1. Radiative corrections FOR PYTHIA
Andrea Bressan
Radiative corrections FOR PYTHIA
2/23/2019
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2. RADIATIVE CORRECTIONS
Three basic channels contribute to lepton-nucleus ℓ𝐴 scattering at different 𝑄 2 and 𝜈
These are the
Elastic scattering 𝜈= 𝑄 2 2 𝑀 𝐴
Quasi elastic scattering 𝜈~ 𝑄 2 2 𝑀 𝑁
Inelastic scattering 𝜈> 𝑄 2 2 𝑀 𝑁 + 𝑚 𝜋
At Born level, 𝑄 2 and 𝜈 are fixed by measuring energy and scattering angle of the lepton and the we can distinguish between the three processes.
In case of an extra (radiated) photon the fixing of 𝑄 2 and from 𝜃 and 𝐸 ′ is removed and the photon has to be included in the kinematic calculation.
2/23/2019
a.b.

3. RADIATIVE CORRECTIONS
The radiative leptonic tensor 𝑆 ℓ, ℓ ′ ,𝑘 is
Gauge invariant
Infrared finite
Universal (for 1𝛾 exchange)
The kinematic is shifted
𝑞 𝜇 = 𝑞 𝜇 − 𝑘 𝜇
2/23/2019
a.b.

4. RADIATIVE CORRECTIONS: Deliverables
Deliverables achieved at the end of the project:
Calculate radiative corrections for transverse polarized observables to measure TMDs and polarized exclusive observables.
Provide proof that the MC phase space constrains on the hadronic final state is equal to calculating radiative corrections for each polarized and unpolarized semi-inclusive hadronic final state independently.
Define a software framework and develop a library based on this framework, which integrates the radiative corrections depending on polarization and other determining factors in a wrapper-software.
2/23/2019

5. The problem for SIDIS
Photon radiation from the muon lines changes the DIS kinematics on the event by event basis
The direction of the virtual photon is changed with respect to the one reconstructed from the muons
This introduces false asymmetries in the azimuthal distribution of hadrons calculated with respect to the virtual photon direction
Smearing of the kinematic distributions (f.i. 𝑧 and 𝑃 ℎ𝑇 )
Due to the energy unbalance, in the lepton plane the true virtual photon direction is always at larger angles with respect to the reconstructed one
In SIDIS, having an hadron in the final state, only the inelastic part of the radiative corrections plays a role

6. Azimuthal asymmetries in SIDIS

7. Meeting with Huber Spiesberger
Obiettive
Set up the collaboration
Start back from HERACLES by stripping away lepto from Djangoh so that we can separate the radiative part and combine it to other generators
Check how we can interface that to PYTHIA6 and PYTHIA8
2/23/2019
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8. Meeting with Huber Spitsberger
2/23/2019
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9. 2/23/2019
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10. PYTHIA 6 Steps: Cross section calculation (LO, NLO)
Full cross section including radiative corrections (NNLO in QED)
Generate according to cross section
Final steps in Pythia using 𝛾 ∗ 𝑁 interactions
2/23/2019
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11. PYTHIA 8 𝛾 ∗ 𝑁 not available in PYTHIA 8
The option to use LHEF to feed events to PYTHIA is under evaluation. Will need to create an HERACLES/LHA interface
Use of MadGraph5?
Adv: MadGraph output the results of a matrix-element calculation as a set of PYTHIA 8 C++ classes, that can then be linked and used within Pythia. 
2/23/2019
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12. Use of MadGraph5?
Can generate hard processes, including higher orders, i.e. ℓ𝑞→ℓ𝑋
2/23/2019
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13. I was not able to get loops:
2/23/2019
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14. Only to QED=3 and QCD=1:
2/23/2019
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15. QED=4 is missing
2/23/2019
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16. END
2/23/2019
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