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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