µ( ) Analysis Collaboration Meeting July 2007 Dr Evie Downie Ph.D. M.Sci. Am.InstP.

Transcription

1 µ( ) Analysis + Dr Evie Downie Ph.D. M.Sci. Am.InstP.

2 INTRODUCTION Brief outline of how & why we choose to measure µ( +) by p(, ' 0p) Brief summary of experimental conditions Notes on conventions Description of analysis as performed for my thesis Thesis results for cross section Thesis results for lin. pol. photon asymmetry Brief comments on very recent results Outlook & conclusion

3 WHY & HOW γp + + γ π pγ' Nucleon structure very difficult to probe γ' Many models µ particularly sensitive to model µ( ++) measured in 1978 (Nefkens et. al.) Add to knowledge of isobar Small cross section ~60nb µ( +) from photon asymmetry, diff. x sec, single spin asymmetry + γ + P π 0 γ γ D. Drechsel et. al. Phys. Lett. B 484 (2000), A. I. Machavariani et. al. Nuc. Phys. A 646 (1999), Wen Tai Chiang et. al. Phys. Rev. C 71 (2005)

4 DATA TAKING Tagger energy MeV Tagged energy range : MeV Diamond radiator Using CB, TAPS, MWPC & PID Integrated luminosity: 3.15 x 1012/barn July / August 2004 Polarisation edge 440MeV 305 hours full target September 2004 & January 2005 Polarisation edge 400MeV 305 hours full target 116 hours empty target All analysis shown in this talk uses the full July/August 2004 data set. luminosity (0.5 x 3.15 x 1012/barn) x total cross section (60nb ) = 94,000 possible p 0γ' events

5 CONVENTIONS 100% of data from 440MeV run (474 files, ~310 hours) black points Data points show data with all cuts except one under study Have analysed Sept. & Jan. data too results at end Using mcgen (JRMA's event generator) ~3x106 events in each plots scaled to data Phase space p(, 0p), p(, 0 0p) backgrounds p(, ' 0p) with E( ') dist. from (1232) B W widths red points p(, ' 0p) with E( ') dist. proportional to 1/E( ') blue points Agreement between simulation & data needs work! Red dotted lines show data cut positions

6 MDM Event Identification Look for 4 cluster events Select identified proton & 3γ Time difference between all γ pairs < 7ns Angle difference between all γpai rs > 30 deg. Only accept photons with θ > 8 deg. Look for best π0 in remaining photons Applied p energy correction from p(γ,π0)/sim. Only events with 300 < Eγ < 500MeV Select Eγ'(cm) > 30 MeV p x < 45, p y <40, p z <75, all MeV/c

7 MDM Event Identification E 0 Data before cuts M Assume non radiative 0 production: Cut on E 0 < 25MeV Cut on M < 40 MeV/c2 Cut on MM2( 0p) < 0.01 (GeV/c2)2 Cut on 115 < IM( 0) < 155 MeV/c2 Use 1/Eγ' type MCGen acceptance

8 MDM Event Identification ρtarget = nuclei / barn based on: length = 47.6mm density = 70.55kg/m3

9 MDM Contamination 2π0 simulation From MC results: 0.002% of p(, 0p) events survive (67/3,000,000) 0.61% of p(, 0 0p) events survive (18,303/3,000,000) p(, 0 0p) due to artificial cluster merging p(, 0 0p) problem as it is inseparable from real events Use two methods to subtract from total x sec measurement

10 MDM Contamination (p(, 0 0p)) Two methods Fitting to IM(π0) b.g. Calculating from Kotulla & MC Selected IM(π0) for final result

11 MDM IM(π0) based subtraction Unsubtracted data p(, 0 0p)fit remaining events

12 MDM Contamination (p(, 0p)) Single pi0 background xsec before subtraction After subtraction Only one method available Calculating from Kotulla & MC MC based on uniform phase space event set

13 MDM Total Cross Section Black July Run Green Jan. Run Blue Triangles All data Red Circles Sept. Run Comparison of cross sections for all runs July & Sept. agree within statistics January agreement much poorer Sept. systematically lower than July

14 Normalised Yield for p(γ,π0p) Black M. Kotulla's thesis Green R. Leukel's thesis Blue Triangles July run Red Circles Sept. run Three hits 1p & 2γ, proton energy corrected 115<Mπ<155MeV Agrees well with prev. results at larger Eγ Affected by M2 trigger prescaling lower down September is systematically lower than July

15 MDM Total Cross Section Black M. Kotulla's thesis Blue this work Systematic error ~14.5% : ~2% from target density ~2.5% from photon flux ~10% from MC model and detector response

16 MDM Simulation Status E( ') E( 0) θ(p) Simulation agrees well with missing energy etc. Clearly differs in E( ') distribution and resulting E( 0) TAPS particle i.d. by T.O.F. not P.S.A. too efficient No CB time response can't apply timing cuts to sim. data JRMA working on model based event generator Need latest model!

17 MDM Photon Asymmetry July E( ')>30MeV September E( ')>30MeV Looked at photon asym. for July and September data Integrated over all theta and: E( ) of MeV for July E( ) of MeV for September Normalised by average polarisation (in tagger channels) Looked at variation with E( ')

18 MDM Photon Asymmetry July E( ')>30MeV September E( ')>30MeV Looked at photon asym. for July and September data Integrated over all theta and: E( ) of MeV for July E( ) of MeV for September Normalised by average polarisation (in tagger channels) Looked at variation with E( ')

19 MDM Photon Asymmetry Asym + stat error Grey shading systematic error Black total Blue 2pi0 cont Red Deg. Lin Pol. Asym + stat error Grey shading systematic error Black total Blue 2pi0 cont Red Deg. Lin Pol.

20 MDM Photon Asymmetry Asym + stat error Grey shading systematic error Unitary Model Asym + stat error Grey shading systematic error Chiral Model

21 Most Recent Work (too young for public appearance) Have migrated analysis from AcquRoot 3v17 to 4v0 Scaler fun! Have added trigger type seperation to real data analysis Have added trigger conditions to analysis of simulated data: Only accept ((NaI_Etot>40MeV)&&(M2 M3)) Cluster multiplicity (M2/M3) calculated on: CB 45x OR of 16, single element threshold of 20MeV TAPS, OR of 128/127, single element threshold of 30MeV All accepted p(, ' 0p) events come from M3 trigger M2 trigger prescaling has NO effect on p(, ' 0p) Trigger reduces p(, 0p) contamination

22 CONCLUSIONS & FURTHER WORK Have as clean a p(, ' 0p) data set as possible (with traditional analysis) Need to subtract p(, 0 0p) & p(, 0p) Will try kinematic fitting with D. Glazier's tools Simulation and event generator need work before publication Need the latest model! Production of fully differential cross section Analysis of single spin asymmetries Currently, variation of asymmetry with E( ') very interesting! Most recent results will be shown on Thursday Morning : )

23 CONCLUSION Thank you! Thesis available at: theses/