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1.
We consider the 2-dimensional Ising model with ferromagnetic nearest neighbour interaction at inverse temperature. LetS N = t be the total magnetization inside anN×N square box, per be the Gibbs state in with periodic b.c., andm() be the spontaneous magnetization. We show the existence of the limit
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2.
We consider the spin-averaged nucleon forward Compton scattering amplitude in heavy baryon chiral perturbation theory including all terms to order . The chiral prediction for the spin-averaged forward Compton scattering amplitude is in good agreement with the data for photon energies110 MeV. We also evaluate the nucleon electric and magnetic Compton polarizabilities to this order and discuss the uncertainties of the various counter terms entering the chiral expansion of these quantities.  相似文献   

3.
The reactione + e - e + e - 00e + e - 6 has been analysed using the full data sample taken with the Crystal Ball detector at the DORIS II storage ring at DESY. The 00 invariant mass spectrum is dominated by the ', for which we determine the radiative width (') to be (4.5±0.3±0.5)keV. Near 1.9 GeV/c2 we observe a second enhancement in the 00 mass distribution. Assuming that these events are created by the production and subsequent decay of a wide resonanceX(1900), we have investigated the decay modes, the invariant mass distributions of the 0 and 00 subsystems and the angular distributions of the final state mesons. We find that the data is best described byJ PC=2. For thisJ P assignment the resonance parameters are (X) BR(X)=(0.95±0.27±0.20) keV tot (X)=(221±92±44)MeV, andM(X)=(1881±32±40) MeV/c2.Deceased  相似文献   

4.
Isotonic and isobaric dependencies of nuclear charge radii in the region between Z=54 and Z=70 are obtained from the analysis of isotope shift data r2 and muonic and electron scattering data on r2. They are compared with the predictions of the droplet model and the Hartree-Fock calculations. The isobaric dependencies of r2 have proven to be especially sensitive to the choice of an effective nucleon-nucleon interaction.  相似文献   

5.
A systematic study of possible deuteronlike twomeson bound states,deusons, is presented. Previous arguments that many such bound states may exist are elaborated with detailed arguments and numerical calculations including, in particular, the tensor potential. This tensor potential which is crucial for the deuteron binding is shown to be very important also in the mesonic case. Especially, in the pseudoscalar3 P 0 pseudoscalar-vector and vector-vector channels the important observation is made that the centrifugal barrier from theP-wave can be overcome by the 1/r 2 and 1/r 3 terms of the tensor potential. In the heavy meson sector one-pion exchange alone is strong enough to form at least deuteronlike and composites bound by approximately 50 MeV. Composites of and states bound by pion exchange alone are expected near the thresholds, while in the light meson sector one generally needs some additional short range attraction to form bound states. The quantum numbers of these states areI=0, andJ PC=0–+, 1++ for the states andI=0,J PC=0++, O–+, 1+– and 2++ for the composites. In the states: b (10545), b1(10562) are predicted and in , one finds the states: b (10590), bQ (10582),h b(10608), b2(10602). Near the threshold the states: c (3870), c0(3870) are predicted, and near the threshold one finds the states: b0(4015), c (4015),h c(4015), c2(4015). Within the light meson sector pion exchange gives strong attraction for and systems with quantum numbers where the best non- candidates exist, although pion exchange alone is not strong enough to support such bound states. Thus, although one cannot conclude with certainty it to be the case, this fact does favour the picture that the (1440) and thef 1 (1420) are mainly composites and thef 0(1710) mainly a bound state, while thef 0(1515) andf 2(1520) could be predominantly composites. If the predicted and states are found, these would support this interpretation of the light states. In channels with exotic flavour orCP quantum numbers pion exchange is generally repulsive or quite weak. Therefore one does not expect that such deuteronlike bound states exist, althoughB*B* may be an exception.  相似文献   

6.
The systematics of-decay modes and radiative widths of highly excited states in28Si has been extended by taking-ray spectra on 60 resonances of the27Al(p,) reaction in the range 1097 keVE p 4492 keV (12643 keVE x 15915 keV) and on the24Mg(,) resonances atE =3355, 3431, 4003 keV (E x =12860, 12925, 13 415 keV). The-decay modes of levels in the sub-resonance region (E x =10–12.5 MeV) were studied with both the27 A1(p, ) reaction and the27 A1(d, n) reaction at Ed=4,5,6 MeV. Information on radiative widths of levels was obtained by measuring the resonance strengthsS =(2I+1) p / for 52 resonances of the27Al(p, ) reaction with an emphasis on prospective T=1 states.  相似文献   

7.
Motivated by nearly unanimous claim that the observed mass spectrum +- is not that expected from pure 0 dominance, we reanalyze all the published data on / +- decays. We find non-resonant contributions. In order to evaluate precisely the magnitude of these terms, we also refit the e+e- +- data to get reliably the 0 parameters and decay amplitude. We show that identifying the non-resonant contribution with the box anomaly predicted by QCD and chiral theories, one achieves a consistent picture. Several checks are performed which show the consistency of our fitted parameters. From four measurements, we determinef 1,f 8 and PS on purely experimental grounds, and we find them in the expected range. Presently available data allow for two solutions, one is consistent with QCD, the other favours integral charge quark models. We show that presently available data do not allow to choose among these two solutions. We discuss the interrelation of uncertainties in e+e- +- physics with our two solutions.  相似文献   

8.
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=">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>  相似文献   

9.
We develop a gauge theory of gravity on the basis of the principal fiber bundle over the four-dimensional space-timeM with the covering group 0 of the proper orthochronous Poincaré group. The field components are constructed with the connection coefficients , and with a Higgs-type field. A Lorentz metricg is introduced with , which are then identified with the components of duals of the Vierbein fields. Associated with there is a spinor structure onM. For Lagrangian densityL, which is a function of , ,, matter field , and oftheir first derivatives, we give the conditions imposed by the requirement of the gauge invariance. The Lagrangian densityL is restricted to be of the formL =L tot (, T klm ,R klmn , k , ), in whichT klm ,R klmn are the field strengths of , , respectively. Identities and conservation laws following from the gauge invariance are given. Particularly noteworthy is the fact that the energy momentum conservation law follows from theinternal translational invariance. The field equation of is automatically satisfied, if those of and of are both satisfied. The possible existence of matter fields with intrinsic energy momentum is pointed out. When is a field with vanishing intrinsic energy momentum, the present theory practically agrees with the conventional Poincaré gauge theory of gravity, except for the seemingly trivial terms in the expression of the spin-angular momentum density. A condition leading to a Riemann-Cartan space-time is given. The field holds a key position in the formulation.  相似文献   

10.
Several topics of relevance to low transverse momentum and 1,2(c ) production in polarized proton-proton collisions are discussed. The leadingO( S 3 ) contributions to the lowp T 1 production cross-sections viagg, qg, andq initial states are calculated as well as the corresponding spin-spin asymmetries. We find that 1 production increases relative to direct and 2 production, providing up to 25% of the observablee * e pairs arising from decays inpp collisions at s=500 GeV. The spin-dependence of 1 production, however, is much smaller than for either direct or 2 production and so will likely be far less useful than either process in probing the polarized gluon structure function of the proton. A subset of theO( S 3 ) radiative corrections to 2 production involving initial state quarks are also performed and compared to leading ordergg2 predictions.  相似文献   

11.
The p interactions with at least one charged secondary produced at polar angle 90° in c.m.s. and having the transverse momentum above 1 GeV/c were investigated. The data were obtained using streamer chamber magnetic spectrometer RISK at 38 GeV/c beam from Serpukhov accelerator. The analyzis of associated production in reconstructed events suggests, that if the transverse momentum of a pair of oppositely charged secondaries compensates the trigger particlep practically completely, this pair is the product of the 0 decay in marked fraction of such events. We observed a large spin-alignment for the 0-mesons selected as described above: the probability of zero spin projection onto the normal to the 0 production plane is equal to 00 T =0.86±0.23. The enhancement of the number of events, in which the 0 picks up practically full momentum transfer carrying by the exchange, and also the enlarged tensor polarization for the 0-mesons in these events could be qualitatively explained as manifestation of direct 0-production via the QCD higher twist processes in the highp p collisions. At the same time, the observed effects are markedly larger than the values predicted with QCD model in which the higher twist corrections were included.  相似文献   

12.
It is shown that one can fit the available data on thea o(980),f o(1300) andK o * (1430) mesons as a distorted 0++ nonet using very few (5–6) parameters and an improved version of the unitarized quark model. This includes all light two-pseudoscalar thresholds, constraints from Adler zeroes, flavour symmetric couplings, unitarity and physically acceptable analyticity. The parameters include a bare or mass, an over-all coupling constant, a cutoff and a strange quark mass of 100 MeV, which is in accord with expectations from the quark model. It is found that in particular for thea 0(980) andf 0(980) the component, in the wave function is large, i.e., for a large fraction of the time the state is transformed into a virtual pair. This component, together with a similar component of for thea 0(980), and , and components for thef 0(980), causes the substantial shift to a lower mass than what is naively expected from the component alone. Mass, width and mixing parameters, including sheet and pole positions, of the four resonances are given, with a detailed pedagogical discussion of their meaning.  相似文献   

13.
In the reactione + e W + W ( ) ( ) we expect that normally the colour singlet systems ( ) and ( ) hadronize independently into two hadron chains or strings. However also the pairs ( ) and ( ) form colour singlets with probability 1/N c 2 =1/9. This probability could be further enhanced by gluon exchange. We therefore expect that the hadronization can give recoupled colour strings between these quark-antiquark pairs with some small probability, and a study of this effect will give interesting information about the vacuum structure. In this paper we discuss a possible experimental signal for recoupled events and show that such events can be identified also when the effect of gluon emission before the recoupling is taken into account.  相似文献   

14.
We parametrise the polarised gluon and sea distribution functions incorporating the interpretation of the EMC experiment that, due to the axial anomaly the observed quark contribution to proton spin at Q 2>=10.7 GeV2. Typical processes to isolate the gluonic and sea content of the proton studied here are the largeP T direct photon production processes (a) using single polarized protonPPX and (b) polarized beam and target protonPPX. In both the above process the dominant contribution comes from the Compton subprocess and so can be used as a clean probe of the gluonic content of the proton. LargeP T muon pair production PP(+)X are also studied and we find that the annihilation subprocess dominates, but not much larger than the Compton subprocess and so may not be a clean probe of the sea content of the proton. The effect of two loop corrections to the parametrisation and asymmetries are also considered, and are found to be negligible.  相似文献   

15.
One expects a similarity of the energy dependence of the difference tot(*p)– tot(*n) for virtual (deep inelastic scatteringQ 2m 2) and real (Q 2=0) photons. Previous analysis of D structure functions with allowence for nuclear shadowing (NS) in the deuteron has led to conclusion that tot(*p)– tot(*n)<0>x<0.015. the=" early=" evidence=" from=" the=" real=" photoproduction=" data="> tot(p)– tot(n)<0. we=" critically=" reexamine=" determinations=" of=" the="> tot(p)– tot(n), using more accurate calculations of NS correction to tot(D), and discuss a possibility of tot(n) tot(p) at moderately high energies.  相似文献   

16.
A mini transmission-ray Compton polarimeter was developed for the measurement of the sign of magnetic moments of radioactive nuclei with low-temperature nuclear orientation. The signs of the magnetic moments of the following isotopes were determined:193Os [=+0.7297(16) N];191m Ir [=+6.20(9) N];192Ir [=+1.924(10) N];194Ir [=+0.39(1) N];195m Pt [=–0.605(15) N].Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday  相似文献   

17.
An analytic gravitational fieldZ (Z y ) is shown to include electromagnetic phenomena. In an almost flat and almost static complex geometryds 2 =zdzdz of four complex variables z=t, x, y, x the field equationsR Rz = –(U U Z ) imply the conventional equations of motion and the conventional electromagnetic field equations to first order if =(Z v) and =(z ) are expressed in terms of the conventional mass density function , the conventional charge density function , and a pressurep as follows: v=const=p/c 2–10–29 gm/cm3.  相似文献   

18.
The data ofJ/-production cross sections from photon, hadron and nucleus-nucleus collisions are plotted against the length of thec final state trajectory in nuclear matter. A value for the absorption cross section per nucleon of abs N =(6.2±0.3) mb is deduced from the baryon and photon induced reactions and abs N =(6.9±1.0) mb from the nucleus-nucles collisions. The equality of cross sections implies that additional suppression effects from a quark-gluon plasma are not visible.  相似文献   

19.
Within the MSSM we calculate the electroweak 1-loop box contributions to the processese + e Z 0 h 0 ande + e Z 0 h 0. We present detailed results for c.m. energies and as well as for tan =2 and tan =50. The box contributions to the processe + e Z 0 h 0 are, depending on and tan , of the order –2 to –20% and toe + e A 0 h 0 of 2 to 10%.  相似文献   

20.
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