Microscopic collectivity: The ridge and strangeness enhancement from string string interactions in Pythia8

Transcription

1 Microscopic collectivity: The ridge and strangeness enhancement from string string interactions in Pythia8 Christian Bierlich Lund University / University of Copenhagen May 15, 2018 Quark Matter 2018, Venice Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 1 / 17

2 Where heavy ions meet proton proton Heavy ion collisions: QGP assumption enables effective theories. Monte Carlos for pp/pythia8 : 1 MPIs treated almost independently, no spatial structure. 2 Parton Shower + Colour Reconnection generally successful but ridge, strangeness enhancement etc. not foreseen by pp models. 4 Opportunity to study the (non perturbative) dynamics of QCD. 5 Approach based on corrections in dense environments. Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 2 / 17

3 Where heavy ions meet proton proton Heavy ion collisions: QGP assumption enables effective theories. Monte Carlos for pp/pythia8 : 1 MPIs treated almost independently, no spatial structure. 2 Parton Shower + Colour Reconnection generally successful but ridge, strangeness enhancement etc. not foreseen by pp models. 4 Opportunity to study the (non perturbative) dynamics of QCD. 5 Approach based on corrections in dense environments. This talk: 1 String hadronization and Colour Reconnection. 2 Microscopic collectivity: String shoving: the ridge and flow. Rope formation: strangeness. 3 Perspectives AA, γ A and jet quenching. Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 2 / 17

4 Hadronization in pp: It all starts with a string (See e.g. hep-ph/ ) Non-perturbative phase of final state. Confined colour fields strings with tension κ 1 GeV/fm. Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 3 / 17

5 Hadronization in pp: It all starts with a string (See e.g. hep-ph/ ) Non-perturbative phase of final state. Confined colour fields strings with tension κ 1 GeV/fm. ( ) Breaking/tunneling with P exp πm2 κ gives hadrons. Lund symmetric fragmentation function ( ) f (z) z 1 (1 z) a bm exp. z a and b related to total multiplicity. Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 3 / 17

6 Hadronization in pp: It all starts with a string (See e.g. hep-ph/ ) Non-perturbative phase of final state. Confined colour fields strings with tension κ 1 GeV/fm. ( ) Breaking/tunneling with P exp πm2 κ gives hadrons. Lund symmetric fragmentation function ( ) f (z) z 1 (1 z) a bm exp. z a and b related to total multiplicity. Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 3 / 17

7 Hadronization in pp: It all starts with a string (See e.g. hep-ph/ ) Non-perturbative phase of final state. Confined colour fields strings with tension κ 1 GeV/fm. ( ) Breaking/tunneling with P exp πm2 κ gives hadrons. u d d s s ud ud u ū ū Lund symmetric fragmentation function ( ) f (z) z 1 (1 z) a bm exp. z a and b related to total multiplicity. Flavours determined by relative probabilities ρ = P strange P u or d, ξ = P diquark P quark Probabilities related to κ by Schwinger equation. Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 3 / 17

8 The role of Colour Reconnection and non-flow CR = reshuffling string configurations (See also: T. Sjöstrand, QM18). Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 4 / 17

9 The role of Colour Reconnection and non-flow CR = reshuffling string configurations (See also: T. Sjöstrand, QM18). Quantifying its contribution Introduces flow like effects (Velasquez et al. PRL 111 (2013) ). Remove the like, or is it non-flow? (CB, V. Pacík, Y. Zhou, in prep.) v2{2} No CR v2{2} v2{2, sub} No CR v2{2, sub} v3{2, sub} No CR v3 v4{2, sub} No CR v4{2, sub} v2{2} 0.08 v n{2} N ch, high mult. trigger ( η < 0.9, 0.1 GeV < p < 3.0 GeV) N ch, high mult. trigger ( η < 0.9, 0.1 GeV < p < 3.0 GeV) (pp at s = 13 TeV, v 2 : η > 1.4, v 3,4 : η > 1.0) Contribution to v 2 {2} disappears: CR not long range. Coefficients are ordered v 2 > v 3 > v 4. Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 4 / 17

10 The microscopic model of collectivity Clearly we need more! Where is the geometry? Proposal: Model microscopic dynamics with interacting Lund strings (In Pythia8 v ; CB, Gustafson, Lönnblad: PLB779 (2018) 58-63; CB: arxiv: [hep-ph]; CB, Gustafson, Lönnblad, Tarasov: JHEP 1503 (2015) 148) Additional input fixed or inspired by lattice, few tunable parameters. Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 5 / 17

11 The microscopic model of collectivity Clearly we need more! Where is the geometry? Proposal: Model microscopic dynamics with interacting Lund strings (In Pythia8 v ; CB, Gustafson, Lönnblad: PLB779 (2018) 58-63; CB: arxiv: [hep-ph]; CB, Gustafson, Lönnblad, Tarasov: JHEP 1503 (2015) 148) Additional input fixed or inspired by lattice, few tunable parameters. τ 0 fm: Strings no transverse extension. No interactions, partons may propagate. τ 0.6 fm: Parton shower ends. Depending on diluteness, strings may shove each other around. τ 1 fm: Strings at full transverse extension. Shoving effect maximal. τ 2 fm: Strings will hadronize. Possibly as a colour rope. Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 5 / 17

12 String shoving with simple geometry (PLB779 (2018) 58-63) Strings = interacting vortex lines. (Old idea: Abramovsky et al.: JETP Lett 47 (1988) 337.) For t, profile known from lqcd (Cea et al.: PRD89 (2014) no.9, ): E(r ) = C exp ( r 2 /2R2) E int (d ) = d 2 r E( r )E( r d ) f (d ) = de int dd = gκd R 2 ( exp d 2 (t) ) 4R 2. Dominated by electric field g = 1. Reality: Type 1 Energy to destroy vacuum. Type 2 Energy in current. Pairwise, momentum conserving, kicks. Room for improvement: How to add a kick to a field? Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 6 / 17

13 The ridge and effects on v 2 {2, sub} Depends on initial state geometry approximated by overlapping 2D Gaussians (room for improvement!). Reproduces ridge with reasonable choice of g = 4. Can be quantified in flow coefficients higher orders unfeasible without better geometrical understanding. 1 Shoving g = 40 Shoving g = GeV <p <3.0 GeV 2.0 < η < v2{2} No CR v2{2} Shoving v2{2} R( φ) 0 No shoving (Pythia8) (CMS pp 7 TeV) v2{2, sub} No CR v2{2, sub} Shoving v2{2, sub} -1 N <35 35 N <90 v2{2} N <110 N R( φ) φ φ N ch, high mult. trigger ( η < 0.9, 0.1 GeV < p < 3.0 GeV) (pp at s = 13 TeV, v 2 : η > 1.4) Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 7 / 17

14 Rope Hadronization (JHEP 1503 (2015) 148) After shoving strings (p and q) still overlap. Combines into multiplet with effective string tension κ. Effective string tension from the lattice κ C 2 κ κ 0 = C 2(multiplet) C 2 (singlet). Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 8 / 17

15 Rope Hadronization (JHEP 1503 (2015) 148) After shoving strings (p and q) still overlap. Combines into multiplet with effective string tension κ. Effective string tension from the lattice κ C 2 κ κ 0 = C 2(multiplet) C 2 (singlet). Easily calculable using SU(3) recursion relations {p, q} 3 = {p + 1, q} {p, q + 1} {p, q 1} }{{}}{{} All anti-triplets All triplets Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 8 / 17

16 Rope Hadronization (JHEP 1503 (2015) 148) After shoving strings (p and q) still overlap. Combines into multiplet with effective string tension κ. Effective string tension from the lattice κ C 2 κ κ 0 = C 2(multiplet) C 2 (singlet). Easily calculable using SU(3) recursion relations {p, q} 3 = {p + 1, q} {p, q + 1} {p, q 1} }{{}}{{} All anti-triplets All triplets Transform to κ = 2p+q+2 4 κ 0 and 2N = (p + 1)(q + 1)(p + q + 2). N serves as a state s weight in the random walk. Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 8 / 17

17 Strangeness enhancement Less sensitive on geometry a game of density. Described strangeness enhancement from pp to AA. No direct comparison to unfolded data... yet. Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 9 / 17

18 Strangeness enhancement Less sensitive on geometry a game of density. Described strangeness enhancement from pp to AA. No direct comparison to unfolded data... yet. 2K 0 s /π ± (Λ + Λ)/π ± 6φ/π ± 6(Ξ + Ξ)/π ± ratio to π + π (Ω + Ω)/π ± e + e DIPSY pp Pythia8 + ropes DIPSY ppb DIPSY PbPb N ch, 2 < η <4, p > 0.15 GeV Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 9 / 17

19 The importance of φ production Very interesting new data! The φ is an excellent laboratory for strangeness effects. Two s-breaks means squared suppression and added sensitivity. g g φ/π ± (p > 0. 1 GeV, η < 1) Pythia 8 + ropes Pythia Nch forward (p > 0. 1 GeV, 3 < η < 5) Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 10 / 17

20 The importance of φ production Very interesting new data! The φ is an excellent laboratory for strangeness effects. Two s-breaks means squared suppression and added sensitivity. g s s g φ/π ± (p > 0. 1 GeV, η < 1) Pythia 8 + ropes Pythia Nch forward (p > 0. 1 GeV, 3 < η < 5) Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 10 / 17

21 The importance of φ production Very interesting new data! The φ is an excellent laboratory for strangeness effects. Two s-breaks means squared suppression and added sensitivity. g φ s s s s g φ/π ± (p > 0. 1 GeV, η < 1) Pythia 8 + ropes Pythia Nch forward (p > 0. 1 GeV, 3 < η < 5) Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 10 / 17

22 The current status Introduced a microscopic model for collectivity. String shoving for ridge and flow, rope formation for strangeness. Microscopic degrees of freedom are string pieces between partons. Implemented in Pythia8, but: 1 Initial state correlations/saturation largely ignored. 2 Proton geometry from naïve model. 3 Extra gluons from string kicks gives technical problems. Remaining talk: Some perspectives. Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 11 / 17

23 Perspective I: Angantyr Pythia8 for AA collisions Initial state geometry less fluctuation dominated.... but MPI model must be extended to nuclear collisions. (CB, G. Gustafson, L. Lönnblad: JHEP 1610 (2016) 139; CB, G. Gustafson, L. Lönnblad, H. Shah: in prep.). See poster by Harsh Shah (739). (1/Nev) dn ch/dη (a) Centrality-dependent η distribution, ppb, SNN = 5 TeV ATLAS Pythia8/Angantyr (generated centrality) (SDTries = 4) Pythia8/Angantyr ( E Pb bins from data) (1/N ev )dn ch /dη 2500 (a) Centrality dependent η distribution PbPb, S NN = 5.02 TeV Pythia8/Angantyr ALICE PbPb S NN = 5.02 TeV η η Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 12 / 17

24 Perspective II: γ A collisions Small system with size if IS under perturbative control. New possible collider interesting for this community. Knowledge of Q 2 provides an additional handle. Q 2 Normal ep Small dense droplet? Collectivity with controlled initial conditions? pp MB Similar to pa. Collectivity? FS multiplicity Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 13 / 17

25 Perspective II: γ A collisions Small system with size if IS under perturbative control. New possible collider interesting for this community. Knowledge of Q 2 provides an additional handle. Q 2 Dipsy toy calc. (γ Au, s γ N = 200 GeV). Normal ep Small dense droplet? Collectivity with controlled initial conditions? pp MB Similar to pa. Collectivity? ( + )/( + + ) Q 2 = 100 GeV 2 Q 2 = 2 GeV 2 Reference FS multiplicity Centrality % Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 13 / 17

26 Perspective III: Jet modifications by shoving Very sensitive to geometry. Disabled in Pythia8. Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 14 / 17

27 Perspective III: Jet modifications by shoving Very sensitive to geometry. Disabled in Pythia8. Toy calculation not real events! Z+jet at 7 TeV, in pp interaction region center. No jet escaping + all strings at equilibrium size. Jet quenching Z+jet, toy study, Anti-kT R = dσ σ dp,z 10 3 Pythia8 Pythia8 + shoving Ratio Z p [GeV] Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 14 / 17

28 Perspective III: Jet modifications by shoving Very sensitive to geometry. Disabled in Pythia8. Toy calculation not real events! Z+jet at 7 TeV, in pp interaction region center. No jet escaping + all strings at equilibrium size. Jet quenching Z+jet, toy study, Anti-kT R = dσ σ dp,jet 10 3 Pythia8 Pythia8 + shoving Ratio Jet-p [GeV] Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 14 / 17

29 Perspective III: Jet modifications by shoving Very sensitive to geometry. Disabled in Pythia8. Toy calculation not real events! Z+jet at 7 TeV, in pp interaction region center. No jet escaping + all strings at equilibrium size. Jet quenching Z+jet, toy study, Anti-kT R = dn jz NZ dx jz Pythia8 Pythia8 + shoving Ratio x jz = p,jet /p,z Modifications to hadronization? (Nachman and Mangano: EPJC 78 (2018) 4, 343) Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 14 / 17

30 Summary Modifications to string hadronization based on microscopic interactions. Dependence on initial state geometry is crucial. Strangeness on density rope formation. Ridge + flow on shape of interaction region string shoving. Jet modifications on microscopic structure... both? Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 15 / 17

31 Summary Modifications to string hadronization based on microscopic interactions. Dependence on initial state geometry is crucial. Strangeness on density rope formation. Ridge + flow on shape of interaction region string shoving. Jet modifications on microscopic structure... both? Extensions to heavy ions ongoing. Already good description of single particle observables. Angantyr available in Pythia8 (v.8.235). Strangeness well described using old Dipsy implementation. Thank you! Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 15 / 17

32 What about the protons? Ratio can be explained. But dynamics of baryon production is still not understood. Important result from ALICE: Eur. Phys. J. C77 (2017) 569 EPOS points to baryon baryon annihilations. Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 16 / 17

33 What about the protons? Ratio can be explained. But dynamics of baryon production is still not understood. Important result from ALICE: Eur. Phys. J. C77 (2017) 569 EPOS points to baryon baryon annihilations p + p/π + + π dnch/dη η < 0. 5 Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 16 / 17

34 Angantyr p spectra 5.02 TeV/nn by ATLAS. Christian Bierlich (Lund/NBI) Microscopic collectivity May 15, QM18 Venice 17 / 17