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High Energy Photon Interactions at the LHC

Krzysztof Piotrzkowski. High Energy Photon Interactions at the LHC. Introduction: LHC as a high energy gg and g p collider and tagging with forward protons Gauge boson photoproduction Luminosity measurement with lepton pairs Associated Higgs photoproduction Comments & Outlook.

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High Energy Photon Interactions at the LHC

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  1. Krzysztof Piotrzkowski High Energy Photon Interactions at the LHC Introduction: LHC as a high energy gg and gp collider and tagging with forward protons Gauge boson photoproduction Luminosity measurement with lepton pairs Associated Higgs photoproduction Comments & Outlook Team: J. de Favereau, O. Militaru, S.Ovyn, T. Pierzchala, X. Rouby and M. Vander Donckt

  2. LHC as a High Energy gg Collider p p • 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 Phys. Rev. D63 (2001) 071502(R) hep-ex/0201027 Observation: Provided efficient measurement of forward-scattered protons one can study high-energy gg collisions at the LHC K.Piotrzkowski - Louvain University

  3. 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. This IS meant for studying production of selected final states in photon interactions at the LHC. K.Piotrzkowski - Louvain University

  4. Kinematics/gg Luminosity VirtualityQ2 of colliding photons vary between kinematical minimum = Mp2x2/(1-x) where x is fraction of proton momentum carried by a photon, and Q2max ~ 1/proton radius2 W2 = s x1 x2 Photon flux 1/Q2 Q2 - Q2min sq2/4 for x>0.0007, Q2<2GeV2 protons scattered at `zero-degree’ angle Use EPA à la Budnev et al.* * error found in the elastic (Q2 integrated) g flux for protons! dWSgg =‘gg : pp luminosity’ Note: it’s few times larger if one of protons is allowed to break up K.Piotrzkowski - Louvain University

  5. Problem: Same signature (one or two very forward protons) has also central diffraction (i.e. pomeron-pomeron scattering) in strong interactions Two processes might interfere, however the transverse momentum of the scattered protons are in average much softer in two-photon case Q2 < 0.01 GeV2 a) `true’ distributions; b) distributions smeared due to beam intrinsic pT; all plots normalized for pT2 < 2 GeV2 Assuming ultimate pT resolution  100 MeV; i.e. neglecting detector effects pT gives powerful separation handle provided that size of gg and pomeron-pomeron cross-sections are not too different K.Piotrzkowski - Louvain University

  6. gg Physics Menu - Highlights H0 s ~ 80 pb W+W- s ~ 10 pb (at W=MH=200 GeV) All ? tt s ~ 1 pb s ~ 100-500 nb + SUSY processes K.Piotrzkowski - Louvain University

  7. SUSY Significant production rates and very clean signatures available - both transverse and longitudinal missing energy for single tags • H/A bosons -ggbbH/A? • Surprises??? K.Piotrzkowski - Louvain University

  8. Photiadevelopment J. de Favereau • Use Pythia6.152 to simulate ggandgpinteractions • Introduce photon spectra for proton beams (forggand gpcase) with proper normalization (pp cross-section calculations) • Elastic and inelastic production possible (but no p dissociation simulation yet) • Direct photo-production • Run Photia with Oscar/Orca K.Piotrzkowski - Louvain University

  9. CMS efficiency J. de Favereau First look at leptonic Final states : p -> XW -> l Efficiency at L1 and HLT (ORCA 8_1_2) L1 : 48 % HLT : 29 % ! No endcap muons in orca : HLT efficiency is underestimated ! p K.Piotrzkowski - Louvain University

  10. Dk,l=(0,0)/(-0.02,0)/(0.02,0)/ (0,0.02)/(-0.02,0.02) J. de Favereau & T. Pierzchala ds/dpT [pb/GeV] Ex.: gg at 1 TeV Anom/SM pT [GeV] Anomalous WW production (II) At a generator level so far: • k changes mostly normalization, l also affects the pT shape • From statistical point of view better than LEP2 limits seems feasible • Looking also into a single W photoproduction K.Piotrzkowski - Louvain University

  11. T.Pierzchala = x K.Piotrzkowski - Louvain University

  12. T.Pierzchala = x K.Piotrzkowski - Louvain University

  13. T.Pierzchala ds/dpT at W=300 and 800 GeV SM ac=10-6GeV-2ac=4.10-6GeV-2 ac=10-6GeV-2 ac=4.10-6GeV-2 K.Piotrzkowski - Louvain University

  14. Gauge boson photoproduction • Hope for large sensitivity in QGC, will study WW anomalous production for LED and strong W sector gg  gg (also not possible at tree level), eg. sensitivity to massive monopole contributions (large pT physics) gg  ZZ suppressed in SM (~10-3), good place to look for BSM K.Piotrzkowski - Louvain University

  15. T.Pierzchala = x K.Piotrzkowski - Louvain University

  16. Precise luminosity measurements at hadron colliders: QED at work Old and successful idea – use a process with the precisely known cross-section and measure its rate – in 1973 Budnev et al. proposed two-photon lepton pair production for pp collisions At the QED only level (protons are point-like charges) the calculations are as precise as for Bhabha scattering, for example, and if the pair pT is small the hadronic corrections are negligible, at 10-4 level – Khoze et al. EPJ C19 (2001) 313. In the gg l+l- case the precision is limited by the experimental uncertainties! K.Piotrzkowski - Louvain University

  17. Main features of the two-photonprocess Large cross-section + clear signatures Example forelectron energy: i=15GeV photon energy: 1, 2me2/ (5GeV, 50eV) forward production dominates pair mass: W2me (< 20MeV) pair pT: PTme (< 20MeV) single electron pT: pT(1),pT(2)me acoplanarity angle:   PT/pT leptons are back-to-back And nothing else produced! K.Piotrzkowski - Louvain University

  18. Forward e+e-pairs in pp Most important distributions for the signal and the backgrounds KP & A. Shamov ‘99: K.Piotrzkowski - Louvain University

  19. Luminosity with very forward pairs in CASTOR QED process for luminosity monitoring (KP & D.Bocian) pp  pp e+e- Electrons are in forward range 5 <  < 7 Cross section ~barns EM calorimetry essential Tracking important (T2?) Can get the luminosity to 1-2%?  small angles of few mrad  high rates of few kHz s varies strongly with pair energy backgrounds K.Piotrzkowski - Louvain University

  20. Forward e+e- pairs in CASTOR in ion collisions at the LHC Recent studies: published in Acta Phys. Pol. B. Use modified LPAIR (ME generator of lepton pairs by Vermaseren), i.e. Introduce new type of projectile, so far only elastic (form-factor) High rates for e+e- pairs within the CASTOR acceptance Excellent candidate for the luminosity measurement for ion collisions K.Piotrzkowski - Louvain University

  21. pp luminosity Try to get first estimate on the systematics: sensitivity to energy scale + resolutions Energy resolution seems to be not too critical (D. Bocian) K.Piotrzkowski - Louvain University

  22. Another possibility (Shamov&Telnov): Measure centrally produced pairs in a given energy range Needs central triggering, hence large lepton pT Cross-section is small – could be used for making final Luminosity calibration From ATLAS TDR K.Piotrzkowski - Louvain University

  23. Calibration&monitoring tool: two-photon ee/mm production Setting W scale + background control + elastic/inelastic separation, and RP luminosity measurement Elastic di-muons Single p tags (ie. x>0.01) + pT(m)>5 GeV |h(m)|<2.5 m-pair invariant mass Note: It does not assume proton trigger! K.Piotrzkowski - Louvain University

  24. Tagging gp interactions - super HERA at CERN Given tagging capability an exciting possibility of measuring photon-proton interactions at the LHC opens up: - significantly higher energy reach and luminosity yield than for gg events is expected • Initial assumptions: • 0.01 < x < 0.1, photon tagging range • 0.005 < x < 0.3, Bjorken-x range for quarks and gluons • (arbitrary for the moment, could be extended) + use MRST2001 (at Q2=104 GeV2) for partons K.Piotrzkowski - Louvain University

  25. Photon-gluon luminosity spectra Note: at Wgg > 400 GeV photon-gluon luminosity is about 10% of the nominal pp K.Piotrzkowski - Louvain University

  26. Photon-quark luminosity spectra Note: at Wgq > 300 GeV photon-quark luminosity is about one third of the nominal pp (and still significant beyond 1 TeV) K.Piotrzkowski - Louvain University

  27. gp Physics Menu - Highlights s ~ 25 pb at W=400 GeV tt s ~ 40 pb for gq Wq at W > 200 GeV Wq • • anomalous W and Z production at Wgq  1 TeV • top pair production - top charge + mass determination? • single top production and anomalous Wtb vertex • SM BEH - for example,g b  H b, g q H W q • SUSY studies (complementary to the nominal ones) - • H+ t production (and H++), b and t spairs, t~c pair, ... • Exotics: compositness, excited quarks, ... K.Piotrzkowski - Louvain University

  28. Diener et al. Already studied at HERA cf. PLB 471 (2000) 411 K.Piotrzkowski - Louvain University

  29. Working position Bellow Detectors a few m apart Comments/Outlook Exciting physics prospects for g interactions @ LHC; RP detectors Essential – full FS reconstruction, background control, trigger, etc. 420m important too, mostly to increase acceptance/event statistics Note: HERA tagging method ‘without’ RP! Routinely used at high L… Parking position RF screen Note: This is an efficient method for non-elastic protons (f!) K.Piotrzkowski - Louvain University

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