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

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

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

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.

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.

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

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

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)

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

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)

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. 84-10, 1984 E.L. Bratkovskaya priv. communication

Results: h Dalitz plot momentum distributions angular distribution

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

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

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))

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

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)

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