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Contribution to the G0 experiment on parity violation : calculation and simulation of radiative corrections and background study Hayko Guler Institut de Physique Nucléaire dOrsay Groupe PHASE

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1. Introduction : From parity violation to strange quarks 2. G0 experiment 3. Electromagnetic radiative corrections 4. Simulations with GEANT 5. Study and calculation of the inelastic background and comparison to experimental data 6. Conclusion and outlook

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1.Introduction : From parity violation to strange quarks 2.G0 experiment 3.Electromagnetic radiative corrections 4.Simulations with GEANT 5.Study and calculation of the inelastic background and comparison to experimental data 6.Conclusion and outlook

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What role do strange quarks play in nucleon properties? proton gluons non-strange sea (u, u, d, d) quarks u u s s strange sea (s, s) quarks valence quarks u u d Spin: Mass: Charge and current: Contribution of s quarks to charge and magnetic current of proton ?

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Electromagnetic form factor of the nucleon Electric form factor Magnetic form factor Q2Q2 Form factor decomposition over quark flavours Proton Neutron Each quark electric charge

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Electromagnetic form factor of the nucleon Electric form factor Magnetic form factor Q2Q2 Form factor decomposition over quark flavors Isospin Symmetry between proton and neutron quark uquark d ( Violation : ~ 1% ) Proton Neutron

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Electromagnetic form factor of the nucleon Electric form factor Magnetic form factor Q2Q2 Form factor decomposition over quark flavors Proton Neutron Electromagnetic interaction : 4 equations and 6 unknowns

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Weak form factors of nucleon Form factor decomposition over quark flavors Electric weak form factor Pseudo-scalar form factor Magnetic weak form factor Axial form factor Weak charge of each quark ( )

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Weak form factors of nucleon Form factor decomposition over quark flavors Electric weak form factor Pseudo-scalar form factor Magnetic weak form factor Axial form factor ( ) em. interaction + weak 6 equations et 6 unknowns Weak coupling measurement Access to strange quarks If we neglect the axial form factor

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Weak process extraction Weak process very small in comparison to electromagnetic interaction : at Q² = 1 (GeV/c)², But, weak interaction violates the symmetry of parity Experimental method : electron-proton elastic scattering, with longitudinally polarized electronse, e R p e, e L p

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Electron-proton scattering cross section e e p p Z0Z0 e e p p + 2 * 2 D/G Z Z 2 2 Z )(M2Reσ MM MMM ++=+ * Parity violation asymmetry calculation

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Asymmetry can be decomposed as S0 PV AAA Parity violation asymmetry Kinematical parameters : Fundamental constants 2 FW G,, sin Asymmetry : A s 2 p M 2 p E s A p M s M p M s E p E 2 F S GG GGGGGG 24 QG A

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Electric and magnetic form factors proton neutron

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Kinematical domain Forward angles (PVA4, Happex, G0) Backward angles (Sample, G0) For G0 : measure at forward angles and backward angles on LH2. AND measure on LD 2 at backward angles. Rosenbluth separation Q 2 = 0.25 (GeV/c) 2

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1.Introduction : From parity violation to strange quarks 2.G0 experiment 3.Electromagnetic radiative corrections 4.Simulations with GEANT 5.Study and calculation of the inelastic background and comparison to experimental data 6.Conclusion and outlook

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G0 experiment Strange form factors separation Q 2 = ( 0.3, 0.5, 0.8 ) (GeV/c) 2 PART 1 : Measurement at forward angles Detect recoil protons between 48 et 77° Q 2 [ 0.16, 1. ] (GeV/c) 2 Liquid hydrogen target PART 2 : Measurement at backward angles Detect electrons ~ 110º Liquid hydrogen target Measure at backward angles Deuterium target

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G0 experiment at forward angles électrons incidents Cible Collimateurs FP détecteurs Electron beam energy = 3 GeV on 20 cm LH 2 target Detect recoil protons ( ~ 62 - 78 o corresponding to 15 - 5 o electrons) Magnet sorts protons by Q 2 in focal plane detectors Full desired range of Q 2 (0.16 - 1.0 GeV 2 ) obtained in one setting Flight time separates p (about 20 ns) and + (about 8 ns)

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G0 experiment at Jefferson laboratory Main components : Superconducting toroidal magnet Jefferson Lab. Polarized source ( 40 µA et P = 75 % ) Large acceptance scintillation detector array (0.9 sr) LH 2 (20 cm) target Custom high count rate electronics (2 MHz per detector) Calendar : Design and construction (1993 - 2001) 1 st Commissioning run (October 2002 / January 2003) 2 nd Commissioning run (December 2003 / February 2004) Forward angles data taking run (February – April 2004) Backward angles data taking run (2005 - 2006)

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G 0 beam monitoring girder superconducting magnet (SMS) detectors (Ferris wheel) cryogenic supply target service module G 0 installed in Hall C at JLAB

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Detectors G0 made up of 8 sectors or octants (4 French et 4 Nord-American ) One octant made up of 16 detectors One detector = pair of Scintillators in coincidence read by photomultipliers

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Beam time structure YO [START] = 31.25 MHz (499MHz / 16) Helicity is flipped at 30 Hz (every 33 ms) MacroPulse (MPS) : 1 helicity state duration (33 ms) Helicity Flip 500 s Data transfer + + + + MPS Quartet Quartets ( + - - +) or ( - + + - ) randomly distributed

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DMCH-16x electronic module Discriminators Mean-Timers Time Digital Converter Histogramming 16 channels X for VXI standard 32 Discriminators 16 Mean-Timers 1/2 Octant 1 DMCH-16X module : 8 detectors EPLD TRIG TDC FIFO DSP Front End DSP VME Lecture Thresholds (Analog 50mV~) Daughter card DFC/MT Histograms over 32ns DFC Right DFC Left Mean Timer Scintillateur Left pm Right pm 250 ps

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32 photomultipliers entries CFD-MT S-DMCH Flash TDC Front End DSPs DSP Concentrator DMCH-16X module (IPN/SEP)

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Time of Flight spectra Pions Inelastic protons Elastic protons 1 4 8 2 3 765 10 12 9 11 14 13 15 16

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1.Introduction : From parity violation to strange quarks 2.G0 experiment 3.Electromagnetic radiative corrections 4.Simulations with GEANT 5.Study and calculation of the inelastic background and comparison to experimental data 6.Conclusion and outlook

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Incident electron energy Electrons interact with target elements : ionization and external radiative corrections External radiative corrections Incident electron Principal scattering Internal radiative corrections Difference between external radiative corrections and internal radiative corrections Scattered Proton

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Ionization External radiative corrections Ionization : Energy loss ~ 5 MeV ( 15 MeV) External_RC: Energy loss ~ 40 MeV 3 GeV But more than 95 % of the electrons energy loss is smaller than 500 MeV Energy loss

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Born cross section and experiment TPTP T elas For a fixed angle P : Born cross section onlyExperimentally TPTP T elas T cut 1 2

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Region 1 treatment Integral calculation : Proton detected : Integration over all directions + Internal Bremsstrahlung diagrams 2

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Asymmetry calculation in 1 st region Necessity to calculate Z 0 exchange diagrams Electromagnetic interaction Weak interaction + +

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2 nd region treatment Only the integral of 2nd zone has a physical meaning : Attenuation factor is calculated using following diagrams : + 2 2 + Real radiative corrections Soft photon emission Born Vertex Vacuum energy Virtual radiative corrections (I)(II) (III)

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2 nd region treatment Three conditions to determine a, b and c coefficients Integral condition : Cross section continuous at E cut Continuity of cross section first derivative at E cut The cross section can be expressed with a polynomial in the proton energy :

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Cross section interpolation Stopped by the collimators Difficulty to interpolate cross section directly Cross section is approximated with polinomial and their coefficients are interpolated with splines in each zone in T P

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1.Introduction : From parity violation to strange quarks 2.G0 experiment 3.Electromagnetic radiative corrections 4.Simulations with GEANT 5.Study and calculation of the inelastic background and comparison to experimental data 6.Conclusion and outlook

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Simulations with GEANT The measured data are time of flights Magnet, collimators, position of the detectors (geometry) and loss into different traversed materials are taken into account by the simulation 1)Random choice of scattering position in LH2 target 2)Electrons energy according to physical distribution 3)Random choice of recoil proton scattering angle 4)Random choice of recoil proton energy 5)Cross section and asymmetry interpolation 6)Normalization (weight calculus) and particle tracking Incident Electron Recoil proton p 0 20 cm

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Weight method Weight method is used to have counting rates with cross section All the variables are chosen to flat distributions Weight expression for e-p scattering depends on the number of particles in the final state : Elastic scattering (2 particles in final state) : Internal radiative corrections or inclusive reactions (3 particles in final state) :

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Kinematical domain

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Effect on time of flight (1-4) Radiative corrections Elastic scattering

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Effect on time of flight (13-16) Radiative corrections Elastic scattering

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Correction on TOF 2 sigma cut (experimentally) Radiative corrections decrease TOF Effect is negligible ( < experimental resolution) Radiative corrections Elastic scattering

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Effect on Q 2 (1-4) Radiative corrections Elastic scattering

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Effect on Q 2 (13-16) Radiative corrections Elastic scattering

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Correction on the Q 2 2 sigma cut (experimentally) Radiative corrections increase Q 2 The effect is < 1 % except for detector 14 Q 2 by détector Q 2 ratio : RC-elas (in %) Radiative corrections Elastic scattering

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Correction on the asymmetry 2 sigma cut (experimentally) Radiative corrections increase the asymmetry The effect is < 1 % except for detector 14 Radiative corrections Elastic scattering

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1.Introduction : From parity violation to strange quarks 2.G0 experiment 3.Electromagnetic radiative corrections 4.Simulations with GEANT 5.Study and calculation of the inelastic background and comparison to experimental data 6.Conclusion and outlook

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Inelastic evaluation Background : inelastic protons under elastic peak Calculated process : electroproduction and photoproduction (in LH2 target only ) Pions Inelastic protons Elastic protons

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Electroproduction generator Example of reaction : e + p e + p + 0 We want to evaluate : With : Dominated by Q 2 ~ 0 Goes to : 3 body kinematical factor Photoproduction amplitude : 2 body kinematical factor Experimental data

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Validity of the model Verification at 650 MeV Flux factor 3 differents calculations have been done : 1.Exact over all terms calculation (effective Lagrangian) 2.Calculation in which we keep only the transverse part 3.Calculation in which we take electroproduction data

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Comparison at 650 MeV

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Comparison of photoproduction to electroproduction The critical length for which photoproduction equivalent to electroproduction is 0.04 radiation length (Tsai) (36cm target). In G0 case, LH2 target of 20 cm, density 0.07 g/cm 3, represents 0.022 radiation length. Electroproduction must dominate on photoproduction

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Cross section comparison Reaction at middle of target for recoil proton different angles Electroproduction : e + p e + p + 0 Photoproduction : + p p + 0

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Time of flight comparison e + p e + p + 0 + p p + 0 ( from LH2 + aluminum window) + p p + 0 ( from LH2)

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Comparison to G0 data (1-4) Comparison at first commissioning data 6-7 mil. Inch of aluminum window

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Comparison to G0 data (12-15) Effect of aluminum windows ? We reproduce ~50% of background Comparison at first commissioning data 6-7 mil. Inch of aluminum window

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Comparison to G0 data 12/03 (1-4)

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Comparison to G0 data 12/03 (11-14)

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1.Introduction : From parity violation to strange quarks 2.G0 experiment 3.Electromagnetic radiative corrections 4.Simulations with GEANT 5.Study and calculation of the inelastic background and comparison to experimental data 6.Conclusion and outlook

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Conclusion Important contributions for coming G0 experimental data interpretation Complete calculation of electromagnetic internal radiative corrections on the proton Radiative corrections effect on time of flight, Q 2 and asymmetry Background simulation containing inelastic protons coming from hydrogen target Actual limitations : aluminum window simulations, and polarization

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Cut energy E cut determination Cross section integral between E min = 2 MeV et E max = E elas must not depend on E cut

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Traiter les divergences Propagator P xi proportionnal to 1/E : infrared divergence for E 0 two domains : Ep E cut et Ep E cut Ep E cut hard photons : non divergente integral Ep E cut soft photons divergente integral E cut Not physical cut but parameter for calculation But : calculer

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Lever la divergence No physical divergence but in calculus Lintégrale de la section efficace de RC est reliée à Born par un facteur datténuation A A contain virtual radiative corrections

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Interpolation pour Ep E cut Difficulté dinterpoler directement la section efficace On approche la section efficace par des polynômes et on interpole leurs coefficients Interpolation (Lagrange) donne trop derreurs sur la valeur de la section efficace Interpolation par des splines Courbes E elas = f( ) pour des énergies incidentes calculées Courbes E elas = f( ) pour lénergie incidente tirée

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Interpolation pour Ep E cut Difficulté dinterpoler directement la section efficace On approche la section efficace par des polynômes et on interpole leur coefficients Interpolation (Lagrange) donne trop derreurs sur la valeur de la section efficace Interpolation par des splines

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DMCH-16X tests Dead time : NPN mode (Next Pulse Neutralisation) caesura (cut off) position Discriminator dead time (~32ns) Differents working modes

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Comparaison aux données de SOS Avant G0, le spectromètre SOS a permit de tester les modèles théoriques (acceptance proche de G0 et E inc =3.245 GeV) On reproduit 70-80 % des données à 58.6 degrés

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Comparaison aux données de SOS Avant G0, le spectromètre SOS a permit de tester les modèles théoriques (acceptance proche de G0 et E inc =3.245 GeV) On reproduit 95 % des données a 65.6 degrés

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Photon number calculation Les électrons rayonnent des photons de Bremsstrahlung dont la distribution en fonction de leur énergie est :

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Weight model verification Comparaison à la loi réelle (cas particulier dune section efficace analytique ) Vérification de la loi reliant lintégrale de la section efficace de RC à Born (à 2% près ) Comparaison avec les données expérimentales

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Strangeness model in asymmetry calculation Modèle de Hammer :

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Q² per detector

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Asymmetry results (preliminary)

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