The Experimental Quest for In-Medium Effects

The Experimental Quest for In-Medium Effects

Romain Holzmann GSI Helmholtzzentrum für Schwerionenphysik, Darmstadt

at

23rd Indian-Summer School of Physics

and

6th HADES Summer School:

Physics @ FAIR

October 3-7, 2011 in Rez/Prague, Czech Republic

Lecture I: Pedestrian’s approach

Lecture II: Experiments galore

Lecture III: HADES at GSI

Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI Lecture III: 2

Lecture III:

Investigating dense matter with HADES at GSI:Present and future


Physics we are after with HADES

(High Acceptance DiElectron Spectrometer)

In very general terms:

Medium modifications of hadrons (e.g. vector mesons) chiral symmetry restoration vs. hadronic effects

enhanced dilepton yields → emissivity of hot & dense hadronic matter in-medium spectral functions

systematic dilepton spectroscopy in AA, pA and A (ρ/ρ0 1-3)


S. Vogel et al.Phys. Rev. C78(2008) 044909

11

2 GeV

30

Exploring the phase diagram at high μB

Probing nuclear matter at SIS: densities: max/0 2 - 3

temperature: T 50 -100 MeV N resonances become important

Andronic et al., Nucl. Phys. A 837 (2010) 65

Trajectories from Ivanov et al., PRC 73 (2006) 044904

HADES operates here!

UrQMDAu+Au

Rapp & WambachAdv. Nucl. Phys. 25(2000)

thermalmodelat =0

System stays above ground statedensity for 10 - 15 fm/c


Hadron production & spectroscopy meson and baryon production

coupling of and to N*

pn vs.pp

strangeness production form factors of and

systematic dilepton (and hadron) spectroscopy in pp, pn and p

(ρ/ρ0 = 0)

Physics we are after with HADES

→ needed to model p+A & A+A

(High Acceptance DiElectron Spectrometer)

In very general terms:

Medium modifications of hadrons (e.g. vector mesons) chiral symmetry restoration vs. hadronic effects

enhanced dilepton yields → emissivity of hot & dense hadronic matter in-medium spectral functions

systematic dilepton spectroscopy in AA, pA and A (ρ/ρ0 1-3)

π0 & η prod.in p+p

Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI Lecture I: 9ECT* Dileptons September 13-17, 2010 R. Holzmann, GSI Darmstadt 9

The HADES detector at GSI

azimuth. symmetry

large coverage: y = 0 - 2

hadron & lepton PID

2% mass resolution

LVL2 lepton trigger

plastic forward wall Physics accessible with HADES:

1. Dielectrons in NN: p+p and n+p2. Dielectrons in HI: from C+C to Au+Au3. Vector mesons in cold matter: p+Nb4. Strangeness production: p+p, p+A, A+A5. Pion-induced reactions: (2012-2016)6. SIS100: (>2017)

/ RPC

Technical paper:G. Agakishiev et al. Eur. Phys. J. A41, 243 (2009)General documentation:http://www-hades.gsi.de


HADES at SIS18

Unilac

SIS18

ESR

HADES

π production target

Measure its:velocity β :momentum p : energy loss in matter dE/dx:Cherenkov (or transition) radiation:calorimetry ► total energy E

This needs a sophisticated detector, e.g. HADES

How to identify a particle?

p = m ∙ βc ►mass

B

A primer for theorists

►Z►e- vs. hadrons


Detector components

“RICH” (electron ID, hadron-blind)

“TOF”()

“Pre-Shower” (electron ID)“MDC” (tracking, )


Technical layout of HADES

Pre-S

hower

TOF

outer MDC

RPC

He pipe

Start + target

Cryostat

beam

outer MDC

inner MDC

B field region

inner MDC

RICH readout

HADES caveHADES sector


The RICH: a hadron-blind detector

hadron-blind, but...

e+

e-

0

~ 15.20

20% 0 Dalitz

e+

e- ~ 2.20

60% γ conversion

► use segmented target

γ > 18


Segmented target

Example: 3.5 GeV p+Nb

93Nb material 12 pellets of Ø = 1.25 mm Δz = 4.5 mm 2.8% interaction prob.

~ 55 mm

beam

Rez 2011 - The Experimental Quest for In-Medium Effects - R. Holzmann, GSI Lecture I: 17

IPN Orsay

FZR

LHE Dubna

GSI

wire planes:10o,-20o,0o,0o,20o,-10o

ORSAY plane

Tracking: the Multiwire Drift Chambers

4 MDC/sector

total 33 m2 area, 27000 cells

y<0.1 mm resolution

Ar-iC4H10 [60-40] gas

and low-Z material

Layer Width/m Height Area[m 2̂]I 76,7 75,5 0,34II 90,5 88,3 0,49III 180,5 178,0 1,88IV 222,4 219,9 2,83


Tracking: superconducting toroidal magnet

Bmax = 0.8 Tesla (mid-plane)

bending power = 0.36 Tm

(typically operated at

70% - 90% of max. field)

field map + tracking planes

Runge-Kutta track fit


Electron/positron identification

ee--

e-

e+

velocity vs. momentum

+ +

RICH patternMDC hit finder &

hit/track matching Pre-Shower condition

Momentum * charge [MeV/C]

DataMonte Carlo

e- e+


Lepton pair reconstruction

21)2/sin(2 ppM inv

RICH rings

lepton/baryon

p1

ee++

e-

p2

Pair reconstruction

0e-

e+

e-

e+

0 e-

e+

uncorrelated pairs

Combinatorial backgroundsubtraction

eeee NN2CB

From: like-sign pairsor event mixing

Signal:

S+-= Ne+e- - CB+-


The HADES Collaboration on tour

Cyprus:Department of Physics, University of Cyprus

Czech Republic:Nuclear Physics Institute, Academy of Sciences of Czech Republic

France:IPN (UMR 8608), Université Paris Sud

Germany:GSI, DarmstadtFZ Dresden-RossendorfIKF, Goethe-Universität FrankfurtII.PI, Justus Liebig Universität GiessenPD E12, Technische Universität München

Italy:Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del SudIstituto Nazionale di Fisica Nucleare, Sezione di Milano

Poland:Smoluchowski Institute of Physics, Jagiellonian University of Cracow

Portugal:LIP-Laboratório de Instrumentação e Física Experimental de Partículas 17 institutions

120+ members

Russia:INR, Russian Academy of ScienceJoint Institute of Nuclear ResearchITEP

Spain:Departamento de Física de Partículas, University of Santiago de CompostelaInstituto de Física Corpuscular, Universidad de Valencia-CSIC


First HADES data: e+e- production in C+C Efficiency-corrected di-electron spectra, normalized to the number of neutral pions:

Ph

ys

.Re

v.

Le

tt 9

8(2

00

7)

05

23

02

Ph

ys

. L

ett

. B

66

3 (

20

08

) 4

3Cocktail generatedwith PLUTO

Checking on DLS: Is there excess e+e- yield? How does the excess evolve with bombarding energy? And with system size? – or – Is there physics beyond free NN?


1 AGeV C+C: HADES confirms DLS

π0, η acceptance

HADES >> DLS

ππ00→e+e–γHadesHades DLSDLS

mid-rapidity

η→e+e–γ

HadesHades DLSDLS

mid-rapidity

vs.

► HADES fully confirms highly controversial DLS findings in C+C:

Porter et al., PRL 79 (1997) 1229

Agakishiev et al., PLB 690 (2010) 118

HADES

DLS


e+e- production in 1.756 GeV/u Ar+KCl

Again, strong overshoot above the cocktail of long-lived sources!

First ω peak seen at SIS energies!

► MLVL1(ω) = (6.5 ± 2.8) ·10-3Cocktail oflong-lived sources:π0, η, and ω

~ 40 counts

±20 % sys.


Tagging quasi-free np reactions in HADES

p+p:Cut View

FW > 7o

d

psp

p

pr

OBE calculationsreproduce pp,but not (yet) np !

d+p: quasi-free np


Preparing a “reference” for A+A

Compare excess over η in Ar+KClwith excess over η in reference

Definition of a ”reference” based on pp and np data:

x2.5 - 3

η contributions subtracted ! yield normalized to M(π0) ►► Excess over free NN!

Excess dilepton yield in HIC

SPS

RHIC

SIS

Low-mass dilepton excess present at all energies,although quite different processes contribute…

► Excitation function of the dilepton yield still largely unknown: HADES & CBM will provide this information at FAIR.


Strangeness production in Ar+KCl

HADES has

high mom resolution high acceptance good particle ID vertexing

1.76 GeV/u Ar+KCl

PID based on dE/dx and TOF

→K+K-

Ξ- → Λπ-

TB = 84

PRC 80 (2009) 025209 PRL 103 (2009) 132310PRC 82 (2010) 021901EPJA 44 (2010) etc.


The Hades upgrade project (2010/11)

Meta detector, < 45 deg.Time res: 350 ps. PreShower pos. res: 1.5 cmLimitation: multihit capability

RPC performance (beam test) Efficiency above 95 % Time res. 50-80 ps Negligible crosstalk < 1%

List of HADES upgrade subprojects:List of HADES upgrade subprojects: RPC - Resistive Plate Chamber FINISHED

Time res. 50-80 ps, high granularity Forward Wall FINISHED

range 0.2 – 7 degrees, centrality, reaction plane DAQ-Upgrade

FINISHED goal 20 kHz for Au+Au LVL1 MDC I rebuild system stability Commissioning

Summer 2011: commissioned with Au beam

1 RPC sector


Next runs at SIS18: 1.25 GeV/u Au+Au

HADES upgrade nearly completed

new MDC inner tracking plane new RPC timing detectors new and faster readout electronics Forward Wall installed

► Getting ready for Au run 2nd Q 2012

Simulated counts for 4 weeks beam

1.25 GeV Au+Au

Expected pair rates/day

+ plenty of strangeness!


Experiments with pion beams:The GSI secondary pion beam line

Momentum of the beam particles reconstructed with precision of 0.3%

Tracking in the beam line: silicon strip detector

Diamond in front of the target for background rejection

• Q doublet defines acceptance = 2.3 msr

• Momenta up to 2.8 GeV/c , p/p = 8%• Beam spot at the HADES focal point:

3σx – 2.0 cm, 3σy – 1.8 cm • H1, H2 & H3 for beam momentum reconstruction (fiber/silicon det.)

p/p = 0.3%

7.5o

dispersive plane

Particle production in the HSD transport model

Thermal

Cassing & Bratkovskayacalculations for FAIR

central Au+Au

SIS100

A Photon Calorimeter for HADES

Adding a calorimeter to HADES offers:

• Better lepton ID• Neutral mesons in p+A & A+A• Direct photons in p+A & A+A• Hadron zoo in p+p & π+p

EbaE //

Photon decays:π0 → γγη → γγη’ → γγω → π0γ → γγγ+ Dalitz decays

Neutral meson detection in A+A

large photon combinatorial background small signal/background ratios

needs a high-resolution EM calorimeter

S/B=0.07 %

WA80

S/B=2.7 %

TAPS

0.8 AGeV Au+Au

200 AGeV S+Au

CB-subtracted mγγ spectra

A. Wolf et al.PRL 69 (98) 5281

R. Albrecht et al.PLB 361 (95) 14

100+100 AGeV Au+Au

PHENIX

S/B = 0.2% – 5%

158 AGeV Pb+Pb

WA98

S/B < 0.5%

Eta Dalitz reconstruction in simulation

η → γ e+e- measured in HADES + calorimeter:

► Potentially interesting, but needs to be explored in simulations!

S/B >1


2017: HADES goes underground

HADESin the CBM cave


The HADES roadmap: 2012-2018

The present planning foresees:

2012: Au+Au run at 1.25 AGeV (dileptons + strangeness)

2013: first pion beam run (physics goals still being discussed)

2014: Ag+Ag run at 1.65 AGeV (dileptons + strangeness)

2015: another pion beam run ??

2016: move HADES to CBM cave at SIS100

2018: first beams from SIS100 ???


HADES2 – 8 GeV/u

CBM8 – 45 GeV/u

Conclusions and outlook

Understanding pp, np & πN processes is essential for A+A !!!

In Ar+KCl onset of “medium” effects strong baryonic contribution to e+e-

first observation of vector mesons 2nd focus on strangeness production

Upgraded HADES will investigate heavy systems up to Au+Au πN and πA reactions + strong strangeness program

Move to SIS100 planned for 2016/17 add lead glass calorimeter do physics at 2 – 8 AGeV

The Experimental Quest for In-Medium Effects

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