Brahim MorenoStudents' seminar at Bosen Workshop ΔVCS and Generalized Parton Distributions

Brahim MorenoStudents' seminar at Bosen Workshop Outline I.Generalized Parton Distributions II.Beam Spin asymmetry III.The experiment at Jlab IV.First look at the Data

Brahim MorenoStudents' seminar at Bosen Workshop Generalized Parton Distributions (GPDs)

Brahim MorenoStudents' seminar at Bosen Workshop In the Bjorken limit: Large Low Fixed General GPDs physics case t γ or meson l’ l γ* NN’ standard notation GPDs appear in the amplitudes of exclusive reactions GPDs are a new way of describing the nucleon l GPDs γ N l’ N’

Brahim MorenoStudents' seminar at Bosen Workshop z x y Nucleon form factor x z y Parton distributionGPDs GPDs : combine information from form factors and parton distribution x z y

Beam Spin Asymmetry

Brahim MorenoStudents' seminar at Bosen Workshop Beam Spin Asymmetry (BSA) general case k = number of independent variables P = polarization of incoming lepton l = lepton, N= nucleon l’= scattered lepton, N’= recoil hadron, M= photon or meson

Brahim MorenoStudents' seminar at Bosen Workshop Beam Spin Asymmetry (BSA) DVCS example Interference between DVCS and Bethe-Heitler processes DVCS BH β,α are combinations of GPDs BSA grants access to nucleon GPDs

Brahim MorenoStudents' seminar at Bosen Workshop Beam spin asymmetry: ΔVCS case e e’ γ*γ N p л -N-Δ transitions at a partonic level - large Nc approximation: ΔVCS can be described in terms of standard GPDs GPDs N-Δ L.L. Frankfurt, M. V. Polyakov,M. Strikman, M.Vanderhaeghen Phys. Rev. Lett. 84: (2000) P.A.M Guichon, L.Mossé, M.Vanderhaeghen Phys. Rev. D (2003)

Brahim MorenoStudents' seminar at Bosen Workshop ++ 2 ΔVCSBH FIRST measurement P.A.M Guichon, L.Mossé, M.Vanderhaeghen Phys. Rev. D (2003)

Brahim MorenoStudents' seminar at Bosen Workshop The experiment at Jefferson lab

Brahim MorenoStudents' seminar at Bosen Workshop Thomas Jefferson Laboratory (USA, Virginia) Hall B

Brahim MorenoStudents' seminar at Bosen Workshop Cherenkov Counters for e/л separation CLAS detector Time-of-flight counters (TOF) Drift chambers (DC) to determine trajectories to detect showering particles Electromagnetic Calorimeter (EC, LAC) Torus magnet of charged particles for separation (DVCS) high energy resolution photon detector Inner calorimeter (IC)

2005 data taking 35 days (from march to may 2005) December 2006 : first thesis published (DVCS BSA) 2008 : second data taking period Chronology my arrival 2005 calibrations 2007 : ongoing analysis (DVCS,,, cross sections,, BSA ) beam energy GeV

Brahim MorenoStudents' seminar at Bosen Workshop First look at the data

Brahim MorenoStudents' seminar at Bosen Workshop Analysis plan Basic event selection: 1 electron, 1 proton, 3 photons - reconstruct Δ particles via neutral pion reconstruction - develop exclusivity cuts - background and contamination studies - Beam Spin Asymmetry results e e’ γ*γ N p л

Which one to choose ? Before going further it would be wise to have a preview of the decay particles of Δ phase space Development of a kinematic filter Delta reconstruction different photon combinations

Brahim MorenoStudents' seminar at Bosen Workshop Phase space generator First look at the data

Brahim MorenoStudents' seminar at Bosen Workshop t random number uniformly distributed Kinematic generator ν: random number uniformly distributed Q2: random number uniformly distributed t 0t mint max e e’ γ*γ N p л t

Prediction for ΔVCS 8% events under 0 GeV DVCS photon = most energetic one

First look at the data Selection cuts

Before cutsAfter cuts

Selection cuts: cut on

Selection cuts A = second resonance region (~1.5 GeV) B = third resonance region (~1.65 GeV)

Brahim MorenoStudents' seminar at Bosen Workshop Complementary slides

Brahim MorenoStudents' seminar at Bosen Workshop Kinematic generator Δ γ p γ 1 

Brahim MorenoStudents' seminar at Bosen Workshop Kinematic generator uniformly distributed

Kinematic generator: validation generator result data

Selection cuts

Brahim MorenoStudents' seminar at Bosen Workshop Data analysis background and contamination

Overview

Brahim MorenoStudents' seminar at Bosen Workshop Data e1-dvcs experiment first part of experiment 35 days (from march to may 2005)approved for 60 days beam energy GeV luminosity to be completed next year accumulated charge hydrogen target

More about GPDs

Standard GPDs γ p’ e e’ γ* p x-ξx+ξ t 4 GPDs for each quark flavour

Transition N-Δ GPDs 3 transition vector GPDs 4 transition pseudo-vector GPDs In the large Nc limit

Particle ID

Brahim MorenoStudents' seminar at Bosen Workshop cut on reconstructed vertex position Particle ID: electron Scattered electron identification Fiducial cuts (EC,DC) Cut on lost energy in inner part of EC: E_in>60 MeV Cut on E/p vs p Momentum threshold : p > 800 MeV Cut on number of p.e’s produced in CC: 10*N > 25 id = 11

Brahim MorenoStudents' seminar at Bosen Workshop Particle ID: electron Fiducial cuts (EC) Cut on lost energy in inner part of EC

Brahim MorenoStudents' seminar at Bosen Workshop Particle ID: electron Cut on E/p vs p

Brahim MorenoStudents' seminar at Bosen Workshop Particle ID: proton recoil proton identification cut on reconstructed vertex position Fiducial cuts (θ,φ) Cut on

Brahim MorenoStudents' seminar at Bosen Workshop photon identification: E > 150 MeV Particle ID: photon detected in IC fiducial cuts to avoid photons with hit near IC edge assume all particles detected in IC are photons detected in EC Fiducial cuts (EC)cut on β = l/t

Brahim MorenoStudents' seminar at Bosen Workshop Fiducial cuts electron proton photon