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

2

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

**

)(

qq

qq

m

m

m

m

Brown-Rho scaling

What are the relevant observables as nuclear density and/or temperature increase?

3

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

4

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 )

5

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

6

HADES … What and where?...HADES … What and where?...

7

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

8

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

10

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

11

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

12

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

13

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

14

C+C @ 2 AGeV – HSD modelC+C @ 2 AGeV – HSD model

vacuum in-medium

( data described quite well )

15

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

16

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

17

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

18

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

19

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

20

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

21

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

22

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