Summary from lecture I
description
Transcript of Summary from lecture I
Summary from lecture ISummary from lecture I
• Meson line shape modifications seen in p+A/+A reactions:1. E325/KEK : downward mass shift (~ 9%) 2. E325/KEK: downward mass shift (~3%) and broadening 3. CBTAPS : downward mass shift (~14%) and 10-fold! broadening.
Strong momentum dependece m(p). No sensitivity to
• .. but G7/CLAS: no mass shift of (~45% broadening) contradiction to
E325/KEK but CB problem in E325? G7/CLAS: no effect on mass shift ... but CLAS acceptance is not
sensitive to CBTAPS no contradiction to CPTABS
New HADES experiment @ GSI : will be sensitive to both /
Dielectrons from HI: SIS (HADES) and Dielectrons from HI: SIS (HADES) and Bevelac (DLS) Bevelac (DLS)
P. Salabura
Jagiellonian University/GSI
SIS (BEVALAC) SIS (BEVALAC) energyenergy regime: 1-2 AGeV regime: 1-2 AGeV
• Final state (Freeze-out) in heavy ion collisions
– approximately 10-15 % pions, baryon
resonances ((1232)) dominated
– up to 200 charged particles (Au+Au)
• Enhancement of baryon density in "fireball"
– Comparable to \ life times : V=1.3\23
fm/c
15 fm/c
Dense matterFreeze-outFirst chance
collisionsAu + Au @ 1 AGeV
UrQMD:J. Phys. G: Nucl. Part. Phys. 25 (1999) 1859–
T60=80MeV
Meson production at SIS/Bevelac energiesMeson production at SIS/Bevelac energies
• Production of vector mesons close to the threshold : SNN< STHR=2MN + m
(Ekinthresh = 1.92 GeV)
– co-operative process :NN N, N NN/
or N, N N*() N/
– production confined to high density phase
– Low production rates: One vector meson decaying into lepton pair per 10 Million
reactions !
• Investigation of NN and N collisions is prerequisite for HI !
mT=( m2 + p2 T)1/2
W. Cassing, E.L. Bratkovskaya / Phys.Rep. 308 (1999) 65Ð233Yield
(arb. units)
e+ee+e- - : example thermal source : example thermal source
•A(m)- Breit-Wigner resonace formula
• (m) Mass dependent decay width
for e+e- reads
• fB(M,T) Boltzmann thermal factor fB(M,T) ~ p E exp(-E/T)
→e+e- from C+C @ 2AGeV
)()(
)(2222
02
02
MMMM
mMA
dM
dN
• no cut-off at M=2m
+ thermal source
Line shape modification of Line shape modification of : :intermediate resonaces intermediate resonaces
D. Schumacher , S. Vogel et.al (UrQMD)
• produced through Baryonic resonance
N*(1520), N*(1720) and
(1700), (1905) involved
e+ e-
N
N*()
DLS puzzle:DLS puzzle:
Data: R.J. Porter et al.: PRL 79(97)1229
Model: E.L. Bratkovskaya et al.: NP A634(98)168, BUU, vacuum spectral function
Strong dilepton enhancement over hadronic cocktails comparable to top SPS energies (CERES)!
DLS puzzle:
• Not explained even by in-medium mass shifts and broadening
• Shape of enhancement consistent with e+e- but cross section to low (TAPS)
TAPSTAPS – Two Arms Photon Spectrometer
Electromagnetic calorimeter : m : m =(2E =(2E11EE22(1-cos((1-cos(1122))))1/21/2
C+C @ 1 AGeV
• small acceptance (mid rapidity)
Acc~10-3
and from TAPS
Cross sections measured and extrapolated to full solid assuming isotropic thermal source at rest in NN CM frame
Converted into pair yields:
The DiLepton Spectrometer at LBLThe DiLepton Spectrometer at LBL
• 1988-1993 at Bevalac• 2 Arm-Spectrometer
– Minimum opening angle: 40°
– Each arm: 40° in Φ, 7.5° in Θ
– Trigger on electron-pairs
– Mass resolution
– 30-40% systematical error
• pp/pd, Ca+Ca• 1993 C+C 1.04 AGeV,
– Mid-Rapidity: 0.69
– Acceptance
– Statistics
e+e-
Pair YieldsComb Net pairs Syst. Error
4760 1919 2841 ± 82 ±30%
HADES detector HADES detector
Side View
START
FWFW
Acceptance: Full azimuth, polar angles 18o - 85o
Pair acceptance 0.35
Particle identification: RICH: CsI solid photo cathode, C4F10 radiator, TOF: 384 scintillator rodsTOFino: 24 scintillator paddles MUL limitation, high granularity RPC from 2008Pre-Shower: 18 pad chambers & lead converters)2' Level single leg electron trigger (Me>=1)e+e->=92%, evt. reduction : 20(pp) -3(ArKCl)
Momentum measurementMagnet: B = 0.36 Tm + MDC: 24 midi drift chambers, single-cell resolution 140 mm, 2005-6: set-up completed (MDC IV)
Phase space coverage: HADES vs. DLSPhase space coverage: HADES vs. DLS
mid-rapidity mid-rapidity
• Thermal π0 and η events: HADES and DLS acceptance• HADES acceptance larger but for low masses (M<0.14 GeV/c2) part of phase space covered by DLS not covered by HADES !
Red dashed lines: constant pair momenta in steps of 100 MeV/c
Hadron IdHadron Id• momentum vs velocity (momentum vs velocity (ββ) measurement: ) measurement:
181800 < <<45<4500 TOFINO TOFINO 454500 < <<85<8500 TOF TOF~450 ps~450 ps ~120 ps~120 ps
Electron identification-RICH
hadron blind had t < lep
C4F10 : t = 18.3
pGeV/c
e+
e-0
~ 15.20
Dalitz decay
20% electrons: pi0 Dalitz
e+
e- ~ 2.20
Conversion
70% : electrons conv.
One ring:Two rings (if Ị needs high res. MDC!
Electron IdElectron Id
• Spatial correlations– RICH rings ↔ MDC tracks– MDC tracks ↔ TOF and PreShower
hits• PID : e+, e-
– β vs momentum correlation– PreShower condition
DATA
C + C @ 2AGeV
• hadron admixture < 3% at 1000 MeV/c
e-
e+
velocity vs. momentum
Pair AnalysisPair Analysis
Signal/ Background rejection
C1C1 – the only pair cut
C2C2 – selection of "clean" tracks
C3- conversion rejection
TOF/ShowerTOF/Shower<9o
RICHRICH
MDC I-IIMDC I-II
C1 C2 C3C1 C2 C3
<90
Close Close pairpair
Shared Shared detector detector
hithit
close close conversioconversio
n n candidatecandidate
Rel
ativ
e su
ppre
ssio
n
C1 C2 C3
C + C @ 2 AGeVC + C @ 2 AGeV
Signal= NSignal= Ne+e-e+e- - CB - CB
CB – Combinatorial BackgroundCB – Combinatorial Background
C + C @ 2 AGeV C + C @ 2 AGeV •Spectra before efficiency correction
normalizated to ½(+ + -) yield
~ 2300023000 signal pairs for full Mee range
~ 30003000 signal pairs for full Mee > 150 MeV/c2
(M(Meeee) ~9 % @ M) ~9 % @ Meeee~0.8 GeV/c~0.8 GeV/c22
2002 set-up with 2 inner MDC only
CB Reconstruction
Combinatorial background:
M < 150 MeV/c2 - sLS
sLs = 2
(checked with MC for HADES )
M > 150 MeV/c2 - mixedOpposite Sign (mOS)
MMeeee > 150MeV/c > 150MeV/c22
MMeeee > 150MeV/c > 150MeV/c22• Normalization done between
150-550 MeV/c2 Mee
• sLS and mOS background show same behavior for Mee > 150 MeV/c2
• For Mee < 150 MeV/c2
deviations due to correlated background eeX
eeee NN
CC 2AGeV
Comparison to Physics Generators
ExperimentExperiment
RawRaw DataData
HADESHADES
AnalysisAnalysis
PhysicsPhysics
PairPair SpectraSpectra
Event GeneratorEvent Generator
EfficiencyEfficiency CorrectionCorrection
dN/dMdN/dM
AcceptanceAcceptance FilterFilter
time consuming but done to time consuming but done to cross-check eff.corrections and cross-check eff.corrections and acc. filtersacc. filters
final comparison: only final comparison: only in HADES acceptancein HADES acceptance
comparison incl. comparison incl. efficiency factors efficiency factors
AccAcc±± (p, (p,, , ΦΦ))
Acceptance and Efficiency Acceptance and Efficiency matricesmatrices
acc
rec
N
NpEff ),,(
• pair production and decay is described by 6 dof (3 production and 3 decay)p (0 – 2 GeV/c), Φ (0o – 60o), Θ (0o – 90o)
and similarlyand similarly
all
acc
N
NpAcc ),,(
acc
rec
N
NpEff ),,(
CC @ 2 AGeVCC @ 2 AGeV
C+C @ 2 AGeVC+C @ 2 AGeV
Coctail A (long lived mesonic components)
0 thermal source, anisotropic angular distribution according to measured +-
isotropic mT scaling
18 %18 % 21 %21 %
systematic errors:systematic errors:15 % - efficiency correction 10 % - combinatorial background11 % - 0 normalization
• Cocktail A: 0 + η + ω
• Cocktail B: Cocktail A + Δ(Ne+e-) + ρ
short lived component
A. Agakichiev Phys.Rev. Lett 98(2007) 052302
C+C @ 1 AGeV
Cocktail A: 0 + η + ω
= “long-lived” components only
Large excess yield
•Good agreement in π0 region•Underestimates the data for
Mee > 0.15 GeV/c2
Cocktail B: Cocktail A + Δ + ρ
Contribution from short lived resonances (ρ, Δ, N*)
•Reduced discrepancy for Mee>0.15 GeV/c2
•Cocktail B underestimates dataPR
ELIMINARY
C+C @ 2AGeV pC+C @ 2AGeV pTT , Y distributions , Y distributions
ωη
MMeeee < 150 MeV/c < 150 MeV/c2 :2 : Data well described,Data well described, 150 < M150 < Meeee < 550 MeV/c < 550 MeV/c2 :2 : Underestimation over whole pUnderestimation over whole p range range (factor 2) (factor 2).. MMeeee > 550 MeV/c > 550 MeV/c22 : : Underestimation for high p Underestimation for high p
Pt Spectra @ 1 AGeV
• Good agreement in π0 region
• Underestimation for Mee> 0.15 GeV/c2
• Excess over Cocktail A (0 + η + ω) enhancement at low Pt
PRELIMINARY
No Off-shell, multi-step processes
Transport models
PRELIMINARY
Comparison to transport models for CC @ 2AGeV (status 2006)s 2006)
• RQMD Tübingen C.Fuchs, D. Cozma• UrQMD Frankfurt M. Bleicher,
D. Schumacher• HSD Gießen (v2.5) E. Bratkovskaya,
W. Cassing
vacuum results
• Large variation of yield in models due to uncertainties in Baryon decays must be fixed by data
Yield above Yield above for C+C @ 2 and 1 for C+C @ 2 and 1 AGeV AGeV
F(2.0) = 2.07 ± 0.21(stat) ± 0.38(sys)
Y
Y
Y
YYF excexc
1
PRELIM
INARY
C + C 2 AGeV Phys. Rev. Lett. 98, 052302 (2007)
F(1.0) = 7.06 ± 0.6(stat) ± 1.58(sys)
Yield above :
Excitation function of Pair Excess (Yexc)
DLS
F(1.04) = 6.5 ± 0.5(stat) ± 2.1(sys)
η
DLS
Yexc
excess scales like pion production ! excess scales like pion production !
Yexc(2.0)/Yexc(1.04) = 2.5 ± .5(stat) ± 1.5(sys)
η
η
(2.0)13 3 (stat)
(1.04)
Y
Y TAPSTAPS
HADES vs DLS : direct comparison for CC at 1 AGeV
2 20 1 2 1/ 21/ / exp( ( ) )t t tP d N dPdy c c P c y y Fit:
Mee < 0.15 GeV/c² 0.15 GeV/c² ≤ Mee ≤ 0.55 GeV/c²
Pt [GeV/c] P t [
GeV/c]
PRELIMINARY
•HADES Data incl. extrapolation in DLS acceptance
HADES and DLS Data agree
PRELIMINARY
DLS Data: R.J. Porter et al.: PRL 79(97)1229
Direct Comparison: HADES vs DLS
PRELIMINARY
J. Carroll – presentationInternational Workshop on Soft Dilepton ProductionAugust 20-22,1997, LBNL
• HADES and DLS agree with each other: Do we have now HADES/DLS puzzle for the next 10 years?
• Hopefully not. • Do we understand elementary sources contributing to dielectron cocktail
at SIS/Bevelac energies?
• Radiation from baryonic matter ?
• NNNNe+e- bremsstrahlung
• NNNN*() NNe+e- bramsstrahlung with resonance excitation
i.e (1232)Ne+e- Delta Dalitz decay
dp and pp @ 1.25 GeVdp and pp @ 1.25 GeV
Strategy: study of e+e- sources in pp and pn at s<sthres (Ekin =1.25 GeV) for production
Only 0, and bremsstrahlung contribute:
• Measure pp+pppe+e- (fix +) - assuming brems (pp) is small
• Measure pn e+e-X with dp reactions – determine brems (pn)
() production in pp, pn @ 1.25 GeV
pp p+ 6.0 mb
pn n+
+
pn p0
=12. mb
(assuming isospin
symmetry)
++ =3 +
S. Teis et al., Z. Phys. A 356 (1997) 421-435
• dominant at 1.25 GeV
2/3+p0
2/3+p0
2/30n0
1/30p-
Resonance model and isospin symmetry:
2/32/3+,0 +,0 = = p(n)p(n)00
NN - bremstrahlungNN - bremstrahlung
1
2
1‘
2‘
• Strong + electromagnetic process
e+
e-
+ =
1
2
1‘
2‘
baryon resonances
+
One Boson Exchange Model
Kaptari, Kampfer Nucl. Phys. A 764 (2006) 338Shyam & Mosel (2003)
NN- bremsstrahlung-dielectron yieldNN- bremsstrahlung-dielectron yield
x2x2
x4x4
total
L.P. Kaptari, B. KämpferNucl. Phys. A 764 (2006) 338
• Large isospin (pn = pp ) effects
Problems in description
• Bremsstrahlung?
• contribution ?
• No 0 visible in data ! cross-check with "known" physics" missing
pp/dp from DLS Data: DLS: W.Wilson
Phys.Rev.C(1998)
C. Fuchs et al.Phys. Rev. C68 014904(2003)
E. Bratkovskaya et al.
nucl-th\0008037 (2000)
eVDMeVDM
1010-1-1
101000
1010-1-1
101000
pp/dp @ 1.25 GeV HADESpp/dp @ 1.25 GeV HADES
~50% analyzed • 17008 signal pairs
S/BS/B
1010
11
0.5 1.0 0.5 1.0
MMeeee
preliminary (run 2006)
pp @ 1.25: comparison to simple pp @ 1.25: comparison to simple modelmodel
• cocktail filtered with HADES acceptance and rec. efficiencynormalized to 0 yield
• only 2 sources:
0 e+e-
+pe+e- decay (BR=4.4*10-5 )
+ yield fixed to 0 with isospin
relation: N(+)=3/2 N(0)
• factor ~2 missing yield for M>0.15 GeV/c2
preliminary not eff. correctedpreliminary not eff. corrected
pne+e- X with d+p @ 1.25 AGeV
forward p spectator tagging in Forward Wall selection of pn reactions (10% contribution from pp, only)
p_spec
pcd
p_c
p_spec
p_c
d+pp_c n 0 p_spec
p_spec
p_c
d+pp_c n p_spec
ns
p_spectp_c
pn @ 1.25 AGeV
(MUL=>2 && FW "p spectator") tag on np -> e+e- X reactions
• ~50% analyzed "online"• 37800 signal pairs
+- > 90
"On-line spectrum" not efficiency corrected
S/BS/B
1010
11
0.5 1.0 0.5 1.0
MMeeee
• cocktail filtered with HADES acceptance and rec. efficiency
• cocktail with and only:
(same as for pp case)
• factor 4-5 missing yield for M>150 MeV/c2 (~3 larger than for pp)!
• larger at higher masses
• clear evidence for additional sources
(bremsstrahlung !? pn>pp)
pn @ 1.25 AGeV cocktail
not efficiency corrected normalized to same 0 yield
p + n @ 1.25 AGeVp + n @ 1.25 AGeV
e+e-e+e- >9 >900
"online spectrum""online spectrum"
p+n vs p+p vs C+C : scaling to p+n vs p+p vs C+C : scaling to VERY PRELIMINARY !VERY PRELIMINARY !
p+p vs p+n• p+n above p+p by a factor of 3
• stronger effect at higher masses
Contribution from bremsstrahlung?
pn Bremsstrahlung > pp Bremsstrahlung
factor ~3-4
p+n vs C+C• fair agreement over whole range
NN – bremsstrahlung !?
Puzzle explained by bremsstrahlung?
HADES – HSD vacuum (version'07)
Inv. mass
• Good agreement
• Undershoot at ~ 0.4 GeV/c2 ?
Pt Distributions
• Mee < 0.15 GeV/c² - 0 dominated
• Mee > 0.15 GeV/c²:
– Bremsstrahlung important at low pt
Summary:Summary:
• Low mass enhancement ("DLS puzzle") :a) HADES+ DLS fully consistent:
b) dielectron enhancement scales with beam energy as pion production
b) preliminary combined pp and pn data @1.25 GeV show enhancement (pn>pp) above "standard cocktail" : 0 e+e- , Ne+e-
Ne+e- BR? • NN bremstrahlung ?• e+e- (for pn – Fermi momentum)
All components can be fixed from new HADES data
Improved cocktail should be then compared to HI data... and finaly fix elementary dielectron cocktail
• Vector meson production a) / region measured in pp @ 3.5 GeV with HADES
b) in –medium modifications ? Ar+KCl measured in 2005 and analysis is almost complete
c) p+Nb(Be) to hunt for / modification in nucleus – run scheduled for beginning of next year
Quo Vadis HADES
2006 2007 2008 2009 2010 2011 2012
p,d+p 1,25/3,5 AGeV EXP S201
p+p 1,25 GeV EXP S201
p+A
upgrade
Ni+Ni
+N,A
Au+Au
SIS
SIS
Currently discussed in a committee
SIS
8 AGeV
back-up slidesback-up slides