Dedicated Arrays: MEDEA GDR studies (E γ = MeV) Highly excited CN E*~ MeV, 4 T 8 MeV

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1 Dedicated Arrays: MEDEA GDR studies (E γ = MeV) Highly excited CN E*~ MeV, 4 T 8 MeV γ-ray spectrum intermediate energy region 10 MeV/A E beam 100 MeV/A - large variety of emitted particles γ-rays, π s, n, p, e ±, α, heavy fragments - wide energy range MeV GDR bremsstrahlung (nucleon.nucleon collisions) The limit of nuclear existence: limiting temperature of Compound Nucleus experimental observable: GDR yield vs. E* for a precise determination of Compound Nucleus excitation energy a study of various reaction products is needed

2 MEDEA Multi Element Detector Array (GANIL-LNS) R R forward wall 120 phoswich detectors : - light charged particles - heavier fragments 10 0 θ φ π array 180 BaF 2 detectors: - γ s - light charged particles High granularity: high multiplicity events & angular resolution R = 55 cm, Δθ ~15 0 (ΔE-E) plastic scintillators NE102A & NE115(τ ~ 2.4 ns & 230ns) crystal dimensions: L= 2mm + 30cm same PMT, separation of signals via PSA ΔE threshold = 14,19,23,54 MeV for p, d, t and α 30 0 θ φ è Ω 3.7 π R = 22 cm, Δθ 15 0 crystal dimensions: Ø= 62mm, L 20 cm, V 1300 cm 3 Large crystal size: reduction of shower leakage through crystal surfaces

3 MonteCarlo Simulations: determination of optimal thickness of BaF2 for detection of γ-rays up to 300 MeV deposited energy efficiency single crystal single crystal 9 crystals cluster NOT much improvement is observed from 20 to 22 cm è MEDEA crystal size: L = 20 cm ~ 10 X0 (radiation length X0 = 2.05 cm) ~ Range 300 MeV protons ~ Range 1 GeV α ΔEγ/Eγ = 12% (@ 662 kev line of 137Cs) Radiation length X0: - typical scale for high-energy electromagnetic cascades: - high-energy electrons: mean distance to reduce to 1/e energy by bremsstralung - high-energy γ s: 7/9 of mean free path for pair production 20 cm

4 Scattering chamber ½ BaF2 ball paraffine shield for γ calibration source ~ 10-5 mbar beam phoswich wall D type BaF2 crystals

5 BaF 2 ball: discrimination of - γ-rays & neutrons : TOF Phoswich wall: ΔE E res PMT identification of γ-rays & light charged particles: 129 Xe (@45MeV/A) Au forward backward particles γ γ particles - γ-rays & light charged particles Fast (ΔE) 129 Xe (@45MeV/A) Au Z=1 Fast p d t Z=2 Fast+Slow Slow (E) PSA of anode output: - fast: ΔE detector - slow: E res = E- ΔE detector

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7 Investigation of Progressive disappearance of GDR with excitation energy LNS Catania: MEDEA-MULTICS-MACISTE Setup Evolution of GDR yield with E* E* [MeV] evidence for progressive quenching of collective motion (GDR) competition between collective motion & particle decay onset of GDR quenching E* 250 MeV E*/A 2.5 MeV statistical decay regime 160 A=

8 Dedicated Arrays: TAPS Low and High energy photons detection Relativistic Heavy Ions Physics Relativistic Heavy Ions: study of nuclear matter under extreme conditions m meson c 2 = γ 2E γ 1E 2(1 cosθ12) reconstruction of invariant mass requires: E γ1, E γ2 photons energies (up to 1 GeV) Θ 12 opening angle between photons ( ) ρ ~ 2-3 ρ 0 T ~ 300 MeV High energy y-rays develop electromagnetic showers nucleons are excited into resonances which decay via mesons emissions neutral mesons decay: π 0 γ + γ (99%) η γ + γ (39%) m π0 = MeV m η = MeV full reconstruction of em shower is needed

9 individual detector telescope TAPS Two/Three Arm Photon Spectrometers (GSI-GANIL) L = 25 cm= 12 X0, Ø = 54 mm BaF2 gain monitor by N2-laser 384 individual BaF2 detectors packed in arrays of 64 modules 64 scintillator module x y = cm2 angular range: target distance: 100 θlab m D 3.5 m precise determination of point of impact of electromagnetic showers 0.01 X0 Array of 64 plastic/baf2 telescopes Veto γ-particle discrimination: - pulse shape analysis -TOF - Veto detectors (particle suppression)

10 Response to electrons above critical energy E c 13 MeV electons generate EM Showers cluster of detectors are needed Response to high-energy photons High-energy photons generate EM Showers cluster of detectors are needed E γ = 186 MeV E e = 43.5 MeV E mean = 19 MeV E mean = 5.6 MeV position resolution: Δx,y ~ 3cm (from center of gavity of deposited energies) position resolution: Δx,y ~ 2.5cm (from center of gavity of deposited energies)

11 Response to charged particles p and α E p = 55 MeV E α = 100 MeV Fast Discrimination against neutrons - high-energy neutrons: (n,p) interactions TOF + response CPV + PSA - low-energy neutrons (<< 100 MeV): (n,γ) interactions TOF only ε ~ 17 % for E n 5 MeV projection Fast+Slow inelastically scattered p (@55MeV) on 12 C ΔE/E~2.4% to 12 C excited invariant mass spectrum π 0 production

12 Dedicated Arrays: TAPS Low and High energy photons detection (KVI-Groningen) Proton-proton 190 MeV study of virtual bremsstrahlung below pion-production threshold Photon invariant (relativistic) mass: M γ = E γ / c 2 p + p p + p + γ* p + p + e + + e - SALAD - 2 wire chambers - 24 plastic scintillators (VETO of elastic channel) liquid hydrogen target σ 3-5 pb Trigger 2 proton events in SALAD (2 charged particle tracks) & 2 lepton events in TAPS (2 charged EM showers)

13 Virtual photons The electron and nucleon interact by the electromagnetic force, the carrier of this is the virtual photon as has different properties to ordinary photons. Take for example two electrons: These repel each other due to the electromagnetic force, we say that there is a mediator or exchange particle which is transferred between them, the photon. If one imagines two ice skaters facing each other and one throws a ball to the other person both skaters will move apart, just as two electrons would repel each other.

14 When delving inside the proton (or neutron) it is not the electron which actually 'probes' the nucleon but the photon. An electron gives some of its energy (and so loses some of its momentum) to the photon. The more momentum which is transferred to the photon, the more energy it has and so the shorter the wavelength of the photon. One can imagine that a longer wavelength photon will only 'see' the whole nucleon and so be elastically scattered, but for shorter wavelength photons it can 'see' the constituents of the nucleon, the quarks inside. This is why physicists want to build larger and larger accelerators, so that they can see more and more of the structure of particles. Virtual photons The electron and nucleon interact by the electromagnetic force, the carrier of this is the virtual photon as has different properties to ordinary photons. Take for example two electrons. These repel each other due to the electromagnetic force, we say that there is a mediator or exchange particle which is transferred between them, the photon. If one imagines two ice skaters facing each other and one throws a ball to the other person both skaters will move apart, just as two electrons would repel each other.