Photoproduction of diffractive dijets in PYTHIA 8 DIS 2021 Ilkka Helenius April 15th, 2021 In collaboration with Christine O. Rasmussen Motivation: Diffractive dijets at HERA [H1: JHEP 1505 (2015) 056] H1 VFPS data H1 VFPS data H1 VFPS data AFG γ-PDF H1 VFPS data AFG γ-PDF NLO H12006 Fit-B × 0.83 × (1+δ ) NLO H12006 Fit-B × 0.83 × (1+δNLO) H12006 Fit-B × 0.83 × (1+δ ) NLO H12006 Fit-B × 0.83 × (1+δ ) hadr hadr hadr hadr H1 4000 H1 H1 H1 [pb] [pb] 100 [pb] [pb] 60000 IP IP DIS IP 1000 DIS γp IP γp /dz 3000 /dz /dx /dx σ σ σ σ 40000 d d d d 50 2000 500 20000 1000 1.5 1.5 1.5 1.5 1 1 1 1 0.5 0.5 0.5 0.5 ratio to NLO ratio to NLO ratio to NLO ratio to NLO 0 0.2 0.4 0.6 0.8 0.01 0.015 0.020 0.2 0.4 0.6 0.8 0.01 0.015 0.02 z x zIP xIP IP IP 2 • H1 data andH1 VFPS factorization-based data NLO calculationH1 VFPS data in DISH1 (highVFPS data Q ) inAFG γ agreement-PDF H1 VFPS data AFG γ-PDF NLO H12006 Fit-B × 0.83 × (1+δ ) NLO H12006 Fit-B × 0.83 × (1+δNLO) H12006 Fit-B2 × 0.83 × (1+δ ) NLO H12006 Fit-B × 0.83 × (1+δ ) • NLO calculation overshoothadr the data in photoproductionhadr (low Q ) hadr hadr ] 2 10 1500 2 H1 H1 ) H1 H1 [pb] Factorization broken in hard diffraction at low Q similarly as in pp γ DIS 1500 DIS γp 1 γp /dy [pb] /dy [pb] /dx 100 σ σ 1000 σ d d d [pb/GeV 2 1 1000 /dQ 50 σ 500 d 500 10-1 1.5 1.5 1.5 1.5 1 1 1 1 0.5 0.5 0.5 0.5 ratio to NLO ratio to NLO ratio to NLO ratio to NLO 0.2 0.3 0.4 0.5 0.6 0.7 5 6 10 20 300.2 0.3 0.4 0.5 0.6 0.7 0 0.2 0.4 0.6 0.8 1 y x y Q2 [GeV2] γ Figure 6: Diffractive2 dijet ep cross sections in the photoproduction kinematic range differential Figure 4: Diffractive dijet DIS cross sections differentialinzIP , xIP , y and Q .Theinnererror bars represent the statistical errors. The outer error bars indicatein zIP , x theIP , statisticaly and xγ .Theinnererrorbarsrepresentthestatisticalerrors.The and systematic outer error bars errors added in quadrature. The overall normalisation unceindicatertainty the of 6% statisticalis not shown. and systematic NLO errors added in quadrature. The overall normalisation QCD predictions based on the H12006 Fit-B DPDF set, correcteuncertaintydtothelevelofstablehadrons, of 6% is not shown. NLO QCD predictions based on the H12006 Fit-B DPDF set are shown as a white line. They are scaled by a factor 0.83andto the account GRV forγ-PDF contributions set, corrected from to the level of stable hadrons, are shown as a white line. proton-dissociation which are present in the DPDF fit butThey not arein the scaled data. by aThe factor inner,0.83 lightto account for contributions from proton-dissociation which shaded band indicates the size of the DPDF uncertainties andare presenthadronisation in the DPDF corrections fit but added not in the data. The inner, light shaded band indicates the size in quadrature. The outer, dark shaded band indicates the totofal the NLO DPDF uncertainty, uncertainties also includingand hadronisation corrections added in quadrature. The outer, dark scale variations by a factor of 0.5 to 2.Foreachvariable,thecrosssectionisshownintheuppershaded band indicates the total NLO uncertainty, also including scale variations by a factor of panel, whereas the ratio to the NLO prediction is shown in0 the.5 tolower2.AvariantoftheNLOcalculationusingtheAFG panel. γ-PDF set is shown as a dashed line. For each variable, the cross section is shown in the upper panel, whereas the ratio to the NLO prediction is shown in the lower panel. 28 30 Outline Outline 1. Event generation in PYTHIA 8 2. Photoproduction, direct and resolved processes 3. Dynamical rapidity gap survival model for hard diffraction 4. Comparison to HERA data 5. Predictions for EIC and UPCs at the LHC [Figure: S. Prestel] 6. Summary & Outlook → 2 PYTHIA 8: A general-purpose Monte Carlo event generator 1. Hard scattering • Convolution of LO partonic cross sections and PDFs 2. Parton showers • Generate Initial and Final State Radiation (ISR & FSR) 3. Multiparton interactions (MPIs) • Use regularized QCD 2 ! 2 cross sections 4. Beam remnants • Minimal number of partons to conserve colour and flavour [Figure: S. Prestel] 5. Hadronization → • Lund string model with color reconnection 3 Event generation in photoproduction Direct processes b b • Photon initiator of the hard process (DIS-like) x k p σ^ • Convolute photon flux fγ with proton PDFs fi and d l ! ! bp kl+X b ⊗ p 2 ⊗ γi kl xp dσ = fγ (x) f (xp; µ ) dσ^ i p remn. • Generate FSR and ISR for proton side b Resolved processes b x remn. • Convolute also with photon PDFs xγ k bp!kl+X b ⊗ γ 2 ⊗ p 2 ⊗ ij!kl dσ = fγ (x) f (xγ; µ ) f (xp; µ ) dσ l j i xp 2 p remn. • Sample x and Q , setup γp sub-system with Wγp • Evolve γp as any hadronic collision (including MPIs) 4 Comparion to HERA photoproduction data ZEUS dijet measurement 2000 b 2 [pb] ZEUS 2 < : b • Q 1 0 GeV obs γ Pythia 8.226 x d resolved 1500 σ/ direct • 134 < Wγp < 277 GeV d jet1 17 < ET < 25 GeV jet1 jet2 • ET > 14 GeV, ET > 11 GeV 1000 b ; b − jet1 2 b • 1 < η < 2:4 b b 500 b Two contributions b 0 1.4 • Momentum fraction of partons in 1.3 1.2 1.1 1.0 b b photon b b jet1 ηjet1 jet2 ηjet2 0.9 b b E e + E e 0.8 b obs T T 0.7 b x = ≈ xγ ratio to Pythia 0.6 γ 0.5 2yEe 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 obs xγ • Sensitivity to process type [ZEUS: Eur.Phys.J. C23 (2002) 615-631] obs • At high-xγ direct processes dominate 5 Hard diffraction in PYTHIA 8 Direct: Hard diffraction in photoproduction b b • Process with a hard scale, desribed with a γ jet colour-neutral Pomeron (IP) exchange jet remn. • Experimentally identified from rapidity gap P Factorization of the diffractive cross section p p • Direct: Pomeron flux and diffractive PDFs Resolved: 2jets b γj!2jets IP 2 p dσ = f (x) ⊗ dσ ⊗ f (zIP; µ ) ⊗ f (xIP; t) direct γ j IP b b • Resolved: photon PDFs γ remn. jet σ2jets = b( ) ⊗ γ ( ; µ2) ⊗ σij!2jets ⊗ IP( ; µ2) ⊗ p( ; ) 3 d resolved fγ x fi xγ d fj zIP fIP xIP t jet 7 remn. P p p 6 2. Reject events where MPIs in γp system (MPI) 3. Evolve γIP system, allow MPIs Hard diffraction in PYTHIA 8 Direct: Hard diffraction in photoproduction b b • Process with a hard scale, desribed with a γ jet colour-neutral Pomeron (IP) exchange jet remn. • Experimentally identified from rapidity gap P Dynamical rapidity gap survival model p p 1. Generate diffractive events with dPDFs (PDF) Resolved: b b γ remn. jet 3 jet 7 remn. P p p 6 3. Evolve γIP system, allow MPIs Hard diffraction in PYTHIA 8 Direct: Hard diffraction in photoproduction b b • Process with a hard scale, desribed with a γ jet colour-neutral Pomeron (IP) exchange jet remn. • Experimentally identified from rapidity gap P Dynamical rapidity gap survival model p p 1. Generate diffractive events with dPDFs (PDF) Resolved: 2. Reject events where MPIs in γp system (MPI) b b γ remn. jet 3 jet 7 remn. P p p 6 Hard diffraction in PYTHIA 8 Direct: Hard diffraction in photoproduction b b • Process with a hard scale, desribed with a γ jet colour-neutral Pomeron (IP) exchange jet remn. • Experimentally identified from rapidity gap P Dynamical rapidity gap survival model p p 1. Generate diffractive events with dPDFs (PDF) Resolved: 2. Reject events where MPIs in γp system (MPI) b b 3. Evolve γIP system, allow MPIs γ remn. jet 3 jet 7 remn. P p p 6 Hard diffraction in PYTHIA 8 Direct: Hard diffraction in photoproduction b b • Process with a hard scale, desribed with a γ jet colour-neutral Pomeron (IP) exchange jet remn. • Experimentally identified from rapidity gap P Dynamical rapidity gap survival model p p 1. Generate diffractive events with dPDFs (PDF) Resolved: 2. Reject events where MPIs in γp system (MPI) b b 3. Evolve γIP system, allow MPIs γ remn. jet 3 jet Implemented from PYTHIA 8.235 onwards 7 remn. [I.H. and C.O. Rasmussen, EPJC 79 (2019) no.5, 413] P Same idea applied for pp collisions at the LHC p p [C.O. Rasmussen and T. Sjöstrand, JHEP 1602 (2016) 142] 6 Comparisons to HERA data H1: [EPJC 51 (2007) 549] ZEUS: [EPJC 55 (2008) 177] Cuts H1 ZEUS 12 2 2 b Data 5 Q [GeV ] 0.01 1.0 10 PDF max [pb/GeV] [pb/GeV] MPI 4 X jet1 W b M 8 b /d E [GeV] 5.0 7.5 σ /d ; b b d T min 3 b σ d 6 b b jet2 2 b Data 4 E [GeV] 4.0 6.5 b T;min PDF 1 MPI 2 b b xmax 0.03 0.025 0 0 IP 2 2 1.5 1.5 1 b b b b 1 b b b b b b PYTHIA setup MC/Data 0.5 MC/Data 0.5 170 180 190 200 210 220 230 240 15 20 25 30 35 40 45 W [GeV] MX [GeV] • dPDFs from H1 fit B LO • PDF selection overshoots the data by 20–50 % • γPDFs from CJKL ref • Impact of the MPI rejection increases with W • pT0 = 3:00 GeV/c (Tuned to inclusive • Stronger suppression in H1 analysis due to jets charged particle data looser cuts on E and xIP )More MPIs T from γp at HERA) 7 Comparisons to HERA data H1: [EPJC 51 (2007) 549] ZEUS: [EPJC 55 (2008) 177] Cuts H1 ZEUS 500 2 2 b b [pb] Data [pb] Data 600 Q [GeV ] 0.01 1.0 PDF PDF max obs γ obs γ x x 400 500 MPI MPI /d /d b jet1 σ σ d d 400 300 E [GeV] 5.0 7.5 b T;min b 300 jet2 b 200 E [GeV] 4.0 6.5 200 T;min b b 100 100 b b max b x 0.03 0.025 0 2.02 IP 2 2 1.8 1.5 1.6 1.4 1 b b b b 1.2 1 b b b b b MC/Data 0 5 MC/Data 0.8 .