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Recent Results from HADES

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DLS pair excess has been confirmed by the HADES CC data : ... New HADES data on elementary reactions provide important input for the understanding of HI data ... – PowerPoint PPT presentation

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Title: Recent Results from HADES


1
Recent Results from HADES
  • Physics Motivation
  • Low mass lepton pair enhancements
  • SPS and DLS data
  • The HADES detector at GSI Darmstadt
  • Experimental Results
  • 12C12C and the DLS Puzzle
  • pp, pd
  • ArKCl
  • Summary and Outlook

2
Electromagnetic Probes Penetrating Probes

PHENIX, STAR
T
  • Experiments at different ?s probe different
    regions of phase diagram
  • RHIC ee pairs and g
  • sQGP
  • SPS ee, mm pairs
  • transition region
  • SIS ee pairs dense
    hadronic matter
  • HADES

Quark Matter
CERES, NA60
TC170 MeV
DLS, HADES
thermal freeze out
Color Superconductor
chemical freeze out
SIS
Hadron Resonance Gas
temperature
Nuclear Matter
baryon chemical potential
1200-1700 MeV
940 MeV
mB
3
CERES Low-mass dilepton enhancement
Nucl-ex/0203004
Nucl-ex/0203004
  • Central N-N collisions exhibit a strong
    enhancement of low-mass dilepton production as
    compared to p-N reactions (CERES, HELIOS, NA60)
  • A large fraction of the excess is probably due to
    pion annihilation, which does not contribute in
    p-N reactions
  • There is no quantitative description of the data
    using vacuum properties of vector mesons
  • Possible explanation
  • in-medium modifications of vector meson
    properties
  • Broadening and/or mass shift of the rho meson

4
The DLS_at_BEVALAC - Puzzle
  • DLS Experiment observed large excess of
    di-electrons when compared to dominant known
    sources
  • Pion, eta Dalitz decays
  • Effect much stronger than at SPS energies
  • Visible also in light ion induced reactions
  • For many years, no conclusive theoretical
    explanation available
  • Experimental problem?
  • New physics?
  • Not well understood old physics?

5
Acceptance Full azimuth, polar angles 18o -
85o Pair acceptance ? 0.35 Particle
identification RICH CsI solid photo cathode,
C4F10 radiator, Time Of Flight Scintillator
paddles ? MUL limitation ?2009 Pre-Shower pad chambers lead
converter 2' Level single leg electron trigger
(Me1) Momentum measurement Magnet B? 0.36
Tm MDC 24 Midi Drift Chambers, single-cell
resolution ? 140 ?m
6
Hadron Identification
  • Momentum vs velocity (ß)
    dE/dx in MDC TOF
  • example Ar KCl _at_ 1.75 A GeV
  • TOF ? 450
  • particle mass spectra with dE/dx (TOF MDC)
    selection
  • ? kaon identifcation

7
Electron Identification
  • Spatial correlations
  • RICH rings ?tracks
  • PID e, e-
  • ß vs momentum correlation
  • PreShower condition

C C _at_ 2AGeV
  • Hadron contamination 1000 MeV)

8
pp _at_ 2.2 GeV Exclusive ?0/ ?
reconstruction
pp?pp?? pp??-?
total signal background
M? 548 MeV/c2 ?/M 3.5
HADES
708 ?b
  • Exclusive reactions
  • Clean and consistent reconstruction of hadronic
    and Dalitz decays for p0, h
  • Cross check for detector simulations

9
  • LOW mass excess "DLS" puzzle"

10
Inclusive ee- pairs from CC collisions
A. Agakichiev accepted by Phys. Lett. B
A. Agakichiev Phys.Rev. Lett 98(2007) 052302
  • Normalization N(?0) ½(N? N?-)
  • Cocktail A ?0 ? ? long-lived component
    (?0/? constraint by TAPS data)

11
Comparison of DLS and HADES Acceptance
12
Comparison to DLS CC _at_1.04 GeV
J. Carroll presentation International Workshop
on Soft Dilepton ProductionAugust 20-22,1997,
LBNL
DLS Data R.J. Porter et al. Phys.Rev.Lett. 79
(1997) 1229
  • Very good agreement between both experiments
  • ? Full confirmation of DLS effect

13
Beam energy dependence of the excess
  • Enhancement scales like pions !
  • Baryon resonance decays ?
  • N-N bremsstrahlung ?

14
Comparison with Up-to-Date Transport Calculations
IQMD M. Thomère et al. Phys.Rev.C75 064902
(2007)
HSD E.L. Bratkovskaya and W. Cassing
arXiv0712.0635v1 and private communication New
treatment of Bremsstrahlung L.P. Kaptari and B.
Kämpfer, Nucl.Phys. A 764 (2006) 338
  • Important contributions from ? Dalitz decay
  • and Bremsstrahlung
  • Cruical input
  • Elementary reactions
  • pp, pn

15
pp and pn 1.25 GeV
  • Not efficiency corrected
  • Not corrected for trigger bias
  • Analysis in progress

Online spectrum (data from May 2007 )
very preliminary
preliminary
PhD thesis T.Galatyuk
  • New precise input of elementary
  • cross sections for model calculations

16
N-N Bremsstrahlung
  • Strong electromagnetic
    process (OBE models)

(simplified picture!)


NN ("quasielastic")
  • E.L Bratkovskaya W. Cassing arXiv 0712.0635v1
  • Bremsstrahlung OBE calculations
  • Kaptari Kämpfer, NPA 764 (2006) 338

E.L. Bratkovskaya and W. Cassing
arXiv0712.0635v1
  • new OBE calculation
  • pn bremsstrahlung 4 larger than before !

17
  • Vector meson production

18
HADES pairs from pp _at_ 3.5 GeV
Preliminary (not efficiency corrected, no
normalization)
  • ??ee- signal (?tot20 nb! ) ?35 MeV/c2
  • Reference for pA (2008)

19
Signal Pairs from ArKCl
  • No efficiency correction
  • Nee- 114.000 pairs (7k for MM?0 )
  • ??ee- decay seen for the first time at
    SIS/Bevelac energies !

Preliminary
Mee- 0.4 GeV/c2
20
Summary and Outlook
  • Low mass enhancement
  • DLS pair excess has been confirmed by the HADES
    CC data
  • No puzzle any more (at least not from the
    experimental point of view)
  • Combined CC, pp and pn data _at_1.25 GeV indicate
    that most of the excess originates from p-n
    reactions
  • Strong isospin dependence of pair production
  • New HADES data on elementary reactions provide
    important input for the understanding of HI data
  • Implications for low mass lepton continuum in a
    baryon rich environment
  • Importance of resonance decays
  • Correct description of Bremsstrahlung
  • Interference between these processes ???
  • Vector meson production
  • ??ee- decay observed for a first time at
    SIS/Bevalac energies
  • pp _at_ 3.5 GeV and ArKCl _at_ 1.75 AGeV

21
HADES runs Outlook plans for next years
pA _at_ 3.5 GeV
upgrade RPC, DAQ
NiNi
pN,A
AuAu
8 AGeV
Subject to Approval
SIS
FAIR
SIS
22
The collaboration
  • Catania (INFN - LNS), Italy
  • Cracow (Univ.), Poland
  • Darmstadt (GSI), Germany
  • Dresden (FZR), Germany
  • Dubna (JINR), Russia
  • Frankfurt (Univ.), Germany
  • Giessen (Univ.), Germany
  • Milano (INFN, Univ.), Italy
  • Munich (TUM), Germany
  • Moscow (ITEP,MEPhI,RAS), Russia
  • Nicosia (Univ.), Cyprus
  • Orsay (IPN), France
  • Rez (CAS, NPI), Czech Rep.
  • Sant. de Compostela (Univ.), Spain
  • Valencia (Univ.), Spain
  • Coimbra (Univ.), LIP, Portugal

23
Sign for Chiral Symmetry Restoration ?
  • According to lattice QCD and model calculations
    (Nambu-Jona-Lasinio), chiral symmetry can be
    (partially) restored
  • At high temperature
  • Experiments at RHIC, LHC
  • At large baryon density
  • SIS, AGS, SPS,
  • (in the future SIS300 _at_ GSI)
  • Even at normal nuclear matter
  • density
  • Pion beams for recoil-free vector
  • meson implantation in cold nuclei

24
Medium Modifications in Hadronic Languague
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