Hans-Jürgen Arends Mainz University

Transcription

1 Recent Results from MAMI Hans-Jürgen Arends Mainz University

2 Dec. 2008: 1557 MeV Sept. 2009: 1604 MeV

3

4 KAOS spectrometer

5 High-precision p(e,e )p measurement at MAMI

6 Motivation (see J. Friedrich and Th. Walcher, EPJ A 17 (2003) 607)

7 Motivation Discrepancies for the proton charge radius 0.809(11) fm: Stanford (Hand et al., 1963) 0.862(12) fm: low Q² at Mainz (Simon et al., 1979) 0.847(09) fm: dispersion relation (Mergell et al., 1996) 0.890(14) fm: Hydrogen Lamb shift (Udem et al., 1997) (see J. Friedrich and Th. Walcher, EPJ A 17 (2003) 607)

8 High-precision p(e,e )p measurement at MAMI "J 94 0'. J ~ 1000 settings (overlapping) ~ 10 9 events 4-, ,.94724/ J. Bernauer et al., to be published r E = <r E2 > 1/2 = fm +/ (stat) +/ (syst) PRELIMINARY +/ (model) +/ (group)

9 Polarisation observables in γp ηp γp ηp diff. cross section S 11 (1535) J P = 1/2 - D 13 (1520) J P = 3/2 - Sensitivity to D 13 : dominance of S 11 Asymmetry with transverse polarised target: T ~ Im (E 0+ * (E 2- + M 2- ))

10 Target asymmetry in γp ηp T ~ Im (E 0+ * (E 2- + M 2- )) Breit-Wigner resonances in J P = 1/2 - and 3/2 + partial waves (standard η MAID) energy dependent phase shift between J P = 1/2 - and 3/2 + partial wave amplitudes Tiator et al., PRC C60 (1999) Phoenix (Bonn): A. Bock et al., PRL 81 (1998)

11 Recoil proton polarisation: p( e, e' p ) η First experiment with MAMI C and the 3-spectrometer setup P y ~ Im (E 0+ * (E 2- + M 2- )) Θ = 120 o ~ T Merkel et al., PRL 99: (2007) energy dependent phase shift between J P = 1/2 - and 3/2 + partial wave amplitudes Breit-Wigner resonances in J P = 1/2 - and 3/2 + partial waves

12 Recoil proton polarisation: p( e, e' p ) η First experiment with MAMI C and the 3-spectrometer setup P y ~ Im (E 0+ * (E 2- + M 2- )) Θ = 120 o ~ T Merkel et al., PRL 99: (2007) energy dependent phase shift between J P = 1/2 - and 3/2 + partial wave amplitudes Breit-Wigner resonances in J P = 1/2 - and 3/2 + partial waves More kinematic settings: W=1525 MeV, Θ=90 o, W=1500 MeV, Θ=120 o

13 Recoil proton polarisation: p( e, e' p ) η Θ = 120 o K. Grießinger et al., to be published target asymmetry measurement with real photons in progress in A2 (MAMI) and ELSA

14 Crystal Ball / TAPS at MAMI since 2003

15 π ο photoproduction near threshold Test of LETs A. Schmidt et al., PRL 87 (2001) S. Kamalov et al., Phys. Rev. C (2001) V. Bernard et al., EPJ A 11 (2001) 209

16 (Dave Hornidge)

17 (Dave Hornidge)

18 Target windows account for ~ 30% at 90 deg and 180 MeV!

19 π 0 production near threshold Preliminary (D. Hornidge, publ. in prep) measurement of T and F in preparation at MAMI and HIγS (H. Weller)

20 η photoproduction γp ηp (see I. Strakovsky, 6B) (E.F. McNicoll et al., in preparation)

21 γ p π o η p blue line: the best fit with D 33 (1700), P 33 (1600), P 31 (1750), F 35 (1905), and Born terms Partial contributions: Red line: D 33 (1700) Green line: P 33 (1600) Black line: P 31 (1750) Dashed red line: F 35 (1905) Dashed blue line: Born terms V. Kashevarov et al.: EPJ A (2009) 141 A. Fix et al., EPJ A 36 (2008) 61

22 γ p π o η p Beam helicity asymmetry (preliminary) to be published Data from July 2007 and April 2009 runs Fourier fit (3 terms) D 33 (1700) only Isobar model 6 resonances 09, More spin observables will be measured (T and F, pol. beam and pol. target)

23 , , π π π π &3;07, 909,! $!7, 4;09,! 8#0; α Г

24 Kaon Photoproduction Decay sub-cluster energy Incident and decay subcluster time difference Decay sub-cluster from K + µ + ν µ decay ~ 20ns Incident subcluster from K + ~3ns K + missing mass % :/0 / 3-:7

25 Kaon Photoproduction γp ΛΚ + (Preliminary) SAPHIR: K.H. Glander et al., Eur Phys. J. A 19, 251 (2004) JLAB (blue): R. Bradford et al., Phys Rev. C 73, (2006) Kaon MAID with S 11 (1650), P 11 (1710), P 13 (1720) and D 13 (1900) Regge-Plus Resonance (RPR) Model: T. Van Cauteren et al. Phys. Rev. C 73, (2006), Pieter Vancraeyveld, The University of Ghent. Priv. com. (2010)

26 Polarized Frozen Spin Target N. Froemmgen P=P 0 exp(t/τ) Frozen spin target fully functioning Polarization > 90% ~1000 hours relaxation time & low He consumption long measurement time! Running with transverse polarized target! SFB443

27 Polarized Frozen Spin Target H. Ortega Spina DNP to achieve ~ 90 % proton, 80 % deuteron Horiz. Dilution cryostat (Dubna), T~ 30 mk Two holding coils: solenoid longitudinal, saddle coil transverse

28 First measurement of transverse spin observable F in γp π 0 p N. Froemmgen dσ dω = dσ dω unpol [ lin 1 P Σ( θ ) cos( 2φ ) γ P P P x y z [ P ] γ [ T ] [ P ]] γ lin circ H ( θ ) sin( 2φ ) + Pγ F ( θ ) lin ( θ ) + Pγ P( θ ) cos( 2φ ) lin circ G( θ ) sin( 2φ ) + P E( θ ) γ F asymmetry: circ. polarized photons, transverse pol. Target Need to seperate out contribution from 12 C and 16 O and 3/4 He Requiring proton removes coherent contributions Other kinematic cuts and remaining underground fitted & subtracted Data shown from 39 hours minus, 39 hours plus pol. test data, Crystal Ball only VERY PRELIMINARY!

29 First measurement of transverse spin observable F in γp π 0 p Background Subtraction on MM(γ, π 0 ) - m p E γ = MeV different Θ π bins

30 First measurement of transverse spin observable F in γp π 0 p PRELIMINARY F SAID MAID,9,,9 0',8-0039, 03 SFB443

31 Dan Watts

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33 Pion production on the deuteron (as a neutron target) π+ Data: full circles: γdà π+nn empty circ.: γpà π+n Curves: models by Arenhövel & Fix (solid) Levchuk (dashed) Schwamb (dash-dotted) Darwish (dotted)

34 Pion production on the deuteron (as a neutron target) π Data: full circles: γd à π pp (MAMI) open circles: Benz et al. (1973) Curves: models by Arenhövel & Fix (solid) Levchuk (dashed) Schwamb (dash-dotted) Darwish (dotted)

35 Helicity dependent γ d π NN diff. cross sections π π + π 0 Data: J. Ahrens et al., Eur. Phys. J. A 44, 189 (2010) Model: Levchuck et al., Phys. Rev. C 74, (2006)

36 Polarized ³He gas target for real photons (with Institute of Physics, Mainz)

37 Setup

38 Helicity difference of total photoabsorption on ³He (preliminary)

39 A1 Collaboration: Summary High-precision p(e,e )p, prelim. charge radius compatible with value from Lamb shift p(e,e p)η recoil polarization agrees with previous T data A2 Collaboration: new π ο photoproduction near threshold, prelim. Σ smaller than previous results new high-precision η photoproduction data helicity asymmetry of γp π ο η p Г /: ,, 10,8-0;, 0, Г /0.,

40 Summary Mainz polarized frozen-spin target with transverse polarization in operation, first preliminary data on F observable for π ο production Polarized D and ³He as neutron targets preliminary helicity-dependent cross sections pol. beam, pol. target, recoil polarimeter available, heading towards a complete experiment