EIC INT Program, Seattle 2010 - Week 5 1

Radiative Correctionsfor Heavy Nuclei

E.C. Aschenauer

EIC INT Program, Seattle 2010 - Week 5 2

Precision Measurement of FL with the EIC

E.C. Aschenauer

d2σ empNC

dxdQ2 =2pαem2 Y+

xQ4 (F2 −y2

Y+FL ±Y−

Y+xF3)

FL ~ αsG(x,Q2): the most “direct” way to G(x,Q2)FL needs various √s longer program

In order to extract FL one needsat least two measurements of theinclusive cross section with a “wide” span in inelasticity parameter y (Q2=sxy)

Coverage in x & Q2 for inclusivecross section measurements

Plots for 4 GeV electrons on 50 – 250 GeV protons

EIC INT Program, Seattle 2010 - Week 5 3

Measuring FL with the EIC

E.C. Aschenauer

Conclusion from this study Dominated by sys. uncertainties gives max. luminosity here: 4fb-1 / A Depending on x & Q2 might be able to take a hit in luminosity need to include detector effects

Lets get a feeling for systematic uncertainties1% energy-to-energy normalization

FL for fixed electron energy (4GeV)and proton energies:50, 70, 100, 250 GeVLuminosity: 4fb-1 each setting

EIC INT Program, Seattle 2010 - Week 5 4

Measure gA(x) impact parameter dependent

E.C. Aschenauer

Stringent requirements on: Momentum resolution t resolution and range

A. Caldwell, H. Kowalski Phys.Rev.C81:025203,2010

Radiative Correction will impact them

EIC INT Program, Seattle 2010 - Week 5 5

Some Info on RadCors Inclusive cross section

σtot = σela + σqela + σinel + σv

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, like bremsstrahlungradiation is proportional to 1/m2 of radiating particle

elastic:

quasi-elastic: scattering on proton of nuclei proton stays intact nuclei breaks up

two photon exchange? Interference terms? E.C. Aschenauer

initial final vacuum loops

EIC INT Program, Seattle 2010 - Week 5 6

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

E.C. Aschenauer

eventssmeared intoacceptance

EIC INT Program, Seattle 2010 - Week 5 7

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 spaceHand particles

to GEANT

EIC INT Program, Seattle 2010 - Week 5 8

What do we know? A lot of radiative correction codes for proton

much less existing for eAall experiments apart from HERMES had m-beams

suppressed radiationHERMES 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

EIC INT Program, Seattle 2010 - Week 5 9

What do we know?

E.C. Aschenauer

dRC(A) =dσ A / dydσ B

A / dy−1 dRC(A)=

1+δRC(A)1+δRC(D)

−1

10-4 < x < 10-3 and 27.5 GeV x 410 GeV

solid: inelastic rad. corrections dashed: inelastic, quasi-elastic and elastic rad. corrections

Huge effects at high y

PbSC

HeD

EIC INT Program, Seattle 2010 - Week 5 10

What do we know?

E.C. Aschenauer

Compton peak relevant if momentumtransfer to nucleus very small

(1−y)σinQe'=yσinQg

effect of nuclear form factor included

EIC INT Program, Seattle 2010 - Week 5 11

What do we know?

E.C. Aschenauer

Two photon exchange

two photon exchange only important for very heavy nuclei

EIC INT Program, Seattle 2010 - Week 5 12

Can we suppress things? elastic/quasi-elastic part: require some hadrons in

detector solid line: inelastic contribution

dashed line: after cuts Eg > 10 GeV E-pz from hadronic state is smaller

E.C. Aschenauer

Need a code, which puts all together to make full calculationsneed to test analysis strategies to suppress rad. corrections

SC

HeD

EIC INT Program, Seattle 2010 - Week 5 13

Djangoh http://wwwthep.physik.uni-mainz.de/~hspiesb/djangoh

/djangoh.html is compiled at BNL and running

eA part is included need to do more studies HERACLES can be interfaced with other MC codes

HERMES code (RADGEN + eA version of lepto) is installed at BNL and close to run. No nuclear effects are included.

can compare results between eA-RADGEN with HERACLES can nPDFs be included?

Hubert Spiesberger is coming to INT next week, juhu E.C.

Aschenauer

and Summary

EIC INT Program, Seattle 2010 - Week 5 14E.C. Aschenauer

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