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Resolution and radiative corrections A first order estimate for pbar p  e + e -

Resolution and radiative corrections A first order estimate for pbar p  e + e -. T. H. IPN Orsay 05/10/2011 GDR PH-QCD meeting on « The nucleon structure via proton-antiproton annihilation. ep scattering vs annihilation.

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Resolution and radiative corrections A first order estimate for pbar p  e + e -

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  1. Resolution and radiative correctionsA first orderestimate for pbar p  e+ e- T. H. IPN Orsay 05/10/2011 GDR PH-QCD meeting on « The nucleon structure via proton-antiproton annihilation

  2. epscattering vs annihilation • In electronscattering (ep ep), usuallyelectrons are detected: • One single scattering angle qwith a smallDW Eeisfixed • Momentumresolutionis good (a few 10-4 in spectrometer) • Electrons travel in vacuum • Cutadjusted to minimize the error on the radiative corrections • In annihilation at PANDA; pbar p  e+ e- • 2 electrons • Detectionat all angles (DW  4p) • Momentumresolutionismoderate (a few % at 1 GeV/c transverse momentum ) • Matteralong the lepton pathlength • Questions • Position of the cut ? • Dependance on the angle ? • Resolution R=sp/p scaleslikepT • X/X0depends on angle • Can the PANDA EMC detect the associated photon(s) • What are the effect of Kalmanfiltering and KinematicalFit?

  3. epscattering vs annihilation • In electronscattering (ep ep), usuallyelectrons are detected: • One single scattering angle qwith a smallDW Eeisfixed • Momentumresolutionis good (a few 10-4 in spectrometer) • Electrons travel in vacuum • Cutadjusted to minimize the error on the radiative corrections • In annihilation at PANDA; pbar p  e+ e- • 2 electrons • Detectionat all angles (DW  4p) • Momentumresolutionismoderate (a few % at 1 GeV/c transverse momentum ) • Matteralong the lepton pathlength • Questions • Position of the cut ? • Dependance on the angle ? • Resolution R=sp/p scaleslikepT • X/X0depends on angle • Can the PANDA EMC detect the associated photon(s) • What are the effect of Kalmanfiltering and KinematicalFit?

  4. The method • p p  e+ e- • ChooseselectedqCM (30°,40°,…,90°) • Calculatecorrespondinglaboratory angle • Calculate the momentumresolutionaccording to(seeTechnical Design Report of CTS, page 87) fitted on STT muons trackswith 0.2 < pT <2.5 GeV/c • Calculate the e+e- invariant mass; minv(e+e-) • Calculate the photon energyaccording to : (conservation of E,P) • Plot Eg distribution widthagainstqCM

  5. Curveissymmetricwrt 90° CM angle • WeakqCMdependance • sggrowslinearlywithpinc • A cutat -2swould correspond to a 8% loss The result Question: which fraction of the hard/soft photons isbelowthis-2slimit? sEphot(MeV) qCM (e+) (deg)

  6. Effect of Bremsstrahlung in detector material • Assumption: 4% X0 • 70% of the electronslose 1 MeV/c or less • 80% of the electronslose 10 MeV/c or less • 90% of the electronslose 100 MeV/c or less • At 80%, the correspondingaverageenergylossisalwaysmuchlessthan the resolution, but still 20% with a higherenergyloss! •  a « full simulation » isnecessary to « measure » the impact of externalBremsstrahlung . Even if trackingcannotresolve a 1 GeV/c electronfrom a 0.99 GeV/c one, canwe ‘detect’ this 10 MeV g in the calorimeter and then put this condition oureventselectionprocess? Still a lot of work Almostindependent of the energy

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