1. Valery Khoze (IPPP, Durham & PNPI, St.Petersburg)
Krakow, 5-8 September, 2017
PHOTON-PHOTON COLLISIONS AT THE LHC
(very selected topics)
Valery Khoze (IPPP, Durham & PNPI, St.Petersburg)
(in collaboration with Lucian Harland-Lang and Misha Ryskin)
5-8

2. Introduction and Motivation. SuperChic- MC and Survival Guide
Photon-initiated processes with rapidity gaps
Summary and Outlook.
The photon PDF and photon-photon Luminosities

3. Antoni, Mariola,Krzysztof, Mateusz, Daniel , Piotr, Rafal,Marta,Boris

4. Modelling Exclusive Photon-Photon collisions

5. In fact, the situation is more complicated due to the effects caused by the polarization structure of the production amplitude.

6. Durham Group-KMR
Tel-Aviv Group- GLM
S. Ostapchenko…
Lonnblad & Zlebcik

7. + absorptive/rescattering effects- survival factor KMR-2001 X 
‘Large’ Pomeron size in the
production of the small size objects.
+ absorptive/rescattering effects- survival factor
KMR-2001

13. Photon-photon Luminosities

14. Not so long ago
worrisome range

16. almost sufficient for the LHC pheno purposes
Including dominant elastic component strongly reduces the PDF uncertainty-
almost sufficient for the LHC pheno purposes

17. (pre ‘750-explosion’) 
HKR-16
HKR,

18. MNSZ, PRL 117, (2016),
LUXqed-photon PDF determined in terms of measured EM proton structure functions F2 and FL.
Currently the most precise calculation when considering inclusive production processes

19. Comparison with LUXqed
Agreement between HKR and LUXqed within 10-20% in the phenomenologically
relevant region

20. Photon-initiated processes with rapidity gaps
Caveat: in the real life, when studying photon-photon processes
we as a rule need to go beyond the inclusive photon PDF ( event selection: rapidity gaps, isolation cuts..)
HKR arXiv:

21. (satisfies veto)
(RG veto in DGLAP equation)

22. Suppression due to LRG veto.
phenomenological objects only-factorization
explicitly violated by rescattering effects

24. gg collisions- applicationsCD
Near beam
Detectors
Process
Installed (AFP)
Installed (CT-PPS)
projects
…and p
…and A
Extensive Program
  , ee QED processes
  QCD (jets..)
  WW anomalous couplings
  squark, top… pairs
  Charginos (natural SUSY)
 New BSM objects
photon-proton/nucleus LHC

25. Diphoton X-Pair Production
HKSS, arXiv:
electroweakinos
(compressed mass BSM scenarios)

26. Challenges Tim Matin, EPS-17, ArxiV:1708.04053
(Mateusz)
(KMR, KMOR-2001)
Mateusz Dyndal, Laurent Schoeffel
Phys.Lett. B741 (2015) 66-70

27. Checked explicitly that taking this model for proton overlap we arrive
To our understanding is essentially a simplified version of the SuperChic (KMR) model for absorption.
Evaluation of Survival factor in SuperChic2 is based on measured elastic cross section.
The difference is due to the fact that SuperChic explicitly incorporates the impact parameter dependence of the dimuon production amplitude.
KMRO-2001
Checked explicitly that taking this model for proton overlap we arrive
at a very similar result to SuperChic.
In any case this is worth revisiting (many sides, many sides ).
'EPA + finite size corrections'    
section 4.3 of 
Usual Suspects: ( SD simulation...)

28. Summary & Outlook
A formalism (HKR-16) is developed allowing to describe photon-induced events with LRG in terms of modified photon PDF with consistent implementation of the soft survival effects.

32. “The - Resonance that Stole Christmas 2015”
750
GeV
ATLAS &CMS seminar on 15 Dec. 2015
The ATLAS announcement of a 3.6  local excess in diphotons with invariant mass ~750 GeV
in first batch of LHC Run –II data, combined with CMS announcing 2.6  local excess.
EW Moriond,
Theoretical community –frenzy of model building: >150 papers within a month.
Unprecedented explosion in the number of exploratory papers.
(More than 600 papers)
If it were not a statistical fluctuation,
a natural minimal interpretation:
scalar/pseudoscalar resonance coupling dominantly to photons.
As an outcome -great improvement in our understanding of photon PDF and
development of the effective tools for analysing potential diphoton resonances.