1. Thermal Radiation Workshop BNL, December 5-7, 2012
Future Dilepton Experiments
Thermal Radiation Workshop BNL, December 5-7, 2012
Itzhak Tserruya

2. Low-Mass Dileptons at a Glance:
Energy Scale
Time Scale 15 20
KEK E235
CERES
DLS
NA60
HADES
STAR 90 95 10 00 05 85
PHENIX
CBM
MPD ?
ALICE
CERES
DLS
NA60
HADES
STAR 10
158
[A GeV] 17
[GeV]
√sNN
200 //
PHENIX
ALICE 1
CBM
MPD
= Period of data taking

3. Outline Top SPS energy Top RHIC energy Low energies
A well wrapped story - CERES, NA60
Top RHIC energy
Challenging results PHENIX
PHENIX - STAR
Low energies
FAIR, NICA, RHIC, SPS
Elementary collisions?
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

4. NA60 – low and intermediate masses
SPS
CERES – low masses
NA60 – low and intermediate masses
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

5. CERES Pioneering Results (I)
Strong enhancement of low-mass e+e- pairs
(wrt to expected yield from known sources)
First CERES result
PRL 75, (1995) 1272
Last CERES result
2000 Pb run PLB 666(2008) 425
Enhancement factor (0.2 <m < 1.1 GeV/c2 ):
5.0 ± 0.7 (stat) ± 2.0 (syst) ± 0.21 (stat) ± 0.35 (syst) ± 0.58 (decays)

6. Dropping Mass or Broadening (I) ?
* Interpretation:
+-    *  e+e-
thermal radiation from HG
CERES Pb-Au 158 A GeV 95/96 data
dropping  meson mass
(Brown et al)
* in-medium modifications of :
broadening  spectral shape
(Rapp and Wambach)
* vacuum ρ not enough to
reproduce data
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

7. Dropping Mass or Broadening (II) ?
* Interpretation:
+-    *  e+e-
thermal radiation from HG
CERES Pb-A 158 A GeV 2000 data
* vacuum ρ not enough to reproduce data
* in-medium modifications of :
broadening  spectral shape
(Rapp and Wambach)
dropping  meson mass
(Brown et al)
Data favor the broadening scenario.
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

8. Quark – Hadron Duality
R. Rapp
In-medium + - ann. rates  perturbative qbarq ann. rates
quark – hadron duality down to m ~ 0.5 GeV/c2
Kämpfer calculations: Thermal radiation from the plasma or just a parametrization of the e+e- yield inspired by quark-hadron duality?
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

9. NA60 Low-mass dimuons Real data ! Superb data!!!
In+In 158 A GeV
Excess shape in agreement with broadening of the  (Rapp-Wambach)
Mass resolution: 23 MeV at the  position
Mass shift of the  (Brown-Rho)
ruled out
S/B = 1/7
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012
Melting of the ρ?

10. The IMR Excess Quark-Hadron duality?
NA60 demonstrated that IMR excess is due to a prompt source.
Renk/Ruppert, PRL 100, (2008)
Hees/Rapp, PRL 97, (2006)
IMR excess can be explained by:
hadronic processes, 4 …
partonic processes, qq annihilation
Quark-Hadron duality?
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

11. Acceptance corrected invariant mass spectrum
Mass spectrum corrected for acceptance in m - pT
Eur. Phys. J. C 59 (2009) 607
LMR: thermal radiation from HG
p+p-  r  m+m-
IMR:
Thermal radiation from HG:
p a1  m+m- (Hees/Rapp) Or
Thermal radiation from QGP
qq  m+m- (Renk/Ruppert)
Quark-Hadron duality?

12. Fit in 0.5<PT<2 GeV/c (as in LMR analysis)
pT distributions
Intermediate mass region
Low-mass region
Fit in 0.5<PT<2 GeV/c (as in LMR analysis)
mT spectra exponential
inverse slopes do not depend on mass.
mT spectra exponential
inverse slopes depend on mass.
 Radial Flow
Thermal radiation from partonic phase
Elliptic flow?
Itzhak Tserruya

13. SPS top energy summary LMR: thermal radiation from HG p+p-  r  m+m-
Eur. Phys. J. C 59 (2009) 607
LMR:
thermal radiation from HG
p+p-  r  m+m-
Resonances melt as the system approaches CSR
IMR:
Thermal radiation from QGP
qq  m+m-

14. RHIC
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

15. Low-mass e+e- Pairs: Prospects at RHIC
At SPS energies, the -meson broadening, that explains both the CERES and NA60 data, relies on a high baryon density.
R. Rapp nucl-th/
What was expected at RHIC?
102
110
Total baryon density
8.6
21.4
33.5 85
p – p
Participants nucleons (p – p )A/Z
20.1
80.4
6.2
24.8
dN( p ) / dy
Produced baryons (p, p, n, n )
RHIC
(Au-Au)
SPS
(Pb-Pb)
Baryon density is almost the same at RHIC and SPS
(the decrease in the participating nucleons transported to mid-rapidity is compensated by the copious production of nucleon-antinucleon pairs)
Strong enhancement of low-mass pairs predicted to persist at RHIC
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

16. Dileptons in PHENIX: Au+Au collisions
PRC 81, (2010)
LMR: Strong enhancement at m= 0.15 – 0.75 GeV/c2.
min. bias ± 0.4 (stat.) ±1.5 (syst.)
central collisions ± 0.5 (stat.) ± 1.3 (syst.)
Enhancement down to very low masses
Enhancement concentrated in central collisions
IMR: agreement with pp charm contribution scaled with Ncoll

17. Comparison to theoretical models
Models that successfully described the SPS data fail in describing the PHENIX results

18. All this is very different from the SPS results New source?
mT distribution of low-mass excess
Excess present at all pair pT but is more pronounced at low pair pT
The excess mT distribution exhibits two clear components
It can be described by the sum of two exponential distributions with inverse slope parameters:
T1 = 92  11.4stat  8.4syst MeV
T2 =  37.3stat  9.6syst MeV
PHENIX
All this is very different from the SPS results New source?
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

19. Dileptons in STAR
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

20. STAR Dileptons in Au+Au collisions
STAR Preliminary
STAR Preliminary
LMR: clear enhancement wrt to cocktail
little centrality dependence
IMR: no clear picture
LMR (MB):
S/B = 1/200
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

21. PHENIX vs. STAR Large quantitative differences Minimum Bias
Enhancement factor in 0.15<Mee<0.75 Gev/c2
Minimum Bias
Central collisions
PHENIX
4.7 ± 0.4 ± 1.5
7.6 ± 0.5 ± 1.3
STAR
1.40 ± 0.06 ± 0.38
1.54 ± 0.09 ± 0.45
Large quantitative differences
Itzhak Tserruya

22. Compare to Rapp, Wambach, v. Hees
STAR central 200 GeV Au+Au
hadronic cocktail (STAR)
Ralf Rapp (priv. comm. to STAR)
Complete evolution (QGP+HG):
cocktail + QGP + HG:
Reasonable agreement with data
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

23. Dileptons in PHENIX: Au+Au collisions
Min bias Au+Au √sNN = 200 GeV
Phys. Rev. C81, (2010)
Integral: 180,000
above p0: 15,000
S/B ≈ 1/200  large statistical and large systematic errors
Cocktail / B ≈ 1/1000
To improve the measurement PHENIX developed a Hadron Blind Detector

24. Run-9 p+p dileptons with the HBD
Fully consistent with published result PR C81, (2010)
Improvement in S/B by a factor of Expected to do better in final analysis
Provide crucial proof of principle and testing ground for understanding the HBD
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

25. Run-10 Au+Au dileptons at √sNN=200 GeV with the HBD
Peripheral
Semi-peripheral
Semi-central +
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

26. Run-10: Data/Cocktail Comparison Run10 – Run4
LMR (m = 0.15 – 0.75 GeV/c2)
Hint of enhancement for more central collisions
Not conclusive given the present level of uncertainties
IMR (m = 1.2 – 2.8 GeV/c2)
Similar conclusions for the IMR
Run 10 consistent with published Run4 results

27. Future LMR: Solve the PHENIX - STAR discrepancy
HBD results in central Au+Au collisions
IMR: higher precision data needed
Higher statistics and direct measurement of charm contribution
Fill the gap between top SPS and top RHIC energy
Preliminary STAR results
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

28. Dileptons with sPHENIX
Hadron Calorimeter
Electromagnetic Calorimeter
Solenoid 2 T
1.4m
Use inner region for dilepton measurement ?
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

29. Fast TPC + active beam pipe
TPC / HBD
Fast TPC + active beam pipe
CsI Readout Plane
active
beam pipe
Pre-Shower / DIRC
0.7 m
0.1 m
EMCal
Dy = 2
Solenoid with < 1 T
TPC Readout
Plane
fast TPC
Readout Pads
TPC provides tracking and eid by dE/dx
HBD provides eid
GEMs are used for both TPC and HBD
Silicon strip with sf ~100 mm dp/p << 1%p
Tracking with TPC
Itzhak Tserruya

30. Future LMR: Solve the PHENIX - STAR discrepancy
HBD results in central Au+Au collisions
IMR: higher precision data needed
Higher statistics and direct measurement of charm contribution
Fill the gap between top SPS and top RHIC energy
Preliminary STAR results
Dilepton v2
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

31. Dileptons v2 First measurements by STAR
Dilepton v2(mee) and v2(pT) results consistent with simulations based on hadronic sources

32. Lower – energies:
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

33. Low energies: testing the model
Explanations of CERES and NA60 results rely on the high baryon density rather than the temperature of the system.
Lower energies  controlled change of conditions: higher baryon density and lower temperature
Phys. Rev. Lett. 91, (2003)
Only available test: CERES measurements at 40 AGeV.
Enhancement factor:
5.9 ± 1.5 ± 1.2 ± 1.8 (cocktail)
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

34. Highest baryon density
RHIC
SPS
Collider
FAIR, NICA
Fixed target
Freeze-out conditions

35. Multi-Purpose Detector (MPD) at NICA
2-nd stage
IT,EC-subdetectors,
Forward tracking chamber(GEM,CPC)
1-st stage
barrel part (TPC, Ecal, TOF)
+ ZDC,FFD, BBC, magnet, …
3-d stage
F-spectrometers
(optional ?)
Toroid
3 stages of putting into operation.
First stage: 2017?
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

36. Compressed Baryonic Matter (CBM) at FAIR
tracking, momentum determination, vertex reconstruction: radiation hard silicon pixel/strip detectors (STS) in a magnetic dipole field
hadron ID: TOF (& RICH)
photons, p0, h: ECAL
PSD for event characterization
high speed DAQ and trigger → rare probes!
electron ID: RICH & TRD
 p suppression  104
muon ID: absorber + detector layer sandwich
 move out absorbers for hadron runs
ECAL
TOF
TRD
RICH
absorber + detectors
STS + MVD
magnet

37. LVM in pA Collisions Cold nuclear matter at highest baryon density
Should broadening effects be visible?
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

38. KEK E235 p+C, 12 GeV
PRL 96, (2006)
PRL 98, (2007)
Interpretation: masses drop by 9.2% (,) and 3.4% (ϕ) at normal nuclear matter density
CBELSA/TAPS: No mass shift. Shape consistent with ω in-medium broadening
CLAS: No effect. Results reproduced by transport model using vacuum mass values of ,  and .
TRW, BNL, Dec. 5-7, 2012

39. Proposed experiment: JPARC – E16
30/50 GeV p beam on Cu, Pb targets
Tracking: GEM, eid: HBD, EMCal a
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012

40. Summary SPS energies: Consistent and coherent picture
Low-mass pair enhancement: thermal radiation from the HG
Approach to CSR proceeds through broadening (melting) of the resonances
IMR enhancement: thermal radiation from partonic phase
Missing: elliptic flow measurements
Higher energies SPS  RHIC:
New source at top RHIC energies? Solve the PHENIX–STAR discrepancy - HBD results in central Au+Au collisions
IMR: need higher precision data: higher statistics and direct measurement of charm contribution
Fill the gap between top SPS and top RHIC energy – STAR, sPHENIX?
Lower energies: explore the phase space of highest net baryon density
CBM at FAIR? MPD at NICA? SPS? RHIC?
LVM in pA collisions: cold nuclear matter at the highest baryon density
JPARC E16 experiment
Itzhak Tserruya
TRW, BNL, Dec. 5-7, 2012