Effects modifying Kinematic R econstruction

1. Effects modifying Kinematic Reconstruction February 2012

2. Inclusive Structure functions in eA or why momentum resolutions are important • How to extract FL: • Measure sr at different √s  vary y •  FL slope of srvs y • F2 intercept of srvs ywith y-axis • Issues: • Lever arm in y • Value of y • At low y: detector resolution for e’ • At high y: radiative corrections and • charge symmetric background Need to combine bins according to the detector resolution Final y-range needs full MC study February 2012

3. Inclusive Structure functions in eA or why momentum resolutions are important • Good momentum resolution • critical for FL • impact depends on size of FL • Systematic uncertainties equally • critical for FL • F2 small effects from either • momentum resolution or/and • systematic uncertainties February 2012

4. lepton kinematics February 2012

5. Effects modifying momentum reconstruction electronhadron from tracking: multiple scattering at low p position resolution at high p external bremsstrahlung dominated by X/Xo internal bremsstrahlung = radiative corrections Tracking: Multiple scattering: dpt/pt = dp/p = dk/k = 4.5e-2 * 1/beta * 1/(B [T]*L_T [m] ) * \sqrt(x/x0) Position resolution: dpt/pt = dp/p = dk/k = 1/(0.3*B[T]) * \epsilon/(L_T^2) * sqrt(720/(N+4)) assume homogenousspace points and materialditribution, tracking is challenging at small angles = big rapidities February 2012

6. Electrons: examples for eSTAR • Can be improved by increasing B and L, • but MAPS have already the best position • resolution and material budget possible. • At Ee’ > 5 - 10 GeV calorimeter resolution • better than tracking • forward rapidities • angle from tracking • Ee’ from calo February 2012

7. Reconstruct Kinematics • Reconstruction of event kinematics • Electron method: scattered electron • Jacquet-Blondel method: hadronic final state February 2012

8. Hadrons cuts: Q2>1GeV2 && 0.01<y<0.9 && 0.1<z Trick to measure energy with hadron calorimeter will be difficult normally hadron calorimeters have to big fluctuations Energy resolution is worth ~40%/√s February 2012

9. Some Info on Internal RadCors final vacuum loops initial February 2012 • Inclusive cross section • stot = sela + sqela + sinel + sv • for all parts photons can be radiated from the incoming and outgoing lepton, high Z-material Compton peak. • radiation is proportional to Z2 of target, for elastic scattering like bremsstrahlung • radiation is proportional to 1/m2 of radiating particle • elastic: • quasi-elastic: scattering on proton in nuclei • proton stays intact • nuclei breaks up • two photon exchange? Interference terms?

10. Why are RadCor important? February 2012 • Modify kinematics  Q2: • initial state: E’beam = Ebeam – Eg • photon goes along the beam line • final state: E’out = Eout – Eg • photon goes somewhere in Calo • Hadronic final state very important to suppress RadCor

11. What do we know? February 2012 • A lot of radiative correction codes for proton • ep • two codes, which are integrated/integratable in MC • Heracles part of DJANGOH and RADGEN (hep-ph/9906408v1) • much less existing for eA • all experiments apart from HERMES had m-beams • suppressed radiation • HERMES uses modified version of RADGEN (hep-ph/9906408v1) • Radiative corrections to deep inelastic scattering on heavy nuclei at HERA I. Akushevich and H. Spiesberger http://www.desy.de/~heraws96/proceedings/nuclei/Akushevich.ps.gz • QED radiative processes in electron-heavy ion collisions at HERA K. Kurek http://www.desy.de/~heraws96/proceedings/nuclei/Kurek.ps.gz

12. What do we know? • 10-3 < x < 10-2 and 5 GeV x 130 GeV Q2 > 1 GeV2Whad>1.4 GeV solid: eps09 dashed-dotted: eps08 dashed: EKS98 dotted: HKN Au Fe He P with EPS09 huge effects at high y and low x February 2012

13. An other example BH vs DVCS • to extract sDVCS need to subtract / suppress BH • for more details see https://wiki.bnl.gov/eic/upload/EIC_DVCS_6.pdf • Systematic uncertainty @ HERA: 5% February 2012

14. What do we know BH Photons Scattered lepton • ePHENIX-idea: reconstruct only high energy leptons with calo • Really bad idea major cut in kinematics pe’<2 GeV Radiative Corrections included pe’<2 GeV Born Q2 Q2 February 2012 x x

15. What do we know from HERMES <5% radiation length for target and trackers The change in shape from red to blue needs to be unfolded February 2012

16. RadCor and smearing unfolding in MC generate observed kinematics xmeas, Q2meas Radiative Correction Code no photon radiated photon radiated xtrue=xmeas, Q2true=Q2meas calculate xtrue, Q2true hand kinematics to generator (lepto, pythia, ..) What subprocess is generated is regulated by phase space Hand particles to GEANT February 2012

17. Why are RadCor important? events smeared into acceptance February 2012 • Modify kinematics  Q2: • initial state: E’beam = Ebeam – Eg • photon goes along the beam line • final state: E’out = Eout – Eg • photon goes somewhere in Calo • RadCor and detector smearing don’t factorize • need to have RadCor implemented in MC to unfold effects on kinematics • unfolding in bins • Ntrue=Nmeas-Nbckg • Migration from bin to bin influences bin size  increased DN

18. What do we know from HERMES February 2012

19. and Summary • Internal and external radiative corrections • big impact on kinematic reconstruction • the tracking and calorimeter resolutions need to be optimized having this in mind • both give long tails in dp/p • internal rad. corrections most important at low Q2  low theta • difficult to simulate in a fast simulator • especially internal radiative corrections • because of physics process dependence • Unfolding procedure developed at HERA • knowledge on formfactors will give systematic uncertainty • detector momentum smearing and radiative corrections don’t factorize in unfolding procedure February 2012

20. BACKUP February 2012