motivations - hades dielectron analysis strategy results & models comparison c+c 2 agev c+c...
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HADES experiment: dilepton spectroscopy in C+C
(1 and 2 AGeV) collisions
Motivations - HADESMotivations - HADESDielectron analysis strategyDielectron analysis strategy
Results & models comparisonResults & models comparisonC+C 2 AGeVC+C 2 AGeVC+C 1AGeVC+C 1AGeV
Witold Przygoda, Jagiellonian University, Cracow,
for the HADES Collaboration
2nd International Conference on Hard and ElectromagneticProbes of High-Energy Nuclear Collisions, Asilomar CA, 2006
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MotivationMotivation
Probe the electromagnetic structure of hot and dense nuclear matter in the time-like region
Additional self-energy terms due to meson-
baryon coupling
p - beams
SIS 18
SIS 200T [MeV] 300
LHC
RHIC
SPS
Partial restoration of chiral symmetry
W. Weise et al.
3/1
0
**
)(
m
m
m
m
Brown-Rho scaling
What are the relevant observables as nuclear density and/or temperature increase?
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The case of moderate beam energiesThe case of moderate beam energies
10 20 30t [fm/c]
≈ 10 fm/c
comparatively long life-time ...at moderate densities
Particle production
at or below threshold :
– co-operative processes
(i.e. multi step processes)
– production confined to the
high density phase !
NN → NΔ
πN
πN → ρ N
multi step processes: i.e.
c 10-15 fm/c
Baryon density:
t( > 2) ≈ 10 fm/c
In-medium invariant massreconstruction
combinatorial background reduction
Vector meson spectroscopy – in-medium effects investigation
Meson Mass[MeV/c2]
Width [MeV/c2]
Life time
c [fm/c]
(Ve+e-)
tot
0 770 150 1.3 4.4x10-5
782 8.4 23.4 7.1x10-5
1020 4.4 44.4 3.1x10-5
2sinppm ee
eeee
T. Renk et al., PRC 66 (2002) 014902
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Invariant mass spectrum decompositionInvariant mass spectrum decomposition
Elementary processes:•Meson Dalitz decays:
•Baryon Dalitza decays:
•Two-body decays:
e+
e-
e+
e-
e+
e-
Example cocktail( DLS data comparedto HSD model )
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The DLS resultsThe DLS results
• The shape (0.05 M 0.35) can be explained by Dalitz decays of0 and if cross sections are scaled appropriately – but in contradiction with TAPS measurement...
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!
Calculation: K. Shekhter, C. Fuchs et al. (Tübingen)Phys. Rev. C68 (2003) 014904
Done using strong or weak (s/w) - N*(1535) coupling
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HADES … What and where?...HADES … What and where?...
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High Acceptance DiHigh Acceptance Di-E-Electron Spectrometerlectron 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 HADES SpectrometerSpectrometer
Side View
START
1 m
Fast particle identification
Pre-Shower: 18 pad chambers & 12 lead converters betweenRICH: CsI solid photo cathode, C4F10 radiator, N0 8090, suppression: 104
TOF: 384 scintil. rods , 150 psTOFino: 24 scintil. paddles, 450 ps temporary solution, RPC in future
Momentum measurement
Magnet: superconducting toroid: B = 0.36 Tm
MDC: 24 multiwire drift chambers, y 100 m single cell resolution
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Experimental Experimental (production) (production) runsruns
• November 2002: C+C 2 AGeV, commissioning and physics runs – target= 2 x 2.5% 650 Mevents650 Mevents– 6 outer drift chambers (MDC) in 4 sectors
• February 2004: p+p 2 GeV– target 5 cm LH2, almost full spectrometer setup 600 Mevents600 Mevents
• August 2004: C+C 1 AGeV– 3x2 % target 2500 Mevents2500 Mevents
• September 2005: Ar+KCl 1.75 AGeV– 4x1.5 % target 1200 Mevents1200 Mevents
• May 2006: p+p 1.25 GeV– Target 5 cm LH2 3000 Mevents3000 Mevents
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log. z axis !
e-
e+
hadron : lepton suppression 10000 : 1
Analysis strategyAnalysis strategy
• Single electron analysis
• Classical: 2-dim cuts on RICH rings, Shower, p vs , hit matching ...
• or: Bayes theorem: cut on pid prob.
• track fitting quality
• e+e- pair analysis
• close pair cuts
• opening angle > 9° (tracks removed)
• Corrections for detector and reconstruction efficiencies acceptance & reconstruction efficiency filters available
ee--
ee++
pp 21)2/sin(2 Minv =
p1
p2TargetTarget
RICH
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C+C @ 2 AGeV - mass spectrumC+C @ 2 AGeV - mass spectrum
•Combinatorial background (CB):– from like-sign pairs
– CB =
•Signal: S+ = Ne+e CB+
eeee NN2
signal < 140 MeV/c2: 20971 countssignal > 140 MeV/c2: 1937 counts
( picture above )no acceptance / efficiency corrections
limited resoultion ( ~DLS level )only inner MDC chambers in 2002
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C+C @ 2 AGeV - mass spectrum correctedC+C @ 2 AGeV - mass spectrum corrected
Efficiency corrected spectra- detector efficiency- reconstruction efficiency
normalized to the pion yield
in HADES acceptance
12C+12C 2AGeV
NNN
2
10
average number of participating nucleons Apart = 8.6
extrapolated charged pion yield N
4 / Apart = 0.135 0.015
PLUTO event gener.(HADES Collaboration)
0 and well known (thermal freezout)based on TAPS measurements
syst. error (~30%):• uncertainty in normalization• reconstruction efficiency corr.• CB construction
red bars – stat+syst err
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C+C @ 2 AGeV – HSD modelC+C @ 2 AGeV – HSD model
vacuum in-medium
( data described quite well )
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C+C @ 2 AGeV – UrQMD modelC+C @ 2 AGeV – UrQMD model
problems in the high mass region
Transport calculation
(vacuum resultvacuum result))
UrQMD FrankfurtM. Bleicher, D. Schumacher
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C+C @ 2 AGeV – RQMD modelC+C @ 2 AGeV – RQMD model
RQMD TübingenD. 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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C+C @ 2 AGeV - comparison with modelsC+C @ 2 AGeV - comparison with models
Included calculations:
• PLUTO evt generator HADES collaboration
• UrQMD Frankfurt M. Bleicher, D. Schumacher
• HSD Gießen (v2.5) E. Bratkovskaya, W. Cassing
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
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C+C @ 2 AGeV – rapidity – exp, PLUTO, HSDC+C @ 2 AGeV – rapidity – exp, PLUTO, HSD
discrepancy in medium (PLUTO, HSD)and high mass (PLUTO) region
dots - experimentdashed line - PLUTOsolid line - HSD
HSD
solid linevacuum
dashed linein-medium
PL
UT
O –
das
hed
H
SD
– s
olid
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C+C @ 2 AGeV – pC+C @ 2 AGeV – pTT – exp, PLUTO, HSD – exp, PLUTO, HSD
PLUTO
HSDsolid line
vacuum
dashed line
in-medium
discrepancyin medium and high massregion
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C+C @ 1 AGeV - preliminaryC+C @ 1 AGeV - preliminary
preliminary
•Comb. backgr. (CB):
from like-sign pairs
CB =
S+ = Ne+e CB+
eeee NN2
not efficiency corrected !
Direct comparisonto DLS data possible
– Exp. Data: no efficiency correction– PLUTO: filtered with HADESacceptance * efficiency
Normalized to π0
70% of the full data statistics
only π0 , η is not sufficient to describe the data – model comparison in the future
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SummarySummary
• 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)
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– 40Ar+39K37Cl @ 1.75 AGeV analysis started soon
– elementary reactions: p+p @ 2.2 GeV, 1.25 GeV, 3.5 GeV
• high momentum resolution achieved (σ = 3.5%)
form factor measurement feasible
in nucleus production
– p, heavy ion: high precision in-medium spectroscopy
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HADES collaborationHADES 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, Slovakia2)Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali del Sud, 95125 Catania, Italy3)Dipartimento di Fisica e Astronomia, Università di Catania, 95125, Catania, Italy4)LIP-Laboratório de Instrumentação e Física Experimental de Partículas, Departamento de Física da Universidade de Coimbra, 3004-516 Coimbra, Portugal5)Smoluchowski Institute of Physics, Jagiellonian University of Cracow, 30059 Cracow, Poland6)Gesellschaft für Schwerionenforschung mbH, 64291 Darmstadt, Germany7)Joint Institute of Nuclear Research, 141980 Dubna, Russia8)Institut für Kernphysik, Johann Wolfgang Goethe-Universität, 60486 Frankfurt, Germany9)II.Physikalisches Institut, Justus Liebig Universität Giessen, 35392 Giessen, Germany10)Istituto Nazionale di Fisica Nucleare, Sezione di Milano, 20133 Milano, Italy11)Dipartimento di Fisica, Università di Milano, 20133 Milano, Italy12)Institute for Nuclear Research, Russian Academy of Science, 117312 Moscow, Russia13)Institute of Theoretical and Experimental Physics, 117218 Moscow, Russia14)Physik Department E12, Technische Universität München, 85748 Garching, Germany15)Department of Physics, University of Cyprus, 1678 Nicosia, Cyprus16)Institut de Physique Nucléaire d'Orsay, CNRS/IN2P3, 91406 Orsay Cedex, France17)Nuclear Physics Institute, Academy of Sciences of Czech Republic, 25068 Rez, Czech Republic18)Institut für Kern- und Hadronenphysik, Forschungszentrum Rossendorf, PF 510119, 01314 Dresden, Germany19)Departamento de Física de Partículas. University of Santiago de Compostela. 15782 Santiago de Compostela, Spain20)Instituto de Física Corpuscular, Universidad de Valencia-CSIC,46971-Valencia, Spain