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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-
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Cold nuclear matter
Accessible in:
p + A / + A / + A
Medium effects:
mass shift/ (collisional) broadening/ reabsorption/ regeneration
Measure: Spectral shape / Cross sections/ Attenuation
BUT: NON conlusive experimental results
meson
P.Mühlich et al., NPA 780 (2006), 187
07.02.2011 WWND 2011
HADESI
04/22/23
observable detector
p MDC (Magnet)
β TOF(ino)
dE/dx MDC
TOF(ino)
e+/e- RICH
HADES[ EPJ A41 243]
Production of strangeness:L. Fabbietti
07.02.2011 WWND 2011
HADESII
22.04.23
HADES[ EPJ A41 243]
Beam: p• Ekin= 3.5 GeV• I ~ 6 · 106 1/s
Target : p• 4 cm LH2 • ~1% reaction prob.
3.5 · 109 collisions
A = 1 A = 93
High purity e+e- pair reconstruction
Beam: p• Ekin= 3.5 GeV• I ~ 2 · 106 1/s
Target : 93Nb • 12 x 0.45 mm• ~3% reaction prob.
9.2 · 109 collisions
observable detector
p MDC (Magnet)
β TOF(ino)
dE/dx MDC
TOF(ino)
e+/e- RICH
07.02.2011 WWND 2011
e+e- pair reconstruction
Comb. Background:• same event e-e- e+e+
• correlated BG from 0 / decays
Signal to BG ratio
07.02.2011 WWND 2011
e+e- sources in p + p
• particle production• π via resonance decays (,N*)• η, ω, ρ via phase space• Δ through 1 π exchange
• particle decays• form factors• mass dep. Width
PLUTO, Fröhlich et al, arxiv:0708.2382
• cross sections in 4π (mb)• : 16 ± 2.6 (from data)• Δ: 7.5 PYTHIA • η: 0.93 ± 0.2 (fit to data)• ω: 0.25 ± 0.05 (fit to data)• ρ: 0.38 ± 0.07 (fit to data)
Δ FF is fixed at the photon point
σω ~ 16 MeV/c2
Analysis by Anar Rustamov
07.02.2011 WWND 2011
e+e- sources in p + p
- N transition form factor
Time like: q2 > 0
Space like: q2 < 0
Two–component VDM type model:Wan/Iachello, IJMP A20, 2005
only relevant for exclusive analysis
Measured in electroproduction
NOT Measured
N
e-
e+
Analysis by Anar Rustamov
07.02.2011 WWND 2011
e+e-
No direct decay (same for p + Nb): reduce BR (2.7 x 10-5) at least by factor of 3
Analysis by Anar Rustamov
07.02.2011 WWND 2011
e+e- in p + Nb
Scaling to same yield in 0 peak
0
Yield/0 (p+Nb/p+p)• IM: 1.51
• HM: 1.37
• In region 1.13
→ diff. production and/or absorption mechansims for diff. sources
→ kinematic observables for diff. mass regions
LM
IM
HM
07.02.2011 WWND 2011
pNb vs. pp: pT and y
Transverse momentum
pT2 = px
2 + py2
Rapidity
y = ½ ln (E+pz)/ (E+pz )
yCM, NN = 1.12
LM LM
yCM, NN
07.02.2011 WWND 2011
pNb vs. pp: pT and y
For both mass bins:
• Higher yield
• At high pt
• Shift to target rap.
add. slow source
IM IM
HM
HM
07.02.2011 WWND 2011
Fast and slow e+e- sources
Decays inside nucleus In – Medium effects
HSD Simulation for HADES proposal
p cut
07.02.2011 WWND 2011
Fast and slow e+e- sources
HADES: Significant e+e- yield with low pair momenta ( ~ 35 % in HM)
p+Nb Ekin= 3.5 GeV
p cut
HM
07.02.2011 WWND 2011
Fast and slow sources in other Exp.
KEK: p + A @ 12 GeV JLAB: + A @ 0.6 -3.8 GeV
R.Muto et al., PRL 98 (2007) 042501 S.Leupold, V.Metag and U.Mosel, nucl-th 0907.2388
07.02.2011 WWND 2011
Fast and slow e+e- sources
High p: free p+p production
Low p: overshoot over p+p
different for , , and
High p Low p
07.02.2011 WWND 2011
Cross sections
p+p:X sect from pp, elastic
p+Nb:X sect from -,acc comp to HARP
Bolshakova et al., EPJC (1997) 1865
Isospin:pd = 2 pp ( DLS: Ekin > 2 GeV )
Wilson et al., PRC 57(1997) 1865
A Scaling:
• Black disc:= 2/3 Glauber model: ~ 0.8W.Cassing et al., PLB 238 (1990) 25
AdMd
dMdR
pp
pApA
)/(
)/(
07.02.2011 WWND 2011
RpNb vs. p
RpNb = 23.9 ± 1.1 RpNb = 27.4 ± 1.4 RpNb = 28.8 ± 2.4
pNb = 0.70 ± 0.10 pNb = 0.73 ± 0.13 pNb = 0.74 ± 0.21
• High p: free NN prod. + same absorption for all sources
LM IM HM
~0.7
07.02.2011 WWND 2011
RpNb vs. p
RpNb = 23.7 ± 0.2 RpNb = 40.9 ± 1.5 RpNb = 48.4 ± 5.3
pNb = 0.70 ± 0.02 pNb = 0.82 ± 0.11 pNb = 0.86 ± 0.36
• 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
07.02.2011 WWND 2011
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)
07.02.2011 WWND 2011
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
07.02.2011 WWND 2011
Outlook
• e+e- - pair production in HI reactions
– Regeneration of VM– Higher densities
– HADES upgrade
• in - induced reactions
– Large X – sections– VM „at rest“
– Beam particle tracking
07.02.2011 WWND 2011
The HADES collaboration
07.02.2011 WWND 2011
EXTRA SLIDES
07.02.2011 WWND 2011
e+e- sources in p + p
07.02.2011 WWND 2011
Collisional width of in GiBUU
free width
Priv. Comm. Janus Weil
07.02.2011 WWND 2011
accelN
accel
accel
Norm
NF
mbddd
dacc 16.0)sin(
125
55
Elastic scattering
Kinematic constraints:0
21 180||
865.2)cot()cot( 221 cm
Kammerud et al. Phys. Rev. D 4 (1971), 5
p + p normalization
Analysis by Anar Rustamov
07.02.2011 WWND 2011
p + Nb normalization
)3()(min 1,, LVLHADEStrigHADES MNFbiasN
- yield in HADES acceptance:
Systematic uncertainty
ddp
NdF
ddp
d
T
HARPnorm
T
HARP ,2
,2
Fit to HARP data: pT > 300 MeV/c
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