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