ω -meson In-medium In-medium properties roperties of the f the -meson near near the the productionthreshold productionthreshold Michaela Thiel Michaela Thiel II. Physikalisches Institut, JLU Giessen II. Physikalisches Institut, JLU Giessen for for the the A2 collaboration A2 collaboration Hadron Hadron 2011 2011 XIV International Conference XIV International Conference on Hadron n Hadron Spectroscopy Spectroscopy Munich Munich 13–17 June 13–17 June 2011 2011 funded by DFG (SFB/TR 16) funded by DFG (SFB/TR 16)
ω properties properties of the of the meson meson ρ =0: well known well known for for =0: m=782.65 MeV m=782.65 MeV Γ =8.49MeV =8.49MeV 1
ω properties properties of the of the meson meson ρ =0: well known well known for for =0: m=782.65 MeV m=782.65 MeV Γ =8.49MeV =8.49MeV what what happens happens in a medium? in a medium? 1
ω properties properties of the of the meson meson ρ =0: well known well known for for =0: model model predictions predictions for for in-medium n-medium masses masses ω / GeV -2 -2 Spectrum / GeV Spectrum E / G E / GeV eV M. Lutz et al. M. Lutz et al. P. Mühlich P. Mühlich et al. et al. m=782.65 MeV m=782.65 MeV NPA 706 (2002) 431 NPA 706 (2002) 431 NPA 780 (2006) 187 NPA 780 (2006) 187 Γ =8.49MeV =8.49MeV what what happens happens in a medium? in a medium? 1
ω properties properties of the of the meson meson ρ =0: well known well known for for =0: model model predictions predictions for for in-medium n-medium masses masses ω / GeV -2 -2 Spectrum / GeV Spectrum E / G E / GeV eV M. Lutz et al. M. Lutz et al. P. Mühlich P. Mühlich et al. et al. m=782.65 MeV m=782.65 MeV NPA 706 (2002) 431 NPA 706 (2002) 431 NPA 780 (2006) 187 NPA 780 (2006) 187 Γ =8.49MeV =8.49MeV mass mass shift? shift? what what happens happens experimental task experimental task broadening? broadening? in a medium? in a medium? 1 structures? structures?
exp. approaches exp. approaches for for studying tudying in-medium n-medium effects effects → + � measurement measurement of the f the meson eson lineshape: lineshape: H X X 1 2 reconstruction reconstruction of invariant mass f invariant mass μ r products: ( ) ρ = + from from 4-momenta of decay 4-momenta of decay products: p , , T p p 1 2 ensure ensure that that decays decays occur occur in the n the medium: edium: = βγ ⋅ τ ≈ � select 1.3 fm( ρ ); 23 fm( ); 23 fm( ω ); 46 fm( ); 46 fm( φ ) select shortlived shortlived mesons: esons: s c 1.3 fm( or ω and and φ mesons � cut cut on low n low meson eson momenta momenta for mesons sensitive to nuclear sensitive to nuclear density ensity at decay at decay point! oint! 2
exp. approaches exp. approaches for for studying tudying in-medium n-medium effects effects → + � measurement measurement of the f the meson eson lineshape: lineshape: H X X 1 2 reconstruction reconstruction of invariant mass f invariant mass μ r products: ( ) ρ = + from from 4-momenta of decay 4-momenta of decay products: p , , T p p 1 2 ensure ensure that that decays decays occur occur in the n the medium: edium: = βγ ⋅ τ ≈ � select 1.3 fm( ρ ); 23 fm( ); 23 fm( ω ); 46 fm( ); 46 fm( φ ) select shortlived shortlived mesons: esons: s c 1.3 fm( or ω and and φ mesons � cut cut on low n low meson eson momenta momenta for mesons sensitive to nuclear sensitive to nuclear density ensity at decay at decay point! oint! � measurement measurement of the f the momentum omentum distribution: istribution: in case in case of a dropping of a dropping in-medium n-medium mass: mass: when when leaving leaving the he nucleus nucleus hadron adron has to become has to become on-shell; on-shell; mass mass generated generated at the at the expense xpense of kinetic of kinetic energy; energy; sensitive to nuclear sensitive to nuclear density ensity at production at production point! oint! advantage: independent of meson advantage: independent of meson lifetime! ifetime! 2
Crystal Ball and TAPS @ MAMI, Mainz Crystal Ball and TAPS @ MAMI, Mainz TAPS ϑ coverage: 1° - � TAPS coverage: 1° - 20° 0° CB ϑ coverage: 20° - � CB E e- : max. 1.6 GeV : max. 1.6 GeV coverage: 20° - 160° 60° e- 4 π setup setup ← beam TAPS LH2-Target CB (inside 2 MWPCs, PID)
Crystal Ball and TAPS @ MAMI, Mainz Crystal Ball and TAPS @ MAMI, Mainz TAPS ϑ coverage: 1° - � TAPS coverage: 1° - 20° 0° CB ϑ coverage: 20° - � CB E e- : max. 1.6 GeV : max. 1.6 GeV coverage: 20° - 160° 60° e- 4 π setup setup solid targets: C, Nb solid targets: C, Nb ← beam TAPS LH2-Target CB (inside 2 MWPCs, PID)
ω−>π 0 γ invariant mass invariant mass spectrum spectrum hadronic decay channel: γ A -> (A-1) A -> (A-1) ω p -> (A-1) p -> (A-1) π 0 γ p -> (A-1) p -> (A-1) γγγ p hadronic decay channel: LH LH 2 Carbon Carbon Niob Niobiu ium prelimi minary 4
background background determination: 2 approaches determination: 2 approaches background background determined determined by by fitting fitting liminary ry reli pre average average deviation eviation from from 1.0 in the 1.0 in the mass mass range range 430 – 430 – 650 MeV: 50 MeV: 1% 1% 5
background background determination: 2 approaches determination: 2 approaches background background determined determined background background determined determined by by fitting fitting from from data data liminary ry reli pre preliminary preliminary average average deviation eviation selecting selecting 4 γ from from 1.0 in the 1.0 in the and 1proton, and 1proton, 1 γ mass mass range range omitting omitting randomly randomly 430 – 430 – 650 MeV: 50 MeV: 1% 1% (M. Nanova et al., 5 PRC 82 (2010), 035209)
background background determination: 2 approaches determination: 2 approaches comparison comparison background background determined determined background background determined determined by by fitting fitting from from data data of both of both approaches approaches liminary ry reli pre preliminary preliminary preliminary preliminary average average deviation eviation selecting selecting agreement agreement within within 2% 2% 4 γ from from 1.0 in the 1.0 in the and 1proton, and 1proton, in the in the lower ower 1 γ mass mass range range omitting omitting randomly randomly mass mass range range ω 430 – 430 – 650 MeV: 50 MeV: 1% 1% near near the the signal signal (M. Nanova et al., 5 PRC 82 (2010), 035209)
of ω comparison comparison of signal signal lineshapes lineshapes ω signal signal lineshapes lineshapes in good agreement in good agreement for for the he two two different ifferent background background determination determination methods ethods in addition: in addition: applying applying a missing-mass a missing-mass cut cut and determine and determine the he background background by by a fit a fit preliminary preliminary 6
of ω comparison comparison of signal signal lineshapes lineshapes ω signal signal lineshapes lineshapes in good agreement in good agreement for for the he two two different ifferent background background determination determination methods ethods in addition: in addition: applying applying a missing-mass a missing-mass cut cut and determine and determine the he background background by by a fit a fit the the signal signal obtained btained with with missing-mass missing-mass cut ut preliminary preliminary has slightly has slightly better better resolution resolution 6
of ω comparison comparison of signal signal for for different nuclei ifferent nuclei with with missing-mass missing-mass cut cut preliminary preliminary ω -meson -meson lineshape lineshape in good in good agreement agreement for or C und und Nb Nb target target slightly slightly broader broader compared ompared to LH to LH 2 signal signal 7
of ω comparison comparison of signal signal for for different nuclei ifferent nuclei with with missing-mass missing-mass cut cut is is this this consistent consistent with with an an ≈ ( Γ med in-medium in-medium broadening broadening 150 MeV) 150 MeV) med determined determined from from the the Transparency ransparency ratio? atio? (M. Kotulla et al., PRL 100 (2008), 192302) preliminary preliminary ω -meson -meson lineshape lineshape in good in good agreement agreement for or C und und Nb Nb target target slightly slightly broader broader compared ompared to to LH LH 2 signal signal 7
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