1. Groupement de Recherche (GDR) QCD
PARTONS AND NUCLEI
1-2 June 2017
IPN Orsay – salle du conseil
Input for the closing discussion
Disclaimer: biased on the fly notes
Groupement de Recherche (GDR) QCD
Raphaël Dupré
Francois Gélis
Hervé Moutarde
Sarah Porteboeuf-Houssais
Ingo Schienbein
a. Interactions simples et multiples entre partons dans les nucléons
b. Physique de la saturation et effets collectifs dans les nucléons et noyaux

2. From nucleon structure to hadronic collisions
Double Parton Scattering:
many estimations of σeff: process and energy independant or not?
towards a clearer physical interpretation (DPS/SPS and GPDs)
What about MPI ?
TMD formalism getting generalized to LHC with saturation. Will the very different kinematics allow for a check of universality ?
Measurement of coherent processes on nuclei open a new avenue to study nuclei. Nuclei allow to play with spin in these processes.

3. from pp to AA
What are the elementary interactions to describe collisions ?
Physics continuum from pp to AA
Hydrodynamics in pp collisions?
Pomerons in EPOS, MPI
RAA interpretation with interplay between soft and hard processes
Importance of saturation
Progress on JIMWLK calculations for LHC and in the small-x field in general.
Many indications but still looking for the silver bullet for CGC?
Gluon TMDs in the small-x limit, their (non-linear) QCD evolution can be obtained from JIMWLK equation
Explain closed and open charm vs. Multiplicty in EPOS (and not hydro)
nPDF
Should they respect sum rules?
Now includes LHC.
Progress in error handling.
A roadmap for the addition of heavy quarks in the future. NNLO and amount of data key.

4. NEW Measurements Many experimental tests proposed:
Exploring reggeon explanation of the anti-shadowing.
Exploring exotic Fock states of the light nuclei and intrinsic  (high x) strangeness and charm.
Tagged measurements at Jlab and EIC
Forward J/Psi + jet at LHC => test of BFKL evolution + NRQCD quarkonium production
Think about measurement in Heavy Ion collisions in term of multiplicity despite Ncoll/Npart
DPS measurement
At LHC : DPS as function of multiplicity
EIC

5. Thank you for this fruitful workshop !

6. https://indico.in2p3.fr/event/13459/
Group a meeting, September 2016 : Simple and multiple interactions between partons in nucleons
Focus on pp and heavy ion collisions initial stages (some inputs):
How a better comprehension of proton structure can lead to a better description of proton-proton collision at high energy ?
Change use of PDF in the direction of TMD’s or GPD’s,
CGC and gluon TMD’s : measurement of di-jet at small x
Heavy quarks production (ccbar, bbar) polarization measurement: the link with TMD ?
Factorization in pA and AA? Which observables can probe factorization breaking ?
Alternative to nPDF’s ?
Link between initial stage in pp and heavy ions, with CGC ? with MPI ? Extension of DPS framework to pA and AA, nuclear GPD’s?
TOOLS : event generators and data fits

7. Partons and Nuclei
The workshop aims at exploring the physics continuum from proton to nucleus with a focus on three topics :
Hadronic collisions initial conditions (from pp to AA)
Color glass condensate and saturation
Multiple correlations within partons and within nucleons
Factorization in AA
Event generators
pp and AA
ep and eA
Partonic structure of nucleus
Nucleus DVCS
Nuclear PDF's and their uncertainties

8. Practical Information
Agenda
WIFI
Lunch

9. Backup
Conclusion slides from first meeting

10. Proton-proton collision : initial stage
How a better comprehension of proton structure can lead to a better description of proton-proton collision at high energy ?
Change use of PDF in the direction of TMD’s or GPD’s,
Naïve guess: observable dependent, can we make a list?
how can we use automatic codes in the context of LHC ?
What do we learn on nucleon structure ?
Cédric Lorcé
What do we learn on non perturbative regime of QCD ?
CGC and gluon TMD’s : measurement of di-jet at small x
C. Marquet
Heavy quarks production (ccbar, bbar) polarization measurement :the link with TMD ?
MPI in pp collision at high energy
2 explicit hard interactions
Thomas Kasemets, Y. Li
More interactions
Z. Conesa Del Valle, S. Porteboeuf-Houssais

11. Heavy ion initial stage
The nucleon is not free in the nucleus
I. Schienbein
Nuclear effects => (anti)-shadowing, EMC (still not understood)
Interactions between nucleons in the nucleus
nPDF’s and realistic uncertainties
Factorization in pA and AA?
Which observables can probe factorization breaking ?
Alternative to nPDF’s ?
Link with initial stage in pp
with CGC done in some region of the phase space
with MPI ?
Extension of DPS framework to pA and AA
nuclear GPD’s?
C. Hadjdakis

12. TOOLS
Event generators level
Data Fits to extract properties : nucleon tomography, PDF, nPDF, GPD (PARTON)
Impact of lattice QCD development? …