HADES experiment: dilepton spectroscopy in C C 1 and 2 AGeV collisions Motivations HADES Dielectron

1
HADES experiment dilepton spectroscopy in CC
(1 and 2 AGeV) collisions Motivations -
HADESDielectron analysis strategyResults
models comparisonCC 2 AGeVCC 1AGeV
2nd International Conference on Hard and
Electromagnetic Probes of High-Energy Nuclear
Collisions, Asilomar CA, 2006

• Witold Przygoda, Jagiellonian University, Cracow,
  
• for the HADES Collaboration

2
Motivation
Brown-Rho scaling

• Probe the electromagnetic structure of
• hot and dense nuclear matter
• in the time-like region

What are the relevant observables as nuclear
density and/or temperature increase?
3
The case of moderate beam energies
Vector meson spectroscopy in-medium effects
investigation
Baryon density Dt(r/r0 2) 10 fm/c
comparatively long life-time ...at moderate
densities
ct ? 10-15 fm/c
In-medium invariant mass reconstruction
combinatorial background reduction
4
Invariant mass spectrum decomposition
Elementary processes

• Meson Dalitz decays
• Baryon Dalitza decays
• Two-body decays

Example cocktail ( DLS data compared to HSD model
)
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The DLS results
Calculation K. Shekhter, C. Fuchs et al.
(Tübingen) Phys. Rev. C68 (2003) 014904
Done using strong or weak (s/w) r - N(1535)
coupling
Data R.J. Porter et al. PRL 79 (1997) 1229 BUU
model E.L. Bratkovskaya et al. NP A634 (1998)
168, in-medium spectral functions
? DLS puzzle!

• The shape (0.05 ? M ? 0.35) can be explained by
  Dalitz decays of p0 and h if cross sections are
  scaled appropriately but in contradiction with
  TAPS measurement...

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HADES What and where?...
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High Acceptance Di-Electron Spectrometer

• Installed at the SIS18, GSI Darmstadt
• Spectrometer with high invariant mass resolution
  and high rate capability
• Utilizes dedicated second level trigger
  processors to select rare events before mass
  storing

• Beams of
• Pions
• Protons
• Nuclei

Geometry Full azimuth, polar angles 18? - 85?
( y 0 2 ) Pair acceptance ? 0.35 80.000
channels, seg. solid or LH2 targets
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HADES Spectrometer
Side View
START
Fast particle identification
Momentum measurement
Magnet super?conducting toroid Br 0.36 Tm
Pre-Shower 18 pad chambers 12 lead converters
between
TOF 384 scintil. rods , s ? 150 ps TOFino 24
scintil. paddles, s ? 450 ps ? temporary
solution, RPC in future
RICH CsI solid photo cathode, C4F10 radiator,
N0 ? 80?90, p - suppression 104
MDC 24 multi?wire drift chambers, sy ? 100 mm
single cell resolution
1 m
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Fast 2nd level trigger
up to 20 kHz LVL1Fast multiplicity trigger
full event information digitised
on-line selection of electron candidates
Suppression 10 - 100
LVL2 triggered events are transported to mass
storage
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Experimental (production) runs

• November 2002 CC 2 AGeV, commissioning and
  physics runs
• target 2 x 2.5 650 Mevents
• 6 outer drift chambers (MDC) in 4 sectors
• February 2004 pp 2 GeV
• target 5 cm LH2, almost full spectrometer
  setup 600 Mevents
• August 2004 CC 1 AGeV
• 3x2 target 2500 Mevents
• September 2005 ArKCl 1.75 AGeV
• 4x1.5 target 1200 Mevents
• May 2006 pp 1.25 GeV
• Target 5 cm LH2 3000 Mevents

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Analysis strategy

• Single electron analysis
• Classical 2-dim cuts on RICH rings, Shower, p
  vs b, hit matching ...
• or Bayes theorem cut on pid prob.
• track fitting quality
• ee- pair analysis
• close pair cuts
• opening angle q 9 (tracks removed)
• Corrections for detector and reconstruction
  efficiencies ? acceptance
  reconstruction efficiency filters available

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CC _at_ 2 AGeV - mass spectrum
limited resoultion ( DLS level )only inner MDC
chambers in 2002
( picture above )no acceptance / efficiency
corrections
signal 140
MeV/c2 1937 counts
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CC _at_ 2 AGeV - mass spectrum corrected
Efficiency corrected spectra - detector
efficiency - reconstruction efficiency ?
normalized to the pion yield
in HADES acceptance
12C12C 2AGeV
PLUTO event gener. (HADES Collaboration) ?0 and
? well known (thermal freezout) based on TAPS
measurements
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CC _at_ 2 AGeV HSD model
vacuum
in-medium
( data described quite well )
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CC _at_ 2 AGeV UrQMD model
Transport calculation (vacuum result) UrQMD
Frankfurt M. Bleicher, D. Schumacher
problems in the high mass region
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CC _at_ 2 AGeV RQMD model
RQMD Tübingen D. Cozma, C. Fuchs

• subthreshold ?/? production (via resonances)
• eVMD model
• in-medium? collisional broadening? decoherence

In-medium problems in the intermediate mass
region
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CC _at_ 2 AGeV - comparison with models

• experimental data
• efficiency corrected
• pair cut ?12 9?theor. models
• vacuum calculations

• Included calculations
• RQMD Tübingen D. Cozma, C. Fuchs
• UrQMD Frankfurt
• M. Bleicher, D. Schumacher
• HSD Gießen (v2.5)
• E. Bratkovskaya, W. Cassing

• Included calculations
• PLUTO evt generator
• HADES collaboration
• UrQMD Frankfurt
• M. Bleicher, D. Schumacher
• HSD Gießen (v2.5)
• E. Bratkovskaya, W. Cassing

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CC _at_ 2 AGeV rapidity exp, PLUTO, HSD
dots - experiment dashed line - PLUTO solid line
- HSD
discrepancy in medium (PLUTO, HSD) and high mass
(PLUTO) region
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CC _at_ 2 AGeV pT exp, PLUTO, HSD
PLUTO
discrepancy in medium and high mass region
HSD
solid line vacuum dashed line in-medium
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CC _at_ 1 AGeV - preliminary

• Comb. backgr. (CB)
• from like-sign pairs
• CB S? Nee? ? CB ?

not efficiency corrected !
Normalized to p0 70 of the full data statistics
preliminary
Direct comparison to DLS data possible

• Exp. Data
• no efficiency correction
• PLUTO
• filtered with HADES
• acceptance efficiency

only p0 , ? is not sufficient to describe the
data model comparison in the future
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Summary

• HADES fully operational 1 month experimental
  runs
• 12C 12C 2 AGeV analyzed (PRL paper submitted
  soon)
• di-electron spectrum efficiency corrected
• systematic errors estimated (based on simulation)
• ?0 in agreement with TAPS / KAOS measurement
• comparison with transport models
• vacuum results failed to describe high mass
  region
• 12C 12C 1 AGeV preliminary
• 5x higher data statistics analysis on-going
• direct comparison to DLS data possible
• A lot of physics ahead for the coming years
• 40Ar39K37Cl _at_ 1.75 AGeV analysis started soon
• elementary reactions pp _at_ 2.2 GeV, 1.25 GeV,
  3.5 GeV
• high momentum resolution achieved (s 3.5)
• ? form factor measurement feasible
• ? in nucleus production
• p, p, heavy ion high precision in-medium
  spectroscopy

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HADES collaboration
G.Agakishiev7, C.Agodi2, H.Alvarez-Pol19,
A.Balanda5, R.Bassini10, G.Bellia2,3, D.Belver19,
J.Bielcik6, A.Blanco4, M.Böhmer14, C.Boiano10,
A.Bortolotti10, J.Boyard16, S.Brambilla10,
P.Braun-Munzinger6, P.Cabanelas19, S.Chernenko7,
T.Christ14, R.Coniglione2, M.Dahlinger6,
J.Díaz20, R.Djeridi9, F.Dohrmann18, I.Durán19,
T.Eberl14, W.Enghardt18, L.Fabbietti14,
O.Fateev7, P.Finocchiaro2, P.Fonte4, J.Friese14,
I.Fröhlich9, J.Garzón19, R.Gernhäuser14,
M.Golubeva12, D.González-Díaz19, E.Grosse18,
F.Guber12, T.Heinz6, T.Hennino16, S.Hlavac1,
J.Hoffmann6, R.Holzmann6, A.Ierusalimov7,
I.Iori10,11, Ivashkin12, M.Jaskula5,
M.Jurkovic14, M.Kajetanowicz5, B.Kämpfer18,
K.Kanaki18, T.Karavicheva12, D.Kirschner9,
I.Koenig6, W.Koenig6, B.Kolb6, U.Kopf6,
R.Kotte18, J.Kotulic-Bunta1, R.Krücken14,
A.Kugler17, W.Kühn9, R.Kulessa5, S.Lang6,
J.Lehnert9, L.Maier14, P.Maier-Komor14,
C.Maiolino2, J.Marín19, J.Markert8, V.Metag9,
N.Montes19, E.Moriniere16, J.Mousa15, M.Münch6,
C.Müntz8, L.Naumann18, R.Novotny9, J.Novotny17,
W.Ott6, J.Otwinowski5, Y.Pachmayer8, V.Pechenov7,
T.Pérez9, J.Pietraszko6, J.Pinhao4, R.Pleskac17,
V.Pospísil17, W.Przygoda5, A.Pullia10,11,
N.Rabin13, B.Ramstein16, S.Riboldi10, J.Ritman9,
P.Rosier16, M.Roy-Stephan16, A.Rustamov6,
A.Sadovsky18, B.Sailer14, P.Salabura5,
P.Sapienza2, A.Schmah6, W.Schön6, C.Schroeder6,
E.Schwab6, P.Senger6, R.Simon6, V.Smolyankin13,
L.Smykov7, S.Spataro2, B.Spruck9, H.Stroebele8,
J.Stroth8,6, C.Sturm6, M.Sudol8,6, V.Tiflov12,
P.Tlusty17, A.Toia9, M.Traxler6, H.Tsertos15,
I.Turzo1, V.Wagner17, W.Walus5, C.Willmott19,
S.Winkler14, M.Wisniowski5, T.Wojcik5,
J.Wüstenfeld8, Y.Zanevsky7, P.Zumbruch6
  1)Institute of Physics, Slovak Academy of
Sciences, 84228 Bratislava, Slovakia 2)Istituto
Nazionale di Fisica Nucleare - Laboratori
Nazionali del Sud, 95125 Catania,
Italy 3)Dipartimento di Fisica e Astronomia,
Università di Catania, 95125, Catania,
Italy 4)LIP-Laboratório de Instrumentação e
Física Experimental de Partículas, Departamento
de Física da Universidade de Coimbra, 3004-516
Coimbra, Portugal 5)Smoluchowski Institute of
Physics, Jagiellonian University of Cracow, 30059
Cracow, Poland 6)Gesellschaft für
Schwerionenforschung mbH, 64291 Darmstadt,
Germany 7)Joint Institute of Nuclear Research,
141980 Dubna, Russia 8)Institut für Kernphysik,
Johann Wolfgang Goethe-Universität, 60486
Frankfurt, Germany 9)II.Physikalisches Institut,
Justus Liebig Universität Giessen, 35392 Giessen,
Germany 10)Istituto Nazionale di Fisica Nucleare,
Sezione di Milano, 20133 Milano,
Italy 11)Dipartimento di Fisica, Università di
Milano, 20133 Milano, Italy 12)Institute for
Nuclear Research, Russian Academy of Science,
117312 Moscow, Russia 13)Institute of Theoretical
and Experimental Physics, 117218 Moscow,
Russia 14)Physik Department E12, Technische
Universität München, 85748 Garching,
Germany 15)Department of Physics, University of
Cyprus, 1678 Nicosia, Cyprus 16)Institut de
Physique Nucléaire d'Orsay, CNRS/IN2P3, 91406
Orsay Cedex, France 17)Nuclear Physics Institute,
Academy of Sciences of Czech Republic, 25068 Rez,
Czech Republic 18)Institut für Kern- und
Hadronenphysik, Forschungszentrum Rossendorf,
PF 510119, 01314 Dresden, Germany 19)Departament
o de Física de Partículas. University of Santiago
de Compostela. 15782 Santiago de
Compostela, Spain 20)Instituto de Física
Corpuscular, Universidad de Valencia-CSIC,46971-Va
lencia, Spain