UPDATE ON DVCS ANALYSIS

Transcription

1 UPDATE ON DVCS ANALYSIS FROM E-6 DATA A. Movsisyan, S. Pisano, H. Avakian INFN-Ferrara Collabon meeting..5

2 Physics Motivation DVCS - so far the most reliable tool to access GPDs: Example of recent results from one of the global fits to world data K. Kumericki et. al. (5): Leading cos(nφ) moments of unpolarized cross sections (weighted by lepton propagators) 8 Krešimir Kumerički : GPD p Large uncertainties in some -t bins for cos(φ) moment: partly driven by the non-complete φ coverage Possible improvement can be achieved trough measurement of DVCS process via ep channel. Aram Movsisyan, DPWG meeting..5

3 General Introduction E-6 experiment: Data collected in -. Electron beam energy GeV Beam Current 7nA 5cm long liquid hydrogen target Average beam polarization 7% Torus current 75 A Total accumulated charge mc Analysis steps: primary identification trough particle id and charge + fixed event topology (gpart=,,4, ep, epγ, epγγ) charged particle momentum correction based on mc (energy loss corrections) z-vertex correction and cuts fiducial volume cuts electron DQ cuts kinematic cuts + exclusivity cuts Aram Movsisyan, DPWG meeting..5

4 Energy loss Correction energy loss corrections obtained from DVCS generator: P gen. /P rec. Proton P_Gen./P_Rec P gen. /P rec p(a+b/p+c/p +d/p ) χ / ndf 944 / 5 p.469 ±.45 p.6 ±.4 p.7 ±.76 p.9967 ±.8e 5 Fit to the mean for protons 6. P gen. /P rec P proton Rec. [GeV] Lepton P_Gen./P_Rec P Gen. /P Rec P proton Rec. [GeV] 8 < θ < < θ <6 6 < θ < < θ <4 4 < θ <8 8 < θ < < θ <6 6 < θ <4 4 < θ <44 44 < θ <48 48 < θ <5 5 < θ <56 56 < θ < P lepton Rec. [GeV] P Rec. [GeV] Aram Movsisyan, DPWG meeting..5 4

5 z Vertex Correction 5 4 Lepton z vtx. before correction Sector Sector Sector Sector 4 Sector 5 Sector Lepton z vtx. 6 after correction 8 Lepton Zvertex χ / ndf.7e+5 / 4 8 p 4.66e+5 ± 9.559e+ p.6575 ±.6 p.48 ±. p 6.8e+4 ± 4.98e+ p4 94 ± 9.7 p5 Proton Zvertex.758e+4 ±.67e+ [cm] - z prot. z lep lepton z proton z vtx. Proton z vtx. before correction [cm] 5 5 [cm] lepton z proton z vtx. Proton z vtx. after correction 4 vtx. [cm] lepton z 5 5 vtx. Corrected lepton vertex is used for photon reconstruction [cm] vtx. [cm] 8 z lep. - z prot. [cm] Z lep Z prot. (.6,.6) [cm] χ / ndf.7e+5 / 4 p 4.66e+5 ± 9.559e+ p.6575 ±.6 p.48 ±. p 6.8e+4 ± 4.98e+ p4 94 ± 9.7 p5.758e+4 ±.67e+ z lep. - z prot. [cm] Aram Movsisyan, DPWG meeting..5 [cm] - z prot. z lep. 6 4 proton z [cm] Z lep ( 8.,.8) vtx. [cm] z lep. [cm]

6 EC Fiducial Volume for leptons U (4, 9) W<9 V < 6 before the cut for photons U (4, 4) W<4 V < 65 after the cut U, V & W distributions in sector. Sector lepton Sector lepton Sector lepton Sector lepton Sector Sector lepton le U [cm] W [cm] Sector 4 lepton Aram Movsisyan, DPWG meeting W [cm] Sector 5 lepton Sector 4 lepton V [cm] Sector 6 Sector lepton 5 le 6

7 CC & DC Fiducial Volume CC fiducial cuts: CC < log( CC ).7 CC +. CC CC < ( CC ) +. CC DC fiducial cuts: f(, p) =C "sin [C + # C 5 (p B max Bcur. C )C 6 (p + C 4 ) B ] max B cur. before the cut after the cut before the cut after the cut <nphe> > 4 before the cut after the cut Aram Movsisyan, DPWG meeting..5 7

8 Electron DQ cuts E calo. /P σ σ 4 cuts on calo. response: E inner >.6 E total > E total >E inner E outer > E/P < 4 5 [GeV] Ecalo. E clao P [GeV] 4 E calo. /P p p+p/x +p*x χ / ndf / p.466 ±.48 p.44 ±.448 p.87 ±.4 p.547 ± 7.4e 5 /P) calo. σ(e.45 χ / ndf / p+p/ x p.9 ± 7.79e 5 p.784 ±.5 Width of E/P Mean of E/P P [GeV] P [GeV] P [GeV] Aram Movsisyan, DPWG meeting..5 8

9 Exclusive pion selection ep sample W > 4[GeV ] P lepton >.6884 [GeV ] N pe > 5 t<.5 [GeV ] Data epγγ data epγγ sample sect_ sect_ sect_ = sect_ epγγ data epγγ sample sect_ sect_ sect_ = sect_ Data.5 <Mx(epX) <.9 [GeV ] Both photons in the same sector P >. [GeV ] M x (epx) [GeV ] θ γγ [deg.] epγγ mc_pion epγγ mc_pion 5 MC epγγ mc_pion sect = sect sect sect 8 epγγ mc_pion sect = sect sect sect Requiring both photons in the same sector, substantially reduces combinatorial background MC M x (epx) [GeV ] θ γγ [deg.] Aram Movsisyan, DPWG meeting..5 9

10 Exclusive pion selection ep sample W > 4[GeV ] P lepton >.6884 [GeV ] N pe > 5 t<.5 [GeV ].5 <M x(epx) <.9 [GeV ] Both photons in the same sector P >. [GeV ] sect = sect & -t<.5 & -.5 < M x (epx) < epγγ data -5. < M x <.8 -. < M x <.8 -. < M x < < M x <.8 -. < M x < < M x < P π epγγ mc_pion Data [GeV] 5 no cut on P π P π <. P π <.4 5 MC Δ θ [deg.] P π [GeV] Aram Movsisyan, DPWG meeting..5

11 Exclusive pion selection ep sample W > 4[GeV ] P lepton >.6884 [GeV ] N pe > 5 t<.5 [GeV ].5 <Mx(epX) <.9 [GeV ] Both photons in the same sector P >. [GeV ] sect=sect & -t<.5 sector { M (epx) <. } x zz Entries 9 Mean RMS N pe 5 5 Distributions of N_phe in 6 sectors after applying all exclusive cuts. sector 4 { M (epx) <. } x zz4 Entries 6 Mean 8.45 RMS sector { M (epx) <. } x zz Entries 456 Mean 8.46 RMS N pe 5 5 sector 5 { M (epx) <. } x zz5 Entries 85 Mean. RMS sector { M (epx) <. } x zz Entries 755 Mean RMS N pe 5 5 sector 6 { M (epx) <. } x zz6 Entries 59 Mean.5 RMS no cut P π >. -.5 < M x (epx) < N pe N pe N pe Comparison of the shapes of N_phe distributions after applying various exclusive cuts. Distributions are scaled according to the maximum value N pe. Aram Movsisyan, DPWG meeting..5

12 Data-MC exclusive pions 5 χ /ndf = χ /ndf = χ /ndf = Q [GeV ] χ /ndf = x Bj χ /ndf = W [GeV ] χ /ndf = M x (epx) [GeV ] t [GeV ] Aram Movsisyan, DPWG meeting..5

13 Data-MC exclusive pions χ /ndf = χ /ndf = χ /ndf = E γ [GeV] χ /ndf = θ γ [deg.] E γ 5 [GeV] χ /ndf = θ γ [deg.] Aram Movsisyan, DPWG meeting P π [GeV] 5 χ /ndf = θ π [deg.].5.5.5

14 Data-MC exclusive pions χ /ndf = χ /ndf = χ /ndf = P lep. [GeV] χ /ndf = P prot. [GeV] χ /ndf = χ /ndf =.585 y θ lep. [deg.] θ prot. [deg.] z vtx. [cm] Aram Movsisyan, DPWG meeting..5 4

15 Data-MC exclusive pions 5 χ /ndf = χ /ndf = χ /ndf =.8559 Δ E [GeV] Δ θ [deg.] χ /ndf = M γ γ [GeV] θ γ γ [deg.] Aram Movsisyan, DPWG meeting..5 5

16 ep & epγ samples: background subtraction ep [ ep sample W > 4[GeV ] P lepton >.8 [GeV ] N pe > 5 t<.5 [GeV ].8 <Mx(epX) <.8 [GeV ] calc. >.4 Background contribution estimated from MC: Data N, (x, Q, t, )= N Data N MC N MC, ( ) (x, Q, t, ) Normalization factor obtained from exclusive pion analysis: Data Data MC (exclusive pion) MC (exclusive pions) M x (epx) [GeV ] Aram Movsisyan, DPWG meeting..5 6

17 binning & statistics 4 8 M x <.8 & -t<.5 & N >.5 & P lep >.8 pe θ γ calc. θ γ calc. θ γ calc. θ γ calc. θ γ calc. θ γ calc. >.4 >.5 >.6 >.7 >.8 > sin(θ)sin(φ) calc. γ ep & epγ ] -t [GeV M (epx) <.8 & P >.8 & EC lep. out. > & θ γ x calc. >.9 & N >5 pe Entries 5664 ] [GeV Q N pe Entries 5664 sin(θ)sin(φ) calc. γ γ sin(θ)cos(φ) calc. ep x Bj. bin x_bj t x Bj γ sin(θ)cos(φ) calc. Aram Movsisyan, DPWG meeting..5 7

18 examples of φ distributions t [.5-.6] t [.6-.] t [.-.8] t [.8-.5] t [.5-.6] t [.5-.4] t [.6-.] t [.4-.5].5 < x Bj. < t [.-.8] t [.8-.5] t [.5-.4] t [.4-.5] < x Bj. < Aram Movsisyan, DPWG meeting..5 8

19 Outlook a. Improve fiducial volume selection (remove inefficient regions). b. Improve Data-MC consistence for pions (test sensitivity to various GPP parameters ). c. Check self-consistence of ep analysis procedure on epγ sample. d. Estimation of systematic uncertainties. Thank you! Aram Movsisyan, DPWG meeting..5 9