1. Dilepton spectroscopy with HADES: now and theng* l+
Dilepton spectroscopy with HADES: now and then
MADAI.us
Tetyana Galatyuk for the HADES Collaboration
Technische Universität Darmstadt / GSI

2. The mission
Search (in this region) for new states of matter with rare and penetrating probes
Stage I (2002 – 2008)
light collision systems  limited granularity of time-of-flight system
Stage II ( )
Heavy collision-systems
p-induced reactions
Stage III ( …)
Reference measurements
Lepton pair excitation function up to 8 GeV/u (medium-heavy systems) and (multi-)strange particle
heating
compression

3. Baryonic matter at 1-2 AGeV Beam Energyl- g* l+
K, L, f, X,
Rare and penetrating probes
HADES
Evolution of average rB
Composition of a hot pDN gas
Elab=30GeV
Elab=11GeV
Rapp, Wambach, Adv.Nucl.Phys. 25 (2000)
Elab=2GeV
t >10 fm/c
Moderate densities but long lifetime:
max/r0 = 1-3,  ~10 fm/c
Baryon dominated:
p densities a factor ~10 lower as compared to SPS regime!
Matter enriched by baryonic resonances (~30%), N/Apart ≈ 10%

4. „If you want to detect something new, build a dilepton spectrometer“ S
„If you want to detect something new, build a dilepton spectrometer“ S. Ting

5. The hades at GSI, Darmstadt, Germany
SIS
HADES strategy:
Excitation function for low-mass lepton pairs and (multi-)strange baryons and mesons
Various aspects of baryon-resonance physics
Beams provided by SIS18: p, proton, nuclei
Full azimuthal coverage, 18 to 85 degree in polar angle
Hadron and lepton identification
Event-plane reconstruction
e+e- pair acceptance 35%
Mass resolution 2 % (r/w region)
~ channels
50 kHz event rate
p+p 3.5 GeV

6. Hades event reconstruction
Recorded data sets
Particle identification by means of:
dE/dx in the MDC and ToF
Velocity vs. momentum
Operational at GSI since 2002
Upgrade 2008 – 2010 e+ e- p- p+ K+ p
d,4He t
3He
RICH rings
Vertex reconstruction

7. Particle spectra in 1.23 AGeV Au+Au collisions
HADES Preliminary
Rapidity:
0.065 – 1.165
Dy = 0.05
HADES Preliminary
Circles: KaoS Ph.D. thesis A.Forster
Squares: HADES K+ p
Fitted with: f(F)=1+2v1*cos(F)+2v2*cos(2F)) F = FK+ – FRP
Open symbols: W. Reisdorf et. al. FOPI collab. Nucl. Phys. A 876 (2012)

8. hadron production in 1.23 AGeV Au+Au collisions
PhD Timo Scheib
K0s
First measurements at such low beam energy!
HADES Preliminary
HADES Preliminary
HADES Preliminary
K0s L
HADES Preliminary L L
HADES Preliminary

9. Strangeness production in 1.76 AGeV Ar+KCl collisions
High-statistics measurement of p+, p-, K+ and K-, K0s, L, f, -
HADES Collab., PRL.103:132301,2009
Eur.Phys.J.A40:45-59,2009 Phys.Rev.C80:025209,2009 Eur. Phys. J. A 47:21, 2011
Thermal equilibrium also at low energies (high mB)?
Production mechanism of multi-strange baryons?
No OZI suppression of f. Can be described with SHM (THERMUS)
-- THERMUS fit: J.Cleymans, J.Phys.G31(2005)S1069
HADES Ar+KCl 1.76 AGeV

10. Surprises in strangeness production
Jan Steinheimer
Experimental challenge: at SIS energies strangeness produced sub-threshold
Ar+KCl 1.76 AGeV
- produced at √s-√sth = -630 MeV
SHM: factor of <20 below the measured yield
UrQMD: dominant process: YY strangeness exchange, but remains short of explaining data
p+Nb 3.5 GeV
- produced at √s-√sth = -70 MeV
Strong constraints on production mechanism
SHM fit in progress (Apart, p0, p-, h, L, K0s, f, w, -)
 Stay tuned ;)
UrQMD: arXiv:
analysis by R.Kotte and C.Wendisch
paper in preparation

11. f production as source of K-
Au+Au 1.23 AGeV
HADES Preliminary
√s-√sth = GeV
First measurements at such low beam energy!
PhD Heidi Schuldes K- f
Ar+KCl 1.76 AGeV
Enhanced f production at low beam energy
18±7% of K- originates from f decays!
Different inverse slope parameters  K- freezes out later compared to K+?
Unique freeze-out criteria when f decay kinematics is taken into account  support for SHM
HADES Collab., Phys.Rev.C80:025209,2009
analysis M. Lorenz

12. Can we establish the qcd phase diagram with dileptons?
LQCD: Z. Fodor et al., hep-lat/
Condensate: B.J. Schaefer and J. Wambach, private comuniction
HADES data: M. Lorenz et al., Nucl. Phys. A (2014) QM14
A. Andronic et al., Nucl. Phys. A 837 (2010) 65
J. Cleymans et al. , Phys. Rev. C 60 (1999)
FOPI data: X. Lopez et al., Phys. Rev. C 76 (2007)

13. Virtual photon radiation from hot and dense QCD matter
Model: Ralf Rapp
STAR: QM2014,
NA60: EPJC 59 (2009) 607, CERES: Phys. Lett. B 666 (2006) 425, HADES: Phys.Rev.C84 (2011)
Highly interesting results from RHIC, SPS, SIS18
 lepton pairs as true messengers of the dense phase mB

14. Characteristics of the dilepton rates ( cocktail )
Characteristic features of
dilepton invariant mass spectra
Low mass:
Continuum enhancement
In-medium modification of vector mesons
Intermediate mass:
QGP thermal radiation
Heavy-flavor modification
Chiral mixing
High mass:
J/ suppression (enhancement)
Drell-Yan, primordial emission
Figure: T. Ullrich
Low mass
Intermediate mass
High mass

15. Fixing important components of the hadronic cocktail
Au+Au
HADES Preliminary
PhD Claudia Behnke p0 h
p0 and h from full conversion method
meson mT-scaling p0
HADES p+Nb Phys. Rev. C 88, (2013)
Crucial component of the cocktail
h cross section provides constraint on D and N* contributions
HADES low mass spectrometer
Segmented target
RICH: X/X0 < 1%!
MDC: X/X0 ≈ 0.42%
 specially optimized to minimize conversion and multiple scattering

16. p0/ pT distribution / yields compared to transport
HADES p+Nb 3.5 GeV: 0 

17. Lepton pairs from pp and np (tagged n) reactions at 1.25 GeV
Exclusive channel pp  ppe+e-
Goal
Reference measurement for Au+Au at 1.23 AGeV
Exploring hadron electromagnetic structure
Results
Remarkable isospin effect!
First measurement of the D transition form factor in the time-like region
Branching ratio (D+pe+e-) = 4.42×10-5 (analysis W. Przygoda, paper in preparation)
Role of p EM form factor
Double D excitation plus "final state" interaction
VDM
QED
HADES data: PLB 690 (2010) 118
M. Bashkanov et al., Eur. Phys. J. A50, 107, (2014)

18. jLab / mami / mit results on baryonic resonances
Magnetic transition form factor
Excitation of a baryon can be carried by the meson cloud
Pion electro-production: g*p  D(1232)P33  pN
Strong hint for dominant contribution to the GM(Q2) from the meson cloud (30% at GM(0) near the photon point)
„Meson cloud”
Quark core
„Meson cloud” q g* l+ l-
I.G. Aznauryan, V.D. Burkert Prog. Part. Nucl. Phys. 67, 1 (2012)) 1846

19. “r meson” in pp and pNb at 3.5 GeV
Vacuum: p+p  ppe+e- 3.5 GeV
Vacuum: p+p 3.5 GeV (GiBUU)
Cold matter: p+Nb 3.5 GeV
Pee < 0.8 GeV/c
HADES: Eur. Phys. J. A (2014) 50
J. Weil et al., Eur. Phys. J. A 48 (2012) 111
HADES: Phys.Lett. B715 (2012) R N g* e+ e- r
“r”-line shape “modified” already in elementary reactions!
 Due to production mechanism via resonances NN  NR  NNr, NN  ND NNpr
Strong broadening of w in cold nuclear matter!
Decay of off-shell r formed in the meson cloud?

20. ”if you are out to describe the truth, leave elegance to the tailor” A
”if you are out to describe the truth, leave elegance to the tailor” A. Einstein Perspectives of the p beam experiments

21. Pion beam run in 2014: Measurement combined with machine developments for SIS100
pA experiments:
In-medium effects (strange and vector mesons)
pp experiments
Resonance-Dalitz decays
Hadronic final states, 1p, 2p to control resonance excitation
Special interest to sub-threshold vector meson production f
July’14: p- + W/C at 1.7 GeV/c
August-September: p- + Pe/C at 0.69, 0.656, 0.748, 0.8 GeV/c

22. e+e- exclusive Online spectra from AuG/sep’14
Inv. mass > 120 GeV/c2
Missing mass  ( GeV/c2)
ONLINE
p- (0.69 GeV/c) Pe
p- (0.69 GeV/c) Pe
ONLINE
 = 32 MeV/c2
N signal =570 (C=260)
Missing mass (GeV/c2)
Mee (GeV/c2)
Crucial to control the interpretation of medium effects from SIS to LHC
Unique chance to study time-like electromagnetic structure of higher lying resonances!

23. Low-mass Dileptons at 1 – 2A GeV
Phys.Lett. B 690 (2010) 118
Phys.Rev.C 84 (2011)
PhD S. Harabasz, T. Kunz, P. Sellheim
C+C: After h subtraction, coincides with (pp+np)
Ar+KCl: First evidence for radiation from the “medium” in this energy regime!
Rapid increase of relative yield reflects the number of D‘s/ N*’s regenerated in fireball

24. Measuring life-time of the hot and dense fireball
Na60 data: EPJC 61 (2009) 711
HADES: Phys.Rev.C84:014902,2011
“r clock”
“R clock”
p+Nb (Apart=2.7): F = 1.7
Ar+KCl (Apart=38): F = 2.5 – 3
Au+Au (Apart=180): F = 8 – 10
In+In 158A GeV
Excess “counts” number of r regenerations!
 D/N* regeneration!

25. In-medium self energy of the rho
SPS, RHIC, LHC π
N-1 Δ
> N* r l+ l- p+ p- N* N r l+
SIS18 l-
Data: EPJC 59 (2009) 607
Model: Rapp, Wambach, van Hees
 - /N* couplings play substantial role in r melting observed in UrHIC
 connection to elementary process of baryon-resonance Dalitz-decays
Thermal Dilepton Production Rates:

26. Low-Mass e+e- Excitation Function: 19.6-200 GeV
compatible with predictions from melting r meson
STAR data: P. Huck et al., QM14
Model: Rapp/Wambach/Hees

27. "Central-cell Trajectory" from UrQMD AuAu at 1.23 AGeV
Master Florian Seck
"Central-cell Trajectory" from UrQMD AuAu at 1.23 AGeV
beam axis
t = 2 fm/c
t = 30 fm/c

28. Dileptons at HADES UrQMD-medium evolution + RW rates
[Endres,van Hees, Weil+Bleicher, in prep]
Thermal rates folded over coarse-grained UrQMD medium evolution
Supports baryon-driven medium effects at SPS and RHIC!
Measure excitation function and… expect the unexpected!
Fate of hadrons  chiral restoration (yet in model dependent way!)

29. Precision Dileptons at SPS (17.3 GeV)
Why measuring dileptons in Intermediate Mass Range: 1 < Mll < 3 GeV/c2?
Precision Dileptons at SPS (17.3 GeV)
Fireball thermometer (no Doppler!)
Measure excitation function and… expect the unexpected!
Onset of QGP radiation
4p mixing: p + w, a1  m+m- is a dominant hadronic source… but may be identified in v2, Teff vs. mass
Correlated charm contribution (decrease with lower the beam energy)
Drell-Yan (is negligible at low beam energy)

30. The “Money plot” Unique temperature measurement
√sNN (GeV)
T (MeV)
Unique temperature measurement
Look for non-monotonic behavior of T (Note, T < Tinitia) as a function of √sNN
Appearance (disappearance) of QGP radiation
Track 1st order phase transition?
What would pp and pA give?
Concluding remarks, TG, 24 May 2013

31. TPD workshop, August 2014

32. Dilepton Excitation Functions
Ralf Rapp October 2014
Low-Mass Excess Intermediate-Mass Slope
√s ≤ 10 GeV very promising regime for dileptons!

33. Future explorations

34. Phase space coverage for e+e- from r decays
yCM
yCM
yCM
Ebeam = 3.5 AGeV
Acc ≈ 20%
Shift towards backward rapidity
Ebeam = 11 AGeV
 Acc ≈ 20%
Ebeam = 1 AGeV
Overall acceptance for di- electron pairs Acc ≈ 35%
With nice mid-rapidity coverage

35. HADES at SIS100: challenges, opportunities
Occupancy in tracking chambers (bmax = 1 fm)
F=2
Cell size is factor of 2 larger
y – radial coordinate in drift chamber
Challenge: limited granularity  sophisticated tracking algorithm
Au+Au 1.23 GeV/u measured
Nb+Nb 3.5 GeV/u ≈ Au+Au at 1.23 GeV/u
Elementary (pAu): occupancy factor of 10 smaller
Au+Au 4 GeV/u occupancy increases by factor of 2! Mission possible?

36. J/y production in pp and pA collisions (Ebeam = 29 GeV)
Full analysis is required before any conclusion made!
e/p separation using EM calorimeter

37. Encouraging prospects for studying QCD matter in the region of finite mB
Explore unknown territory of the nuclear matter phase diagram with HADES at SIS18:
Unique possibility to characterize properties of baryon dominated matter with rare probes:
contributions from the dense/early phase a quite featureless  strong broadening of in-medium states!(?)
interesting observations in strangeness production
 this state of matter might be much more exotic than a hadron gas
HADES and CBM at FAIR: establish a complete excitation function of dilepton production up to energies of 40 AGeV:
baryon dominated to meson dominated fireballs!
from "transport" to "thermal expansion" models!
from "no QGP" to "QGP”?
The program needs reference measurements for which HADES is an ideal detector system (beams at GSI in 2017 – 2020!)

38. The hades collaboration
Catania, Italy
Coimbra, Portugal
Cracow, Poland
GSI Damstadt, Germany
TU Darmstadt, Germany
Dresden, Germany
Dubna, Russia
Frankfurt, Germany
Giessen, Germany
Lisboa, Portugal
München, Germany
Milano, Italy
Moscow, Russia
Nicosia, Cyprus
Orsay, France
Rez, Czech Rep.
Santiago de Compostela, Spain
18 institution partners
~100 collaborators

39. Thank you!

40. And …
RHIC (BES) + CBM + HADES! allows for overlap and independent confirmation of results
SIS100 HADES meets CBM
Only at SIS300 CBM meets RHIC BES!

41. motivation  Experimental test
Mass de-generation and deconfinement are closely related to the fate of the QCD condensates in the medium!
Establish the nature of phase transitions
Understand generation of mass in strong interactions
 establish connections between chiral order parameters and vector-isovector spectral function
S. Borsanyi et al. [Wuppertal-Budapest Collaboration], JHEP (2010) 073.
 Experimental test

42. Dileptons, hadronic resonances and phase diagram of matter
P. Hohler and R. Rapp, PLB 731 (2014) 103
In-medium r spectral function
Temperature dependence of the chiral quark condensate
S. Borsanyi et al., JHEP 1009, 073 (2010)
Thermal Lattice QCD
-- Hadron resonance gas
effective hadronic theory
1. h = mq h|qq|h > 0 contains quark core + “pion cloud” π
N-1 Δ
> N* r + q qq - q +
2. Excitation of the vacuum (melting of condensate) matches spectral medium effects