STAR measurement on di -lepton spectrum from p+p collisions at 200 GeV
Inclusive e + e - pair production in p+p and p+Nb collisions at E = 3.5 GeV
description
Transcript of Inclusive e + e - pair production in p+p and p+Nb collisions at E = 3.5 GeV
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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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
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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
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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
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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
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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
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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
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e+e- pair reconstruction
Comb. Background:• same event e-e- e+e+
• correlated BG from 0 / decays
Signal to BG ratio
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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
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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
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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
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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
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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
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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
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Fast and slow e+e- sources
Decays inside nucleus In – Medium effects
HSD Simulation for HADES proposal
p cut
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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
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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
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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
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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
)/(
)/(
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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
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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
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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 !
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Transport models - pT
UrQMD
HSD
GiBUU
Different , , contributions !
Constrain models ?
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Slow and fast sources (GiBUU)
Collisional width in GiBUU for • momentum dependent
• 20 – 90 MeV ( 2 – 11 x vac)
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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
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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
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The HADES collaboration
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EXTRA SLIDES
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e+e- sources in p + p
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Collisional width of in GiBUU
free width
Priv. Comm. Janus Weil
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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
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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