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### Recent Developments at A2 Real Photon Facility ###

Explore current progress at the MAMI real photon facility, covering topics like nucleon excitation, experimental setup with g-beam and Crystal Ball detector, quark model classification, and excitations in the Nucleon resonance spectrum. Learn about proton polarizabilities, spin polarizabilities, and exciting baryons from Lattice QCD. Discover groundbreaking measurements of spin observables and the convergence of multipoles. Dive into the fascinating world of particle physics with cutting-edge research in photon interactions. ###

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### Recent Developments at A2 Real Photon Facility ###

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  1. Institut für Kernphysik  Recent developements at the A2 real photon facility at MAMI 1.-Introduction Physics topics: Excitation of Nucleons and Polarizabilities 2.-Experimental setup: g- beam and detector - Tagger + Crystal Ball@MAMI Frozen Spin Target 3.-Active Target developement April 10th, 2019 Andreas Thomas forthe A2 Collaboration

  2. Introduction Physics: Quark Model Classification of Baryons qqq; only uds Oktett Dekuplett Simple Constituent quark picture: Proton p(938): |uud> ~ |hhi> Spin 1/2 Delta D(1232): |uud> ~ |hhh> Spin 3/2 M1-Transition (Small 2.5% E2)

  3. Introduction: Excitation Spectrum of the Nucleon H He Hg Löhrig, Metsch, Petry, Eur.Phys.J. A10 (2001) 395-446 Atom Nucleon The light baryon spectrum in a relativistic quark model

  4. What is the nature of the Nucleon Resonances? -Excitation inner deg. of freedom -Molecule -Quark – Diquark Structure -Dynamical Generation - …….? Unpolarised total photoabsorption cross section Phys. Rev. Lett. 87, 022003 (2001) Phys. Rev. Lett. 84, 5950 (2000) Nucl. Phys. A642, 561 (1998) Phys. Rev. C 53, 430 (1996); SP01 Nucl. Phys. A645, 145 (1999)

  5. Nature and Properties of nucleon resonances Polarisation observables used to disentangle broad, overlapping resonances. lin lin circ g Beam P P P g g g unpol æ p ö æ p p ö + - ç ÷ ç ÷ Target 0 , , è 2 ø è 4 4 ø æ ö s d S ç ÷ P - - unpol W è d ø P - - H F Beam x Target P T P - - y P - - G E z

  6. Parameter • 1604MeV, sE=0.100MeV • max. 40mA polarised • eh=9 nm rad, ev=0.5 nm rad • ~6500h/year as MAMI B !

  7. A2 Tagging system (Glasgow, Mainz) Production and energy measurement of the Bremsstrahlung photons. 1. Glasgow Tagging Spectrometer EPJ A 37, 129 (2008) Determination of the degree of polarization of the electron beam (Moeller Polarimeter). Circularly pol. photons. 2. Coherent production of linearly polarized photons on a diamond radiator 3.

  8. Polarised Photons @ MAMI C Linear Polarisation Eg = 75 ... 1480 MeV DEg = 4 MeV Ng = 2 . 105 s-1 MeV-1 Circular Polarisation Transfer High Polarisation High Photon Flux

  9. Vertex detector: 2 Cylindr. MWPCs 480 wires, 320stripes PID detector: 24 thin plastic detectors gp S11  ph p0p0p0 gggggg 4p photon Spectrometer @ MAMI TAPS: 366 BaF2 detectors 72 PbWO4 detectors Max. kin. energy: p+- : 180 MeV K+- : 280 MeV P : 360 MeV Crystal Ball: 672 NaJ detectors Max. kin. energy: m+- : 233MeV p+- : 240 MeV K+- : 341 MeV P : 425 MeV

  10. HelicityDependence E of Meson Photoproduction on the Proton and Neutron 1998- 2003 Mainz and Bonn 2010- 2016 New Mainz Exp. withCBall Gerasimov-Drell-Hearn sumrule (GDH) Simultaneous measurement of E and G

  11. Simultaneous measurement of G and E for p0 production (F.Afzal, K.Spieker) G E

  12. Redline: MAID 2007 blueline: SAID PR15 greenline: JUBo2015-B blackline: BG2014-2 T in p0-photoproduction J. R.M. Annandet al. Phys. Rev. C 93, 055209 – Published 31 May 2016 Black Circles – new MAMI Measurement, redtriangles Bonn CBELSA, greentrianglesolderdata.

  13. New double polarizationdatafromseveralfacilities CLAS, Jlab Crystal Barrel, ELSA Crystal Ball, MAMI With a varietyofnewmeasurementsofspin observables it comes to a convergence of the multipoles in the region of leading resonances using PWA. Excited baryons from Lattice QCD: R.Edwards et al., Phys. Rev. D84 (2011) 074508

  14. Proton Polarizabilities • Determination of the scalar polarizabilities of the proton using beam asymmetry Σ3 in Compton scattering • V.Sokhoyan et al., Eur. Phys. J. A (2017) 53 New measurementofthe Proton ScalarPolarisabilitiesvia beamasymmetry in Compton processfinished in July 2018. [PhDE.Mornacchi] morethan 1 Million Comptons!

  15. Spin Polarizabilities • Spin Vector polarizabilities describe spin response to an incident photon • Four vector pol. (γE1E1 γM1M1 γE1M2 γM1E2) appear at 3rd order in eff. Hamiltonian • Only two linear combinations of vector polarizabilities measured: The Forward S.P. g0was determined in GDH-Experiment at ELSA and MAMI (DAPHNE) : The Backward S.P. gpwas determined from dispersive analysis of backward angle Compton scattering. [B. Pasquini et al., Proton Spin Polarizabilities from Polarized Compton Scattering (2007).]

  16. Theory: Nucleon Vector Spin Polarisibilities Status 2014 G. Gellas, T. Hemmert, and Ulf-G. Meißner, Phys. Rev. Lett. 85, 14 (2000). K.B. Vijaya Kumar, J.A. McGovern, M.C. Birse, Phys. Lett. B 479, 167 (2000). D. Djukanovic, Ph.D. Thesis, University of Mainz, 2008. R.P. Hildebrant et al., Eur. Phys. J. A 20, 293 (2004). D. Babusci et al., Phys. Rev. C 58, 1013 (1998). B. Holstein, D. Drechsel, B. Pasquini, and M. Vanderhaeghen, Phys. Rev. C 61, 034316 (2000). S. Kondratyuk and O. Scholten, Phys. Rev. C 64, 024005 (2001). B. Pasquini, D. Drechsel, and M. Vanderhaeghen, Phys. Rev. C 76, 015203 (2007). J. Ahrens et al., Phys. Rev. Lett. 87, 022003 (2001). M. Schumacher, Prog. Part. Nucl. Phys. 55, 567 (2005).

  17. PolarizedTarget Polarization= Orientation of Spins in a magneticfield Ideally: All spins in fielddirection P=100% Complicatedinterplaybetween Polarisingforce ~ magneticfield B and Depolarisingforce ~ thermal motionofspinparticles (temperature T – relaxation)

  18. Magnetic moment in magnetic field: DE B=0T B=2.5T B=0T B=2.5T electron proton Thermal equilibrium Boltzmann distribution Trick: Transfer of the high electron polarization to the nucleon via m-wave irradiation (DNP)

  19. Target material CH3 CH3 CH3 CH3 N O Saturated electrons of target material not polarized (Pauli principle) Radicals in material by chemical or radiative doping Free electrons 30mm Ammonia Butanol LiD N Dilution factor (e.g. fButanol=10/74) determines quality of target material Tempo H H H

  20. Additional challenges for the analysis of experiments with Frozen Spin Target  Dilution Factor. Butanol Carbon Hydrogen

  21. Pionphotoproduction off of a proton is 75-100 times more likely than Compton (in the 240-280 MeV range)  Kinematic overdetermination used for cuts (missing mass, proton angle, …). Test with ‘substraction target’. • Σ2x300 hours measurement • Σ2x300 hours measurement • Curves from:- • B. Pasquini, D. Drechsel, M. Vanderhaeghen, • Phys. Rev. C 76 015203 (2007) • B. Pasquini, D. Drechsel, M. Vanderhaeghen, • Phys. Rept. 378 99 (2003)

  22. Measurements of the Proton Spin-Polarizabilities with Double-Polarized Compton Scattering P.P.Martel et al.,PRL 114 (2015) 112501 Eg= 273 – 303MeV

  23. Next Step: Compton with longitudinal PolarizedTarget preliminary Spin polarizabilities of the proton by measurement of Compton double-polarization observables D. Paudyal, G.Huber et al.,tobepublished 2019 • Main problems: • Low energeticrecoilprotons do not escapefromthetargetand do not reachthedetector. • Events areproduced on thebackgroundnuclei (Carbon, coherent, incoherent, k~13%). ).

  24. New Developement: ActivePolarizedTarget

  25. ActivePolarizedTarget T=45mKelvin after 5 daysby3He/4He mixtureVacuum in beampipe

  26. Detector Electronics at 150Kelvin [M.Biroth et al., IEEE Transaction on Nuclear Science, Vol. 64, Issue 6, June 2017] SiPMsgain depends strongly from the temperature ~1% K-1. Therefore it is necessary to control the 25V bias voltage to ~10mV and to have a stable temperature. [PhDM.Biroth, Mainz]

  27. Run June 2016

  28. First count rate asymmetriesfrom June 2016 fdistributionforp0production Target + Target -

  29. Investigation ofdilutionfactorforp0production Proton 𝜋0 photo production Recoil proton Background reactions by scattering on 12C or heavy nuclei Coherent 𝜋0 Recoil proton Recoil nucleus

  30. Recoil protons from scattering on H and a broad distribution from incoherent scattering on 12C

  31. Conclusions Data takingwithCBall TAPS detectorsystemstarted2010 at MAMI C. All directionsofpolarizationweremeasuredforprotonsanddeuterons in Butanol. Analysis formesonproductionand Compton processisongoing. The activepolarisedprotontarget was in operation in our 4pdetectorsystem in 2016. Outlook R&D forpolarisedactiveszintillatortargetforthresholdproductionand Compton will continue. Analysis offirstdataproofs light output. New activetargetinsertwithbetter light transportsystem, fibers, Scintillatingtargetcontainerwith Butanol. Measurement of 4 Vector Spin Polarisabilities in Compton process. Neutron ScalarPolarisabilitieswithheliumtargetstarts in 2019.

  32. ThankYou!

  33. M. Biroth, P. Achenbach, E. Downie, and A. Thomas, “Silicon photomultiplier properties at cryogenic temperatures,” Nucl. Instrum. Methods Phys. Res. A, vol. 787, pp. 68–71, Jul. 2015. P. Achenbach, M. Biroth, E. Downie, and A. Thomas, “On the operation of silicon photomultipliers at temperatures of 1–4 kelvin,” Nucl. Instrum. Methods Phys. Res. A, vol. 824, pp. 74–75, Jul. 2016. M. Biroth, P. Achenbach, E. Downie, and A. Thomas, “A low-noise and fast pre-amplifier and readout system for SiPMs,” Nucl. Instrum. Methods Phys. Res. A, vol. 787, pp. 185–188, Jul. 2015.

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