Michael weber for the hades collaboration
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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

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Michael weber for the hades collaboration

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 p0

    • Cross sections

  • Comparison with transport models

  • Conclusions

WWND 2011


Phase diagram
Phase diagram

  • Learn about properties of QCD matter at different (T,r)

    • EM structure of matter

    • hadrons in matter

http://www.ice.csic.es/en/graphics/phase.jpg

WWND 2011


Phase diagram1

o, 

w,r

o,

e+

e-

g*

e+

e-

w,r,f

g*

Phase diagram

  • Learn about properties of QCD matter at different (T,r)

    • EM structure of matter

    • hadrons in matter

  • Penetrating probe:

    • Dielectrons

    • Direct coupling of g*

      to VM (JP=1-) w,r,f

http://www.ice.csic.es/en/graphics/phase.jpg

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Dense and hot matter

e+

e-

e+

e-

e+

e-

e+

e-

Dense and hot matter

  • Accessible in:

    A+ A reactions

LHC

RHIC

SPS

FAIR

SIS

e+

e-

Dense matter at SIS:

J. Stroth

http://www.ice.csic.es/en/graphics/phase.jpg

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Cold nuclear matter

e+

e-

Cold nuclear matter

  • Accessible in:

    p + A / g + A / p + A

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Cold nuclear matter1
Cold nuclear matter

r meson

  • Accessible in:

    p + A / g + A / p + A

  • Medium effects:

    mass shift/ (collisional) broadening/ reabsorption/ regeneration

  • Measure: Spectral shape / Cross sections/ Attenuation

  • BUT: NON conlusive experimental results

P.Mühlich et al., NPA 780 (2006), 187

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Hadesi
HADESI

HADES

[ EPJ A41 243]

Production of strangeness:

L. Fabbietti

21.08.2014

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Hadesii
HADESII

HADES

[ EPJ A41 243]

High purity e+e- pair reconstruction

A = 1

A = 93

  • Beam: p

  • Ekin= 3.5 GeV

  • I ~ 6 · 106 1/s

  • Target : p

  • 4 cm LH2

  • ~1% reaction prob.

  • 3.5 · 109 collisions

  • 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

21.08.2014

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E e pair reconstruction
e+e- pair reconstruction

  • Signal to BG ratio

  • Comb. Background:

  • same event e-e- e+e+

  • correlated BG from p0 / h decays

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E e sources in p p
e+e- sources in p + p

  • particle production

    • π via resonance decays (D,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)

    • π: 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)

σω ~ 16 MeV/c2

Δ FF is fixed at the photon point

WWND 2011

Analysis by Anar Rustamov


E e sources in p p1
e+e- sources in p + p

D - N transition form factor

Space like: q2 < 0

Measured in electroproduction

N

D

g*

e-

e+

Two–component VDM type model:

Wan/Iachello, IJMP A20, 2005

only r relevant for D

exclusive analysis

NOT Measured

Time like: q2 > 0

WWND 2011

Analysis by Anar Rustamov


H e e
h e+e-

No direct decay (same for p + Nb):

 reduce BR (2.7 x 10-5) at least by factor of 3

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Analysis by Anar Rustamov


E e in p nb
e+e- in p + Nb

Scaling to same yield in p0 peak

Yield/p0 (p+Nb/p+p)

  • IM: 1.51

  • HM: 1.37

  • In w region 1.13

    → diff. production and/or absorption mechansims for diff. sources

    → kinematic observables for diff. mass regions

LM

IM

HM

p0

h, D

r,w,f

WWND 2011


Pnb vs pp p t and y
pNb vs. pp: pT and y

yCM, NN

LM

LM

Transverse momentum

pT2 = px2 + py2

Rapidity

y = ½ ln (E+pz)/ (E+pz )

yCM, NN = 1.12

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Pnb vs pp p t and y1
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
Fast and slow e+e- sources

  • Decays inside nucleus

  • In – Medium effects

p cut

HSD Simulation for HADES proposal

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Fast and slow e e sources1
Fast and slow e+e- sources

HM

p cut

p+Nb Ekin= 3.5 GeV

HADES: Significant e+e- yield with low pair momenta ( ~ 35 % in HM)

WWND 2011


Fast and slow sources in other exp
Fast and slow sources in other Exp.

KEK: p + A @ 12 GeV

JLAB: g + A @ 0.6 -3.8 GeV

S.Leupold, V.Metag and U.Mosel, nucl-th 0907.2388

R.Muto et al., PRL 98 (2007) 042501

WWND 2011


Fast and slow e e sources2
Fast and slow e+e- sources

Low p

High p

  • High p: free p+p production

  • Low p: overshoot over p+p

    different for r, w, and f

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Cross sections
Cross sections

  • p+p:

  • X sect from spp, elastic

  • p+Nb:

  • X sect from sp-,acc comp to HARP

  • Bolshakova et al., EPJC (1997) 1865

  • Isospin:

  • spd = 2 spp ( DLS: Ekin > 2 GeV )

  • Wilson et al., PRC 57(1997) 1865

  • A Scaling:

  • Black disc: a = 2/3 Glauber model: a ~ 0.8

    • W.Cassing et al., PLB 238 (1990) 25

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R pnb vs p
RpNb vs. p

LM

HM

IM

a~0.7

  • High p: free NN prod. + same absorption for all sources

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R pnb vs p1
RpNb vs. p

LM

HM

IM

a~0.7

  • High p: free NN prod. + same absorption for all sources

  • Low p : enhanced prod. (secondary processes)

    and/or lower absorption in IM and HM

WWND 2011


A scaling for vector mesons
A scaling for vector mesons

Fit with Gaussians:

  • High p:

    apNb,w = 0.69 ± 0.27

    apNb,f = 1.04 ± 2.50

  • Low p:

    apNb,w = 0.62 ± 0.36

Data : p+A @ 12. GeV KEK E325

 = 0.710 ± 0.021(stat) ± 0.037(syst)

 = 0.937 ± 0.049(stat) ± 0.018(syst)

  • w: momentum dependent absorption ?

  • f: production in whole nucleus volume (statistics!) ?

T. Tabaru et al.. Phys.Rev. C 74(2006)

WWND 2011


Transport models m
Transport models - M

Different D, h, r contributions !

GiBUU

UrQMD

HSD

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Transport models p t
Transport models - pT

Different D, h, r contributions !

 Constrain models ?

GiBUU

UrQMD

HSD

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Slow and fast sources gibuu
Slow and fast sources (GiBUU)

Collisional width in GiBUU for w

  • momentum dependent

  • 20 – 90 MeV ( 2 – 11 x Gvac)

WWND 2011


Summary
Summary

  • e+e- - pair production p+p and p+Nb at E = 3.5 GeV ( M, pT and y)

  • clear w signal observed (sw/Mw ~ 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) ~ Aa

    • High p : all masses a ~ 0.7

    • Low p : p0 region: a ~ 0.7

      h, Dregion: a ~ 0.82

      r,w,f region: a ~ 0.86

      BUT w a ~ 0.62

       in - medium omega width

  • Comparison with transport models

     Better understanding of sources in p + p

WWND 2011


Outlook
Outlook

  • e+e- - pair production in HI reactions

    • Regeneration of VM

    • Higher densities

    • HADES upgrade

  • in p- induced reactions

    • Large X – sections

    • VM „at rest“

    • Beam particle tracking

WWND 2011


The HADES collaboration

Thank you

WWND 2011


EXTRA SLIDES

WWND 2011


E e sources in p p2
e+e- sources in p + p

WWND 2011


Collisional width of w in gibuu
Collisional width of w in GiBUU

free width

WWND 2011

Priv. Comm. Janus Weil


P p normalization
p + p normalization

Elastic scattering

Kinematic constraints:

Kammerud et al. Phys. Rev. D 4 (1971), 5

WWND 2011

Analysis by Anar Rustamov


P nb normalization
p + Nb normalization

p- yield in HADES acceptance:

Systematic uncertainty

Fit to HARP data: pT > 300 MeV/c

WWND 2011


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