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Dubna, November 2003 Joachim Stroth
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
Dubna, November 2003 Joachim Stroth
A photon ...
e
e
q
q
*
Dubna, November 2003 Joachim Stroth
.... hadronizes via Vector Meson Dominance
e
e
* 0
Dubna, November 2003 Joachim Stroth
Di-electron Spectroscopy in Heavy Ion Collisions
p
n
++
K
p
Penetrating probes: information from the early stage low branching ratio, O (10-5)
e+
e-
Dubna, November 2003 Joachim Stroth
Nuclear matter under extreme conditions
DATA: Fit of statistical model to measured abundances in the final state
P. Braun-Munzinger, J. Stachel et al.
Dubna, November 2003 Joachim Stroth
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 !?
Dubna, November 2003 Joachim Stroth
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)
Dubna, November 2003 Joachim Stroth
Modification of meson spectral function through coupling to resonances
Nuclear Physics A, Volume 632, 9 March 1998, W. Peters, M. Post, H. Lenske, S. Leupold and U. Mosel
Modification of the -Meson spectral function depends on....
relative momentum to the medium
the density of the surrounding medium
normal
nuclear ground state density
twice
Dubna, November 2003 Joachim Stroth
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
Dubna, November 2003 Joachim Stroth
Extended Vector Meson Dominance
Still experimental data in the low mass region above the theoretical expectation
Shekhter et al., PRC 68 (2003)
Dubna, November 2003 Joachim Stroth
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.)
Dubna, November 2003 Joachim Stroth
High acceptance dielectron spectrometer HADES
GeometrySix sectors form a hexagonal frustum:
inin, , 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 (cmdrift
chamber.
Lepton identification & trigger RICH
– Radiator: C4F10
– Spherical mirror– Photon Detector: CsI photo cathode
META (TOF & Pre-Shower)– TOF plastic scintillators– Lead Shower detector
• LVL2 trigger on Electrons – Fast (~200 s)– Highly selective
(suppression up to1/100)
Dubna, November 2003 Joachim Stroth
Dubna, November 2003 Joachim Stroth
Omega production in A
Selective measurement of medium modification ant nuclear ground state density
uncertainties in calculations (interferences, el. form-factors, res N*,)
needs data from
e+
e-
208Pb-
HADES
W.Schoen et al.
Acta Phys.PolB27(1996)2959
M.Effenberger et al. Nucl-th/9901039
neenp
XeeN
Dubna, November 2003 Joachim Stroth
The current experimental program of HADES
11/2002:11/2002: Commissioning (12C+12C)
– 36 M events
– no outer drift chambers
11/2002: 11/2002: Production run (12C+12C)
– 200 M events, 44 % LVL2 triggered
– 4 Sectors with outer tracking(4/2)
10/2003:10/2003: Commissioning (p+lH2)
– 6 Sectors with outer tracking (6/4)
02/2004:02/2004: Production run (p+lH2)
Dubna, November 2003 Joachim Stroth
Electron identification using the RICH
• hadron contamination < 2%• p/ separation for p < 1000 MeV/c
C+C, 2AGeV
p*q [MeV/c]
v/c
Tracking+TOF
q*p [MeV/c]
v/c
Dubna, November 2003 Joachim Stroth
Tracking with the drift chambers and more
FE electronics
threshold
t1
t2
drift cell
Dubna, November 2003 Joachim Stroth
Pairs from C+C @2 AGeV
Nov02(60% of data) CB
Me+e- [MeV/c2]
Cou
nts
/10
MeV
CB combinatorial background
! no close pair rejection
NNNCB 2
signalCB
ee0 Preliminary
Dubna, November 2003 Joachim Stroth
Nov02
Preliminary
Nov01
Nov02 data scaled down by 10
0e+e-
Me+e- [MeV/c2]
Nov02 C+C @2 AGeVC
ou
nts
/MeV
shapes of the inv. mass distributions are consistent
50k pairs in Nov02 (60% of data)
Nov02: 4 sectors equipped with outer MDC
Not acceptance corrected
Dubna, November 2003 Joachim Stroth
Signal pairs from C+C
Me+e- [MeV/c2]
dN
/dM
[1/
MeV
]
Me+e- [MeV/c2]
CB subtracted but not acceptance corrected !
normalized by number of LVL1 triggers
different magnetic field settings for 1AGeV
1 AGeV 2 AGeV
Preliminary
Dubna, November 2003 Joachim Stroth
Nuclear matter at the highest densities
The futureCompressed Baryonic Matter
Experiment
Dubna, November 2003 Joachim Stroth
Di-electron spectroscopy at the future facility
Radiation hard Silicon pixel/strip detectors
magnet
1 m
Dubna, November 2003 Joachim Stroth
Electrons from Dalitz (pt vs y) HADES at SIS HADES at SIS 100100
e+ e-
1
0
1
00 3 0 3
e+ e-
0 3 0 3
2 GeV/u 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
C+C
Dubna, November 2003 Joachim Stroth
Feasibility study : e+ e- with CBMwith CBM
CBM experimental concept:
Electron identification after tracking!
Background from conversion dominatese+e- vertex cuts is essential:
SNR 3 in 1 M eventsstudy ongoing, tracking needed
Dubna, November 2003 Joachim Stroth
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
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