Analysis of    production ► Data taking ► Reaction identification ► Results for double polarization observable F ► Summary Based on data taken in the period from Febrary 23 to March 8, 2010 V.L. Kashevarov. 15 th Crystal Collaboration Meeting, Mainz,8-10 March 2010

Experimental conditions: - electron beam: 855 MeV, 2nA, 82% polarization - 2 mm collimator -10 mm Cu radiator - circularly polarized photon beam (N+/N– = 1.009) - transverse polarized butanol target - tagged energy range: 150 – 600 MeV - detectors: CB and PID Good data files: #24823–24862 (~39 hours) polarization from 77.4% to 74.5% (plus) #24866–24000 (~39 hours) polarization from 83% to 80% (minus) NT– / NT+ = Data taking V.L. Kashevarov. 15 th Crystal Collaboration Meeting, Mainz,8-10 March 2010

V.L. Kashevarov. Crystal Collaboration Meeting, Edinburg, September 2009  p →  o  p E  = 1.0 – 1.1 GeVE  = 1.1 – 1.2 GeV Expected missing mass spectra for butanol target red line: background contribution from 12 C and 16 O (data from June 2008 run, 12 C target) blue line: investigated reraction (data from July 2007 run, LH 2 target) Reaction identification - analysis of data taken with a carbon target using the same procedure as for runs with LH 2 target; -normalization of the photon flux to LH 2 target run; - taking into account the number of 12 C nuclei in a carbon target with respect to butanol ( 16 O = 4/3 12 C)

Main steps to select good events: - (2 or 3 clusters) and (0 or 1 PID strip) - PID  2 neutral clusters ( + proton if 3 clusters) - invariant mass cut   o - kinematic cut - Tagger  initial photon energy and random subtraction - missing mass cut - background subtraction  p →  o  p V.L. Kashevarov. 15 th Crystal Collaboration Meeting, Mainz,8-10 March 2010 Reaction identification

Invariant mass cut: 110 – 170 Mev  p →  o  p Reaction identification V.L. Kashevarov. 15 th Crystal Collaboration Meeting, Mainz,8-10 March 2010

Random subtraction: cut for peak 6 ns, for random 1150 ns  p →  o  p Reaction identification V.L. Kashevarov. 15 th Crystal Collaboration Meeting, Mainz,8-10 March 2010

 p →  o  p Reaction identification V.L. Kashevarov. 15 th Crystal Collaboration Meeting, Mainz,8-10 March pion pion + proton Missing mass spectra: 160 – 200 MeV 200 – 250 MeV 250 – 300 MeV 300 – 400 MeV 400 – 500 MeV 500 – 600 MeV

 p →  o  p Reaction identification V.L. Kashevarov. 15 th Crystal Collaboration Meeting, Mainz,8-10 March –200 MeV Missing Mass spectra 200 – 250 MeV

 p →  o  p Reaction identification V.L. Kashevarov. 15 th Crystal Collaboration Meeting, Mainz,8-10 March – 500 MeV Missing Mass spectra 500 – 600 MeV

 p →  o  p Reaction identification V.L. Kashevarov. 15 th Crystal Collaboration Meeting, Mainz,8-10 March pion pion + proton Data for F asymmetry calculation 160 – 200 MeV 200 – 250 MeV 250 – 300 MeV 300 – 400 MeV 400 – 500 MeV 500 – 600 MeV

 p →  o  p V.L. Kashevarov. 15 th Crystal Collaboration Meeting, Mainz,8-10 March 2010 Double polarization observable F

For tomorrow: - new calibration for CB - additional cuts for (2 clusters + 1 PID strip) trigger - simulation - target asymmetry T For future: - add TAPS, MWPC - tagger 160 – 820 MeV - two runs: 400 MeV and 855 MeV  p →  o  p Summary V.L. Kashevarov. 15 th Crystal Collaboration Meeting, Mainz,8-10 March 2010