VISIM Meeting, Monbachtal 2007. Low Mass Lepton Pairs – past, present and future Joachim Stroth, Univ. Frankfurt/GSI. introduction pair spectra excess yield thermal radiation transport p T spectra next generation experiments. Electromagnetic structure of dense/hot matter. GR. - PowerPoint PPT Presentation
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VISIM Meeting, Monbachtal 2007
Low Mass Lepton Pairs Low Mass Lepton Pairs – – past, present and futurepast, present and future
Joachim Stroth, Univ. Frankfurt/GSI• introduction• pair spectra• excess yield
- thermal radiation- transport
• pT spectra• next generation experiments
Electromagnetic structure of dense/hot matterElectromagnetic structure of dense/hot matter
Lepton pairs, Lepton pairs, can probe the electromagnetic structure of nuclear matter under extreme conditions.
They couple through time-like photons and test the spectral propertiesspectral properties of hadronic/quark-gluon matter on the femto-scale.
time reversed processes of reactions in a e+e- collider.
intr
od
ucti
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x
qq-bar
- +
ph
2p 2h
phonon
e.g.
GR
Exploring the phase diagram of matterExploring the phase diagram of matter
Chemical freeze-out puts landmarks in the experimentally unknown regions.
Universal conditions for freeze-out?
Limiting temperature Tmax?
QCD inspired models demonstrate the melting of the condesates.
P. Braun-Munzinger, K. Redlich, J. Stachel (e.g. nucl-th/0304013)J. Cleymans, K. Redlich (e.g. PRC 60 054908)
LQCD explores unknown regions from solid grounds at B=0.
Tc = Tmax?
Tc = 170 MeV or TC = 190 MeV?
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Schäfer, Wambachpriv. communication
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Schäfer, Wambachpriv. communication
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LeupoldJ.Phys.G32:2199,2006
LHCRHIC
SPSFAIR
SIS
AGS
F. Karsch, QM04
Z. Fodor & Katz, hep-lat/0402006
3fm/GeV6.0
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The ObservableThe Observable
xxxxp
dvTd
Rd
dMdydp
NdcollB
tt
),..(),(),(0
43
Hydro, statistical expansion models, ..
Nuclear many body theory,
detailed balance, ..
Spectrometer
V
Thermal emission...oVT ,, 00
isentropic expansion
l+
l-
... or microscopic transport
l+l-
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on
Overview on experiments (low-mass pairs) Overview on experiments (low-mass pairs)
time (advance in technology)
LHCLHC
RHICRHIC
SPSSPS
SIS300SIS300
SIS18SIS18BevalacBevalac
SIS 100SIS 100AGSAGS
Inner Tracker
HPID
upgrade
TPC
CCBBMMGAP
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Experimental challenges Experimental challenges
ResolutionResolutionHelps to self–analyze the spectral shape
Excellent (low-mass tracking) Good statistics
Acquire good statisticsAcquire good statistics Permits a multi-differential analysis
Good pair acceptance ("4" spectrometer) High trigger rates Trigger
Minimize signal-to-backgroundMinimize signal-to-backgroundReduces the systematic and statistical error
Contributions from conventional sourcesContributions from conventional sources Partially self-analyzing (see resolution) Need to measure neutral mesons or rely on models
PDG6.20.5 · 10-8π0→e+e-
PT71 · 10-8π0→e+e-
PT51 · 10-9η→e+e-
PDG<7.7 · 10-5η→e+e-
PDG5.80.8 · 10-6η→μ+μ-
BRDecay
Compilation by R. Holzmann.
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Pair spectra
ee++ee-- yields (HADES) yields (HADES)
Completed runs (results)– C+C 2 AGeV (final)
• 1 108 events analyzed
• 23 103 signal pairs
• 2.3 102.3 10-4-4 signal pairs/event signal pairs/event
annihilation now accepted as dominant source Data disproves a scenario assuming a purely shifting Smallest contribution from cocktail to the excess for pt < 0.5 GeV/c
– Excess suppressed on the low-mass side due to acceptance!
non-trivial behavior of slope parameter beyond M = 1 GeV/c2. continuum pairs show flow Hot ?
H. Specht + NA60, INPC07
PPtt Spectra 1 AGeV C+C Spectra 1 AGeV C+C
Good agreement in π0 region
Underestimation for Mee> 0.15 GeV/c2
Excess over Cocktail A (0 + η + ω) enhancement at low Pt
PhD Yvonne Pachmayer, Frankfurt
pT d
istr
ibu
tion
s
next generation experiments
PHENIX with Hadron Blind DetectorPHENIX with Hadron Blind Detector
HBD concept: – windowless CF4 Cherenkov detector – 50 cm radiator length– CsI reflective photocathode – Triple GEM with pad readout– Reverse bias (to get rid of
ionization electrons in the radiator gas)
signal electron
Cherenkov blobs
partner positronneeded for rejection e+
e-
pair opening
angle~ 1 m
next
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exp
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HADESHADES2 – 8 AGeV2 – 8 AGeV
CBMCBM8 – 45 AGeV8 – 45 AGeV
From HADES to CBM @ FAIRFrom HADES to CBM @ FAIRn
ext
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0.3TBmaxy
Dielectron reconstruction in CBMDielectron reconstruction in CBM
Fast, high-precision tracking using silicon sensors.
No electron identification before tracking
CCBBMM
next
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exp
eri
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MVD + STS
ee 0
ee
fake
pair
Track SegmentFull Track
Track Fragment
Invariant mass spectra Au+Au 25 AGeV Invariant mass spectra Au+Au 25 AGeV
ππ0 0 γγee++ee--
ππ00ee++ee--
ηη γγee++ee--
Identified e+e- After all cuts applied
All eAll e++ee--
Combinatorial bgCombinatorial bg
ρρ ee++ee--
ee++ee--
φφ ee++ee--
No optimization of cuts Free cocktail only (without medium contribution) Simulated statistics is 100k events
PhD Tetyana Galatyuk GSI/Frankfurt
CCBBMM
Simulations Au+Au 25 AGeV: Different analysis strategies for low-
mass and high-mass pairs
Low efficiency for small invariant masses and/or low pt (enhancement region).
Challenging muon detector (high particle densities) Micro-pattern gas detectors with pad
readout.
The muon option in CBMThe muon option in CBMCCBB
MM
next
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20 20 20 30 35 100 cm20 20 20 30 35 100 cm
12
34
5
FeFe
Muon Chamber System Muon Chamber System
MuCh MuCh for measurements of:for measurements of: low mass charmoniumlow mass charmonium vector mesonsvector mesons
1 2 3 4 5
Detector requirementsDetector requirements
high rate capability (up to 1 MHz/cmhigh rate capability (up to 1 MHz/cm22) ) high granularity (up to 1 hit/cmhigh granularity (up to 1 hit/cm22 per central Au+Au per central Au+Au collision) collision) position resolution < 300 position resolution < 300 μμmm
Muon pairs (CBM)Muon pairs (CBM)
signals
J/ψ
Ψ'
backgroundsignals
ρ
ω
φ
η
ηDalitz
background
PhD Ana Kiseleva, GSI/St. Petersburg
CCBBMM
Acceptance in pt and mAcceptance in pt and minv inv planeplane
electrons muons
CCBBMM
(My) conclusions(My) conclusions
The quality of data will finally be determined by systematical errors.
High statistics needed toa llow multi-differential analyses.
Understanding the cocktail requires the measurement of neutral mesons ().
Systematic measurements are needed to fully exploit the capabilities of low-mass lepton pair spectroscopy:
Compare low / high beam energies to study effects of the fireball expansion.
Use elementary reactions to constrain spectral functions.
Trigger (at FAIR energies):
e+e-: most likely not possible : difficult without introducing huge bias
Excitation function of the enhancement can possibly signal a critical slowing-down of the expansion.