DVCS and extraction of cross sections in Hall A

Transcription

1 DVCS and xtraction of cross sctions in Hall A Eric FUCHEY Ph.D Studnt Laboratoir d Physiqu Corpusculair UMR 6533 CNRS/INP3 Unirsité Blais Pascal Clrmont Frrand

2 Outlin Gnralizd Parton Distributions / DVCS Apparatus for Hall A DVCS xprimnt at Jffrson Laboratory 3 Cross sctions xtraction mthod 4 Rsults 5 Conclusions

3 Gnralizd Parton Distributions / DVCS Ultimat goals of p scattring: Accss to th quarks and gluons contnt of th nuclon Undrstand QCD Form Factors => Charg distribution (Elastic scattring) Parton Distribution Functions => Quark momntum distribution (Dp Inlastic Scattring) GPDs => corrlats both (Exclusi procsss) 3

4 Gnralizd Parton Distributions 4 GPDs, dpnding on 3 ariabls : H, H, E, E x,ξ,t H x,0,0 =q x H x,0,0 =Δq x Ji sum ruls: dxh q x, ξ, t =F q t dxe q x, ξ, t =F q t dx H q x, ξ, t =g q t dx E q x, ξ, t =h q t A A 4

5 Dply Virtual Compton Scattring DVCS: «clanst way to accss GPD s» Rlant ariabls of study: Q = k k ' x = Bj Q k k q p q t = k k ' q ' x ξ p q x ξ +c.t. p 5

6 DVCS Cross sction T =T BH T DVCS Cross sction of th procss is (Blitsky Kirchnr Müllr hp ph/008) : 4 d σ α dq dx dtd φ Bj γγ { BH T T DVCS 6 I } 6

7 DVCS cross sction : BKM modl BKM: Harmonic dcomposition of cross sction (φγγ dpndnc) GPD s ncapsulatd in harmonic cofficints => xtraction of GPD s by knowing DVCS cross sction as a function of φγγ ) T BH α P φ P φ T Iα { DVCS α c DVCS 0 P φ P φ [ 0 c B H cos nφ s B H sin φ n = n c DVCS cos nφ s DVCS sin nφ n= { { c BH I 3 n [ n c c I cos nφ s I sin nφ 0 n= n n ] } ] } } 7

8 GPD dpndnt trms in DVCS cross sction: φγγ dpndnc Bilinar DVCS amplitud harmonics: «DVCS trms» linar DVCS amplitud harmonics: «intrfrnc trms» 8

9 Apparatus for Hall A DVCS xprimnt Common Hall A apparatus 9

10 ddicatd DVCS apparatus DVCS in Hall A: E00 0 (p) and E03 06 (n): PbF Elctromagntic calorimtr Proton Array 0

11 3 Cross sctions xtraction mthod Kinmatical domain: 3 kinmatics Ent slction: Cut on rconstructd missing mass

12 3 Cross sctions xtraction mthod Ida: Simulating DVCS nts by MC x ={k ', x, Q, t, φ, φ } > at rtx, w ha kinmatic ariabls: Bj γγ > Th dtctors masurs anothr st of kinmatic ariabls: x ={k ', x Bj, Q, t, φ, φγ γ } => In th simulation, w comput mapping functions from rtx kinmatic ariabls to masurd ons : K x x Λ X indpndnt quantitis (obsrabls): j Λ F x with associatd kinmatic factors : => w can dfin mapping matrics as : K Λ = x i,j Bin i x Bin j Λ drk x x F x

13 3 Cross sctions xtraction mthod => That lads to an xpctd numbr Λ Λ MC Y i = Ldt K X [ ] of counts pr bin: j i,j j,λ Fit with xprimntal data by a χ Y i Y i ] [ mthod to gt our obsrabls => χ = σ i ] [ 0 (Bth Hitlr, π and accidntal subtractd from xprimntal yilds) Λ, Λ' Λ Finally, w gt : X = [ α ]J, j ' β jλ' j j ', Λ' with: Exp i Exp MC α Λ Λ' i,j ' β Λ Λ ' i,j ' = i [ Ldt ] = Y i Exp i Ki Λ,j Ki Λ',j ' [ Ldt ] K [ / σ Λ i,j [ Exp / σ i Exp ] i ] 3

14 GPD dpndnt trms in DVCS cross sction: φγγ dpndnc Bilinar DVCS amplitud harmonics: «DVCS trms» linar DVCS amplitud harmonics: «intrfrnc trms» 4

15 4 Rsults Carlos Muñoz Camacho t al : nucl x/ xbj = 0.36, Q =.3 GV, t = 0.8 GV 5

16 4 Rsults Rmaining problms to rsol : 3 kinmatics to ha sral constraints on th fit, and furthr on GPD s. Unfortunatly, rmoing of nutral pions could ha bn prformd ONLY at Q =.3 GV Ral part of intrfrnc trms cannot b xtractd for Q =.5 and.9 GV: > May caus problms to xtract GPD s Not abl to fit ral part of DVCS AND intrfrnc trms. 6

17 4 Rsults Blu crosss: CDVCS (F,F*) = 0 Rd crosss: CI(F) = 0 Black opn circls: Data 7

18 5 Conclusions First DVCS xprimnt in Hall A was a succss: scaling, at last for imaginary part of CI(F) First unpolarizd DVCS cross sctions in alnc quark rgion (xbj>0.) BUT, thr ar still problms to fix. => ncssity of gtting nw nts with improd apparatus => Nxt Hall A DVCS xprimnt (May 009) 8