1. Exclusive w/h production in pp collisions at Ekin=3.5 GeV with HADES
Khaled Teilab
for the HADES collaboration

2. Outline Motivation HADES experiment Analysis ppw/h- degrees of freedom
Results

3. Motivation
determination of the total and differential exclusive production cross sections
determination of the angular distributions
study of the role of resonances in the production of w and h mesons

4. The High Acceptance Di-Electron Spectrometer (HADES)
SIS 18, GSI, Germany
magnetic spectrometer with multi-wire drift chambers for charged particles tracking
measurement of Cherenkov radiation, particle energy loss, time-of-flight, and electromagnetic showers.

5. Analysis
pp→ppp+p-p0
w→p+p-p0 (89.2 %)
h→p+p-p0 (22.7 %)
selection of events with 3 positively and one negatively charged tracks
identification of protons and charged pions via dE/dx in the drift chambers
kinematic refit
constraint: missing mass of p0 (1-C fit)
peaks at the same position as in simulation
full GEANT simulation
detector effects well-understood
Preliminary
ω- and h-peaks: fitted by scaling the signal shape as given by simulation.

6. ppw/h-degrees of freedom
4 degrees of freedom (f-symmetry taken into account)
2 Dalitz plot masses
emission angle of w/h in the reaction center-of-mass frame
angle -relative to the beam axis- of protons in their common rest mass frame
Pluto 4p simulation

7. Results: w Dalitz plot momentum distributions angular distribution
production cross section

8. Dalitz plot
symmetrized Dalitz plot (efficiency- and acceptance-corrected)
deviation from phase space ?
resonant production observed in gp reactions
Preliminary
J. Barth et al.
Eur. Phys. J. A 18, 117 (2003)

9. Momentum distributions
Preliminary
Preliminary
momentum distribution of protons agrees with phase space simulation
small deviation in the case of w

10. Angular distribution
slightly anisotropic distribution (√s- √s0=517 MeV)
anisotropy is smaller than measured by DISTO (√s- √s0=319 MeV)
Preliminary
blue line: F. Balestra et al.
Phys. Rev. C 63, 16 (2001)

11. Production cross section
spp→ppw= 137 ± 27 mb
in agreement with established energy dependence
Preliminary
F. Balestra et al.
Phys. Rev. C 63, 16 (2001)
COSY-TOF Collaboration
Phys. Rev. Lett. B 522, 16 (2001)
F. Hibou et al.
Phys. Rev. Lett. 83, 492 (1999)
V. Flaminio et al.
CERN-HERA Report No , 1984
E.L. Bratkovskaya
priv. communication

12. Results: h
Dalitz plot
momentum distributions
angular distribution

13. Dalitz plot N(1535) clearly observed N(1535) contribution ≈ 40%
Preliminary
Preliminary
Tbeam (GeV)
Q(MeV)
N(1535)
2.15
324
59%
2.5
412
51%
2.85
554
43%
DISTO Measurements
I. Fröhlich
priv. communication

14. Momentum distributions comparison to phase space simulation
Preliminary
Preliminary
proton momentum distribution doesn’t agree with phase space simulation
h momentum distribution doesn’t agree with phase space simulation

15. Momentum distributions comparison to 60% phase space + 40% N(1535) simulation
Preliminary
Preliminary
proton momentum distribution agrees with Pluto simulation (including 40% N(1535))
h momentum distribution agrees with Pluto simulation (including 40% N(1535))

16. Angular distribution inside the resonance region
Preliminary
Preliminary
inside the resonance region
outside the resonance region

17. Summary
differential production cross section of w/h mesons measured at Ekin=3.5 GeV
Dalitz plot for w production shows deviation from phase space
angular distribution of w mesons is less anisotropic compared to DISTO measurement at Ekin=2.85 GeV
contribution of N(1535) to the production of h mesons about 40%
angular distribution of h mesons is anisotropic (both for resonant and non-resonant production)

18. Thank you for your Attention