effects modifying kinematic r econstruction
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February 2012 1
Effects modifying Kinematic Reconstruction
E.C. Aschenauer
February 2012 2
Inclusive Structure functions in eA or why momentum resolutions are important
E.C. Aschenauer
How to extract FL: Measure sr at different √s vary y
FL slope of sr vs y
F2 intercept of sr 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
Need to combine bins according to the detector resolutionFinal y-range needs full MC study
February 2012 3
Inclusive Structure functions in eA or why momentum resolutions are important
E.C. Aschenauer
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
E.C. Aschenauer
February 2012 5
Effects modifying momentum reconstruction
E.C. Aschenauer
electron hadron from tracking: multiple scattering at low p position resolution at high pexternal bremsstrahlung dominated by X/Xointernal 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 homogenous space points and material ditribution, tracking is challenging at small angles = big rapidities
February 2012 6
Electrons: examples for eSTAR
E.C. Aschenauer
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 resolutionbetter than tracking forward rapidities
angle from tracking Ee’ from calo
February 2012 7
Reconstruct Kinematics
E.C. Aschenauer
Jacquet-Blondel method: hadronic final state
Reconstruction of event kinematics
Electron method: scattered electron
February 2012 8
Hadrons
E.C. Aschenauer
cuts: Q2>1GeV2 && 0.01<y<0.9 && 0.1<z
Trick to measure energy with hadron calorimeter will be difficultnormally hadron calorimeters have to big fluctuationsEnergy resolution is worth ~40%/√s
February 2012 9
Some Info on Internal RadCors
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 bremsstrahlungradiation 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?
E.C. Aschenauer
initial final vacuum loops
February 2012 10
Why are RadCor important?
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
E.C. Aschenauer
February 2012 11
What do we know?
A lot of radiative correction codes for proton ep
two codes, which are integrated/integratable in MCHeracles part of DJANGOH and RADGEN (hep-ph/9906408v1)
much less existing for eAall 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.gzQED radiative processes in electron-heavy ion collisions at HERA
K. Kurek
http://www.desy.de/~heraws96/proceedings/nuclei/Kurek.ps.gz
E.C. Aschenauer
February 2012 12
What do we know?
E.C. Aschenauer
10-3 < x < 10-2 and 5 GeV x 130 GeV Q2 > 1 GeV2 Whad>1.4 GeV
AuFeHePwith EPS09
solid: eps09dashed-dotted: eps08dashed: EKS98dotted: HKN
huge effects at high yand low x
February 2012 13
An other example BH vs DVCS
E.C. Aschenauer
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
E.C. Aschenauer
BH Photons
Scattered lepton
ePHENIX-idea: reconstruct only high energy leptons with caloReally bad idea major cut in kinematics
Q2
x
pe’<2 GeVBorn
Q2
x
pe’<2 GeVRadiative Corrections included
February 2012 15
What do we know from HERMES
E.C. Aschenauer
<5% radiation length for target and trackers
The change in shapefrom red to blue needs to be unfolded
February 2012 16
RadCor and smearing unfolding in MC
E.C. Aschenauer
generate observed kinematicsxmeas, Q2
meas
Radiative Correction Code
photon radiated no photon radiated
xtrue=xmeas, Q2
true=Q2meas
calculatextrue, Q2
true
hand kinematics togenerator (lepto, pythia, ..)
What subprocess isgenerated is regulated
by phase space
Hand particlesto GEANT
February 2012 17
Why are RadCor important?
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
E.C. Aschenauer
eventssmeared intoacceptance
February 2012 18
What do we know from HERMES
E.C. Aschenauer
February 2012 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 dp/p
internal rad. corrections most important at low Q2 low theta
difficult to simulate in a fast simulatorespecially 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
and Summary
February 2012 20E.C. Aschenauer
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