Central Exclusive Production (CEP) at LHCb Ronan McNulty (UCD Dublin) on behalf of the LHCb collaboration Meson 2018 12 June 2018, Krakow. 1 R. McNulty, CEP at LHCb
Overview 1. Central Exclusive Physics (CEP) 2. LHCb and HeRSCheL Detector 3. Analyses: • pp at 13 TeV NEW • PbPb at √ s NN = 5 TeV • pPb and Pb-p at 8 TeV 4. Physics reach for CEP 2 R. McNulty, CEP at LHCb
Elastic scattering p p σ elastic ≈ 35% σ diffractive ≈ 10% σ inelastic ≈ 55% 3 R. McNulty, CEP at LHCb
Elastic scattering Pomeron (soft) p 0 + p It’s QCD – but not as we normally see it. It’s colour-free σ elastic ≈ 35% σ diffractive ≈ 10% σ inelastic ≈ 55% 4 R. McNulty, CEP at LHCb
Experiment J/ ψ , ϒ χ c J/ ψ J/ ψ Future Theory Elastic scattering Pomeron (soft) p 0 + p It’s QCD – but not as we normally see it. It’s colour-free σ elastic ≈ 35% σ diffractive ≈ 10% σ inelastic ≈ 55% 5 R. McNulty, CEP at LHCb
Diffraction Pomeron (hard and soft) 0 + p No activity “rapidity gap” p σ elastic ≈ 35% σ diffractive ≈ 10% σ inelastic ≈ 55% 6 R. McNulty, CEP at LHCb
Central Exclusive Production (CEP) Photon / Pomeron “rapidity gap” p Photon / Pomeron “rapidity gap” p Elastic diffractive: clean environment to study vacuum, and to produce mesons. σ elastic ≈ 35% σ diffractive ≈ 10% σ inelastic ≈ 55% 7 R. McNulty, CEP at LHCb
Central Exclusive Production (CEP) QED Photo-production Double pomeron exchange Laboratory to study • physics of the vacuum • soft/hard QCD • saturation • exotics (tetraquarks, glueballs, hybrids) Experimentally: Reconstruct central system and identify rapidity gaps 8 R. McNulty, CEP at LHCb
Veto (Run 1) 7,8 TeV Rough LHCb coverage y=-10 y=-2 y=0 y=2 y=10 Elastic Scattering Single Diffraction Double Diffraction Central Exclusive Production (elastic) Central Exclusive Production (inelastic) 9 R. McNulty, CEP at LHCb
Veto (Run 2) 13 TeV Rough LHCb coverage y=-10 y=-2 y=0 y=2 y=10 Elastic Scattering Single Diffraction Double Diffraction Central Exclusive Production (elastic) Central Exclusive Production (inelastic) 10 R. McNulty, CEP at LHCb
Overview 1. Central Exclusive Physics 2. LHCb and HeRSCheL Detector 3. Analyses: • pp at 13 TeV • pPb and Pb-p at 8 TeV • PbPb at √ s NN = 5 TeV 4. Physics reach for CEP 11 R. McNulty, CEP at LHCb
The LHCb detector Int. J. Mod. Phys. A 30 (2015) 1530022 300 mrad Fully instrumented: 2 < η < 5 Veto region (Run 1): -3.5< η <-1.5 Veto region (Run 2): -10< η <-5, 5< η <10 12 R. McNulty, CEP at LHCb
13 R. McNulty, CEP at LHCb
14 R. McNulty, CEP at LHCb
High Rapidity Shower Counters at LHCb (HeRSCheL) JINST 13 (2018) P04017 15 R. McNulty, CEP at LHCb
16 R. McNulty, CEP at LHCb
Scintillators, light-guides and PMTs 17 R. McNulty, CEP at LHCb
Backward stations Installation finished in 2014 -114 m -19.7 m -7.5 m 18 R. McNulty, CEP at LHCb
Acceptance JINST 13 (2018) P04017 Showers induced by high-rapidity particles interacting with machine elements Ideally wish to veto on any activity: threshold depends on signal and noise. 19 R. McNulty, CEP at LHCb
Sample 1: Response to CEP events (QED µµ) arXiv:1806.04079 20 R. McNulty, CEP at LHCb
Sample 1: Response to CEP events arXiv:1806.04079 First bin is > 95% pure CEP QED di-muons. 21 R. McNulty, CEP at LHCb
Sample 2: Non-CEP events (J/ ψ dissociation) arXiv:1806.04079 22 R. McNulty, CEP at LHCb
HeRSCheL discriminant for physics signals arXiv:1806.04079 CEP QED looks like empty-empty events Evidence for pile-up (much reduced in p-Pb/Pb-p running) 23 R. McNulty, CEP at LHCb
Overview 1. Central Exclusive Physics 2. LHCb and HeRSCheL Detector 3. Analyses: • pp at 13 TeV • PbPb at √ s NN = 5 TeV • pPb and Pb-p at 8 TeV 4. Physics reach for CEP 24 R. McNulty, CEP at LHCb
pp / p-Pb / Pb-p / PbPb data-taking γγ γ P PP p/A p/A p-p Dominant p-Pb Enhanced Supressed Pb-Pb Strongly Enhanced Supressed enhanced 25 R. McNulty, CEP at LHCb
Vector meson production in pp collisions Data-taking Energy Integrated Paper year Luminosity 2010 7 TeV 37 pb -1 JPG 40 (2013) 045001 J/ ψ ψ (2S) 2011 7 TeV 930 pb -1 JPG 41 (2014) 055002 2015 13 TeV 204 pb -1 arXiv:1806.04079 Data-taking Energy Integrated Paper NEW year Luminosity 2011 7 TeV 945 pb -1 JHEP 09 (2015) 084 ϒ 2012 8 TeV 1985 pb -1 Data-taking Energy Integrated Paper year Luminosity 2011 7 TeV 945 pb -1 J/ ψ +J/ ψ JPG 41 (2014) 115002 J/ ψ + ψ (2S) 2012 8 TeV 1985 pb -1 26 R. McNulty, CEP at LHCb
Photo-production Note: • soft/hard transition σ ~ x λ • • g(x,Q 2 ) (down to x =2E-6) JHEP 11 (2013) 085 10.3204/DESY-PROC-2012-03/58 27 R. McNulty, CEP at LHCb
Cross-section measurement J/ ψ / ψ (2S) Purity: (found from data) 1. non-resonant bkg (1% / 16%) 2. Feeddown (5% / 0%) 3. Inelastic J/ ψ / ψ (2S) production (18% / 11%) Number of events observed d σ pN dy = Luminosity A ε L Δ y Acceptance Efficiency: (found from data) P ( n ) = µ n e − µ (MC) 1. Trigger n ! 2. Tracking & muon id. 3. Single interaction beam-crossing 28 R. McNulty, CEP at LHCb
Sample: events with two muons and no other charged or neutral activity. arXiv:1806.04079 29 R. McNulty, CEP at LHCb
Inelastic background Signal Background d σ d σ dt ~ exp( b bkg t ) Regge theory: dt ~ exp( b sig t ) b sig ~ 6 GeV − 2 b bkg ~1 GeV − 2 30 R. McNulty, CEP at LHCb
Inelastic background J/ ψ d σ dt ~ e bt Regge theory: b -slope of signal is same with/without HeRSCheL b -slope of bkg changes (because you veto higher- p T events) New Technique: N HRC = ε N sig + β (p T )N bkg N anti-HRC = [1- ε ]N sig + [1- β (p T )] N bkg ε known from QED sample Pure bkg sample obtained Subtract bkg from total => Signal derived 31 R. McNulty, CEP at LHCb
Sample purity arXiv:1806.04079 (consistent with 7 TeV pp and HERA extrapolation) 32 R. McNulty, CEP at LHCb
Cross-section measured in LHCb acceptance Systematic uncertainties factor two smaller than previous analysis 33 R. McNulty, CEP at LHCb
Differential cross-sections J/ ψ and ψ (2S) arXiv:1806.04079 NLO agrees better than LO 34 R. McNulty, CEP at LHCb
Photo-production cross-section Photo-production (HERA / fixed target) LHCb measure Gap Photon Survival Flux HERA measured power-law: Use this for W- solution (in previously measured region). LHCb measures W+ 35 R. McNulty, CEP at LHCb
Photo-production cross-section arXiv:1806.04079 J/ ψ 36 R. McNulty, CEP at LHCb
Photo-production cross-section arXiv:1806.04079: ψ (2S) 37 R. McNulty, CEP at LHCb
Pb-Pb collisions LHCb-CONF-2018-003 (in preparation) 38 R. McNulty, CEP at LHCb
Pb-Pb collisions (sensitive to nPDF and saturation) Coherent Incoherent R. McNulty, CEP at LHCb 39
Pb-Pb collisions LHCb-CONF-2018-003 (in preparation) Coherent HeRSCheL suppresses Incoherent incoherent events 40 R. McNulty, CEP at LHCb
Pb-Pb collisions LHCb-CONF-2018-003 (in preparation) 41 R. McNulty, CEP at LHCb
Dipions in pA/Ap p/A • pp->p( ππ )p has contributions from double-Pomeron-exchange (f0, f2 etc) & photoproduction ( ρ ). • Difficult to disentangle (e.g. f0 appearing as shoulder on ρ ) • Difficult to separate exclusive from dissociation • pA->p( ππ )A has enhanced photoproduction • Remarkably clean resonance • x down to 10 -6 , W up to 1 TeV 42 R. McNulty, CEP at LHCb
Overview 1. Central Exclusive Physics 2. LHCb and Herschel Detector 3. Analyses: • pp at 13 TeV • PbPb at √ s NN = 5 TeV • pPb and Pb-p at 8 TeV 4. Physics reach for CEP 43 R. McNulty, CEP at LHCb
Odderon g Bzdak, Motyka, Szymanowski, Cudell PRD 75 (2007) 094023 arXiv:0808.2216 Predictions in pessimistic-central-optimistic scenarios 44 R. McNulty, Central Exclusive Production at LHCb
Odderon-Pomeron Interference Brodsky, Rathsman, Merino, PLB461 (1998) 114. Hagler, Pire, Szymanowski, Teryaev, EPJ26 (2002) 261. Bolz, Ewerz, Maniatis, Nachtmann, Sauter, Schoening, JHEP 1501 (2015) 151. 45 R. McNulty, CEP at LHCb
9 Saturation y: 6 4 2 0 2 4 6 8 7 6 5 log 10 (Q 2 ) [GeV 2 ] 4 LHCb: Collision between one well 3 understood parton and one unknown or large 2 DGLAP-evolved parton. 1 0 -6 -5 -4 -3 -2 -1 0 -1 log 10 (x) 46 R. McNulty, CEP at LHCb
9 Saturation y: 6 4 2 0 2 4 6 8 7 6 5 log 10 (Q 2 ) [GeV 2 ] 4 LHCb: Collision between one well 3 understood parton and one unknown or large 2 DGLAP-evolved parton. J/ ψ 1 0 ρ -6 -5 -4 -3 -2 -1 0 -1 log 10 (x) 47 R. McNulty, CEP at LHCb
Exotics: Glueballs, Hybrids, Tetraquarks etc. Double-pomeron-exchange processes Glue Laboratory Inclusive X(3872) Eur.Phys.J. C72 (2012) 1972 Clean environment for meson production. Spin and parity analysis possible. 48 R. McNulty, CEP at LHCb
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