Braunschweig, W.
POL
Max results
Sort by Reverse order

Showing 10 of 165 results

Date

Photoproduction of meson pairs: First measurement of the polarization observable I^s

The CBELSA & TAPS collaborations Gutz, E. ; Sokhoyan, V. ; van Pee, H. ; et al.
Phys.Lett.B 687 (2010) 11-15, 2010.
Inspire Record 840021 DOI 10.17182/hepdata.42248

The polarization observable I^s, a feature exclusive to the acoplanar kinematics of multi-meson final states produced via linearly polarized photons, has been measured for the first time. Results for the reaction g p -> p pi0 eta are presented for incoming photon energies between 970 MeV and 1650 MeV along with the beam asymmetry I^c. The comparably large asymmetries demonstrate a high sensitivity of I^s to the dynamics of the reaction. Fits using Bonn-Gatchina partial wave analysis demonstrate that the new polarization observables carry significant information on the contributing partial waves.

18 data tables
Table 1

Measured beam asymmetry I_S as a function of the angle between the reaction plane and the plane of the two final state particles with the the proton as the recoiling particle for the cm energy range 1642 to 1770 MeV.

Table 2

Measured beam asymmetry I_S as a function of the angle between the reaction plane and the plane of the two final state particles with the the proton as the recoiling particle for the cm energy range 1770 to 1898 MeV.

Table 3

Measured beam asymmetry I_S as a function of the angle between the reaction plane and the plane of the two final state particles with the the proton as the recoiling particle for the cm energy range 1898 to 1994 MeV.

More…

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…

Angular distributions of leptons from J/psi's produced in 920- GeV fixed-target proton-nucleus collisions

The HERA-B collaboration Abt, I. ; Adams, M. ; Agari, M. ; et al.
Eur.Phys.J.C 60 (2009) 517-524, 2009.
Inspire Record 810555 DOI 10.17182/hepdata.57473

A study of the angular distributions of leptons from decays of J/psi's produced in p-C and p-W collisions at sqrt{s}=41.6 GeV has been performed in the Feynman-x region -0.34 < x_F < 0.14 and for transverse momentum up to 5.4 GeV/c. The data were collected by the HERA-B experiment at the HERA proton ring of the DESY laboratory. The results, based on a clean selection of 2.3 x 10^5 J/psi's reconstructed in both the e^+ e^- and mu^+ mu^- decay channels, indicate that J/psi's are produced with longitudinal polarization. The magnitude of the effect is maximal at low p_T. For p_T >1 GeV/c a significant dependence on the reference frame is found: the polar anisotropy is more pronounced in the Collins-Soper frame and almost vanishes in the helicity frame, where, instead, a significant azimuthal anisotropy arises.

9 data tables
Table 1

Output parameters obtained by fitting the distributions.

Table 2

Values of the parameters Lambda_theta, Lambda_phi et Lambda_theta_phi measured in the Collins-Soper frame as functions of the average reconstructed p_T for combined carbon and tungsten data.

Table 3

Values of the parameters Lambda_theta, Lambda_phi et Lambda_theta_phi measured in the Collins-Soper frame as functions of the average reconstructed x_F for combined carbon and tungsten data.

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.


Neutron-proton analyzing power at 12 MeV and inconsistencies in parametrizations of nucleon-nucleon data

Braun, R.T. ; Tornow, W. ; Howell, C.R. ; et al.
Phys.Lett.B 660 (2008) 161-166, 2008.
Inspire Record 778429 DOI 10.17182/hepdata.50912

We present the most accurate and complete data set for the analyzing power Ay(theta) in neutron-proton scattering. The experimental data were corrected for the effects of multiple scattering, both in the center detector and in the neutron detectors. The final data at En = 12.0 MeV deviate considerably from the predictions of nucleon-nucleon phase-shift analyses and potential models. The impact of the new data on the value of the charged pion-nucleon coupling constant is discussed in a model study.

1 data table
Table 1

The measured analysing power at 12 MeV. Errors contain statistics and systematics added in quadrature.


Differential cross section and analyzing power measurements for polarized n(d) elastic scattering at 248-MeV

Maeda, Y. ; Sakai, H. ; Fujita, K. ; et al.
Phys.Rev.C 76 (2007) 014004, 2007.
Inspire Record 756614 DOI 10.17182/hepdata.25172

The differential cross sections and vector analyzing powers for nd elastic scattering at En=248 MeV were measured for 10°–180° in the center-of-mass (c.m.) system. To cover the wide angular range, the experiments were performed separately by using two different setups for forward and backward angles. The data are compared with theoretical results based on Faddeev calculations with realistic nucleon-nucleon (NN) forces such as AV18, CD Bonn, and Nijmegen I and II, and their combinations with the three-nucleon forces (3NFs), such as Tucson-Melbourne 99 (TM99), Urbana IX, and the coupled-channel potential with Δ-isobar excitation. Large discrepancies are found between the experimental cross sections and theory with only 2N forces for θc.m.>90°. The inclusion of 3NFs brings the theoretical cross sections closer to the data but only partially explains this discrepancy. For the analyzing power, no significant improvement is found when 3NFs are included. Relativistic corrections are shown to be small for both the cross sections and the analyzing powers at this energy. For the cross sections, these effects are mostly seen in the very backward angles. Compared with the pd cross section data, quite significant differences are observed at all scattering angles that cannot be explained only by the Coulomb interaction, which is usually significant at small angles.

6 data tables
Table 1

Cross section for N DEUT elastic scattering for data taken in 2003 in the backward direction in the centre-of-mass. Statistical errors only are given.

Table 2

Cross section for N DEUT elastic scattering for data taken in 2000 in the backward direction in the centre-of-mass. Statistical errors only are given.

Table 3

Cross section for N DEUT elastic scattering in the forward direction in the centre-of-mass. Statistical errors only are given.

More…

Polarization of J / psi and psi(2S) mesons produced in p anti-p collisions at s**(1/2) = 1.96-TeV

The CDF collaboration Abulencia, A. ; Adelman, Jahred A. ; Affolder, T. ; et al.
Phys.Rev.Lett. 99 (2007) 132001, 2007.
Inspire Record 747876 DOI 10.17182/hepdata.42742

We have measured the polarizations of J/ψ and ψ(2S) mesons as functions of their transverse momentum pT when they are produced promptly in the rapidity range |y|<0.6 with pT≥5  GeV/c. The analysis is performed using a data sample with an integrated luminosity of about 800  pb−1 collected by the CDF II detector. For both vector mesons, we find that the polarizations become increasingly longitudinal as pT increases from 5 to 30  GeV/c. These results are compared to the predictions of nonrelativistic quantum chromodynamics and other contemporary models. The effective polarizations of J/ψ and ψ(2S) mesons from B-hadron decays are also reported.

2 data tables
Table 1

Polarization parameter ALPHA for J/PSI production.

Table 2

Polarization parameter ALPHA for PSI(2S) production.


eta photoproduction on the proton revisited: Evidence for a narrow N(1685) resonance?

Kuznetsov, V. ; Polyakov, M. ; Boiko, T. ; et al.
2007.
Inspire Record 745642 DOI 10.17182/hepdata.41745

Revised analysis of $\Sigma$ beam asymmetry for $\eta$ photoproduction on the free proton reveals a resonant structure at $W\sim 1.69$ GeV. Comparison of experimental data with multipole decomposition based on the E429 solution of the SAID partial wave analysis and including narrow states, suggests a narrow ($\Gamma \leq 15$ MeV) resonance. Possible candidates are $P_{11}$, $P_{13}$, or $D_{13}$ resonances. The result is considered in conjunction with the recent evidence for a bump-like structure at $W\sim 1.67 - 1.68$ GeV in quasi-free $\eta$ photoproduction on the neutron.

5 data tables
Table 1

Measured beam asymmetry for a mean scattering angle of 43 degrees.

Table 2

Measured beam asymmetry for a mean scattering angle of 65 degrees.

Table 3

Measured beam asymmetry for a mean scattering angle of 85 degrees.

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.


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…