共查询到20条相似文献,搜索用时 31 毫秒
1.
J. Smith D. Thomas W. L. van Neerven 《Zeitschrift fur Physik C Particles and Fields》1989,44(2):267-290
The complete order α S QCD corrections to the cross section and differential distributions for \(p + \bar p \to W + \gamma + X\) are presented. At the quark level this involves the computation of the contributions from the reactions \(q + \bar q \to W + \gamma + g and q(\bar q) + g \to W + \gamma + q + (\bar q)\) . We discuss how these corrections modify the factorization property of the lowest order amplitude and give results for future experiments at CERN and Fermilab. 相似文献
2.
Bernd A. Kniehl 《Zeitschrift fur Physik C Particles and Fields》1992,55(4):605-618
The \(ZHf\bar f\) four-point function is calculated in the one-loop approximation of the Standard Model and full analytic results are presented. The loop contributions due to both light and new heavy fermions are inspected in detail. The dominant mechanisms of Higgs-boson production from fermions are compared. The effect of radiative corrections on the cross section of \(f\bar f \to ZH\) including bremsstrahlung is studied. The spectrum of hard bremsstrahlung is integrated analytically. The implications for Higgs-boson searches at futuree + e ? colliders in the energy range 200 \(200GeV \le \sqrt s \le 1.5TeV\) , which includes both LEP 2 and the Next Linear Collider, are analyzed. ForM H <2m t weak corrections in the modified on-mass-shell scheme are generally negative and feebly vary withM H , while forM H >2m t , they strongly increase withM H and may take large positive values. Electromagnetic corrections dramatically reduce the cross section close to theZH-production threshold, while they may considerably enhance it far above this threshold. 相似文献
3.
K. Numata 《Zeitschrift fur Physik C Particles and Fields》1991,52(4):691-700
It was reported that the contributions of the non-standardWWγ couplings called λγ and \(\bar \lambda _\gamma \) to the anomalous magnetic moments and the electric dipole moments of fermions depend on regularization schemes of the loop integral. We find that this dependence does not exist in the contributions of the λγ and \(\bar \lambda _\gamma \) couplings to the flavor changing neutral current (FCNC) processes of quarks such asb→sγ. By utilizing the experimental upper bound of the branching ratio of the processB→K *γ, we obtain the allowed regions of λγ and \(\bar \lambda _\gamma \) that do not depend on regularization schemes of the loop integral. The cut-off independent constraints of the other non-standardWWγ couplings called Δκλ and \(\tilde \kappa _\gamma \) are also obtained. 相似文献
4.
We investigate \(M^0 - \bar M^0 \) mixing and CP violation in the minimal left-right symmetric gauge model with spontaneous P and CP violation. The dominant contributions to the mixing amplitude including QCD corrections are calculated explicitly for \(B^0 - \bar B^0 \) . While the amount of mixing is not much changed with respect to the standard model leftright symmetry can give rise to significantly larger CP violation in the \(B_s^0 - \bar B_s^0 \) system (up to two orders of magnitude for the dilepton charge asymmetry). Sizable CP violating effects require that the left-right contribution to theK L K S mass difference has the same sign as the standard model contribution. We also comment on \(D^0 - \bar D^0 \) mixing including a careful discussion of the standard model prediction for the short distance part. 相似文献
5.
S. Groote H. Liivat I. Ots T. Sepp 《The European Physical Journal C - Particles and Fields》2010,66(1-2):271-281
In searching for indications of new-physics scalar particle and unparticle couplings in $e^{+}e^{-}\to t\bar{t}$ , we consider the role of transversely polarized initial beams at e + e ? colliders. By using a general relativistic spin density matrix formalism for describing the particles spin states, we find analytical expressions for the differential cross section of the process with t or $\bar{t}$ polarization measured, including the anomalous coupling contributions. Thanks to the transversely polarized initial beams these contributions are first order anomalous coupling corrections to the Standard Model (SM) contributions. We present and analyze the main features of the SM and anomalous coupling contributions. We show how differences between SM and anomalous coupling contributions provide means to search for anomalous coupling manifestations at future e + e ? linear colliders. 相似文献
6.
Recent evidence for the top mass in the region of 160 GeV for the first time provides an opportunity to use the full power of relativistic quantum field theoretical methods, available also for weakly bound systems. Because of the large decay width Γ of the top quark individual energy-levels in “toponium” will be unobservable. However, the potential for the $t\bar t$ system, based on a systematic expansion in powers of the strong coupling constant α s can be rigorously derived from QCD and plays a central role in the threshold region. It is essential that the neglect of nonperturbative (confining) effects is fully justified here for the first time to a large accuracy, also justbecause of the large Γ. The different contributions to that potential are computed from real level corrections near the bound state poles of the $t\bar t$ -system which for Γ≠0 move into the unphysical sheet of the complex energy plane. Thus, in order to obtain the different contributions to that potential we may use the level corrections at that (complex) pole. Within the relevant level shifts we especially emphasize the corrections of orderO(α s 4 m t ) and numerically comparable ones to that order also from electroweak interactions which may become important as well. 相似文献
7.
A. V. Anisovich V. V. Anisovich V. N. Markov N. A. Nikonov 《Physics of Atomic Nuclei》2002,65(3):497-512
The quark structure of φ(1020) and f 0(980) is studied on the basis of data on the radiative decays φ(1020) → γπ 0, γη, γη′, γ a 0(980), γ f 0(980) and f 0(980) → γγ. The partial widths are calculated under the assumption that all the mesons under consideration are $\bar qq$ states: φ(1020) is a dominantly $s\bar s$ state ( $\eta ' = n\bar nsin\theta + s\bar scos\theta $ component contributes not more than 1%); η, η′, and π 0 are standard $q\bar q$ states, $\eta = n\bar ncos\theta - s\bar ssin\theta $ and $\eta ' = n\bar nsin\theta + s\bar scos\theta $ with θ?37°; and f 0(980) is a e5 meson with the flavor wave function $n\bar ncos\varphi + s\bar ssin\varphi $ . The transition φ → γπ 0 specifies the admixture of the $n\bar n$ component in the φ meson: it is on the order of 0.5%. We argue that this order of $n\bar n$ value does not contradict data on the decay φ(1020) → γ a 0(980). The partial widths calculated for the decays φ → γη, γη? are in reasonable agreement with experimental data. The measured branching-ratio value Br(φ→γf 0(980))=(3.4±0.4 ?0.5 +1.5 ×10?4) requires 25°≤|?|≤90°. For the decay f 0(980) → γγ, the agreement with data, Γ(f 0(980) → γγ)=0.28 ?0.13 +0.09 keV, is attained at either ?=85°±8° or ?=?46°±8°. A simultaneous analysis of the decays φ(1020) → γ f 0(980) and f 0(980) → γγ favors the solution with the negative mixing angle of ?=?48°±6°, setting f 0(980) very close to the flavor octet (? octet=±54.7°). 相似文献
8.
Andrzej J. Buras Jennifer Girrbach Diego Guadagnoli Gino Isidori 《The European Physical Journal C - Particles and Fields》2012,72(10):1-10
The decay B s →μ + μ ? is one of the milestones of the flavor program at the LHC. We reappraise its Standard Model prediction. First, by analyzing the theoretical rate in the light of its main parametric dependence, we highlight the importance of a complete evaluation of higher-order electroweak corrections, at present known only in the large-m t limit, and leaving sizable dependence on the definition of electroweak parameters. Using insights from a complete calculation of such corrections for $K\to\pi\nu\bar{\nu}We present O(?? s ) results on the decays of polarized W ± and Z bosons into massive quark pairs. The NLO QCD corrections to the polarized decay functions are given up to the second order in the quark mass expansion. We find a surprisingly strong dependence of the NLO polarized decay functions on finite quark mass effects even at the relatively large mass scale of the W ± and Z bosons. As a main application we consider the decay t??b+W + involving the helicity fractions ?? mm of the W + boson followed by the polarized decay $W^{+}(\uparrow)\to q_{1}\bar{q}_{2}$ for which we determine the O(?? s ) polar angle decay distribution. We also discuss NLO polarization effects in the production/decay process $e^{+}e^{-}\to Z(\uparrow)\to q\bar{q}$ . 相似文献
9.
We study the production of charmed mesons (D) and baryons (?? c ) in antiproton-proton ${(\bar{p}p)}$ annihilation close to their respective production thresholds. The elementary charm production process is described by either baryon/meson exchange or by quark/gluon dynamics. Effects of the interactions in the initial and final states are taken into account rigorously. The calculations are performed in close analogy to our earlier study on ${\bar{p}p \to \bar{\Lambda} \Lambda}$ and ${\bar{p} p \to \bar{K} K}$ by connecting the processes via SU(4) flavor symmetry. Our predictions for the ${\bar{\Lambda}_c \Lambda_c}$ production cross section are in the order of 1 to 7 mb, i.e. a factor of around 10?C70 smaller than the corresponding cross sections for ${\bar{\Lambda} \Lambda}$ However, they are 100 to 1000 times larger than predictions of other model calculations in the literature. On the other hand, the resulting cross sections for ${\bar{D} D}$ production are found to be in the order of 10?2 ?C 10?1 ??b and they turned out to be comparable to those obtained in other studies. 相似文献
10.
A. S. Kurilin S. N. Bazylev V. A. Bednyakov A. G. Dolbilov M. Yu. Doroshenko E. S. Kuzmin S. V. Podolsky A. A. Semenov Yu. Yu. Stepanenko V. V. Tikhomirov V. N. Bolotov V. A. Duk A. A. Khudyakov V. A. Lebedev A. I. Makarov A. Yu. Polyarush G. I. Britvich Yu. P. Guz F. N. Novoskoltsev V. F. Obraztsov A. P. Ostankov V. K. Semenov O. P. Yushchenko 《Physics of Particles and Nuclei Letters》2010,7(1):21-26
The rare decay K L 0 → π0ν $ \tilde v $ branching ratio measurement is one of the clearest Standard Model test. Calculations based on the SM predict Br(K L 0 → π0ν $ \tilde v $ ) ≈ 2.8 × 10?11, but the most accurate experimental value Br(K L 0 → π0ν $ \tilde v $ ) < 6.7 × 10?8 (90% C.L.). We present design of a new experimental setup KLOD (U-70 accelerator, IHEP, Protvino) for K L 0 → π0ν $ \tilde v $ branching ratio measurement. Sensitivity of the KLOD experiment will be enough for registration of 2.4 events K L 0 → π0ν $ \tilde v $ for every 10 days of the data taking (according to SM predictions). 相似文献
11.
The $t\bar t$ system allows a truly perturbative treatment of the potential. Completing previous computations, we calculate the contributions of QCD box graph corrections, which make the “relativistic”O(α 4) corrections in the non-Abelian case differ from the well known corrections of the same order in QED. 相似文献
12.
S. Groote J. G. K?rner J. A. Leyva 《The European Physical Journal C - Particles and Fields》2009,63(3):391-406
We provide analytical results for the O(α s ) corrections to the polar angle dependence of the longitudinal spin–spin correlation asymmetry in $e^{+}e^{-}\to q\bar{q}$ . For top quark pair production the O(α s ) corrections to the longitudinal spin–spin asymmetry are strongly polar angle dependent and can amount up to ?4% in the q 2-range from above $t\bar{t}$ threshold up to $\sqrt{q^{2}}=1000\ \mbox {GeV}$ . The O(α s ) radiative corrections to the correlation asymmetry are below ≈1% in the forward direction where the cross section is largest. In the $e^{+}e^{-}\to b\bar{b}$ case the O(α s ) corrections reduce the asymmetry value from its m b =0 value of ?100% to approximately ?96% for q 2-values around the Z peak and are practically independent of the value of the polar angle θ. This reduction can be traced to finite anomalous contributions from residual mass effects which survive the m b →0 limit. We discuss the role of the anomalous contributions and the pattern of how they contribute to spin-flip and non-flip terms. 相似文献
13.
P. N. Kopnin 《Physics of Atomic Nuclei》2008,71(8):1445-1453
It is shown that, within the Standard Model extended by including a singlet quark heavy enough to prevent its direct detection at LHC, the mass differences $ \Delta m_{B_d } $ and $ \Delta m_{B_s } $ and the parameter of CP violation in K-meson oscillations, ? K , acquire universal corrections of about 5 to 10%. Implicit experimental constraints on the mass of this new quark are discussed. 相似文献
14.
The secondary acceptor A1 of the electron transport chain(s) of photosystem (PS) I is a phylloquinone (vitamin K1, VK1). Pulse electron paramagnetic resonance and electron nuclear double resonance (ENDOR) experiments at X-band frequencies were performed on the photoaccumulated acceptor radical A 1 ·? and the radical pair state P 700 ·+ A 1 ·? in PS I ofThermosynechococcus elongatus. The data obtained were compared with data from the respective radical anion of VK1 in organic solvents. The unusualg tensor magnitude of A 1 ·? is explained by the hydrophobic binding pocket of this radical. The hyperfine couplings and the spin (and charge) density distribution is very different for A 1 .? in PS I and VK 1 ·? in frozen alcoholic solution. This is attributed to a rather strong one-sided hydrogen bond to A 1 ·? . The presence of a hydrogen bond to A 1 ·? has only a minor effect ong. The hyperfine coupling constants of A 1 ·? determined from the radical pair spectra deviate only slightly from those derived from photoaccumulated A 1 ·? in PS I treated with dithionite at high pH. ENDOR resonances of the proton in a H bond were detected and an estimate of the strength and geometry of this bond to A 1 ·? was obtained. The significance of the hydrogen bond and other (hydrophobic) interactions of A1 with the surrounding are briefly discussed. 相似文献
15.
Johannes Blümlein 《Zeitschrift fur Physik C Particles and Fields》1995,65(2):293-298
The QED radiative corrections are calculated in the leading log approximation up to $\mathcal{O}(\alpha ^2 )$ for different definitions of the kinematical variables using jet measurement, the ‘mixed’ variables, the double angle method, and a measurement based onθ e andy JB . Higher order contributions due to exponentiation of soft radiation are included. 相似文献
16.
H. Cobbaert P. R. Hobson R. Arnold J. L. Bailly J. F. Balland M. Barth J. H. Bartley M. Boratav F. W. Bullock M. Callichio M. Coupland H. Drevermann B. G. Duff O. Erriquez M. J. Esten D. Geiregat K. Geissler F. Grard V. P. Henri A. Herve F. F. Heymann J. Hrubec D. C. Imrie E. Johannsson J. Kesteman P. Lecoq G. J. Lush G. Maurer M. t. Muciaccia S. Natali S. Nuzzo G. Neuhofer P. Olivier R. Roosen F. Ruggieri A. Taurok S. P. K. Tavernier M. C. Touboul A. M. Touchard O. R. Williams 《Zeitschrift fur Physik C Particles and Fields》1987,36(4):577-591
In the first holographic bubble chamber experiment — the HOBC experiment — we have accumulated a total of 40000 holograms with particle interactions. We have determined the total charm pair cross section inpN collisions to be 23.3 ?7.7 +10 μb and 3.6 ?1.7 +2.3 μb for 360 and 200 GeV/c incident protons respectively. We have assumed a linear dependence of the cross section on the atomic number of the target. This experiment has demonstrated the feasibility of holographic recording in small bubble chambers. Assuming that the charm cross section can be described by the standard QCD factorized expression with gluon fusion and quark-antiquark annihilation, we have used our measured charm cross sections with other measurements to determine the effective charmed quark mass to be 1.8 ?0.35 +0.25 GeV/c2. TheK factor, which describes the importance of the higher order corrections, is calculated to be 9.8 ?6.9 +12.5 (See noted added in proof.) 相似文献
17.
Robert Fleischer 《Zeitschrift fur Physik C Particles and Fields》1993,58(3):483-497
We investigate CP-violating phenomena both in semi-inclusive and exclusive penguin-inducedB-meson decays by using low energy effective Hamiltonians for |ΔB|=1, ΔC=ΔU=0 transitions including leading and next-to-leading order OCD corrections. In particular, we discuss the renormalization scheme dependences arising beyond the leading order and their explicit cancellation for the physical transition amplitudes. In order to estimate the hadronic matrix elements needed for the exclusive penguin modes, we apply both the Bauer, Stech, Wirbel model and the meson model of Brodsky and Lepage. Numerical results are presented for semi-inclusive \(b \to q'\bar qq(q',q \in \{ d,s\} )\) modes and the exclusive decaysB ?→K ? K 0, \(B^ - \to \pi ^ - \bar K^0 \) , and \(B_d^0 \to K^0 \bar K^0 \) . 相似文献
18.
V. V. Pogosov W. V. Pogosov D. P. Kotlyarov 《Journal of Experimental and Theoretical Physics》2000,90(5):908-918
Analytical expressions for the binding energy of electrons and positrons in dielectric clusters, analyzed in this work, neglect the elastic effects. Therefore, we present the density-functional theory for neutral liquid clusters that experience the spontaneous deformation. Using the 1/R-expansion, R being the cluster radius, the exact analytical expressions for the size corrections to the chemical potential, surface tension, and atomic density are derived from the condition of mechanical equilibrium. The problem of calculating these corrections is reduced to calculating the quantities for a liquid with a flat surface. The size compression and tension of density occur in the 1/R and 1/R 2 orders respectively. The sizes of charged rigid and elastic critical clusters, for which the electron or positron binding energy is close to zero, are calculated for Xe N ? , Kr N ? , Ar N ? , Ne N + , He N + . The calculations show significant contribution of self-compression to the binding energy of the excess electron in contrast to the positron. 相似文献
19.
The observability of a charged Higgs boson produced in association with a W boson at future muon colliders is studied. The analysis is performed within the MSSM framework. The charged Higgs is assumed to decay to $t\bar{b}We study $B_{s}^{0} \to J/\psi f_{0}(980)$ decays, the quark content of f 0(980) and the mixing angle of f 0(980) and ??(600). We calculate not only the factorizable contribution in the QCD factorization scheme but also the nonfactorizable hard spectator corrections in QCDF and pQCD approach. We get a result consistent with the experimental data of $B_{s}^{0} \to J/\psi f_{0}(980)$ and predict the branching ratio of $B_{s}^{0}$ ?CJ/???. We suggest two ways to determine f 0?C?? mixing angle ??. Using the experimental measured branching ratio of $B_{s}^{0} \to J/\psi f_{0}(980)$ , we can get the f 0?C?? mixing angle ?? with some theoretical uncertainties. We suggest another way to determine the f 0?C?? mixing angle ?? using both experimental measured decay branching ratios $B_{s}^{0} \to J/\psi f_{0}(980) (\sigma)$ to avoid theoretical uncertainties. 相似文献
20.
M. Seto Yu. Maeda T. Matsuyama H. Yamaoka H. Sakai S. Masubuchi S. Kazama 《Hyperfine Interactions》1992,68(1-4):213-216
A nonconjugated conducting polymer (1,4-rans-polyisoprene) at different iodine doping levels has been studied with the 27.7-keV Mössbauer resonance of129I. At the light doping level, almost all iodines are covalently bonding to the carbon atoms, breaking the double bonds of the main chain. At the medium doping level, other iodine species are found, which are idendified as anion species, l?, l 3 ? and l 3 ? .At the heavy doping level, polyiodide anions, l 3 ? and l 5 ? , increase as compared to the covalently bonding iodine atoms and addtionally molecular iodine l2 exists. 相似文献