# Presentation: 084135

## HADES experiment: dilepton spectroscopy in C+C (1 and 2 AGeV) collisions Motivations - HADESDielectron analysis strategyResults & models comparisonC+C 2 AGeVC+C 1AGeV

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

**2nd International Conference on Hard and Electromagnetic**
**Probes of High-Energy Nuclear Collisions, Asilomar CA, 2006**

**Notes:**
In the following 30 minutes I will report on the status of the HADES project and present you first preliminary results. The title of my talk is – if you like – the program of HADES.

## Motivation

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

**Brown-Rho scaling**

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

**Notes:**
By detecting lepton pairs, we would like to study the electromagnetic structure of dense nuclear matter in the time-like region. address questions in this field are those listed here:
You all know, that hadron properties do change while hadrons are subjected to a medium. In some cases, if you like, they are starting to dissolve, other broad resonance structure (like the sigma) might narrow done. 
Two main features are made responsible for such effects:
1. non-perturbative QCD tells us, that in vacuum chiral symmetry is spontaneously broken. The order parameter for the breaking is the chiral condensate. Model calculations show that this condensate depletes while matter density increases. It is conjectured that in consequence hadron masses will change.
2. Secondly, once a hadron is surrounded by others, additional self-energy terms will modify its spectral function.
To study changes of hadron properties in different reactions is the objective of the HADES project.          

## The case of moderate beam energies

- comparatively long life-time ...at moderate densities

- c 10-15 fm/c

- Baryon density:
******t(************ > 2) ****≈**** 10 fm/c**

**In-medium invariant mass**
**reconstruction**

**combinatorial background reduction**

**Vector meson spectroscopy ****– in-medium effects investigation**** **

| Meson | Mass
[MeV/c2] | Width  
[MeV/c2] | Life time
c [fm/c] | (Ve+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 |

**Notes:**
Time evolution of the the total baryon, nucleon and DELTA-resonance density in units 
of RHO/RHO0. The densities are calculated in a sphere of 2 fm radius around the collision center. 
The hot and dense reaction phase lies between 5 and 20 fm/c during which approximately 10% of 
the nucleons are excited to DELTA-resonances. 

## Invariant mass spectrum decomposition

**Elementary processes:**

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

- Example cocktail
- ( DLS data compared
- to HSD model )

## The DLS results

- The shape (0.05  M  0.35) can be explained by Dalitz decays of0 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.****  (T****ü****bingen)**
**Phys. Rev. C6****8**** **** ****(2003)****  014904**

**Done using strong or weak (s/w) **
****** ****- N*(1535) coupling**

## HADES ... What and where?...

## High Acceptance Di-Electron Spectrometer

- 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

**Notes:**
HADES is optimized for the detection of low-mass vector mesons!

Experiences from DLS called for large acceptance.

## HADES Spectrometer

**Side View**

**START**

- 1 m

**    **_**Fast particle identification**_

**Pre-Shower**: 18 pad chambers & 12 lead converters between

**RICH**: CsI solid photo cathode, C4F10 radiator,  N0   8090,    suppression: 104

**TOF**:  384 scintil. rods ,   150 ps
**TOFino**: 24 scintil. paddles,   450 ps      temporary solution, **RPC** in future

**    **_**Momentum measurement**_

- Magnet: superconducting toroid:  B = 0.36 Tm

**MDC****: **24 multiwire drift chambers, y  100 m single cell resolution

**Notes:**
RICH has to cope with a rather short radiator. Solid VUV photo cathode (CsI)

## Fast 2nd level trigger

- up to 20 kHz LVL1Fast multiplicity trigger

- full event information digitised

**on-line selection of ****electron candidates**

- LVL2 triggered events are transported to mass storage

- Suppression 10 - 100

## Experimental (production) runs

_**November 2002**_**:** **C+C 2 AGeV**, commissioning and physics runs
- target= 2 x 2.5% 	**650 Mevents**
- 6 outer drift chambers (MDC) in 4 sectors
_**February 2004**_**: **p+p 2 GeV
- target 5 cm LH2, almost full spectrometer setup	**600 Mevents**
_**August 2004:**_ **C+C 1**** ****AGeV**
- 3x2 % target	**2500 Mevents**
_**September**__** 200**__**5**__**:**_ Ar+KCl 1.75 AGeV
- 4x1.5 % target	**1200 Mevents**
_**May**__** 200**__**6**__**:**_ p+p 1.25 GeV
- Target 5 cm LH2	**3000 Mevents**

## Analysis strategy

-  **Single electron analysis**
** **_C__lassical_: 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)
** ****C****orrections for detector**** **** ****and reconstruction efficiencies****                      ******** acceptance & reconstruction**** efficiency filters available **

## C+C @ 2 AGeV - mass spectrum

- signal **< **140 MeV/c2:  **20971** counts
- signal **>** 140 MeV/c2:    **1937** counts

*( picture above )*no acceptance / efficiency corrections

_**limited resoultion**_** ( ~DLS level )****only inner MDC chambers in 2002**

## C+C @ 2 AGeV - mass spectrum corrected

**E****fficiency corrected spectra**
- -  detector efficiency
- -  reconstruction efficiency
-   normalized to the pion yield

- in HADES acceptance

**12****C+****12****C  2AGeV**

**PLUTO** event gener.
- (HADES Collaboration)
******0** and **** well known
- (thermal freezout)
- based on TAPS measurements

## C+C @ 2 AGeV – HSD model

- vacuum

- in-medium

- ( data described quite well )

## C+C @ 2 AGeV – UrQMD model

- problems in the
- high mass region

- Transport calculation  (**vacuum result****)**
- UrQMD Frankfurt
- M. Bleicher, D. Schumacher

## C+C @ 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

## C+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

## C+C @ 2 AGeV – rapidity – exp, PLUTO, HSD

**discrepancy** in medium (PLUTO, HSD)
- and high mass (PLUTO) region

**dots** - experiment
**dashed line** - PLUTO
**solid line** - HSD

## C+C @ 2 AGeV – pT – exp, PLUTO, HSD

- C+C @ 2 AGeV – pT – exp, PLUTO, HSD

**PLUTO**

**HSD**

**solid line**
- vacuum
**dashed line**
- in-medium

**discrepancy**
- in medium
- and high mass
- region

## C+C @ 1 AGeV - preliminary

**preliminary**

- Comb. backgr. (CB):
- from like-sign pairs
**CB =**** ****S****+****** =** N****e+e******** ******** ****C****B****+**** ******

- not efficiency corrected !

**Direct comparison**
**to DLS data possible**

**Exp. Data**:
- no efficiency correction
**PLUTO**:
- filtered with HADES
- acceptance * efficiency

**Normalized to π****0**
**70% of the full data statistics**** **

- only π0 , η is not sufficient to describe the data – model comparison in the future

## 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)
-  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

## 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)Departamento de Física de Partículas. University of Santiago de Compostela.
-      15782 Santiago de Compostela, Spain
- 20)Instituto de Física Corpuscular, Universidad de Valencia-CSIC,46971-Valencia, Spain