Baldini, R.
Polarization
[2.0, 3.0]
Max results
Sort by Reverse order

Showing 10 of 133 results

Differential cross section and recoil polarization measurements for the gamma p to K+ Lambda reaction using CLAS at Jefferson Lab

The CLAS collaboration McCracken, M.E. ; Bellis, M. ; Meyer, C.A. ; et al.
Phys.Rev.C 81 (2010) 025201, 2010.
Inspire Record 840934 DOI 10.17182/hepdata.54967

We present measurements of the differential cross section and Lambda recoil polarization for the gamma p to K+ Lambda reaction made using the CLAS detector at Jefferson Lab. These measurements cover the center-of-mass energy range from 1.62 to 2.84 GeV and a wide range of center-of-mass K+ production angles. Independent analyses were performed using the K+ p pi- and K+ p (missing pi -) final-state topologies/ results from these analyses were found to exhibit good agreement. These differential cross section measurements show excellent agreement with previous CLAS and LEPS results and offer increased precision and a 300 MeV increase in energy coverage. The recoil polarization data agree well with previous results and offer a large increase in precision and a 500 MeV extension in energy range. The increased center-of-mass energy range that these data represent will allow for independent study of non-resonant K+ Lambda photoproduction mechanisms at all production angles.

241 data tables
Table 1

Differential cross section as a function of COS(THETA(K)) for the centre-of-mass range 1.62-1.63 GeV.

Table 2

Differential cross section as a function of COS(THETA(K)) for the centre-of-mass range 1.63-1.64 GeV.

Table 3

Differential cross section as a function of COS(THETA(K)) for the centre-of-mass range 1.64-1.65 GeV.

More…

Electroproduction of $\phi(1020)$ mesons at $1.4\leq Q^2\leq$ 3.8 GeV$^2$ measured with the CLAS spectrometer

The CLAS collaboration Santoro, J.P. ; Smith, E.S. ; Garc con, M. ; et al.
Phys.Rev.C 78 (2008) 025210, 2008.
Inspire Record 781974 DOI 10.17182/hepdata.50913

Electroproduction of exclusive $\phi$ vector mesons has been studied with the CLAS detector in the kinematical range $1.6\leq Q^2\leq 3.8$ GeV$^{2}$, $0.0\leq t^{\prime}\leq 3.6$ GeV$^{2}$, and $2.0\leq W\leq 3.0$ GeV. The scaling exponent for the total cross section as $1/(Q^2+M_{\phi}^2)^n$ was determined to be $n=2.49\pm 0.33$. The slope of the four-momentum transfer $t'$ distribution is $b_{\phi}=0.98 \pm 0.17$ GeV$^{-2}$. The data are consistent with the assumption of s-channel helicity conservation (SCHC). Under this assumption, we determine the ratio of longitudinal to transverse cross sections to be $R=0.86 \pm 0.24$. A 2-gluon exchange model is able to reproduce the main features of the data.

5 data tables
Table 1

Axis error includes +- 18.6/18.6 contribution.

Table 2

Axis error includes +- 18.6/18.6 contribution.

Table 3

Axis error includes +- 18.6/18.6 contribution.

More…

Analyzing power A(y) for omega meson production in proton-proton collisions

Abdel-Bary, M. ; Brinkmann, K.Th. ; Clement, H. ; et al.
Phys.Lett.B 662 (2008) 14-18, 2008.
Inspire Record 784829 DOI 10.17182/hepdata.26964

We report on a determination of the analyzing power Ay in the reaction studied with the TOF spectrometer located at the COSY-accelerator (Forschungszentrum Juelich, Germany). This spectrometer is very well suited for polarization measurements due to its rotational symmetry and full coverage of the azimuthal angle. For a beam momentum of p=3065MeV/c corresponding to an excess energy of epsilon (Porson) =129MeV Ay is found to be compatible with zero.

1 data table
Table 1

Analysing power measurements.


Separated structure functions for the exclusive electroproduction of K+ Lambda and K+ Sigma0 final states.

The CLAS collaboration Ambrozewicz, P. ; Carman, D.S. ; Feuerbach, R.J. ; et al.
Phys.Rev.C 75 (2007) 045203, 2007.
Inspire Record 732363 DOI 10.17182/hepdata.4994

We report measurements of the exclusive electroproduction of $K^+\Lambda$ and $K^+\Sigma^0$ final states from a proton target using the CLAS detector at the Thomas Jefferson National Accelerator Facility. The separated structure functions $\sigma_T$, $\sigma_L$, $\sigma_{TT}$, and $\sigma_{LT}$ were extracted from the $\Phi$- and $\epsilon$-dependent differential cross sections taken with electron beam energies of 2.567, 4.056, and 4.247 GeV. This analysis represents the first $\sigma_L/\sigma_T$ separation with the CLAS detector, and the first measurement of the kaon electroproduction structure functions away from parallel kinematics. The data span a broad range of momentum transfers from $0.5\leq Q^2\leq 2.8$ GeV$^2$ and invariant energy from $1.6\leq W\leq 2.4$ GeV, while spanning nearly the full center-of-mass angular range of the kaon. The separated structure functions reveal clear differences between the production dynamics for the $\Lambda$ and $\Sigma^0$ hyperons. These results provide an unprecedented data sample with which to constrain current and future models for the associated production of strangeness, which will allow for a better understanding of the underlying resonant and non-resonant contributions to hyperon production.

531 data tables
Table 1

Cross sections for incident energy 2.567 GeV for the Q**2 range 0.5 to 0.8 GeV**2 and W range 1.6 to 1.7 GeV.

Table 2

Cross sections for incident energy 2.567 GeV for the Q**2 range 0.5 to 0.8 GeV**2 and W range 1.70 to 1.75 GeV.

Table 3

Cross sections for incident energy 2.567 GeV for the Q**2 range 0.5 to 0.8 GeV**2 and W range 1.75 to 1.80 GeV.

More…

Mechanism of the close-to-threshold production of the eta meson.

Czyzykiewicz, R. ; Moskal, P. ; Adam, H.-H. ; et al.
Phys.Rev.Lett. 98 (2007) 122003, 2007.
Inspire Record 731185 DOI 10.17182/hepdata.41775

Measurements of the analysing power for the p(pol)p --> ppeta reaction have been performed in the close-to-threshold energy region at beam momenta of p_{beam}=2.010 and 2.085 GeV/c, corresponding to excess energies of Q=10 and 36 MeV, respectively. The determined analysing power is essentially consistent with zero implying that the eta meson is produced predominantly in the s-wave at both excess energies. The angular dependence of the analysing power, combined with the hitherto determined isospin dependence of the total cross section for the eta meson production in nucleon-nucleon collisions, reveal a statistically significant indication that the excitation of the nucleon to the S_{11}(1535) resonance, the process which intermediates the production of the eta meson, is predominantly due to the exchange of the pi meson between the colliding nucleons.

2 data tables
Table 1

Analysing power measurements for excess energy 10 MeV.

Table 2

Analysing power measurements for excess energy 36 MeV.


First measurement of beam-recoil observables C(x) and C(z) in hyperon photoproduction.

The CLAS collaboration Bradford, R.K. ; Schumacher, R.A. ; Adams, G. ; et al.
Phys.Rev.C 75 (2007) 035205, 2007.
Inspire Record 732402 DOI 10.17182/hepdata.31496

Spin transfer from circularly polarized real photons to recoiling hyperons has been measured for the reactions $\vec\gamma + p \to K^+ + \vec\Lambda$ and $\vec\gamma + p \to K^+ + \vec\Sigma^0$. The data were obtained using the CLAS detector at Jefferson Lab for center-of-mass energies $W$ between 1.6 and 2.53 GeV, and for $-0.85<\cos\theta_{K^+}^{c.m.}< +0.95$. For the $\Lambda$, the polarization transfer coefficient along the photon momentum axis, $C_z$, was found to be near unity for a wide range of energy and kaon production angles. The associated transverse polarization coefficient, $C_x$, is smaller than $C_z$ by a roughly constant difference of unity. Most significantly, the {\it total} $\Lambda$ polarization vector, including the induced polarization $P$, has magnitude consistent with unity at all measured energies and production angles when the beam is fully polarized. For the $\Sigma^0$ this simple phenomenology does not hold. All existing hadrodynamic models are in poor agreement with these results.

34 data tables
Table 1

Coefficients Cx and Cz for the reaction GAMMA P --> K+ LAMBDA for incident energy = 1.032 GeV and W = 1.679 GeV.

Table 2

Coefficients Cx and Cz for the reaction GAMMA P --> K+ LAMBDA for incident energy = 1.132 GeV and W = 1.734 GeV.

Table 3

Coefficients Cx and Cz for the reaction GAMMA P --> K+ LAMBDA for incident energy = 1.232 GeV and W = 1.787 GeV.

More…

Deeply virtual and exclusive electroproduction of omega mesons.

The CLAS collaboration Morand, L. ; Dore, D. ; Garcon, M. ; et al.
Eur.Phys.J.A 24 (2005) 445-458, 2005.
Inspire Record 681604 DOI 10.17182/hepdata.43499

The exclusive omega electroproduction off the proton was studied in a large kinematical domain above the nucleon resonance region and for the highest possible photon virtuality (Q2) with the 5.75 GeV beam at CEBAF and the CLAS spectrometer. Cross sections were measured up to large values of the four-momentum transfer (-t < 2.7 GeV2) to the proton. The contributions of the interference terms sigma_TT and sigma_TL to the cross sections, as well as an analysis of the omega spin density matrix, indicate that helicity is not conserved in this process. The t-channel pi0 exchange, or more generally the exchange of the associated Regge trajectory, seems to dominate the reaction gamma* p -> omega p, even for Q2 as large as 5 GeV2. Contributions of handbag diagrams, related to Generalized Parton Distributions in the nucleon, are therefore difficult to extract for this process. Remarkably, the high-t behaviour of the cross sections is nearly Q2-independent, which may be interpreted as a coupling of the photon to a point-like object in this kinematical limit.

85 data tables
Table 1

Total cross sections and interference terms (TT and TL).

Table 2

Differential cross sections DSIG/DT for Q**2 = 1.725 GeV**2 and W = 2.77 GeV.

Table 3

Differential cross sections DSIG/DT for Q**2 = 1.752 GeV**2 and W = 2.48 GeV.

More…

Measurement of the reaction gamma p --> K0 Sigma+ at photon energies up to 2.6-GeV.

Lawall, R. ; Barth, J. ; Bennhold, C. ; et al.
Eur.Phys.J.A 24 (2005) 275-286, 2005.
Inspire Record 680746 DOI 10.17182/hepdata.43595

The reaction gamma p --> K0 Sigma+ was measured in the photon energy range from threshold up to 2.6 GeV with the SAPHIR detector at the electron stretcher facility, ELSA, in Bonn. Results are presented on the reaction cross section and the polarization of the Sigma+ as a function of the kaon production angle in the centre-of-mass system, cos(Theta_K^{c.m.}), and the photon energy. The cross section is lower and varies less with photon energy and kaon production angle than that of gamma p --> K+ Sigma0. The Sigma+ is polarized predominantly at cos(Theta_K^{c.m.}) \approx 0. The data presented here are more precise than previous ones obtained with SAPHIR and extend the photon energy range to higher values. They are compared to isobar model calculations.

14 data tables
Table 1

Axis error includes +- 10/10 contribution (Normalization uncertainty already included.).

Table 2

Axis error includes +- 10/10 contribution (Normalization uncertainty already included.).

Table 3

Axis error includes +- 10/10 contribution (Normalization uncertainty already included.).

More…

Polarization transfer in proton Compton scattering at high momentum transfer.

The Jefferson Lab Hall A collaboration Hamilton, D.J. ; Mamyan, V.H. ; Aniol, K.A. ; et al.
Phys.Rev.Lett. 94 (2005) 242001, 2005.
Inspire Record 660894 DOI 10.17182/hepdata.19389

Compton scattering from the proton was investigated at s=6.9 (GeV/c)**2 and \t=-4.0 (GeV/c)**2 via polarization transfer from circularly polarized incident photons. The longitudinal and transverse components of the recoil proton polarization were measured. The results are in excellent agreement with a prediction based on a reaction mechanism in which the photon interacts with a single quark carrying the spin of the proton and in disagreement with a prediction of pQCD based on a two-gluon exchange mechanism.

1 data table
Table 1

Polarization transfer parameters.


Exclusive eta production in proton-proton reactions.

Balestra, F. ; Bedfer, Y. ; Bertini, R. ; et al.
Phys.Rev.C 69 (2004) 064003, 2004.
Inspire Record 653991 DOI 10.17182/hepdata.25225

Differential cross sections for the exclusive reaction p⃗p→ppη observed via the η→π+π−π0 decay channel have been measured at Tbeam=2.15GeV, 2.50GeV, and 2.85GeV (excess energies 324MeV, 412MeV, and 554MeV). The influence of the N(1535)S11 resonance is clearly seen in the invariant mass and momentum dependent differential cross sections. The extracted resonance parameters are compatible with existing data. No significant evidence for further resonance contributions has been found. In addition, angular distributions of the ppη final state have been measured. The polar angle distribution of the η shows an anisotropy with respect to the beam axis for the lowest beam energy, which vanishes for the higher energies. The sign of this anisotropy is negative and expected to be sensitive to the dominant production mechanism. In contrast, the proton polar angle in the pp rest frame tends to be more strongly aligned along the beam axis with increasing beam energy. The analyzing power Ay is compatible with zero for all beam energies.

8 data tables
Table 1

Differential cross section for incident kinetic energy 2.15 GeV, divided by the phase space as a function of the invariant mass of the ETA and the final state proton with the lower value of ABS(T). This is proportional to the square of the decay matrix element ABS(M)**2 of the P-ETA system.

Table 2

Differential cross section for incident kinetic energy 2.50 GeV, divided by the phase space as a function of the invariant mass of the ETA and the final state proton with the lower value of ABS(T). This is proportional to the square of the decay matrix element ABS(M)**2 of the P-ETA system.

Table 3

Differential cross section for incident kinetic energy 2.85 GeV, divided by the phase space as a function of the invariant mass of the ETA and the final state proton with the lower value of ABS(T). This is proportional to the square of the decay matrix element ABS(M)**2 of the P-ETA system.

More…