Multiple scattering in EPOS: Implications for charm production - - PowerPoint PPT Presentation

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-0

Multiple scattering in EPOS: Implications for charm production

K.W. in collaboration with

• B. Guiot, Iu. Karpenko, T. Pierog

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-1

D-meson multiplicity vs charged multiplicity

5 10 1 2 3 4 5 6 7 Nch / < Nch > N / < N > ALICE ND1 ND2 ND4 ND8 diagonal

ALICE arXiv:1505.00664v1

Significant deviation from the diagonal

(linear increase)

in particular for large pt

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-2

PYTHIA 8.157

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Already understanding a linear increase is a challenge!

(Only recent Pythia versions can do)

Even much more the deviation from linear (towards higher values)

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-4

Trying to understand these data in the EPOS framework:

Two important issues:

Multiple scattering Collectivity

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-5

EPOS: Based on multiple scattering and flow Several steps: 1) Initial conditions: Gribov-Regge multiple scattering approach, elementary object = Pomeron = parton ladder, using saturation scale Qs ∝ Npart ˆ sλ (CGC) 2) Core-corona approach to separate fluid and jet hadrons 3) Viscous hydrodynamic expansion, η/s = 0.08 4) Statistical hadronization, final state hadronic cascade

arXiv:1312.1233 , arXix:1307.4379

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-6

Initial conditions: Marriage pQCD+GRT+energy sharing

(Drescher, Hladik, Ostapchenko, Pierog, and Werner, Phys. Rept. 350, 2001)

For pp, pA, AA: σtot =

• cut P
• uncut P
• (squared amplitude)

A B

uncut −G cut G

• dσexclusive

cut Pom : G = 1 2ˆ s2Im {FT {T}}(ˆ s, b), T = iˆ s σhard(ˆ s) exp(R2

hardt)

Nonlinear effects considered via saturation scale Qs ∝ Npart ˆ

sλ

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-7 σtot =

• d2b
• A
• i=1

d2bA

i dzA i ρA(

• (bA

i )2 + (zA i )2) B

• j=1

d2bB

j dzB j ρB(

• (bB

j )2 + (zB j )2)

• m1l1

. . .

• mABlAB

(1 − δ0Σmk)

• AB
• k=1

mk

• µ=1

dx+

k,µdx− k,µ lk

• λ=1

d˜ x+

k,λd˜

x−

k,λ

• AB
• k=1

1 mk! 1 lk!

mk

• µ=1

G(x+

k,µ, x− k,µ, s, |

b + bA

π(k) −

bB

τ(k)|) lk

• λ=1

−G(˜ x+

k,λ, ˜

x−

k,λ, s, |

b + bA

π(k) −

bB

τ(k)|)

• A
• i=1
• 1 −
• π(k)=i

x+

k,µ, −

• π(k)=i

˜ x+

k,λ

α

B

• j=1
• 1 −
• τ(k)=j

x−

k,µ −

• τ(k)=j

˜ x−

k,λ

α

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-8

Core-corona procedure (for pp, pA, AA):

Pomeron => parton ladder => flux tube (kinky string) ✗ ✖ ✔ ✕ String segments with high pt escape => corona, the others form the core = initial condition for hydro depending on the local string density

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2

• 2
• 1

1 2 x (fm) y (fm) core- corona 5.7fm 5 Pomerons η = -1.00

pPb

10

• 4

10

• 3

10

• 2

10

• 1

1 10 10 2 10 3 2 4 6 pt dn/dptdy pPb 5TeV 20-40% pions x 100 protons corona core EPOS3.076

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-9

Core => Hydro evolution (Yuri Karpenko)

Israel-Stewart formulation, η − τ coordinates, η/S = 0.08, ζ/S = 0 ∂;νT µν = ∂νT µν + Γµ

νλT νλ + Γν νλT µλ = 0

γ (∂t + vi∂i) πµν = −πµν − πµν

NS

τπ + Iµν

π

γ (∂t + vi∂i) Π = −Π − ΠNS τΠ + IΠ

T µν = ǫuµuν − (p + Π)∆µν + πµν, ∂;ν denotes a covariant derivative, ∆µν = gµν − uµuν is the projector or-

thogonal to uµ,

πµν, Π shear stress tensor, bulk pressure πµν

NS = η(∆µλ∂;λuν + ∆νλ∂;λuµ) − 2 3 η∆µν∂;λuλ

ΠNS = −ζ∂;λuλ Iµν

π

= − 4

3 πµν∂;γuγ − [uνπµβ + uµπνβ]uλ∂;λuβ

IΠ = − 4

3 Π∂;γuγ

Freeze out:

at 168 MeV, Cooper-Frye E dn

d3p =

• dΣµpµf(up),

equilibrium distr

Hadronic afterburner: UrQMD

Marcus Bleicher, Jan Steinheimer

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-10

Results

Detailed studies of pt spectra and azimuthal anisotropies (dihadron corr., vn) in pp, pA:

arXiv:1312.1233 [nucl-th]. Published in Phys.Rev. C89 (2014) 6, 064903. arXiv:1307.4379 [nucl-th].

Published in Phys.Rev.Lett. 112 (2014) 23, 232301.

arXiv:1011.0375 [hep-ph]. Published in Phys.Rev.Lett. 106 (2011) 122004 arXiv:1004.0805 [nucl-th]. Published in Phys.Rev. C82 (2010) 044904.

In the follwing : An example of an asymmetric space-time evolution (high mult pp event, 7TeV)

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-11

pp @ 7TeV EPOS 3.119

x [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 y [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 50 100 150 200 250 300 350

= 0.10 fm/c) J 0 τ = 0.0 ,

s

η ] (

3

energy density [GeV/fm

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-12

pp @ 7TeV EPOS 3.119

x [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 y [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 10 20 30 40 50 60

= 0.29 fm/c) J 0 τ = 0.0 ,

s

η ] (

3

energy density [GeV/fm

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-13

pp @ 7TeV EPOS 3.119

x [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 y [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 5 10 15 20

= 0.48 fm/c) J 0 τ = 0.0 ,

s

η ] (

3

energy density [GeV/fm

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-14

pp @ 7TeV EPOS 3.119

x [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 y [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 1 2 3 4 5 6 7 8 9

= 0.68 fm/c) J 0 τ = 0.0 ,

s

η ] (

3

energy density [GeV/fm

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-15

pp @ 7TeV EPOS 3.119

x [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 y [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 1 2 3 4

= 0.87 fm/c) J 0 τ = 0.0 ,

s

η ] (

3

energy density [GeV/fm

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-16

pp @ 7TeV EPOS 3.119

x [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 y [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 0.5 1 1.5 2 2.5

= 1.06 fm/c) J 0 τ = 0.0 ,

s

η ] (

3

energy density [GeV/fm

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-17

pp @ 7TeV EPOS 3.119

x [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 y [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 0.2 0.4 0.6 0.8 1 1.2 1.4

= 1.25 fm/c) J 0 τ = 0.0 ,

s

η ] (

3

energy density [GeV/fm

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-18

pp @ 7TeV EPOS 3.119

x [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 y [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

= 1.44 fm/c) J 0 τ = 0.0 ,

s

η ] (

3

energy density [GeV/fm

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-19

pp @ 7TeV EPOS 3.119

x [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 y [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 0.1 0.2 0.3 0.4 0.5 0.6

= 1.63 fm/c) J 0 τ = 0.0 ,

s

η ] (

3

energy density [GeV/fm

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-20

pp @ 7TeV EPOS 3.119

x [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 y [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

= 1.83 fm/c) J 0 τ = 0.0 ,

s

η ] (

3

energy density [GeV/fm

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-21

pp @ 7TeV EPOS 3.119

x [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 y [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 0.05 0.1 0.15 0.2 0.25 0.3 0.35

= 2.02 fm/c) J 0 τ = 0.0 ,

s

η ] (

3

energy density [GeV/fm

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-22

pp @ 7TeV EPOS 3.119

x [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 y [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 0.05 0.1 0.15 0.2 0.25

= 2.21 fm/c) J 0 τ = 0.0 ,

s

η ] (

3

energy density [GeV/fm

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-23

pp @ 7TeV EPOS 3.119

x [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 y [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 0.05 0.1 0.15 0.2

= 2.40 fm/c) J 0 τ = 0.0 ,

s

η ] (

3

energy density [GeV/fm

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-24

pp @ 7TeV EPOS 3.119

x [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 y [fm]

• 2
• 1.5
• 1
• 0.5

0.5 1 1.5 2 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

= 2.59 fm/c) J 0 τ = 0.0 ,

s

η ] (

3

energy density [GeV/fm

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-25

Charm – multiplicity correlations

Notations (always at midrapidity)

(D-meson = average D+, D0, D∗+)

Nch: Charged particle multiplicity ND1: D-meson multiplicity for 1 < pt < 2 GeV/c ND2: D-meson multiplicity for 2 < pt < 4 GeV/c ND4: D-meson multiplicity for 4 < pt < 8 GeV/c ND8: D-meson multiplicity for 8 < pt < 12 GeV/c

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-26

Heavy quark (Q) production in EPOS multiple scattering framework

Q Q Q Q Q Q Born SLC TLC SLC TLC

as light quark production

(but non-zero masses : mc = 1.3, mb = 4.2)

In any of the ladders during SLC

(space-like cascade)

during TLC (time-like cascade) in Born

Implemented by Benjamin Guiot, UTFSM, Valparaiso (for- mer PhD student in Nantes)

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-27

Multiple scattering (EPOS3, basic): NDi ∝ Nch ∝ NPom

”Natural” linear behavior

(first approximation)

In the following: NPom as reference

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-28

The actual calculation (EPOS basic)

2 4 0.5 1 1.5 2 2.5 3 3.5 4 Nch / < Nch > N / < N > EPOS 3.117 basic ND1 ND2 ND4 ND8 diagonal

Indeed essen- tially a linear increase ... even more than linear !

(in particular for large pt)

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-29

More than linear increase amazing :

2 4 6 2 4 6 8 10 12 14 NPom N / < N > EPOS 3.117 basic Nch ND1 ND2 ND4 ND8

D multiplici- ties increase less than Nch vs NPom How to un- derstand ND8(Nch) more than linear ?

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-30

But crucial: Fluctuations

ch

N NPom Nch

*

N ch and N Pom are correlated, but not one-to-one (=> two-dimensional probability distribution)

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-31

We define normalized multiplitities n = N/ N for nch and nDi In the following we consider fixed values nch∗

• f normalized charged multiplicities

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-32

Consider nD1 for some given nch∗

2 4 6 2 4 6 8 10 12 14 NPom EPOS 3.117 basic nD1(NPom,nch*) prob(NPom,nch*) * 10 nch*

nD1 =

• NPom

prob(NPom, nch

∗)

× nD1(NPom, nch

∗)

≈ nch

∗

having used nD1(NPom, nch

∗)

≈ nch

∗

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-33

The precise calculation:

(red point)

2 4 6 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 nch nD1 nD1(nch) diagonal nD1(nch*)

• n the

diagonal! Perfectly linear!

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-34

Now nD8 for given nch∗

2 4 6 2 4 6 8 10 12 14 NPom EPOS 3.117 basic nD8(NPom,nch*) prob(NPom,nch*) * 10 nch*

nD8 =

• NPom

prob(NPom, nch

∗)

× nD8(NPom, nch

∗)

> nch

∗

because

nD8(NPom, nch

∗)

increases strongly towards small NPom

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-35

The precise calculation:

(red point)

2 4 6 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 nch nD8 nD8(nch) diagonal nD8(nch*)

above the diagonal! non-linear!

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-36

More than linear increase since

The number of Pomerons fluctuates

for given multiplicity

ND8 increases strongly

towards small NPom for given multiplicity => it is favored to produce high pt D mesons for fewer (and more energetic) Pomerons

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-37

The effect is actually too small!

5 10 0.5 1 1.5 2 2.5 3 3.5 4 4.5 Nch / < Nch > N / < N > ALICE EPOS3 basic ND1 ND2 ND4 ND8 diagonal

Too little deviation from the diagonal in particular for large pt

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-38

But anyhow, basic EPOS (w/o hydro) reproduces neither spectra nor correlations => full approach (EPOS w hydro + cascade) (with or without hadronic cascade makes no difference)

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-39

Full EPOS3

5 10 1 2 3 4 5 6 7 Nch / < Nch > N / < N > ALICE EPOS3 full ND1 ND2 ND4 ND8 diagonal

Significant non-linear in- crease!

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-40

How to understand the increased non-linearity?

2 4 6 n nch nD1 nD2 2 4 5 10 NPom nD4 5 10 NPom nD8 5 10 NPom EPOS 3.117 basic full

Little change for nDi

(as expected)

But signifi- cant reduc- tion of nch

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-41

Not the charm production is increased with increasing “collision activity” but the charged particle multiplicity is reduced when including a hydrodynamical expansion Collision activity = Pomeron number

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MPI at the LHC– 2015 – Trieste – Klaus Werner – Subatech, Nantes 0-42

Why such a multiplicity reduction?

Basic EPOS: Pomerons > Strings > String fragmentation (independent

• f

event activity) Full model: Pomerons > Strings > Fluid, collectivity (collective energy in- creases with event ac- tivity)

10

• 4

10

• 3

10

• 2

10

• 1

1 10 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 pt (GeV/c) dn/dηd2pt (c2/GeV2) charged ptls |η| <0.8 hydro, no trv flow pure string

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Why is the non-linearity of NDi(Nch) more pronounced at high pt ?

Naive expectation: Nch reduction should affect all pt ranges in the same way...

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Pt dependence

2 4 6 2 4 6 8 10 12 14 NPom EPOS 3.117 basic nD8(NPom,nch*) prob(NPom,nch*) * 10 nch* nchfull

Broader NPom distribution with hydro + strongly dropping

nD8

makes big effect

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Summary

Significant non-linear increase

• f NDi(Nch)

5 10 1 2 3 4 5 6 7 Nch / < Nch > N / < N > ALICE EPOS3 full ND1 ND2 ND4 ND8 diagonal

(in particular for high pt) understandable in terms

• f

multiple scat- tering and flow