1. E.C. AschenauerFebruary 20121

2. Inclusive Structure functions in eA or why momentum resolutions are important E.C. Aschenauer February 20122 How to extract F L :  Measure  r at different √s  vary y  F L slope of  r vs y  F 2 intercept of  r vs y with 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 charge symmetric background Need to combine bins according to the detector resolution Final y-range needs full MC study

3. Inclusive Structure functions in eA or why momentum resolutions are important E.C. Aschenauer February 20123  Good momentum resolution critical for F L critical for F L  impact depends on size of F L  Systematic uncertainties equally critical for F L critical for F L  F2 small effects from either momentum resolution or/and momentum resolution or/and systematic uncertainties systematic uncertainties

4. lepton kinematics E.C. Aschenauer February 20124

5. Effects modifying momentum reconstruction E.C. Aschenauer February 20125 electron hadron from tracking: multiple scattering at low p from tracking: multiple scattering at low p position resolution at high p position resolution at high p external bremsstrahlung dominated by X/Xo dominated by X/Xo internal bremsstrahlung = radiative corrections = 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 homogenous space points and material ditribution, tracking is challenging at small angles = big rapidities

6. Electrons: examples for eSTAR E.C. Aschenauer February 20126 Can be improved by increasing B and L, but MAPS have already the best position resolution and material budget possible. At E e’ > 5 - 10 GeV calorimeter resolution better than tracking  forward rapidities  angle from tracking  E e’ from calo

7. Reconstruct Kinematics E.C. Aschenauer February 20127  Jacquet-Blondel method: hadronic final state  Reconstruction of event kinematics  Electron method: scattered electron

8. Hadrons E.C. Aschenauer February 20128 cuts: Q2>1GeV 2 && 0.01 1GeV 2 && 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

9. Some Info on Internal RadCors  Inclusive cross section   tot =  ela +  qela +  inel +  v for all parts photons can be radiated from the incoming and outgoing lepton, high Z-material Compton peak. radiation is proportional to Z 2 of target, for elastic scattering like bremsstrahlung radiation is proportional to 1/m 2 of radiating particle  elastic:  quasi-elastic: scattering on proton in nuclei proton stays intact proton stays intact nuclei breaks up nuclei breaks up  two photon exchange? Interference terms? E.C. Aschenauer February 20129 initial final vacuum loops

10. Why are RadCor important?  Modify kinematics  Q 2 :  initial state: E’ beam = E beam – E  photon goes along the beam line  final state: E’ out = E out – E  photon goes somewhere in Calo  Hadronic final state very important to suppress RadCor E.C. Aschenauer February 201210

11. What do we know?  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  -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 I. Akushevich and H. Spiesberger http://www.desy.de/~heraws96/proceedings/nuclei/Akushevich.ps.gz http://www.desy.de/~heraws96/proceedings/nuclei/Akushevich.ps.gz QED radiative processes in electron-heavy ion collisions at HERA K. Kurek K. Kurek http://www.desy.de/~heraws96/proceedings/nuclei/Kurek.ps.gz http://www.desy.de/~heraws96/proceedings/nuclei/Kurek.ps.gz E.C. Aschenauer February 201211

12. What do we know? E.C. Aschenauer February 201212  10 -3 1 GeV 2 W had >1.4 GeV AuFeHeP with EPS09 solid: eps09 dashed-dotted: eps08 dashed: EKS98 dotted: HKN huge effects at high y and low x

13. An other example BH vs DVCS E.C. Aschenauer February 201213 to extract  DVCS need to subtract / suppress BH  for more details see https://wiki.bnl.gov/eic/upload/EIC_DVCS_6.pdf https://wiki.bnl.gov/eic/upload/EIC_DVCS_6.pdf  Systematic uncertainty @ HERA: 5%

14. What do we know E.C. Aschenauer February 201214 BH Photons Scattered lepton ePHENIX-idea: reconstruct only high energy leptons with calo Really bad idea major cut in kinematics Q2Q2Q2Q2 x p e’ <2 GeV Born Q2Q2Q2Q2 x Radiative Corrections included

15. What do we know from HERMES E.C. Aschenauer February 201215 <5% radiation length for target and trackers The change in shape from red to blue needs to be unfolded

16. RadCor and smearing unfolding in MC E.C. Aschenauer February 201216 generate observed kinematics x meas, Q 2 meas Radiative Correction Code photon radiated no photon radiated x true =x meas, Q 2 true =Q 2 meas calculate x true, Q 2 true hand kinematics to generator (lepto, pythia,..) What subprocess is generated is regulated by phase space Hand particles to GEANT

17. Why are RadCor important?  Modify kinematics  Q 2 :  initial state: E’ beam = E beam – E  photon goes along the beam line  final state: E’ out = E out – E  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 N true =N meas -N bckg  Migration from bin to bin influences bin size influences bin size  increased  N  increased  N E.C. Aschenauer February 201217 events smeared into acceptance

18. What do we know from HERMES E.C. Aschenauer February 201218

19.  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  p/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 E.C. Aschenauer February 201219 and Summary

20. E.C. Aschenauer February 201220 BACKUP