Rope Hadronization, Geometry and Particle Production in pp and p A Collisions Christian Bierlich Advisors: G¨ osta Gustafson, Leif L¨ onnblad, Torbj¨ orn Sj¨ ostrand. Other collaborators: Jesper Roy Christiansen, Andrey Tarasov. Lund University Jan 27, 2017 Defense of Thesis for the degree of Doctor of Philosophy Christian Bierlich (Lund) Ropes and Particles Jan 27, Thesis defense 1 / 21
Introduction Quarks and gluons are the building blocks of protons and neutrons. They are ”confined” by the strong nuclear force. The Quark Gluon Plasma (QGP) is a hypothesized state of deconfined quarks and gluons existing at high pressure/temperature. QGP investigated in heavy ion experiments since 1980s. Recent data from LHC has revealed QGP–like behaviour in pp and p A . Question: Can ”QGP–effects” be modeled without assuming a thermalized liquid? Find a method for extrapolating pp to p A and AA . 1 Develop a microscopic description of small system QGP behaviour. 2 Combine and compare to data. 3 Compare to existing, macroscopic predictions. 4 This thesis is concerned with the two first steps. Christian Bierlich (Lund) Ropes and Particles Jan 27, Thesis defense 2 / 21
Overview DIPSY and pp extrapolations (arXiv:1607.04434 [hep-ph]). Geometry of a p A collision. 1 Parametrization of colour fluctuations. 2 Particle production and comparison to data. 3 The Rope Hadronization model (arXiv:1412.6259 [hep-ph] and arXiv:1507.02091 [hep-ph]). Corrections to hadronization in dense environments. 1 Effects on strangeness. 2 Comparison to data. 3 String shoving (arXiv:1612.05132 [hep-ph]). ”The ridge”. 1 Pressure from string overlaps. 2 Results. 3 Christian Bierlich (Lund) Ropes and Particles Jan 27, Thesis defense 3 / 21
Extrapolation from pp to p A Big Picture goal: A general purpose MC event generator for HI built on microscopic models only. Obvious difference from small → large systems: Geometry. A good description of basic event properties is essential. We need space–time description of event structure. Extrapolation = geometry + colour fluctuations (CF). CF based on the DIPSY initial state model. Result: A model for extrapolating Pythia pp to p A events. From CB, Gustafson and L¨ onnblad, arXiv:1607.04434 [hep-ph]. Christian Bierlich (Lund) Ropes and Particles Jan 27, Thesis defense 4 / 21
Glauber models and the wounded cross section Reproduce ”centrality” ∝ forward particle production Standard Glauber, absorptive channels only: d σ w d 2 b = d σ abs = 2 � T ( b ) � − � T ( b ) � 2 d 2 b Diffraction contributes in the forward direction. Wounded nucleons updated with CF (SD + DD in Good–Walker). d σ w d 2 b = d σ abs d 2 b + d σ SD , t d 2 b + d σ DD = d 2 b � � � T � 2 2 � T � p , t − p . t Christian Bierlich (Lund) Ropes and Particles Jan 27, Thesis defense 5 / 21
Parametrization of colour fluctuations Pioneered in Glauber-Gribov formalism (Alvioli and Strikman: arXiv:1301.0728 [hep-ph]) : Much faster than full DIPSY – feasible to do HI simulation. Modified parametrization: Fitted with pp data only. σ 2 ( σ/σ 0 − 1) 2 log 2 ( σ/σ 0 ) � � � � 1 P tot ( σ ) = exp − → P tot ( σ ) = √ exp − Ω 2 2Ω 2 σ + σ 0 Ω 2 π 0.030 DIPSY GG Ω = 0.37 0.025 GG Log-normal Ω = 0.25 GG Log-normal Ω = 0.33 0.020 P winc ( σ ) 0.015 0.010 0.005 0.000 0 50 100 150 200 σ [mb] Christian Bierlich (Lund) Ropes and Particles Jan 27, Thesis defense 6 / 21
Types of wounded nucleons We obtain: The number of wounded nucleons incl. diffractive excitation. 1 Given a T ( b ) assumption, which are which! 2 We now have input to a model for particle production – FritiofP8. 10 0 Black Disk GG Ω =0 . 82 GG Log-normal Ω =0 . 43 10 -1 2x2 model -2 10 P ( N w ) -3 10 -4 10 -5 10 0 10 20 30 40 50 60 N t w inc Christian Bierlich (Lund) Ropes and Particles Jan 27, Thesis defense 7 / 21
Results (Data: ATLAS) Very good agreement with centrality observable. ”Absorptive” overshoots. Measuring the exact region where diffractive excitation is important. Sum E ⟂ , − 4 . 9 <η < − 3 . 2 , p ⟂ > 0 . 1 GeV 10 -1 FritiofP8 Absorptive dN/ ( Nd Σ E ⟂ ) [GeV − 1 ] DIPSY 10 -2 10 -3 10 -4 10 -5 10 -6 0 20 40 60 80 100 120 140 160 180 Σ E ⟂ [GeV] Christian Bierlich (Lund) Ropes and Particles Jan 27, Thesis defense 8 / 21
b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b Multiplicity Data: ATLAS Reproducing central collisions well. Does better than DIPSY in central collisions. Future: Implementation by ATLAS would be better. Centrality 0 - 1 % Centrality 10 - 20 % 60 dN / d η dN / d η 100 Data Data 50 FritiofP 8 FritiofP 8 Absorptive Absorptive 80 DIPSY 40 DIPSY 60 30 40 20 20 10 0 0 1 . 4 1 . 4 1 . 3 1 . 3 MC/Data 1 . 2 MC/Data 1 . 2 1 . 1 1 . 1 1 . 0 1 . 0 0 . 9 0 . 9 0 . 8 0 . 8 0 . 7 0 . 7 0 . 6 0 . 6 0 . 5 0 . 5 - 2 - 1 - 2 - 1 0 1 2 0 1 2 Christian Bierlich (Lund) Ropes and Particles Jan 27, Thesis defense 9 / 21
What to do in busy events? Events as just described are quite busy. Strings are fluxtubes i.e. confined fields. Interference in overlap regions must be treated. From CB, Gustafson, L¨ onnblad and Tarasov, arXiv:1412.6259 [hep-ph] and CB and Christiansen, arXiv:1507.02091 [hep-ph]. Christian Bierlich (Lund) Ropes and Particles Jan 27, Thesis defense 10 / 21
Experimental motivation Hadronic flavour description works for e + e − (Data: SLD, LEP and PDG avg.) . Not even inclusively in pp (Data: ATLAS, CMS, ALICE and LHCb) . 0.6 0 . 7 Ratio of integrated yields 7000 GeV Data Ratio of integrated yields LEP 91.2 GeV Data 0.5 0 . 6 Dipsy D IPSY Rope 0 . 5 0.4 Pythia 8 Def. D IPSY 0 . 4 0.3 P YTHIA 8 0 . 3 0.2 0 . 2 0.1 0 . 1 0.0 0 . 0 1.4 1 . 3 1.2 1 . 2 1 . 1 1.0 MC/data MC/data 1 . 0 0.8 0 . 9 0 . 8 0.6 0 . 7 0.4 0 . 6 0.2 0 . 5 K ± /π Λ /K 0 p/π Λ /K 0 Ξ / Λ Ω / Ξ p/π K/π φ/K Ξ / Λ Ω / Ξ s s Christian Bierlich (Lund) Ropes and Particles Jan 27, Thesis defense 11 / 21
String Hadronization (See e.g. hep-ph/0603175) Non-perturbative phase of final state. Confined colour fields ≈ strings with tension κ ≈ 1 GeV/fm. − π m 2 � � Breaking /tunneling with P ∝ exp ⊥ gives hadrons. κ Longitudinal components from: � − bm 2 � f ( z ) ∝ z − 1 (1 − z ) a exp ⊥ . z a and b related to total multiplicity. Flavours determined by relative probabilities: ρ = P strange , ξ = P diquark P u or d P quark Probabilities are related to κ via tunneling equation. Christian Bierlich (Lund) Ropes and Particles Jan 27, Thesis defense 12 / 21
Dipole coherence effects Overlapping gives coherence effects. The simplest example: Two q ¯ q pairs act coherently. Two distinct possibilities: c 1 c 1 ¯ c 2 c 2 ¯ Case (a), c 1 = c 2 : r ⊕ r ¯ r ⊕ ¯ r Case (b), c 1 � = c 2 : r ⊕ b ¯ r ⊕ ¯ ¯ g g b Christian Bierlich (Lund) Ropes and Particles Jan 27, Thesis defense 13 / 21
Rope formation Multiplet structure from SU(3) Random Walk procedure (Biro et al. Nucl.Phys.B 245 (1984) 449–468) Highest multiplet gets larger effective string tension: κ �→ ˜ κ = h κ from number of overlapping strings. Calculable as secondary Casimir operator of multiplet. κ/κ = C 2 (multiplet) κ ∝ C 2 ⇒ h = ˜ 1 GeV/fm Confirmed on the lattice, static case (Bali: arXiv:hep-lat/0006022) . Christian Bierlich (Lund) Ropes and Particles Jan 27, Thesis defense 14 / 21
Effect on hadronization parameters Strange quark breakup supression: − π ( m 2 s − m 2 � u ) � ρ = exp . κ 1 . 2 ρ ˜ Large effect on ˜ ξ 1 . 0 hadronic flavours. a ˜ ˜ b Baryons also affected 0 . 8 Effective parameter by junctions. 0 . 6 Smaller effect on 0 . 4 hadron p ⊥ and multiplicity 0 . 2 (tunable). 0 . 0 1 2 3 4 5 6 7 h (Enhancement of string tension) Christian Bierlich (Lund) Ropes and Particles Jan 27, Thesis defense 15 / 21
b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b b Effect in pp I (Data: STAR and CMS) Improvement inclusively. Tail of p ⊥ spectrum not fully understood. Linked to ”flow” effects. Better observable which isolates strangeness and baryons. p / π + Ratio p ⊥ distribution √ s = 200 GeV Λ /K 0 S versus transverse momentum at √ s = 7000 GeV 0 . 8 N ( p ) / N ( π + ) S ) N ( Λ ) / N ( K 0 1 . 4 Data 0 . 7 Rope 1 . 2 0 . 6 DIPSY 1 Pythia 0 . 5 0 . 8 0 . 4 0 . 6 0 . 3 Data 0 . 4 Rope 0 . 2 0 . 2 DIPSY 0 . 1 Pythia 0 0 - 0 . 2 1 . 4 1 . 4 MC/Data 1 . 2 MC/Data 1 . 2 1 1 0 . 8 0 . 8 0 . 6 0 . 6 1 2 3 4 5 6 7 0 2 4 6 8 10 p ⊥ [GeV] p T [GeV/ c ] Christian Bierlich (Lund) Ropes and Particles Jan 27, Thesis defense 16 / 21
Effect in pp II (ALICE: arXiv:1606.07424 [nucl-ex]) Strangeness enhancement for central events. Signal linked to Quark Gluon Plasma in Heavy Ion Physics. Not shown: (lack of) baryon enhancement in data. Christian Bierlich (Lund) Ropes and Particles Jan 27, Thesis defense 17 / 21
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