E.C. AschenauerFebruary 20121

Inclusive Structure functions in eA or why momentum resolutions are important E.C. Aschenauer February 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

Inclusive Structure functions in eA or why momentum resolutions are important E.C. Aschenauer February  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

lepton kinematics E.C. Aschenauer February 20124

Effects modifying momentum reconstruction E.C. Aschenauer February 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

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

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

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

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 initial final vacuum loops

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

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/ v1)  much less existing for eA all experiments apart from HERMES had  -beams suppressed radiation HERMES uses modified version of RADGEN (hep-ph/ v1) Radiative corrections to deep inelastic scattering on heavy nuclei at HERA I. Akushevich and H. Spiesberger I. Akushevich and H. Spiesberger QED radiative processes in electron-heavy ion collisions at HERA K. Kurek K. Kurek E.C. Aschenauer February

What do we know? E.C. Aschenauer February  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

An other example BH vs DVCS E.C. Aschenauer February to extract  DVCS need to subtract / suppress BH  for more details see  Systematic HERA: 5%

What do we know E.C. Aschenauer February 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

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

RadCor and smearing unfolding in MC E.C. Aschenauer February 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

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 events smeared into acceptance

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

 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 and Summary

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