photon scattering. With the aid of two parameters, determined
from the experimental data, we separate the interactions into two categories corresponding to short (“soft”) and long (“hard”)
distance processes. The photon–photon cross section thus receives contributions from three sectors, soft–soft, hard–hard and
hard–soft. The additive quark model is used to describe the soft–soft sector, pQCD the hard–hard sector, while the hard–soft
sector is determined by relating it to the system. We calculate and display the behaviour of the total photon–photon cross section and its various components and polarizations
for different values of energy and virtuality of the two photons, and discuss the significance of our results.
Received: 12 January 2000 / Published online: 6 April 2000 相似文献
20.
M. Maniatis A. von Manteuffel O. Nachtmann 《The European Physical Journal C - Particles and Fields》2007,49(4):1067-1076
Determining the global minimum of Higgs potentials with several Higgs fields like the next-to-minimal supersymmetric extension
of the standard model (NMSSM) is a non-trivial task already at the tree level. The global minimum of a Higgs potential can
be found from the set of all its stationary points defined by a multivariate polynomial system of equations. We introduce
here the algebraic Groebner basis approach to solve this system of equations. We apply the method to the NMSSM with CP-conserving
as well as CP-violating parameters. The results reveal an interesting stationary-point structure of the potential. Requiring
the global minimum to give the electroweak symmetry breaking observed in Nature excludes large parts of the parameter space. 相似文献