Summary from the AFP Physics Review

1. Summary from the AFP Physics Review • Reviewers: Phil Allport, Daniel Froidevaux, Richard Hawkings, Giuseppe Iaccobucci, Paul Newman • Two main documents provided in advance: • AFP contribution to Phase-I upgrade Letter of Intent • ‘Physics cases within the AFP project’ (ATL-COM-PHYS-2012-775) • Review committee consulted with 3 prominent theorists in run-up to review • Physics review 13:00-18:00 on Tuesday 18th September • https://indico.cern.ch/conferenceDisplay.py?confId=208822 • Many thanks to all participants for an interesting and lively discussion Richard Hawkings AFP Kick-off meeting, 20/09/2012 Richard Hawkings

2. Review charge from ATLAS management • We ask the review committee to address the following charge in a brief written report: • Briefly comment on the physics case of the AFP project as put forward by the proponents, in terms of reach both for standard model diffractive physics and new physics • Evaluate: • The significance of that physics case, in the context of the overall ATLAS program • The feasibility of achieving the physics goals, e.g. in light of detector performance requirements and required data sets • The capabilities of the analysis team to achieve the physics goals, e.g. in light of the level of commitment to the proposed program and in light of the effort that will required to execute the program in all aspects from data quality, calibration, and alignment, through simulation and reconstruction, to final data analysis Richard Hawkings

3. Main physics case presented • Two physics studies presented in some detail, with full simulation of ATLAS detector + transport of protons to AFP with parameterised detector response • Measurements at high pileup (μ=23 or 46), requiring high int-L (30-300 fb-1) • QED process: γγ→WW→lvlv (high mass) • Sensitivity to anomalous QGC a0W two orders of magnitude better than in central production • Probe of BSM physics which may affect couplings • Exclusive dijet production (medium mass) • Need 10-6 rejection of inclusive dijets to see signal • Exploiting kinematic correlations, ‘missing mass’ • Some discussion of other physics cases • QCD measurements – diffraction, double pomeron exchange, W-asym, jet-gap-jet to probe BFKL • BSM searches – γγ complementary to central • ‘Invisible’ decays e.g. magnetic monopoles • Extra b/g rejection from missing-mass • Need for level-1 AFP trigger Richard Hawkings

4. Summary of feedback from theorists • Consistent picture from all three theorists consulted • AFP could enrich the physics program of ATLAS • Interesting program of diffractive physics could be carried out • In particular, strong Central Exclusive Production (CEP), pp→pXp • Recent Tevatron measurements; active interchange with theorists • But… puzzled by the ‘thin’ physics case made in the AFP note • This is not enough by itself to justify the resources needed for AFP • Authors acknowledge these are only examples to demonstrate detector potential / performance – not a comprehensive survey • Much more could be developed, e.g. low-luminosity diffraction studies, heavy flavour, charged particle pair-production • Potential needs to be set in context of full ATLAS physics program • Debate on relevance of aQGC studies in light of current / future VV results • Should emphasize what can be done ‘better, sooner, uniquely’ by AFP • ( Interesting to study 126 GeV Higgs in CEP, but not possible with AFP ) Richard Hawkings

5. Feedback from reviewers I – physics concerns • Reviewers thank the AFP proponents for the interesting and detailed studies presented • In particular promising detailed simulation work on aQCG and exclusive dijets • However, these studies by themselves do not constitute a convincing physics case for AFP • There is potential for a broad physics case, but it has not yet been made • In particular, the diffractive / soft-QCD physics program needs to be better developed • More on this later … Richard Hawkings

6. Feedback II – technical concerns • The measurements studied in detail look feasible, with some caveats: • Background from ‘random’ coincidences of forward protons from pileup • Large uncertainties (factor 5-10) from modelling of diffractive processes in Pythia8 – what could be learned from data, in particular from ALFA measurements? • Need to develop methods for calibration measurements of SM processes • E.g. measurement of SM WW process, although rate is challenging (lvqq not lvlv) • Strategy to calibrate 10-6 rejection needed for excl-dijets with small systematics? • Acceptance depends on poorly-known proton ‘survival probabilities’ • Is trigger (esp. LVL1) from AFP feasible? (needed for ‘invisible’ processes) • Using timing detectors with coarse segmentation to implement mass cut • Trigger rates, robustness against background? • Trigger strategy for tagged processes relying on central activity at low mass • General concern about beam backgrounds in harsh environment of AFP • Beam-halo, showers from collimators - ALFA data suggests worse than expected • Study together with LHC machine people – what can be learned from simulations? • Need full simulation of AFP in ATLAS framework to study proton overlap b/g Richard Hawkings

7. Feedback III – strengthening the physics case • AFP program needs to be seen in context of full ATLAS physics program • Rather than isolated measurements – demonstrate complementarity and the unique gain brought by AFP • Particularly for BSM searches where quantitative comparisons are needed • Clear need to strengthen the soft-QCD/diffractive physics studies over the full mass range • Some suggestions for this… • Consider single diffractive disassociation (pp->Xp) and DPE (pp→pXp) • Assess accessible kinematic range (ζ, pT, zpom) and calculate rates for representative processes (e.g. di-jets, W/Z, direct-γ, heavy flavour) • How does reach evolve from low-luminosity to high luminosity/high-pileup, including trigger strategy? • Will help put AFP potential into context with previous and planned measurements • E.g. ATLAS, CMS, TOTEM, ALFA in corresponding timeframe Richard Hawkings

8. Feedback IV – strengthening the community • The AFP community, and the fraction engaged in physics studies, are small • Encouraging signs of new people joining and becoming effective, but many names are ‘just’ commitments to get involved at a future date • Need larger AFP commitment to ‘data preparation’ (e.g. calibration) and engagement with other areas of ATLAS (e.g. trigger) as part of physics preparation • Need to enlarge the community from outside the existing AFP team to ensure a broad physics program is covered in a credible way • Suggest to organise a workshop open to all ATLAS and the theory / phenomenology community to gauge and generate interest • Suggest ‘short-term’ (6-12 mth) milestones where concrete progress needed • AFP physics community should get involved in ALFA data analysis (particularly on diffractive physics) both to get experience with ATLAS environment (e.g. software) and to refine the predictions (e.g. pileup, backgrounds) for AFP • This will also help ALFA, and strengthen the overall forward physics effort in ATLAS • Development of MC generators, in particular γγ without proton disruption • Development of AFP simulation and integration with ATLAS infrastructure • Quantitative studies of possibilities in QCD and BSM physics (see previous slide) Richard Hawkings

9. Summary • Encouraging progress and impressive studies shown – physics measurements with AFP look feasible, including at high luminosity • A number of points require further studies to consolidate this, e.g.: • Background from LHC beam halo and collimators • Robustness of AFP tag rejection against non-diffractive processes • Strategy and rates for LVL1 trigger where needed • However, a coherent and compelling physics case has not yet been presented • A case could potentially be made, involving more focus on on soft-QCD/diffractive physics, BSM searches, and a better integration with the rest of the ATLAS physics program • Such a broader physics program will need a larger team of physicists actively engaged in (preparation for) physics analysis • Need to enlarge the currently active AFP physics community • Engagement with ALFA program would be very constructive Richard Hawkings