1 New results on Central Exclusive Processes (from dipion to 750 GeV bump) V.A. Khoze ( IPPP, Durham and PINP ) (Based on works with L.Harland-Lang and M.Ryskin)

2 Motivation and a bit of theoretical background. (to refresh our memory ) Selected CEP samples Summary and Outlook. LHC as a High Energy  Collider “The  - Resonance that Stole Christmas”

3 A BIT OF HISTORY Full Acceptance Detector – J. Bjorken (1991) FELIX LOI (1997) TOTEM LOI (1997) TOTEM TDR (2004) FP-420 TDR (2008) CT-PPS (2014) AFP (2011) June

4 Forward Physics at the LHC

5 CENTRAL EXCLUSIVE PRODUCTION PROCESSES

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9 “soft” scattering can easily destroy the gaps gap eikonal rescatt: between protons enhanced rescatt: involving intermediate partons H soft-hard factoriz n conserved broken Previously Subject of hot discussions : S² X

Diffractive Processes at the LHC The LHC Run I data (equivalent to the CR proton energy above the knee region) have already provided important constraints on the QCD-inspired models (and MCs). Previously successful theoretical models of the pre-LHC era did not perform well under the trial by LHC Run I fire. The Run II data will drastically improve our theoretical knowledge and, in particular, will be extremely useful in refining the models used in HE air shower physics.. 10

11 Low Mass SD Im T~  T Survival factor S 2 Optical theorem Regge poles,cuts Pomerons, d  /dt DD, DPE Welcome to the world of difficult physics! Current theoretical models for soft hadron interactions are still incomplete, and their parameters are not fully fixed. Four (ideologically close) MP- models allowed good description of the data in the ISR-Tevatron range: KMR,GLM, Ostapchenko, KP. The differences between the results of other models wildly fluctuate. P P P Reggeon Field Theory, Gribov- 1986

12 Remarkable theory expectations. Some CEP Samples Helsinki CDF Dijet/3 jet CEP. “Gluon factory”..

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16 ALICE, CDF, RHIC, CMS- new data are coming

17 (MHV-technique) More results are expected to come

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23 Dijet CEP as a gluon factory ( 2012)

24 HKR-15

25 The only MC generator which consistently incorporates the calculation of survival factors and Sudakov effects

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29 Process p p CD Near beam Detectors photon-proton LHC Extensive Program   , ee QED processes   QCD (jets..)   WW anomalous couplings   squark, top… pairs   Charginos New BSM objects, 750 GeV bump …and  p LHC as a High Energy  Collider Approved (AFP) Installed (CT-PPS) projects  First LHC data on lepton pairs, WW

30 (SuperChic 2 HKR ) C.F. von Weizsacker, 1934 E.J. Williams, 1934 E. Fermi, 1925

31 KMR-02 p p

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33 Strong interaction between colliding protons (rescattering or absorptive corrections). Even in the fully exclusive case:   Notorious survival factor. Usually, for photon-photon central production. However, in the case of absorption effects could be very small. In particular, for low absorpt. correction 2  < 0.3%. Will be additionally suppressed by the muon acoplanarity cuts. (large impact parameters ) schematically with C~0.1, KMOR, Eur.Phys.J.C19:313 (2001) Other approaches/calculations overlook polarization structure Good potential for an independent luminosity measurements

34 15 years back

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37 “The  - Resonance that Stole Christmas” ATLAS &CMS seminar on 15 Dec 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. Theoretical community –frenzy of model building: >150 papers within a month. Unprecedented explosion in the number of exploratory papers. So far most statistically significant deviation from SM at the LHC. If not a statistical fluctuation, a natural minimal interpretation: scalar/pseudoscalar resonance coupling dominantly to photons. + ~10 more 750 GeV

38 Assuming the 750 GeV- resonance survives and couples dominantly to photons : Main aim: to Resonance spin-parity, searches for CP-violating effects via asymmetry in proton distributions... HKR- Within this scenario if, then arXiv: With good missing mass resolution: separation between resonance states. Exclusive case

39 Important consequences of the production: depletion of multi-jet activity ( due to the ‘coherent’ photon component); Asymmetric jet distribution; Comparatively low transverse momentum of the resonance.

40 In principle: a possibility to search for invisible modes (dark matter particles etc), sharp peak in the missing mass spectrum but extremely challenging if not impossible H (BKMR, Eur.Phys.J. C36 (2004) ) (in the large pile-up environment) For high total width -sizeable branchings into other SM (or BSM) particles. New colourless heavy fermions: ( still relatively unconstrained, ( ) )

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42 arXiv: DURHAM with my Durham hat on M. Neubert

43 recently released. In the forward proton mode the LHC becomes a high energy photon-photon collider. Assuming that 750 GeV bump is not a statistical fluctuation it may signal the first hint of physics beyond SM at the LHC. The state-of-the-art results for the photon-photon luminosities are shown.

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46 KMR- Eur.Phys.J. C74 (2014) 2, 2756

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50 Exclusive QED Lepton Pair Production First proposed for luminometry by. V. Budnev et al, First studies of feasibility for the dimuons at the LHC: A.Shamov and V.Telnov-1998 (ATLAS TDR-99 ). Strong-interaction effects- KMOR, First observation of exclusive by CDF: New studies of exclusive leptons: CMS, ATLAS and LHCb Eur.Phys.J.C19: ,2001 Phys.Rev.Lett.98:112001,2007 Myth: Reality Pure QED process –thus, theoretically well understood (higher-order QED effects- reliably calculable). Strong interaction effects (we collide protons after all).

Could be potentially very useful for the accurate luminosity calibration 51

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