Hadron Structure in Dense Nuclear Matter

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Hadron Structure in Dense Nuclear Matter

• Vector mesons
• Di-electron spectroscopy in heavy ion collisions
• The HADES spectrometer ...
• ... and the future of di-electron spectroscopy
• Summary

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A photon ...
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... hadronizes ...
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.... hadronizes via Vector Meson Dominance
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Di-electron Spectroscopy in Heavy Ion Collisions

• Penetrating probes
• information from the early stage
• low branching ratio, O (10-5)

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Nuclear matter under extreme conditions

• DATA Fit of statistical model to measured
  abundances in the final state
• P. Braun-Munzinger, J. Stachel et al.

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Reasons for Medium Modifications

• Meson self energy in medium
• many more degrees of freedom (spreading)
• Broadening !?

• Dynamical mass generation by spontaneous Chiral
  Symmetry breaking
• mq ??10 MeV (current quark mass)
• mu,d ??mp,n / 3 ? 300 MeV(constituent quark
  mass)
• mass shift !?

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Time dependence of the Chiral Condensate

• B. Friman et al. Eur. Phys. J. (1998)
• Method quark-gluon string model (Toneev at al.
  NP A519(1990)463c)

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QCD Anregungsspektrum

• Wie entstehen aus (nahezu) masselosen Quarks
  Hadronen mit Massen von typisch 1 GeV und mehr?
• Die Chirale Symmetrie ist im Grundzustand der
  QCD spontan gebrochen!
• Leichte Mesonen (Mltlt1 GeV)p, h, K
• Keine Paritätsduplettsz.B. M(r) ? M(a1)
• Durch Kopplung der Quarks an die virtuellen
  Quark-Antiquarkpaare des chiralen Kondensats
  erhalten sie dynamisch eine Masse

D(1600)
D(1232)
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Modification of meson spectral function through
coupling to resonances

• Modification of the r-Meson spectral function
  depends on....
• relative momentum to the medium
• the density of the surrounding medium

normal nuclear ground state
density twice

• Nuclear Physics A, Volume 632, 9 March 1998, W.
  Peters, M. Post, H. Lenske, S. Leupold and U.
  Mosel

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Di-electrons measured with DLS at Berkeley

• Daten R.J. Porter et al. PRL 79(97)1229
• Modell E.L. Bratkovskaya et al. NP
  A634(98)168, BUU, Spektralfunktionen im
  Vakuum

DLS
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Extended Vector Meson Dominance

• Still experimental data in the low mass region
  above the theoretical expectation

Shekhter et al., PRC 68 (2003)
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Bratislava (SAS, PI), Catania (INFN - LNS),
Cracow (Univ.), Darmstadt,(GSI), Dresden (FZR),
Dubna (JINR, LHE), Frankfurt (Univ.),Giessen
(Univ.), Milano (INFN, Univ.), Moscow (ITEP,
INR, MEPhI), Munich (Tech. Univ.), Nicosia
(Univ.), Orsay (IPN),Rez (CAS, NPI), Sant. de
Compostela (Univ.), Valencia (Univ.)
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High acceptance dielectron spectrometer HADES

• Geometry
• Six sectors form a hexagonal frustum
• 2p in f, 18 lt J lt 85
• 35 pair acceptance
• Tracking
• Superconducting toroid (6 coils)
• Bmax 0.7 T,
• Bending power 0.34 Tm
• MDC (multiwire drift chamber)
• Low mass design
• four planes of small cell ( 1 cm) drift chamber.
• Lepton identification trigger
• RICH
• Radiator C4F10
• Spherical mirror
• Photon Detector CsI photo cathode
• META (TOF Pre-Shower)
• TOF plastic scintillators
• Lead Shower detector

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Omega production in ?A
Selective measurement of medium modification ant
nuclear ground state density
M.Effenberger et al. Nucl-th/9901039
W.Schoen et al. Acta Phys.PolB27(1996)2959
HADES

• uncertainties in calculations (interferences, el.
  form-factors, res N,?)
• needs data from

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The current experimental program of HADES

• 11/2002 Commissioning (12C12C)
• 36 M events
• no outer drift chambers
• 11/2002 Production run (12C12C)
• 200 M events, 44 LVL2 triggered
• 4 Sectors with outer tracking(4/2)
• 10/2003 Commissioning (plH2)
• 6 Sectors with outer tracking (6/4)
• 02/2004 Production run (plH2)

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Electron identification using the RICH
CC, 2AGeV
TrackingTOF

• hadron contamination lt 2
• p/? separation for p lt 1000 MeV/c

v/c
v/c
pq MeV/c
qp MeV/c
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Tracking with the drift chambers and more

• FE electronics

drift cell
t1
t2
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Hadronenspektroskopie

• Flache Akzeptanz über einen weiten Bereich des
  Phasenraums

Pionen
Protonen
Arbeit von Peter Zumbruch, GSI
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Pairs from CC _at_2 AGeV
Preliminary
Nov02 (60 of data)
signal
CB
CB
Counts/10 MeV
Mee- MeV/c2
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Nov02 CC _at_2 AGeV
Not acceptance corrected
Counts/MeV
Mee- MeV/c2

• shapes of the inv. mass distributions are
  consistent
• ?50k pairs in Nov02 (60 of data)
• Nov02 4 sectors equipped with outer MDC

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Signal pairs from CC
Preliminary
1 AGeV
2 AGeV
dN/dM1/MeV
Mee- MeV/c2
Mee- MeV/c2

• CB subtracted but not acceptance corrected !
• normalized by number of LVL1 triggers
• different magnetic field settings for 1AGeV

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Nuclear matter at the highest densities
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Di-electron spectroscopy at the future facility
1 m
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Electrons from h Dalitz (pt vs y) HADES
at SIS 100
2 GeV/u
CC
8 GeV/u

• particle multiplicity higher in forward region
• pion acceptance by 20-30 lower at 8 GeV/u than
  at 2 GeV/u
• single lepton (from eta Dalitz) acceptance by
  10-20 lower
• dilepton acceptance by 20 lower

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Feasibility study ? ? e e-
with CBM
CBM experimental concept Electron
identification after tracking! Background from ?
conversion dominates ee- vertex cuts is
essential SNR ? 3 in 1 M events study ongoing,
tracking needed
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Summary

• Dielectrons are ideal probes for the dense phase
  of nuclear matter.
• Creation and propagation well understood (QED).
• High penetrability
• The disadvantage of small branching ratios can
  partly be compensated by using state of the art
  micro electronics
• First results of the HADES spectrometer are
  arriving
• Conduct systematic investigation of heavy
  collisions up to 2 GeV/u
• Complemented by a series of experiments using
  proton and pion beams
• The future accelerator facility will provide
  ideal conditions to create nuclear matter at the
  highest densities
• HADES can cover beam energies up to 8 GeV/u
• Conceptually new technique for dielectron
  spectroscopy with CBM