07.02.2011 WWND 2011 Michael Weber for the HADES collaboration Inclusive e + e - pair production in p+p and p+Nb collisions at E = 3.5 GeV Introduction HADES experiment Effects in cold nuclear matter Relative to 0 Cross sections Comparison with transport models Conclusions Technische Universität München
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Inclusive e + e - pair production in p+p and p+Nb collisions at E = 3.5 GeV
Michael Weber for the HADES collaboration. Inclusive e + e - pair production in p+p and p+Nb collisions at E = 3.5 GeV. Technische Universität München. Introduction HADES experiment Effects in cold nuclear matter Relative to p 0 Cross sections Comparison with transport models - PowerPoint PPT Presentation
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07.02.2011 WWND 2011
Michael Weber
for the HADES collaboration
Inclusive e+e- pair production in p+p and p+Nb collisions at E = 3.5 GeV
Introduction
HADES experiment
Effects in cold nuclear matter Relative to 0
Cross sections
Comparison with transport models
Conclusions
Technische Universität München
07.02.2011 WWND 2011
Phase diagram
Learn about properties of QCD matter at different (T,)EM structure of matter
hadrons in matter
http://www.ice.csic.es/en/graphics/phase.jpg
07.02.2011 WWND 2011
Phase diagram
Learn about properties of QCD matter at different (T,)EM structure of matter
hadrons in matter
Penetrating probe:Dielectrons
Direct coupling of *
to VM (JP=1-)
e+
e-
e+
e-
http://www.ice.csic.es/en/graphics/phase.jpg
07.02.2011 WWND 2011
Dense and hot matter
LHC
SPS
FAIR
SIS
e+
e-
e+
e-
e+
e-
e+
e-
e+
e-
RHIC
http://www.ice.csic.es/en/graphics/phase.jpg
Accessible in:
A+ A reactions
Dense matter at SIS:J. Stroth
07.02.2011 WWND 2011
Cold nuclear matter
Accessible in:
p + A / + A / + A
e+
e-
07.02.2011 WWND 2011
Cold nuclear matter
Accessible in:
p + A / + A / + A
Medium effects:
mass shift/ (collisional) broadening/ reabsorption/ regeneration
• High p: free NN prod. + same absorption for all sources
• Low p : enhanced prod. (secondary processes)
and/or lower absorption in IM and HM
LM IM HM
~0.7
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A scaling for vector mesons
Fit with Gaussians:
• High p:
pNb, = 0.69 ± 0.27
pNb, = 1.04 ± 2.50
• Low p:
pNb, = 0.62 ± 0.36
• : momentum dependent absorption ?
• : production in whole nucleus volume (statistics!) ?
T. Tabaru et al.. Phys.Rev. C 74(2006)
Data : p+A @ 12. GeV KEK E325
= 0.710 ± 0.021(stat) ± 0.037(syst)
= 0.937 ± 0.049(stat) ± 0.018(syst)
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Transport models - M
UrQMD
HSD
GiBUU
Different , , contributions !
07.02.2011 WWND 2011
Transport models - pT
UrQMD
HSD
GiBUU
Different , , contributions !
Constrain models ?
07.02.2011 WWND 2011
Slow and fast sources (GiBUU)
Collisional width in GiBUU for • momentum dependent
• 20 – 90 MeV ( 2 – 11 x vac)
07.02.2011 WWND 2011
Summary
• e+e- - pair production p+p and p+Nb at E = 3.5 GeV ( M, pT and y)• clear signal observed (/M ~ 2%)• significant e+e- - yield with low pair momenta (p < 800 MeV/c)
• Additional prod. w.r.t p+p at intermediate masses ( hard pT and target rapidity )
• A scaling of differential cross sections: (p+Nb/p+p) ~ A
– High p : all masses ~ 0.7 – Low p : 0 region: ~ 0.7
region: ~ 0.82 region: ~ 0.86
BUT ~ 0.62 in - medium omega width
• Comparison with transport models Better understanding of sources in p + p