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High energy photon interactions @ LHC

Krzysztof Piotrzkowski Université Catholique de Louvain. High energy photon interactions @ LHC. LHC as a high energy gg and g p collider Tagging photoproduction at LHC Benchmark processes in gg and g p Summary/Outlook.

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High energy photon interactions @ LHC

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  1. Krzysztof Piotrzkowski Université Catholique de Louvain High energy photon interactions @ LHC LHC as a high energy gg and gp collider Tagging photoproduction at LHC Benchmark processes in gg and gp Summary/Outlook On behalf of the Louvain Photon GroupJ. de Favereau, V. Lemaître, Y. Liu, S. Ovyn, T. Pierzchała, KP and X. Rouby

  2. LHC as a High Energy gg Collider p p Phys. Rev. D63 (2001) 071502(R) hep-ex/0201027 • Highlights: • gg CM energy W up to/beyond 1 TeV (and under control) • Large photon flux F therefore significant gg luminosity • Complementary (and clean) physics to ppinteractions, eg studies of exclusive production of heavy particles might be possible opens new field of studying very high energy gg (and gp) physics DISCLAIMER: This is NOT meant for studying all photon interactions at the LHC but those for which the QCD background is strongly suppressed, as for example in the exclusive production of leptons or gauge bosons. K. Piotrzkowski - UCLouvain

  3. How measure these events? RP p scattered p p p beam Measure (gg) X in the CMS or ATLAS detector and the scattered protons using very forward detectors.. ..i.e. ‘Roman pot’ detectors put as far (> 100 m) from the IP and as close to the beam (2 mm) as possible K. Piotrzkowski - UCLouvain

  4. Forward proton trajectories (for high luminosity optics) J.de Favereau & X.Rouby K. Piotrzkowski - UCLouvain

  5. Proton Detectors at 220m from IP5: Totem …or, Proton Detectors at 420m from IP1/5: FP420 See talk by B.Cox Beampipes ~ 7 m See talk by J.Whitmore K. Piotrzkowski - UCLouvain

  6. gp interactions @ LHC – super HERA @ CERN Photon-proton interactions can also be tagged at the LHC; and have significantly higher energy reach and luminosity yield than for gg events • Example assumptions: • 0.01 < x1 < 0.1, photon tagging range • 0.005 < x2 < 0.3, Bjorken-x range for partons + use MRST2001 (at Q2=104 GeV2) for proton pdf Ex:Photon-gluon luminosity S(W)=fg(x1)fp(x2) W2=4Epx1x2 dspp/dW = Ssgg/q spp= dWSsgg/q K. Piotrzkowski - UCLouvain

  7. Selecting photon-proton events at low luminosity At LHC luminosity up to 1033 (small event pileup) rapgap signature can be used: For example, forward energy flows (into 5>|h|>3) for two hemispheres (red-photon and blue-proton) is compared for associated WH photo- production Finally, exclusivity cuts can be applied, by requiring of just two opposite tracks, for example… S.Ovyn K. Piotrzkowski - UCLouvain

  8. Exclusive lepton pairs known Done at HERA, being done at Tevatron! Key signature: Acoplanarity angle for dileptons Calibration process both for luminosity and energy scales, has striking signatures and can be well triggered and reconstructed by central detectors alone gg  mm Y.Liu DY:qq mm K. Piotrzkowski - UCLouvain

  9. T. Pierzchała (using Calchep) K. Piotrzkowski - UCLouvain

  10. T. Pierzchała (using Calchep) Minimal K. Piotrzkowski - UCLouvain

  11. Single W photoproduction: Studied at HERA Diener et al. cf. PLB 471 (2000) 411 K. Piotrzkowski - UCLouvain

  12. Higgs and top photoproduction Associated photoproduction of WH has significant cross-section at LHC and much better signal-to-background ratio; low mass region should be accesible. Important backgrounds to WH deserve their own studies, as photo-production of top pairs, WZ, or single top (as at HERA): Single top production (gq t) could be used to study anomalous gqt coupling; level of Wq background (~ 100 fb/GeV) indicates possibility of significant improvement wrt HERA K. Piotrzkowski - UCLouvain

  13. Needs large suppression, more difficult at high luminosities Q1: Can one select photon-induced events among very many pp interactions? Inclusive (pp) vs. photo-production: Examples Process/s[pb] pp gg or gp WW ~ 70 0.2 tt ~ 600 1.5 WH ~ 1.2 0.03 Q2: What about diffractive irreducible backgrounds? A: For above, only important for top photo-production (similar size) K. Piotrzkowski - UCLouvain

  14. Anomalous quartic gauge couplings K. Piotrzkowski - UCLouvain

  15. (suppressed by 10-3) assuming no background gg ZZ Two-photon production of W and Z boson pairs at LHC is ideal to study quartic gauge couplings a0W, acW, a0Z, acZ (LEP limits are poor due to limited phase space) • Should be possible to detect these events (esp. fully leptonic decays) even at highest pp luminosities K. Piotrzkowski - UCLouvain

  16. Exclusive two-photon pair production Large cross-section for WW pairs extending to very high invariant masses – possibility of searches for physics BSM T. Pierzchała (using Calchep) Muon pairs produced with invariant masses beyond 100 GeV, hence pairs of massive charged particles could be searched for K. Piotrzkowski - UCLouvain

  17. SUSY: chargino case Simple production mechanisms and decay modes: Charged Leptons and Missing energy WW is background K. Piotrzkowski - UCLouvain

  18. Summary/Outlook • High-energy (at electroweak scale and beyond) photon interactions have significant cross-sections at the LHC! • Tagging high energy photon (and diffractive) interactions at LHC can be done by supplementing central detectors with very forward spectrometers. • This offers new, exciting and complementary physics studies in parallel to ‘nominal’ ones • We should make sure that from Day 1 of LHC running triggers and selection algorithms for exclusive events in pp are in place… • We must make the best of the LHC! K. Piotrzkowski - UCLouvain

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