共查询到20条相似文献,搜索用时 31 毫秒
1.
W. Bernreuther G. W. Botz D. Bruß P. Haberl O. Nachtmann 《Zeitschrift fur Physik C Particles and Fields》1995,68(1):73-80
We discuss the effect of CP-violatingZb $\bar b$ Zb $\bar b$ G andZb $\bar b$ γ couplings on the width Γ(Z→b $\bar b$ X). The presence of such couplings leads in a natural way to an increase of this width relative to the prediction of the standard model. Various strategies of a direct search for such CP-violating couplings by using CP-odd observables are outlined. The number ofZ bosons required to obtain significant information on the couplings in this way is well within the reach of present LEP experiments. 相似文献
2.
The two photon couplings of hadronic states are believed to be key pointers to their parton constitutents. With the aim of studying these, we present a method of analysing data on γγ→ππ (andK \(\bar K\) ), which embodies the constraints of unitarity and analyticity while respecting the QED low energy theorem required by gauge invariance. We apply this analysis to presently available data on ππ production and find that within the existing uncertainties few definitive conclusions can yet be drawn in the resonance region. For instance, even the claim that thef-resonance has a largely helicity two coupling is shown not to be established. We illustrate the importance of the angular dependence of the data to reach almost all conclusions not only on the helicity structure off-production but also on the couplings of the scalar states to this vital channel. In the near threshold region, however, we confirm the overwhelming dominance of the QED Born amplitude modified by final state interactions in contradiction with several recent datasets on the π+π? channel. We show how the new Crystal Ball experiment on π+00 production not only confirms this conclusion on the near threshold cross-section but angular analysis of their data with its better statistics using the method we present should shed light on the nature of the scalar mesons in the 1 GeV region. 相似文献
3.
Andrzej Czarnecki A. N. Kamal Qiping Xu 《Zeitschrift fur Physik C Particles and Fields》1992,54(3):411-417
We have analysed the recent data onD→ππ and \(K\bar K\) decays from ARGUS, CLEO and E691. (i) We find that Bauer, Stech and Wirbel (BSW) model does fairly well in explaining all data if we assume that final state interactions simply rotate the amplitudes in the complex plane. However, to get a good fit one needs to raiseD→K transition amplitudes by (5–10)% over the BSW values and lowerD→π amplitudes by a similar amount. (ii) We show that all the data can also be understood in a coupled channel inelastic model. (iii) We also find that the Isgur, Scora, Grinstein and Wise (ISGW) model-form factors, if extrapolated to small momentum transfers (t) by a single pole formula, yield branching ratios too small in comparison to data. We propose an alternate scheme to interpolate between BSW form factors att=0 and ISGW form factors att=t max. 相似文献
4.
The implications of the model with a SU(2)-singlet up-type quark, heavy enough not to be produced at the LHC, namely, the contribution of the new quark to the branching ratios of the K → πν $ \bar \nu $ , B → πν $ \bar \nu $ , and B → Kν $ \bar \nu $ decays are investigated. It is shown that the deviation from the Standard Model can be up to 10% in the case of a 5-TeV quark. Precise measurements of these branching ratios in future experiments will allow for the observation of the contributions of the new quark or to impose stronger constraints on its mass. 相似文献
5.
A. V. Berezhnoy 《Physics of Atomic Nuclei》2005,68(11):1866-1872
Contributions of various color flows to the cross section for the gluonic production of Bc mesons are calculated. This is essential for simulating events involving Bc mesons with the aid of the PYTHIA package because the method used in PYTHIA to perform the hadronization of final partons and hadron remnants depends on the type of color flow. A modified method of partition into color flows is proposed. 相似文献
6.
Daniel Froidevaux Elżbieta Richter-Was 《Zeitschrift fur Physik C Particles and Fields》1995,67(2):213-225
A detailed study of associated Standard Model Higgs production (WH and
) at the LHC (or a possible upgraded Tevatron collider), where the Higgs boson decays to
pairs, is reported for 80m
H
<120 gev.=" even=" for=">120>b-tagging performances of the detector, the signal cannot be cleanly extracted from the background. For an integrated luminosity of 104
pb
–1 andm
H
=100 GeV, one can expect at best 110 reconstructed
decays fromWH production, above a resonant background of 150WZ events and a non-resonant background of 4800 events, and 100 reconstructed
pairs (of which 50 from
decay) from
production, above a background of 4000 events. The main difficulty in extracting these two channels is in the expected low signal rate after reconstruction, the need for accurate control of all the background sources and for extremely goodb-tagging performance. Nevertheless, for a few years of running at a luminosity of 1033 cm–2s–1,
channel may be the best way to probe the region 80m
H
<100>100> 相似文献
7.
Ch. de la Vaissière H. Muirhead S. N. Ganguli Ph. Gavillet M. Mazzucato C. Dionisi R. Blokzijl J. C. Kluyver G. F. Wolters E. W. Kittel M. Zralek B. Foster P. Grossman 《Zeitschrift fur Physik C Particles and Fields》1979,1(1):3-17
We have investigated the properties of off-shell \(\bar K\) K and \(\bar p\) p annihilations into pions by using the interactionsK ? p → Λ + pions at 4.2 GeV/c. The properties considered are multiplicities, hadronic temperatures and angular distributions. These properties appear more akin to those of \(\bar p\) p annihilations in flight than to that of \(\bar p\) p annihilation at rest despite the fact that the annihilation energy is small. 相似文献
8.
《Nuclear Physics B》1988,296(3):569-581
The cross sections for Ψ-production in the semihard collisions are calculated at s ⪢ |t|, mΨ2 and at not too large a jet effective mass mX2≲mΨ2 + |t| for the process γγ→ΨX. We found these cross sections in the lowest nontrivial QCD order (two-gluon exchange in the t-channel): σ(γγ→ΨX) ≈ 1035 cm2, σ(γγ→ΨΨ)=2×10−36 cm2. The polarization of Ψ in these processes is transversal (contrary to the longitudinal one of light mesons ϱ0, ω, ϕ in similar processes). 相似文献
9.
V. P. Druzhinin 《中国物理 C》2010,34(6):816-821
We present measurements of the γγ* → π^0 transition form factor for the momentum transfer range Q^2=4-40 GeV^2 and the γγ* → ηc transition form factor for the range Q^2=2-50 GeV^2. The current status of measurements of the meson-photon transition form factors for the η and η' mesons is discussed. The results of the measurement of the ηc mass, total and two-photon widths are also presented. 相似文献
10.
A. G. Shuvaev V. A. Khoze A. D. Martin M. G. Ryskin 《The European Physical Journal C - Particles and Fields》2008,56(4):467-477
We calculate the amplitude of $gg\to b\bar{b}$ production for the colour singlet, J z =0, di-gluon state at $\mathcal{O}(\alpha_{\mathrm{S}}^{2})$ order. We consider the cancellation and a realistic cut-off, of the infrared divergent terms. We show that the one-loop radiative QCD contributions effectively reduce the Born level result for the central exclusive $b\bar{b}$ cross section at the LHC. This process is essentially the only irreducible QCD background to the exclusive $H\to b\bar{b}$ signal. 相似文献
11.
N. R. Soni B. R. Joshi R. P. Shah H. R. Chauhan J. N. Pandya 《The European Physical Journal C - Particles and Fields》2018,78(7):592
The mass spectra and decay properties of heavy quarkonia are computed in nonrelativistic quark-antiquark Cornell potential model. We have employed the numerical solution of Schrödinger equation to obtain their mass spectra using only four parameters namely quark mass (\(m_c\), \(m_b\)) and confinement strength (\(A_{c\bar{c}}\), \(A_{b\bar{b}}\)). The spin hyperfine, spin-orbit and tensor components of the one gluon exchange interaction are computed perturbatively to determine the mass spectra of excited S, P, D and F states. Digamma, digluon and dilepton decays of these mesons are computed using the model parameters and numerical wave functions. The predicted spectroscopy and decay properties for quarkonia are found to be consistent with available data from experiments, lattice QCD and other theoretical approaches. We also compute mass spectra and life time of the \(B_c\) meson without additional parameters. The computed electromagnetic transition widths of heavy quarkonia and \(B_c\) mesons are in tune with available experimental data and other theoretical approaches. 相似文献
12.
B. V. Batyunya I. V. Boguslavsky I. M. Gramenitsky R. Lednický V. Vrba E. G. Boos D. I. Ermilova V. V. Samoilov T. Temiraliev P. Villanen E. Walck R. K. Dementiev I. A. Korzhavina E. M. Leikin V. I. Rud L. A. Tikhonova S. V. Levonian I. Herynek M. Lokajíček J. Řídký V. Šimák M. Suk A. Valkárová G. O. Kuratashvili T. P. Topuriya V. D. Tsintsadze 《Zeitschrift fur Physik C Particles and Fields》1984,25(3):213-223
InclusiveK s 0 , Λ and \(\bar \Lambda\) -production has been investigated in \(\bar p\) p-interactions at 22.4 GeV/c. Total and topological cross sections and multiplicity characteristics of neutral strange particles have been determined. DifferentialK s 0 and Λ-cross sections and also characteristics of annihilation processes with neutral kaon production have been studied. It is shown that the difference of the shapes of the invariantx-distributions forK-mesons in the fragmentation region for annihilation and non-annihilation processes can be described in the framework of the “dual” valon model, but not by considering the current (undressed) quark recombination mechanisms only. The polarization of Λ and \(\bar \Lambda\) -hyperons has been measured. 相似文献
13.
The three-body decays χ b0,2 → J/ ψc $\bar c$ and the decays x bJ → J/ ψD $\bar D$ related to them are studied. The differential widths with respect to these decays are calculated analytically, and their total widths are evaluated numerically. The duality relation between these decays and the two-body decays x b0,2 → J/ ψ(c $\bar c$ ) is verified. The possibility of observing these decays at the LHC and Tevatron colliders is discussed. 相似文献
14.
We consider contributions to
c
+
, and
from excited states. The calculations are performed within the MIT-bag model and a heavy quark bag model. Because the mass of
c
+
is rather big compared to the strange baryons, excited baryon states with mass close to that of
c
+
in some cases give significant pole contributions to the decay amplitudes of
c
+
. 相似文献
15.
A. G. Schneider-Neureither H. J. Pirner B. Kerbikov J. Mahalanabis 《Zeitschrift für Physik A Hadrons and Nuclei》1992,344(3):317-323
We fit the scattering lengths in the triplets-,p- andd- waves for the two channels \(\bar pp \to \bar \Lambda \Lambda\) and \(\bar \Lambda \Lambda \to \bar \Lambda \Lambda\) near theΛ production threshold to the differential cross section \(\frac{{d\sigma }}{{d\Omega }}(\bar pp \to \bar \Lambda \Lambda )\) and to the polarization P. 相似文献
16.
U. Gensch R. Klein H. J. Schreiber M. Walter H. Graessler D. Kuhn D. R. O. Morrison F. Triantis R. Barloutaud C. Cochet D. Denegri M. L. Faccini-Turluer A. Givernaud E. P. Kistenev A. A. Minaenko D. I. Patalakha E. Kozlovsky J. Macnaughton France-Soviet Union Collaboration CERN-Soviet Union Collaboration 《Zeitschrift fur Physik C Particles and Fields》1979,2(1):7-10
Antilambda production is studied inK ? p interactions at 32 GeV/c. Both total and differential cross sections are presented. The inclusive \(\bar \Lambda \) production cross section amounts to 109±7 μb. A remarkable energy dependence is observed, σ( \(\bar \Lambda \) ) increasing by a factor of four between 14.3 and 32 GeV/c. Thep ⊥ 2 distribution exhibits an exponential fall-off with a slope of 3.3±0.2 (GeV/c)?2. Most of the \(\bar \Lambda \) 's are emitted in the forward hemisphere. The invariantx distribution increases between 14.3 and 32 GeV/c. Data are presented for \(\bar \Lambda \) production inK - p→Λ \(\bar \Lambda \) +X K - p→ \(\bar \Lambda \) K n +X, andK - p→ \(\bar \Lambda \) p+X. 相似文献
17.
Charmonium ( \({c \bar{c}}\) ) bound states in few-nucleon systems, 2H, 4He and 8Be, are studied via Gaussian Expansion Method (GEM). We adopt a Gaussian potential as an effective \({(c \bar{c})}\) –nucleon (N) interaction. The relation between two-body \({(c \bar{c})}\) –N scattering length \({a_{c\bar{c}-N}}\) and the binding energies B of \({(c \bar{c})}\) –nucleus bound states are given. Recent lattice QCD data of \({a_{c\bar{c}-N}}\) corresponds to \({B \simeq 0.5}\) MeV for \({(c \bar{c})-^{4}}\) He and 2 MeV for \({(c \bar{c})-^{8}}\) Be in our results. 相似文献
18.
We discuss the use of fermion polarization for studying neutral Higgs bosons at a photon collider. To this aim we construct
polarization asymmetries which can isolate the contribution of a Higgs boson ϕ in γγ → f
, f = τ/t, from that of the QED continuum. This can help in getting information on the γγϕ coupling in case ϕ is a CP eigenstate. We also construct CP-violating asymmetries which can probe CP mixing in case ϕ has indeterminate CP. Furthermore, we take the MSSM with CP violation as an example to demonstrate the potential of these
asymmetries in a numerical analysis. We find that these asymmetries are sensitive to the presence of a Higgs boson as well
as its CP properties over a wide range of MSSM parameters.
相似文献
19.
L. S. Geng E. Oset B. S. Zou 《The European Physical Journal A - Hadrons and Nuclei》2008,38(2):239-245
We study the reactions J/ψ → $ \bar \Lambda $ K - p and J/ψ → $ \bar \Lambda $ π+π-Λ with a unitary chiral approach. We predict the ratio of the invariant-mass distributions of these two reactions at the Λ(1520) peak position, which is free of the unknown production mechanism and reflects only the properties of the Λ(1520) . An experimental measurement of this ratio will provide the couplings of the Λ(1520) to its decay channels, allowing to test the predictions of the chiral unitary approach on this resonance, which appears as dynamically generated in that approach. 相似文献
20.
J. Bartels A. Fridman A. Schwarz Tai Tsun Wu 《Zeitschrift fur Physik C Particles and Fields》1984,23(3):295-300
In the present note we further explore the possibility of measuring the number of \(\bar vv\) generations by means of \(Z^0 \to \bar vv\) decays. We investigate in particular the case where the radiative transitionse + e ? →γZ 0 are studied on theZ 0 resonance itself. The various background reactions are discussed as well as the statistical significance that can be obtained for an additional \(\bar vv\) generation. 相似文献