Christian Müntz (Univ. Frankfurt) for the HADES Collaboration, CPOD 2007 1 Challenges in Physics & Instrumentation Results from Heavy Ion and Elementary

Christian Müntz (Univ. Frankfurt) for the HADES Collaboration, CPOD 2007 1

Challenges in Physics & Instrumentation

Results from Heavy Ion and Elementary Reactions

Summary & Outlook

Dilepton MeasurementsDilepton Measurementswith HADESwith HADES

Christian Müntz Christian Müntz (Univ. Frankfurt),(Univ. Frankfurt),for the HADES Collaborationfor the HADES Collaboration


The CollaborationThe Collaboration

GSIGSI

SISSIS

Catania (INFN - LNS), Italy

Cracow (Univ.), Poland

Darmstadt (GSI), Germany

Dresden (FZD), Germany

Dubna (JINR), Russia

Frankfurt (Univ.), Germany

Giessen (Univ.), Germany

Milano (INFN, Univ.), Italy

Munich (TUM), Germany

Moscow (ITEP,MEPhI,RAS),

Russia

Nicosia (Univ.), Cyprus

Orsay (IPN), France

Rez (CAS, NPI), Czech Rep.

Sant. de Compostela (Univ.), Spain

Valencia (Univ.), Spain

Coimbra (Univ.), LIP, Portugal


© A.Drees

OrientationOrientation

Sources for dileptonSources for dilepton

production in (ultra-)production in (ultra-)

relativistic HICsrelativistic HICs

Add…Add…

Accuracy

Significance

Systematics


10 20 30t [fm/c]

≈ 10 fm/c

PhysicsPhysics Motivation Motivation

Vector mesons (VM)Vector mesons (VM): Optimum choice!Optimum choice!

VM life time comparable to system life time

Interplay with baryonic resonances

Decay in dileptons: Direct probe, final state

interaction minimized!

The SIS heavy ion energy regime:The SIS heavy ion energy regime:

Probing nuclear matter at “moderate”…

- Densities (/o = 1…3), and

- Temperatures (T < 100 MeV)

A long life time of the dense system (up tp 10 fm/c)

The all-dominant presence of baryonic resonances (“resonance matter”, 33), N/Apart ≈ 10%

The sub-threshold production of Kaons and Vector Mesons: Multi-step processes confined to the dense phase


The MissionThe Mission

HHigh igh AAcceptance cceptance DDiiEElectron lectron SSpectrometerpectrometer

Focus on the spectroscopy of vector mesons ()

Consistent picture in pp, pA, A and AA reactions

Supplemented by hadron spectroscopy, incl. K0

s, ,

Instrumental challenge!Instrumental challenge!

VM: rare probe:

1 VM per 1-10 Million reactions!

Large background from conversion and 0-Dalitz decay

Spectrometer with a …Spectrometer with a …

High geometric acceptance & invariant mass resolution

High background rejection & rate capability, dedicated LVL2 trigger


The SetupThe Setup

START

Acceptance: Full azimuth, polar angles 18o - 85o

Pair acceptance 0.35 About 80k detector channels

Forward

Hodoscope

<7o

Side View

Opening angle > 9o

Pair acceptance


Completed RunsCompleted Runs

Physics Runs in…

p, d, - induced A + A Status/Comment

2002 C + C 2 AGeV Published!

2004 C + C 1 AGeV Analysis finished

2004 p + p 2.2 GeV Analysis finished

2005 Ar + KCl 1,75 AGeV Analysis ongoing

2006 p + p 1.25 GeV Analysis ongoing

2007 p + p 3.5 GeV

d + p 1.25 AGeV

… online results!

2008 p + A 3.5 GeV

2008/9 Upgrade RPC, DAQ

2009 Ni + Ni Planned

2010 + N, A

2011 Au + Au

> 2011 Hades goes FAIR (8 AGeV)


Hadrons: Advances in Particle IDHadrons: Advances in Particle ID

Standard PID via time-of-flight & momentum

NewNew: dE/dx from tracking (MDC)

Dedicated cuts to increase (e.g. kaon) signal.MDC I MDC II MDC III MDC IV

Truncated mean is calculated from all measurements of a track

particle track

K+

p+-

K-

Ar + KCl, 1.75 AGeV


Ar + KCl, 1.75 AGeVAr + KCl, 1.75 AGeV

Invariant mass distributionsInvariant mass distributions30% of total statisticsPreliminary!Mixed event technique background (Ks

o,) 0

SK

p KK

Ph

D t

hesis

A

.Sch

mah


Hadrons: Charged Pions Hadrons: Charged Pions

C + C, 2 AGeVC + C, 2 AGeV

Anisotropy:

Used for the Normalization of dilepton spectra, properly extrapolated to 4

π+y =

0.1-0.20.2-0.30.3-0.40.4-0.50.5-0.60.7-0.80.8-0.90.9-1.01.0-1.11.1-1.21.2-1.31.4-1.51.5-1.61.6-1.71.7-1.8

*) 11% syst, error, in agreement with KaoS, TAPS **) preliminary

1 AGeV **) 2 AGeV *)

N< -+>/Apart 0.069 ± 0.008 0.137 ± 0.015


Details moved to the backup slides…!Details moved to the backup slides…!

Lepton candidate selectionLepton candidate selection

Spatial correlations

PID

Background rejectionBackground rejection

ConversionConversion

00-Dalitz-Dalitz

Combinatorial backgroundCombinatorial background

Same event like sign pairsSame event like sign pairs

Mixed event opposite sign pairsMixed event opposite sign pairs

Lepton Analysis: TechnicalitiesLepton Analysis: Technicalities

e+

e- ~ 0.70

Conversion

e+

e-

0

~ 2.20

Dalitz


C + C, 2 AGeV, vs. Hadronic CocktailC + C, 2 AGeV, vs. Hadronic Cocktail

► Cocktail A:Cocktail A: 0 + η + ω (long lived)

► Cocktail B: A & Cocktail B: A & Δ(Ne+e-), ρ

(short lived)18 %18 % 21 %21 %

systematic errors:systematic errors:15 % - efficiency correction 10 % - combinatorial background11 % - 0 normalization

Ph

D th

esis

: M.

Su

dol

PRL 98, 052302 (2007)PRL 98, 052302 (2007)- Normalized to ½(+ + -) yield - M <150 MeV/c2: ~23000 counts

- M-≥150 MeV/c2: ~ 3000 counts

(M(Meeee) ~9 % @ M) ~9 % @ Meeee~0.8 GeV/c~0.8 GeV/c22

Event generator PLUTOEvent generator PLUTO :

thermal source (T=80MeV)

polar angle distribution from charged analysis

η (TAPS data)

ρ, ω: m -scaling

Δ scales with


pp┴┴, y distributions compared to cocktail, y distributions compared to cocktail

► C + C, 2 AGeVC + C, 2 AGeV


C + C, 1 AGeV, preliminary dataC + C, 1 AGeV, preliminary data

Preliminary!Preliminary!- Normalized to ½(+ + -) yield - M <150 MeV/c2: ~17780 counts- M-≥150 MeV/c2: ~ 646 counts

Event generator PLUTOEvent generator PLUTO : Thermal source (T=55MeV) polar angle distribution from charged analysisη (TAPS data) ρ, ω: m -scalingΔ scales with

22-25 %22-25 %

systematic errors:systematic errors:20 % - efficiency correction 10 % - combinatorial background11 % - 0 normalization

Ph

D th

esis

: Y. P

ach

mayer, T

. Ch

rist

► Cocktail B: A & Cocktail B: A & Δ(Ne+e-), ρ (short lived)

PRELIMINA

RY

► Cocktail A:Cocktail A: 0 + η + ω (long lived)


Comparison 1 – 2 AGeVComparison 1 – 2 AGeV

PRELIMINA

RY


PRELIM

INARY

Comparison 1 – 2 AGeVComparison 1 – 2 AGeV

Inv. Mass spectrum normalized to hadronic cocktail of long lived mesonic components

Agreement @ Mee < 0.15 GeV/c2.

Large relative excess compared to cocktail A, similar in shape.

Quantitative analysis: deduce the absolute excess yield Yexc (beyond η), making use of the TAPS η data:

Excess Excess (beyond η) scales like pions.scales like pions.

DLS…DLS…

C + C 2 AGeV Phys. Rev. Lett. 98, 052302 (2007)

η

η

(2.0)13 3 (stat)

(1.04)

Y

Y TAPS:TAPS:

Yexc(2.0)/Yexc(1.0) = 2.3

± 0.6(stat) ± 1.0(sys)


1 AGeV: Comparison to DLS1 AGeV: Comparison to DLS

Different phase spaceDifferent phase space coverage of HADES and DLS

ExtrapolationExtrapolation of HADES data:

Inspired by the thermal model

HADES & DLS Filters applied

Processed separately for low (M<150GeV/c2) and high inv. masses

DLS Data:

R.J. Porter et al.: PRL 79(97)1229

PRELIMINARY

DLS data (C+C, 1AGeV) confirmed by HADES!


pp┴┴ Distributions compared to the Cocktail Distributions compared to the Cocktail

PRELIMINARY

PRELIMINARY

PRELIMINARY

J. Carroll – presentationInternational Workshop on Soft Dilepton ProductionAugust 20-22,1997, LBNL


Heavy Ion Heavy Ion → Elementary Reactions→ Elementary Reactions

C + C summary:C + C summary:

DLS data confirmed

Significant excess @ Mee > 150 MeV/c2

- Energy excitation function like pions.

- Evidence for missing yield @ low-pt

Contributions of pN Bremsstrahlung and N*(Contributions of pN Bremsstrahlung and N*() decay?) decay?

No precise data available! (N*() Ne+e- BR, EM transition FF)

Measure Measure elementary reactionselementary reactions, e.g.:, e.g.:

DiElectron sources in pn, pp below the DiElectron sources in pn, pp below the ηη threshold threshold

Measure pp+pppe+e- (fix +, brems (pp) is small)

Measure pn e+e-X with dp reactions → brems (pn)

- Experimental technique: tag projectile spectator protons!


p+n tagging in d+p reactionsp+n tagging in d+p reactions

Installation of the (rearranged) Forward Hodoscope FH, formerly used at Bevalac and KaoS/SIS (for event plane analysis).

p_spec

pTd

pT

FH, Θ < 7o,added 2007

(n)LH2 target

(Orsay)

pp contamination 10% only.

Preliminary online results from May 2007May 2007

ToF-Tagging of the projectile spectator proton with the Forward Hodoscope FH (Θ < 7o).


p+p, p+np+p, p+nee++ee-- X, 1.25 GeV X, 1.25 GeV

Not corrected for efficiency; in the HADES acceptance, 50% of available statistics

Red line: Pluto hadronic cocktail (properly treated for acceptance/efficiency)

Only 2 sources: 0 e+e- , + pe+e- (BR=4.4*10-5 )

(+ yield fixed to 0 with isospin relation: N(+)=3/2 N(0))

PRELIMINARY

PRELIMINARY

n + p, 1.25 GeV

e+e- > 90

PhD thesis T.Galatyuk Online spectrum► Factor 2 (pp), 4-5 (np) missing for M > 150 MeV/c2

► Evidence for additional sources!


Online: p+p, 3.5 GeVOnline: p+p, 3.5 GeV

May 2007May 2007, preliminary, online results!

No final calibration/alignment!

ee++ee-- pair analysis pair analysis:

not shifted! Preliminary calibration…

Extra yield below VM pole mass.

S/BS/B1010

11

0.5 1.0 0.5 1.0

MMeeee

Preliminary

Preliminary

PRELIMINARY


Summary & OutlookSummary & Outlook

Physics Runs in…

p, d, - induced A + A Status/Comment

2002 C + C 2 AGeV Published!

2004 C + C 1 AGeV Analysis finished

2004 p + p 2.2 GeV Analysis finished

2005 Ar + KCl 1,75 AGeV Analysis ongoing

2006 p + p 1.25 GeV Analysis ongoing

2007 p + p 3.5 GeV

d + p 1.25 AGeV

… online results!

2008 p + A 3.5 GeV

2008/9 Upgrade RPC, DAQ

2009 Ni + Ni Planned

2010 + N, A

2011 Au + Au

> 2011 Hades goes FAIR (8 AGeV)

►HADES took off and is contributing with high-quality

data to the understanding of the di-electron production

in heavy ion collisions in the SIS energy regime,

characterized by VM production close to the threshold

and the crucial role of baryonic resonances.

►The physics program will be continued by aiming at

heavier systems and pion-induced reactions.


Towards FAIRTowards FAIR

HADESHADES2 – 8 AGeV2 – 8 AGeV

CBMCBM8 – 45 AGeV8 – 45 AGeV

Documents

Christian Müntz (Univ. Frankfurt) for the HADES Collaboration, CPOD 2007 1 Challenges in Physics & Instrumentation Results from Heavy Ion and Elementary