Post on 30-Jan-2016
description
Wolfgang Kühn, Universität Giessen
Recent Results from HADES
Physics Motivation Low mass lepton pair enhancements
SPS and DLS data The HADES detector at GSI Darmstadt Experimental Results
12C+12C and the DLS Puzzle p+p, p+d Ar+KCl
Summary and Outlook
Wolfgang Kühn, Universität Giessen
Electromagnetic Probes – Penetrating Probes
Experiments at different s probe different regions of phase diagram
RHIC ee pairs and sQGP
SPS ee pairs transition
region
SIS ee pairs dense
hadronic matter HADES
Color Superconductor
Quark Matter
Hadron Resonance Gas
Nuclear Matter
SIS
DLS, HADES
CERES, NA60
PHENIX, STAR
B
T
TC~170 MeV
940 MeV 1200-1700 MeVbaryon chemical potential
tem
per
atu
re
thermal freeze out
chemical freeze out
Wolfgang Kühn, Universität Giessen
CERES: Low-mass dilepton enhancement
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
Nucl-ex/0203004
Nucl-ex/0203004Nucl-ex/0203004
Wolfgang Kühn, Universität Giessen
The DLS@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?
Wolfgang Kühn, Universität Giessen
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 <450, RPC from 2009Pre-Shower: pad chambers & lead converter2' Level single leg electron trigger (Me>=1)
Momentum measurementMagnet: B = 0.36 Tm + MDC: 24 Midi Drift Chambers, single-cell resolution 140 m
Side view
Wolfgang Kühn, Universität Giessen
Hadron Identification• Momentum vs velocity (Momentum vs velocity (ββ) + dE/dx in MDC & TOF: ) + dE/dx in MDC & TOF:
• example: Ar + KCl @ 1.75 A GeVTOF: >450
• particle mass spectra with dE/dx (TOF & MDC) selection
kaon identifcation
Wolfgang Kühn, Universität Giessen
Electron Identification Spatial correlations
RICH rings ↔tracks PID : e+, e-
β vs momentum correlation
PreShower condition
DATA
C + C @ 2AGeV
• Hadron contamination < 5% (p>1000 MeV)
e-
e+
velocity vs. momentum
with RICH condition
Wolfgang Kühn, Universität Giessen
pp0ppe+e-
ppppe+e-
Nexp= 2726 ± 53,SIM=2677
Nexp= 195 ± 19, SIM=196
p+p @ 2.2 GeV : Exclusive 0/ reconstruction
Exclusive reactions Clean and
consistent reconstruction of hadronic and Dalitz decays for 0,
Cross check for detector simulations
totalsignalbackground M 548 MeV/c2
/M 3.5 %
pppp pp+-°
HADES70±8 b
Wolfgang Kühn, Universität Giessen
LOW mass excess : "DLS" puzzle"
Wolfgang Kühn, Universität Giessen
Inclusive e+e- pairs from C+C collisions
• Normalization N(0)= ½(N+ + N-)
• Cocktail A: 0 + η + ω long-lived component (0/ constraint by TAPS data)
• Cocktail B: Cocktail A + Δ(Ne+e-) + ρ short lived component
A. Agakichiev Phys.Rev. Lett 98(2007) 052302 A. Agakichiev accepted by Phys. Lett. B
Wolfgang Kühn, Universität Giessen
Comparison of DLS and HADES Acceptance
mid-rapidity mid-rapidity
Wolfgang Kühn, Universität Giessen
Comparison to DLS C+C @1.04 GeV
DLS Data: R.J. Porter et al.:
Phys.Rev.Lett. 79 (1997) 1229
J. Carroll – presentationInternational Workshop on Soft Dilepton ProductionAugust 20-22,1997, LBNL
Very good agreement between both experiments
Full confirmation of DLS effect
Wolfgang Kühn, Universität Giessen
Beam energy dependence of the excess
TAPSTAPS
Photon dataR. Averbeck et al., TAPS Col., Z.Phys. A 359 (1997) 65R. Holzmann et al., TAPS Col., Phys.Rev. C 56 (1997) R2920
Enhancement scales like pions !Enhancement scales like pions !
• Baryon resonance decays ? Baryon resonance decays ?
• N-N bremsstrahlung ?N-N bremsstrahlung ?
Wolfgang Kühn, Universität Giessen
Important contributions from Δ Dalitz decay and Bremsstrahlung
Cruical input: Elementary reactions
pp, pn
Comparison with Up-to-Date Transport Calculations
IQMD: M. Thomère et al.
Phys.Rev.C75 064902 (2007)HSD: E.L. Bratkovskaya and W. Cassing arXiv:0712.0635v1 and private communication
New treatment of Bremsstrahlung: L.P. Kaptari and B. Kämpfer, Nucl.Phys. A 764 (2006) 338
Wolfgang Kühn, Universität Giessen
preliminary
Online spectrum (data from May 2007 )
very preliminary
PhD thesis T.Galatyuk
pp and pn 1.25 GeV
Not efficiency corrected Not corrected for trigger bias Analysis in progress
New precise input of elementarycross sections for model
calculations
Wolfgang Kühn, Universität Giessen
Vector meson production
Wolfgang Kühn, Universität Giessen
HADES pairs from pp @ 3.5 GeV
Preliminary (not efficiency corrected, no normalization)Preliminary (not efficiency corrected, no normalization)
preliminary
online calibration
~70% statistics
e+e- signal (tot~20 nb! ) ~35 MeV/c2
• Reference for p+A (2008)
Wolfgang Kühn, Universität Giessen
Signal Pairs from Ar+KCl
PreliminaryPreliminary• No efficiency correction
Ne+e- = 114.000 pairs (~7k for M>M
0 )
• e+e- decay seen for the first time at SIS/Bevelac energies !
Me+e- > 0.4 GeV/c2
Wolfgang Kühn, Universität Giessen
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 @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 e+e- decay observed for a first time at SIS/Bevalac energies
pp @ 3.5 GeV and Ar+KCl @ 1.75 AGeV
Wolfgang Kühn, Universität Giessen
HADES runs: Outlook & plans for next years
2008 2009 2010 2011 2012
p+A @ 3.5 GeV
upgrade: RPC, DAQ
Ni+Ni
+N,A
Au+Au
SIS
SIS
Subject to Approval
8 AGeV
FAIR
Wolfgang Kühn, Universität Giessen
The collaborationSISSIS 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