BGO-OD Experiment at ELSA. Russell Johnstone, Physikalisches Institut, Bonn University. SPIN2010, Jülich

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1 BGO-OD Experiment at ELSA Russell Johnstone, Physikalisches Institut, Bonn University SPIN2010, Jülich

2 Introduction New experiment at ELSA in Bonn: BGO-OD. Systematic investigation of meson photoproduction off the nucleon. Mixed charged/neutral decays. Λ(1405) (Σπ)/K-p/π0Λ K identification ( φ). Beam polarisation (lin./circ.) and recoil polarisation Hadronic spin and spin/angular-momentum structure.

3 Spin observables Transverse observables. Linearly polarised beam. Relative orientations of angular momentum in nucleon-meson system and of nucleon spin. Linear photon polarisation induces nucleon spin flips. cos2φ azimuthal asymmetry.

4 Spin observables Also longitudinal observables (E, Pz). Can act as spin filter. Determine quantum numbers of new resonances. Requires circularly polarised photon beam. Also either polarised target or recoil polarimetry.

ELSA Accelerator Electron accelerator. Energy: 0.5-3.

5 ELSA Accelerator Electron accelerator. Energy: GeV Intensity: ~1 na. Longitudinally polarised electrons (~60-80%).

6 Experimental hall D.Elsner 08 Crystal Barrel BGO - Open Dipole

7 Experimental area

8 BGO BGO ball (INFN, P. Levi Sandri, R. Di Salvo, A. Fantini) Large solid angle calorimeter. 480 crystals, (15 in θ and 32 in φ). Each crystal is 24 cm (~21 r.l.) long and is wrapped in a 30 μm thick aluminised mylar reflector. Acceptance and resolution: 25ᵒ<θ<155ᵒ 0ᵒ<φ<360ᵒ Δφ=11.25ᵒ Δθ=6ᵒ~10ᵒ

9 Tracking inside BGO Cylindrical MWPC (P.Pedroni & A. Braghieri, INFN Pavia and INR Moscow.) Prototype tested in beam. 2 concentric layers for full tracking. Acceptance: 0ᵒ<φ<360ᵒ 20ᵒ<θ<160ᵒ, full tracking Expected resolutions: Δφ=2ᵒ Δz=300 μm Δθ=1ᵒ additional Si-tracking detectors K. Brinkmann

10 Momo Momo (R.Jahn, Bonn) Not fully assembled. One module tested. ~1.5 mm spatial resolution, yielding +50,000 pixels.

11 Scifi2 Scifi2 (S.Böse, Bonn) Fully assembled and working. 2 ns (FWHM) timing resolution. horizontal fibres

12 Dipole magnet Permanent loan from DESY. gap extension: vertical 54cm 84cm ( ±5,2 ± 8 ) (horizontal ± 13,5 )

13 Dipole magnet magnetic field measurement at GSI (Darmstadt) dipole magnet assembled in Bonn Imax = 1340A Bymax ~ 0.5T

Drift chamber Drift chambers (J. Hannappel, Bonn) 8 planar double layer drift chambers (developed and built by PNPI Gatchina, RUS). 4 wire orientations. total area covered: ~ 2.5 m x 1.

14 Drift chamber Drift chambers (J. Hannappel, Bonn) 8 planar double layer drift chambers (developed and built by PNPI Gatchina, RUS). 4 wire orientations. total area covered: ~ 2.5 m x 1.2 m spatial resolution: < 300 µm 5 cm x 5 cm insensitivity spot in the center of each chamber for suppressing electromagnetic background. (diploma D. Hamman, diploma T.Schwan & bachelor V.Ratza)

15 Time-of-flight walls ToF walls (B. Bantes, Bonn) 4 layers. 2 walls installed and in operation during test beamtime in 2010 Time resolution of σ(t) ~250 ps.

16 Simulation Magnetic field map. The field measurements of the dipole magnet were carried out at the GSI in Darmstadt. Both measured field and simulated field can be used. Simulation (R. Johnstone, Bonn & G. Mandaglio, Messina)

17 Simulation Geometry has been completed. Forward detector setup. (Bonn) BGO, inner detector, target. (Messina) Working on event generator and data extraction.

18 Status & outlook Tagger Prototype tested in beam in June & Sep BGO Setup in exp. area complete. Inner detector Successful test of prototype chamber in photon beam. Momo Setup in exp. area for beam test April One module tested. SciFi2 Assembled in exp. area. 1st tests during beamtimes Magnet Gap extended. Installed in area. Drift chambers All 8 chambers installed in Bonn. All tested in lab. 4 tested in beam. ToF 2 walls installed & in operation.

19 Conclusions New detector setup at ELSA: BGO-OD. BGO for full calorimetry of both charged and neutral particles. Forward spectrometer setup (vertex tracking, magnet, ToF) allows particle ID. Multiple meson final states, charged, neutral and mixed. e.g. Λ(1405), ω π+π-π0 K and K0 identification. Spin degrees of freedom Recoil proton/ hyperon polarisation. Linearly/circularly polarised photon beams.

20 BGO-OD Member institutions: Univ. of Bonn, Phys. Inst. Univ. of Bonn, HISKP INFN-LNF Frascati, Inst. Sup. di Sanità & INFN Roma1, Italy Univ. of Pavia, INFN Pavia, Univ. of Torino & INFN Torino, Italy Univ. of Roma Tor Vergata and INFN Roma2, Italy Univ. of Messina, Italy Univ. of Edinburgh, UK Nat. Sc. Center Kharkov Inst. of Phys. & Techn., Ukraine Univ. of Moscow, Russia Petersburg Nucl. Phys. Inst. (PNPI), Gatchina, Russia Univ. of Basel, Switzerland spokespersons Paolo Levi-Sandri Hartmut Schmieden Technical co-ordinator Daniel Elsner

21 Thank you for your attention!

22 Tagging system new tagging system detector layout: simulation with VMC + Geant3 (G. Siebke) new front end electronics based on Glasgow/Mainz design (F. Messi) prototype tested in beam in June & Sep 2010

3 possible lengths (3, 6, 12 cm) and 4 cm diameter.

23 Target INFN-Roma2 and the University of Messina under the coordination of Marina Manganaro. Liquid H2 or D2 in a Mylar cell. 3 possible lengths (3, 6, 12 cm) and 4 cm diameter. Helium cycle cryostat lowers cell to working temperature of 17 K. Total thickness of the 3 Mylar caps is 21 μm (ρ=1.39 g/cm3).

24 Recent results Møller polarimeter: Møller target (PhD S. Kammer) measurement of ELSA electron beam polarisation in parallel to data taking precision better than 2% after 10 minutes e- beam Møller detector Tagging magnet online monitor (also used for ELSA tuning, see talk W. Hillert) count rate asymmetry N N AZZ = N N beam polarisation B P = AZZ T P a ZZ

25 Recent results Møller polarimeter CB beamtime Nov09 with polarised ELSA beam Electron polarisation / % Time evolution of ELSA beam polarisation Time averaged ELSA beam polarisation mean polarisation: 64% Time / a.u. Significant drops in polarisation indicate accelerator issues

Recent results Polarisation observables linearly polarised photons: Pγlin circularly polarised photons: Pγcirc longitudinally polarised protons: PT,z dσ = dσ0 [ 1- Pγlin ( Σ cos 2Φ - G PT,z sin 2Φ) -

26 Recent results Polarisation observables linearly polarised photons: Pγlin circularly polarised photons: Pγcirc longitudinally polarised protons: PT,z dσ = dσ0 [ 1- Pγlin ( Σ cos 2Φ - G PT,z sin 2Φ) - E Pγcirc PT,z ] linearly polarised photons beam asymmetry Σ circularly polarised photons longitud. polarised protons double polarisation asymmetry E linearly polarised photons longitud. polarised protons double polarisation asymmetry G

27 Backup Ewald Cross section for photoproduction of single pseudoscalar mesons 2 d = 0 ( 1 P cos 2 d P x P F P H sin 2 P x T x P z T z P y P Pcos 2 P y P z P E P Gsin 2 P x L x P z L z P x P O x sin 2 P C x P y P Tcos 2 P P z P O z sin 2 P C z )

transported to Gau Odernheim (~160km) @ Frank, Hoffmann GmbH

28 Dipole magnet modification gap extension: vertical 54cm 84cm ( ±5,2 ± 8 ) (horizontal ± 13,5 ) complete magnet (94t) transported to Gau Odernheim Frank, Hoffmann GmbH ( ) parts modified new parts and alignment tools manufactured

29 Drift chamber Diploma T. Schwan & bachelor V. Ratza: Efficiency Determination of efficiency: Check of insensitive spot 94% per chamber (2 layers) suppression of at least a factor 100 in center of DC Threshold High voltage [V]

Highlights of N* experiments at ELSA. Friedrich Klein Physikalisches Institut University of Bonn

Highlights of N* experiments at ELSA Friedrich Klein Physikalisches Institut University of Bonn Highlights of N* experiments at ELSA ELSA facility Selected recent data Projects NSTAR Mission Find laws