Deuterons at LHC: snowballs in hell via hydrodynamics and hadronic - PowerPoint PPT Presentation

Deuterons at LHC: “snowballs in hell” via hydrodynamics and hadronic afterburner Dmytro (Dima) Oliinychenko November 20, 2018 in collaboration with: Volker Koch LongGang Pang Hannah (Petersen) Elfner

Deuteron in heavy ion collisions • Bound state of proton and neutron, binding energy 2.2 MeV • Deuteron yield in Pb+Pb collisions at √ s NN = 2 . 76 TeV: N d = gV 2 π 2 Tm 2 K 2 ( m / T ), T = 155 MeV Snowballs in hell. A. Andronic, et al., arXiv:1710.09425 Deuteron: rapid chemical freeze-out at 155 MeV, like hadrons? 1

Methodology: hybrid approach • CLVisc hydro L. G. Pang, H. Petersen and X. N. Wang, arXiv:1802.04449 [nucl-th] • SMASH hadronic afterburner J. Weil et al. , PRC 94, no. 5, 054905 (2016) • Treat deuteron as a single particle • implement deuteron + X cross-sections explicitly 2

Most important deuteron production/disintegration reactions Largest d + X disintegration rate → largest reverse production rate Most important = largest σ inel d + X n X d + X [mb] ( √ s − √ s thr = [0 . 05 , 0 . 25] GeV) dN X σ inel X dy | y =0 π ± 80 - 160 732 K + < 40 109 K − < 80 109 50 - 100 33 p ¯ p 80 - 200 33 γ < 0 . 1 comparable to π ? π + d are the most important because of pion abundance 3

Reactions with deuteron implemented in SMASH • π d ↔ π np , π d ↔ np , elastic π d ↔ π d • Nd ↔ Nnp , elastic Nd ↔ Nd • ¯ Nd ↔ ¯ Nnp , elastic ¯ Nd ↔ ¯ Nd • CPT conjugates of all above – reactions for anti-deuteron • all are tested to obey detailed balance within 1% precision π d ↔ π np is the most important at high (LHC) energies Nd ↔ Nnp is the most important at low (AGS) energies 4

Reactions of deuteron with pions SMASH πd total total 400 el - σ πd→NN tot - σ πd σ πd πd→πnp [Arndt et al] πd elastic elastic πd→pp πd→pp 300 σ [mb] 100 2 2.2 2.4 2.6 2.8 3 √s [GeV] π d ↔ π np is the most important at LHC energies σ inel π d > σ el π d , not like for hadrons 5

Reactions of deuteron with (anti-)nucleons 250 (a) tot - σ pd el σ pd [Carlson et al] 200 σ Nd→Nnp SMASH σ [mb] 50 0 2.8 2.85 2.9 2.95 3 3.05 3.1 √s [GeV] Nd ↔ Nnp , ¯ Nd ↔ ¯ Nnp : large cross-sections but not important at LHC energies, because N and ¯ N are sparse 6

Reactions of deuteron with (anti-)nucleons 350 (b) σ pd inelastic [Bizzarri et al] 300 σ Nd→Nnp SMASH 250 σ [mb] 100 50 0 2.8 2.9 3 3.1 3.2 √s [GeV] Nd ↔ Nnp , ¯ Nd ↔ ¯ Nnp : large cross-sections but not important at LHC energies, because N and ¯ N are sparse 6

Transverse momentum spectra 10 4 π x 5 Hydro + decays 1000 Hydro + afterburner same, no BB annihil. ALICE, PbPb, 0-10% K 1/2π p T d 2 N d /dydp T p x 0.2 1 d 10 −3 10 −4 0 1 2 3 4 5 p T [GeV] Pion and kaon spectra not affected by afterburner Proton spectra: pion wind effect and B ¯ B annihilations ( ∼ 10%) 7

Obtaining B 2 ( p T ) coalescence parameter d 2 Nd 1 pT dpT dy | pd T =2 pp 2 π B 2 ( p T ) = T � 2 � d 2 Np 1 2 π pT dpT dy 10 hydro + afterburner ALICE, PbPb, 0-10% 8 B 2 [GeV 2 /c 3 ] (x 10 4 ) 6 4 2 0 0 0.5 1 1.5 2 2.5 p T /A [GeV] Reproducing B 2 without any free parameters 8

B 2 ( p T ) for different centralities Pb+Pb, 2.76 TeV 70 60-80% 40-60% 60 20-40% B 2 [GeV 2 ] × 10 4 10-20% 0-10% 10 0 0 0.5 1 1.5 2 2.5 p T [GeV] Works well for all centralities 9

p T -spectra for different centralities 100 Pb+Pb, 2.76 TeV (c) p 1/N ev 1/2πp T d 2 N/dp T dy [GeV -2 ] 1 0-10% x4 10-20% x2 20-40% 40-60% 60-80% 10 −5 0 1 2 3 4 5 p T [GeV] 10

p T -spectra for different centralities Pb+Pb, 2.76 TeV (d) 0.1 d 1/N ev 1/2πp T d 2 N/dp T dy [GeV -2 ] 0-10% x8 10-20% x4 20-40% x2 40-60% 60-80% 10 −6 0 1 2 3 4 5 p T [GeV] 10

Does deuteron freeze out at 155 MeV? Only less than 1% of final deuterons original from hydrodynamics 0.03 0-10% Pb+Pb, √s = 2.76 TeV inelastic elastic deuteron 1/N ev dN coll /dt 0 0 20 40 60 80 t of last collision [fm/c] Deuteron freezes out at late time Its chemical and kinetic freeze-outs roughly coincide 11

Is π d ↔ π np reaction equilibrated |y| < 1 0.1 Reactions / event 0.01 πpn → πd: formation πd → πpn: disintegration 10 −3 (πpn → πd) - (πd → πpn) (πd → πpn) + (πpn → πd) 20 rel. diff. [%] 0 −20 −40 0 10 20 30 40 50 t [fm/c] After about 12-15 fm/c within 5% π d ↔ π np is equilibrated 12

Deuteron yield 0.8 PbPb, 0-10%, √s = 2.76 TeV, |y| < 1 0.6 deuteron multiplicity default d init 0.4 0.2 dN/dy| ALICE × (Δy = 2) d 0 0 20 40 60 80 100 t [fm/c] The yield is almost constant. Why? Does afterburner really play any role? 13

Deuteron yield 0.8 PbPb, 0-10%, √s = 2.76 TeV, |y| < 1 0.6 deuteron multiplicity default d init no deuteron init 0.4 0.2 dN/dy| ALICE × (Δy = 2) d 0 0 20 40 60 80 100 t [fm/c] No deuterons at particlization: also possible. Here all deuterons are from afterburner. 13

Deuteron yield 0.8 PbPb, 0-10%, √s = 2.76 TeV, |y| < 1 0.6 deuteron multiplicity deuteron x3 init default d init no deuteron init 0.4 0.2 dN/dy| ALICE × (Δy = 2) d 0 0 20 40 60 80 100 t [fm/c] No deuterons at particlization: also possible. Here all deuterons are from afterburner. 13

Deuteron yield 0.8 PbPb, 0-10%, √s = 2.76 TeV, |y| < 1 deuteron x3 init 0.6 deuteron multiplicity default d init no deuteron init w/o BB annihilation 0.4 0.2 dN/dy| ALICE × (Δy = 2) d 0 0 20 40 60 80 100 t [fm/c] Without B ¯ B annihilations yield coincidence is less impressive 13

Deuteron yield 0.8 PbPb, 0-10%, √s = 2.76 TeV, |y| < 1 deuteron x3 init default d init 0.6 deuteron multiplicity no deuteron init w/o BB annihilation Freeze-out at 165 MeV 0.4 0.2 dN/dy| ALICE × (Δy = 2) d 0 0 20 40 60 80 100 t [fm/c] But it persists if T of particlization is changed to 165 MeV 13

Toy model of deuteron production: no annihilations • only π , N , ∆, and d • isoentropic expansion • pion number conservation • baryon (not net!) number conservation ( s π ( T , µ π ) + s N ( T , µ B ) + + s ∆ ( T , µ B + µ π ) + s d ( T , 2 µ B )) V = const ( ρ ∆ ( T , µ B + µ π ) + ρ π ( T , µ π )) V = const ( ρ N ( T , µ B ) + ρ ∆ ( T , µ B + µ π ) + 2 ρ d ( T , 2 µ B )) V = const 14

Toy model of deuteron production: results Nucleon Deuteron yield(V)/yield(V 0 ) Pion 1.2 Delta 1 0.8 0.6 T 0.3 μ B [MeV] μ π 0.2 0.1 0 1 1.5 2 2.5 3 V/V 0 No annihilation: deuteron yield grows, like in simulation. 15

Toy model of deuteron production: results Nucleon Deuteron yield(V)/yield(V 0 ) Pion 1.2 Delta 1 0.8 0.6 T 0.3 μ B [MeV] μ π 0.2 0.1 0 1 1.5 2 2.5 3 V/V 0 T particlization = 165 MeV. Relative yields are similar, like in simulation. 15

Toy model of deuteron production: results Nucleon Deuteron yield(V)/yield(V 0 ) Pion 1.2 Delta 1 0.8 0.6 T 0.3 μ B [MeV] μ π 0.2 0.1 0 1 1.5 2 2.5 3 V/V 0 V / V 0 Annihilation out of equilibrium: µ B = µ B a + V / V 0 , a = 0 . 1 T particlization = 155 MeV. 15

Toy model of deuteron production: results Nucleon Deuteron yield(V)/yield(V 0 ) Pion 1.2 Delta 1 0.8 0.6 T 0.3 μ B [MeV] μ π 0.2 0.1 0 1 1.5 2 2.5 3 V/V 0 V / V 0 Annihilation out of equilibrium: µ B = µ B a + V / V 0 , a = 0 . 1 T particlization = 165 MeV. Qualitatively similar to our simulation. 15

Summary • π d ↔ π pn : most important deuteron producing / disintegrating reaction at LHC • deuteron does not freeze-out at 155 MeV • chemical and kinetic freeze-outs of deuteron roughly coincide • deuteron yield stays constant after particlization, as thermal model assumes • reason: interplay of π d ↔ π pn (d ↑ ) close to equilibrium and B ¯ B annihilations out of equilibrium (d ↓ ) Outlook • Deuteron: lower energies / smaller systems • Relation to proton density fluctuations and critical point 16

Light nuclei production is related to nucleon density fluctuations in coordinate space Kaijia Sun et al., Phys. Lett. B 774, 103 (2017) ∆ n ≡ � ( δ n ) 2 � � n � 2 , N t · N p / N 2 d ≈ g (1 + ∆ n ) , g ≈ 0 . 29 Dingwei Zhang, poster at Quark Matter 2018 Can one reproduce this with pure cascade? 17

SMASH transport approach S imulating M ultiple A ccelerated S trongly-interacting H adrons 18

SMASH transport approach J. Weil et al., Phys.Rev. C94 (2016) no.5, 054905 • Monte-Carlo solver of relativistic Boltzmann equations BUU type approach, testparticles ansatz: N → N · N test , σ → σ/ N test • Degrees of freedom • most of established hadrons from PDG up to mass 3 GeV • strings: do not propagate, only form and decay to hadrons • Propagate from action to action (timesteps only for potentials) action ≡ collision, decay, wall crossing � • Geometrical collision criterion: d ij ≤ σ/π • Interactions: 2 ↔ 2 and 2 → 1 collisions, decays, potentials, string formation (soft - SMASH, hard - Pythia 8) and fragmentation via Pythia 8 19