122201670
SPIN TRANSFER IN FRAGMENTATION PROCESSES AND HYPERON POLARIZATION IN DEEP-INELASTIC SCATTERING
We present the results for the polarizations of different octet hyperons produced in the current fragmentation regions of μ- N or νμ N deep-inelastic scatterings using different models for spin transfer in fragmentation processes. We found that measuring the polarization of Σ+ produced in these processes can give a good test to the validity of the different spin transfer models. Measuring PΣ+(T) in transversely polarized case should be able to give an useful check whether in high-energy fragmentation process the polarization transfer mechanisms are the same for both the longitudinally polarized and transversely polarized cases. A comparison with the existing data is made.
208983302
Measurements of Lambda and anti-lambda polarization in longitudinally polarized proton- proton collisions at JSNN = 200 GeV at STAR
hyperons in longitudinally polarized proton-proton collisions at fi = 200 GeV are presented. The A(A) candidates are reconstructed at mid-rapidity (171 < 1) with the time projection chamber of the STAR experiment at RHIC, using 0.5pb-1 collected in 2003 and 2004 with beam polarizations of up to 45%. Their mean longitudinal momentum fraction ZF is about 8 x ~ O ~ and their mean transverse momentum p~ is about 1.5 GeV. The analysis uses asymmetries of counts for different spin states of the colliding proton beams and does not require detailed knowledge of the detector acceptance. The preliminary A(&) polarization values are consistent with zero within their statistical uncertainties of 0.05. Preliminary results for the longitudinal polarization of A and Hyperon polarization measurements in high energy polarized p p collisions can give insight into the spin transfer from a polarized quark to a polarized baryon [l]. Hyperon polarization can also shed light on the the polarized parton distribution functions [2]. Anti-Lambda polarization provides sensitivity to Q3 [3]. The A and A have been studied widely because of their sizable production cross sections and self-analyzing decay properties in the decay channel A --+ p7r(A -+ @+) with a branching ratio of 64%. The polarization is usually extracted from the angular distribution of the decay (anti-)proton in the A(A) rest frame: dN Ntot --A(cos 6 ) ( l + aP cos e), dcos6 2 where Ntot is the total number of A(&)s, a! = +(-)0.642 f 0.013 is A(&) decay parameter [4], P is the A(A) polarization, e is the angle between the (anti-)proton momentum in the A(&) rest frame and the polarization direction, and A(cos8) is the detector acceptance. In the longitudinal case the polarization direction is the moving direction of A(A). In the notation above, we have omitted the dependence of the acceptance function on variables other than cos 0 for notational clarity. The data sample considered here consists of about 8M events, or about 0.5 pb-l, recorded in 2003 and 2004 by the Solenoid Tracker at RHIC (STAR) experiment [5] in proton-proton collisions at J;F = 200 GeV with longitudinal beam polarizations up to 45%. The A(&) reconstruction is made via decay A --t p r (A + p7r+). The A(A) candidates are reconstructed from two tracks with opposite curvature and a topology that is consistent with hyperon decay.
119471137
Spin alignment of vector meson in e+e- annihilation at Z0 pole
We calculate the spin density matrix of the vector meson produced in e+e- annihilation at Z^0 pole. We show that the data imply a significant polarization for the antiquark which is created in the fragmentation process of the polarized initial quark and combines with the fragmenting quark to form the vector meson. The direction of polarization is opposite to that of the fragmenting quark and the magnitude is of the order of 0.5. A qualitative explanation of this result based on the LUND string fragmentation model is given.
118961681
Spin alignments of vector mesons in deeply inelastic lepton-nucleon scattering
We extend the calculations of the spin alignments of vector mesons in $e^+e^-$ annihilation in a recent Rapid Communication to deeply inelastic lepton-nucleon scatterings. We present the results for different mesons in the current fragmentation regions of $\mu^- N$$ \to$$ \mu^- VX$ at high energies and $\nu_\mu N $$\to$$ \mu^- VX$ at both high and low energies. We also present the predictions for $\nu_\mu N$$ \to$$ \mu^- VX$ at NOMAD energies in the target fragmentation region using a valence quark model.
14189975
Spin alignment of the high p T vector mesons in polarized pp collisions at high energies
Using the same method as that used in $e^+e^-$ annihilation and lepton-nucleon deep-inelastic scattering, we calculate the spin alignment of vector mesons with high transverse momenta in high energy $pp$ collisions with one longitudinally polarized beam. We present the results obtained at RHIC energies. We also study the spin alignment of such vector mesons in the case of a transversely polarized proton beam and present its relation to the transversity distribution in the nucleon. Numerical results obtained using simple models for the transversity distributions are also given. These results show that there exist significant spin alignment in both cases, and they can be measured in experiments such as those at RHIC.
123007697
Contribution of Vector Meson Dominance to the Single-Spin Azimuthal Asymmetry in Semi-inclusive Pion Electro-Production
We calculate the contribution of vector meson dominance to deeply inelastic lepton-nucleon scattering in the kinematic region of the HERMES experiment. The results obtained show that this contribution is quite significant. Together with the fact that there exist very striking left-right asymmetries for hadrons produced in single-spin hadron-hadron collisions, these results imply that the single-spin azimuthal asymmetry observed by HERMES cannot be simply regarded as a pure fragmentation effect.
122744149
The colour-singlet technipion P0 and the recent experimental results at LEPII
We study the contributions of the technipion P0 predicted by the technicolour theory to the process e+e-→Zb. Our results show that the production cross section σ is very small. The value of the cross section σ is smaller than 3×10-3 fb for most technicolour models. It is impossible for the recent experimental results at LEPII to be explained within the framework of technicolour theory.
5505221
The rare top decay t → cg in topcolor assisted technicolor models
In the framework of topcolor-assisted technicolor(TC2) models, we calculate the contributions of flavor changing scalar couplings involved the neutral top-pion � 0 and top-Higgs h 0 to the branching ratio Br(t −→ cg). We find that the value of Br(t −→ cg) can reach 1 × 10 3 with reasonable values of the parameters in TC2 models, which may be testable in the future experiments.
17399206
Production and decay of the neutral top pion in high-energy e+ e- colliders
We study the production and decay of the neutral top-pion � 0 predicted by topcolor-assisted technicolor(TC2) theory. Our results show that, except the dominant decay modes b ¯, ¯ and gg, the � 0 t can also decay into and Z modes. It can be significantly produced at high energy e + e collider(LC) experiments via the processes e + e → � 0 and e + e → Z� 0 t. We further calculate the production cross sections of the processes e + e → � 0 → ¯ and e + e → Z� 0 → Z¯ tc. We find that the signatures of the neutral top-pion � 0 can be detected via these processes.
119223958
Suggestion for measuring the weak dipole moment of τ lepton at Z factory
Three new observables for Z-factory to measure the weak dipole moment of $\tau$ lepton ($d_w^\tau$) are proposed. As those observables employed at LEP-I, the new observables depend on the real and imaginary parts of $d_w^\tau$ linearly, thus we calculate the slopes, i.e. the linear coefficients of the dependence, precisely and find that the obtained slopes are much lager than those employed at LEP-I. It means that the signal for the weak dipole moment $d_w^\tau$ may be enhanced quite a lot, if one employs the new observables. Being superior to those at LEP-I, we recommend measuring the weak dipole moment $d_w^\tau$ in terms of the new observables if re-analyzing the data of LEP-I or doing the measurement at a possible Z-factory in the near future.