DIPSY, ropes and shoving

Introduction

Rope fragmentation

Rope Shovingˇ

DIPSY, ropes and shoving

Leif Lönnblad

(with Christian Bierlich and Gösta Gustafson)

Department of Astronomyand Theoretical Physics

Lund University

CERN 2017-06-15

Ropes and Shoving 1 Leif Lönnblad Lund University

Introduction

Rope fragmentation

Rope Shovingˇ

Nature Phys. 13 (2017) 535-539


Introduction

Rope fragmentation

Rope Shovingˇ

Outline

String hadronisation in dense environments

Understanding Impact parameter geometry

From pp to pA to AA

[arXiv:1412.6259, arXiv:1607.04434, arXiv:1612.05132]


Introduction

Rope fragmentation

Rope Shovingˇ

Outline


→ Ropes and Shoving


From pp to pA to AA



Introduction

Rope fragmentation

Rope Shovingˇ

Outline




→ DIPSY vs. Pythia8

From pp to pA to AA



Introduction

Rope fragmentation

Rope Shovingˇ

Outline




→ DIPSY vs. Pythia8

From pp to pA to AA

→ resurrecting Fritiof in Pythia8



Introduction

Rope fragmentation

Rope Shovingˇ

The Lund Model

The tunnelling mechanism: P ∝ e−πm2

q⊥κ ≡ e−

πm2q

κ e−πp2

⊥

κ

The fragmentation function: p(z) = N(1−z)a

z e−bm2⊥/z

Many parameters depends (implicitly) on κ.


Introduction

Rope fragmentation

Rope Shovingˇ

The Lund Model (short version)


q⊥κ ≡ e−

πm2q

κ e−πp2

⊥

κ


z e−bm2⊥/z



Introduction

Rope fragmentation

Rope Shovingˇ

The Lund Model


q⊥κ ≡ e−

πm2q

κ e−πp2

⊥

κ


z e−bm2⊥/z



Introduction

Rope fragmentation

Rope Shovingˇ

Overlapping strings

How do we treat strings that overlap in space–time?


Introduction

Rope fragmentation

Rope Shovingˇ

Take the simplest case of two simple, un-correlated, completely

overlapping strings, with opposite colour flow.

•

•

•

•

q1

q2

q3

q4

1/9: A colour-singlet

8/9: A colour-octet

The string tension affects all details in the Lund string

fragmentation.

It is proportional to the Casimir operator C(8)2 = 9

4C

(3)2 .


Introduction

Rope fragmentation

Rope Shovingˇ

And for parallel colour flows:.

•

•

•

•

q1

q2

q3

q4

1/3: An anti-triplet

2/3: A sextet

C(6)2 = 5

2C(3)2

The anti-triplet case is related to string junctions and baryon

production (popcorn mechanism).


Introduction

Rope fragmentation

Rope Shovingˇ

A random walk in colour-space

3

6

3

10

8

8

1

[Biro, Nielsen, Knoll (1984)]


Introduction

Rope fragmentation

Rope Shovingˇ

The Rope Model

Partially overlapping string pieces in impact parameter and

rapidity.

Reconnect to get colour singlets.

Random walk for the rest to get higher colour multiplets

(ropes).

The rope will break one string at the time.

Calculate an effective string tension of a break-up, e.g.

the first string to break in a sextet has an effective

κeff ∝ C62 − C3

2 = 32C3

2

The second breakup has standard κ ∝ C32

Rescale the PYTHIA8 parameters accordingly.


Introduction

Rope fragmentation

Rope Shovingˇ


Rope fragmentationˆ

Rope Shoving

DIPSY vs. PYTHIA8ˇ

Will overlapping strings in high multiplets generate a transverse

pressure?

[Abramovsky, Gedalin, Gurvich, Kancheli (1988)]



Rope Shoving

DIPSY vs. PYTHIA8ˇ

Rope Shoving

All strings are sliced into dy slices.

In each (small) time–step dt , each string will get a kick

from other strings:

dp⊥

dydt=

C0td

R2exp

(

− d2

2R2

)

.

Momentum conservation is observed.

Transverse kicks resolved pairwise.

Longitudinal recoil absorbed by kicking dipole.

“kick” → “kink” = gluon



Rope Shoving

DIPSY vs. PYTHIA8ˇ

Rope Shoving

All strings are sliced into dy slices.

In each (small) time–step dt , each string will get a kick

from other strings:

dp⊥

dydt=

C0td

R2exp

(

− d2

2R2

)

.

Momentum conservation is observed.

Transverse kicks resolved pairwise.

Longitudinal recoil absorbed by kicking dipole.

This could give rise to a Ridge!

“kick” → “kink” = gluon


Rope Shovingˆ

DIPSY vs. PYTHIA8

Fritiofˇ

DIPSY

[Avsar, Flensburg, Gustafson, Lönnblad (2005–2011)]


Rope Shovingˆ

DIPSY vs. PYTHIA8

Fritiofˇ

DIPSY

Formulated in impact parameter space and rapidity.

Implements BFKL evolution to leading log(++).

Naturally treats saturation and MPI.

“Trivial” to extend to pA and AA.

Does not describe pp Minimum Bias very well.

[Mueller, Patel (1994)]


Rope Shovingˆ

DIPSY vs. PYTHIA8

Fritiofˇ

PYTHIA8

Describes pp Minimum Bias very well.

As well as most other things.

Does not have explicit impact parameter dependence.

Now available with a UserHooks

Cannot do heavy ions.

Yet!

UserHook written by Bierlich


DIPSY vs. PYTHIA8 ˆ

Fritiof

Resultsˇ

Remember Fritiof?

Simple picture of pp collisions

Flat rapidity plateau.

High mass diffractions dσ/dM2X ∝ M

−2(1+ǫ)X were ǫ is small.

Works surprisingly well for√

s ≤ ISR.

Fritiof + Glauber gives heavy Ion collisions.

Works very well at low energies.

But at higher energies we need to worry about multiple

(semi-)hard parton–parton scatterings.



Fritiof

Resultsˇ

Remember Fritiof?

?





s ≤ ISR.







Fritiof

Resultsˇ

Remember Fritiof?

multiple soft gluon exchanges





s ≤ ISR.







Fritiof

Resultsˇ

Remember Fritiof?

Longitudinal excitation of both protons

P+dQ−

Q−P−

dQ+

Q+





s ≤ ISR.







Fritiof

Resultsˇ

Remember Fritiof?

String ends evenly distributed in rapidity





s ≤ ISR.







Fritiof

Resultsˇ

Remember Fritiof?

Hadronises as if doubly diffractive excitation





s ≤ ISR.







Fritiof

Resultsˇ

Remember Fritiof?

The picture in pA





s ≤ ISR.







Fritiof

Resultsˇ

Remember Fritiof?

The picture in pA





s ≤ ISR.




(semi-)hard parton–parton scatterings. PYTHIA8!



Fritiof

Resultsˇ

p

ν1

ν2

ν3

ν4

ν5



Fritiof

Resultsˇ

p

ν1

ν2

ν3

ν4

ν5

IP


Fritiofˆ

Results

Outlook

Does it work?


Fritiofˆ

Results

Outlook

Does it work?

YES!


Fritiofˆ

Results

Outlook

The ALICE plot with nuclei (DIPSY)

101 102 103

Nch, 2<|η|<4, p⟂ > 0.15 GeV

10-3

10-2

10-1

ratio to π

+π−

2K 0s /π

±

6φ/π±

2(Λ+Λ)/π±

6(Ξ+Ξ)/π±

16(Ω+Ω)/π±

e+ e−

DIPSY pp

Pythia8 + ropes

DIPSY pPb

DIPSY PbPb

[http://home.thep.lu.se/dipsy]


Fritiofˆ

Results

Outlook

The Ridge!

Pythia 8 default

Pythia 8 + shoving

0.5

0.6

0.7

0.8

0.9

1.0The ridge, 2 < |∆η| < 4

dN

d∆

φ

-1 0 1 2 3 40.50.60.70.80.91.01.11.21.31.4

∆φ

Ra

tio


Fritiofˆ

Results

Outlook

Centrality-dependent pseudo-rapidity distribution

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 bb 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 bb 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 bb 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 bb b

ATLASb

Fritiof/Pythia8

-2 -1 0 1 20

10

20

30

40

50

60

70

80

90

Centrality-dependent η distribution, pPb,√

SNN = 5 TeV.

η

(1/

Nev)

dN

ch/

dη

[arXiv:1508.00848]


Fritiofˆ

Results

Outlook

Outlook

We have all the ingredients: Rope hadronisation String shoving Heavy Ions with PYTHIA8-improved Fritiof

Currently being implemented as a plug-in to/in PYTHIA8.


Fritiofˆ

Results

Outlook

extra plots


Fritiofˆ

Results

Outlook

b bb 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 bb b b b

b b b bb b b b b b b b b b b b b b b

Datab

FritiofP8

Absorptive

0

2

4

6

8

10

Centrality 60-90%

dN

/d

η

-2 -1 0 1 2

0.6

0.8

1

1.2

1.4

MC

/D

ata


Fritiofˆ

Results

Outlook

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 bDatab

FritiofP8

Absorptive

0

20

40

60

80

100

Centrality 0-1%d

N/

dη

-2 -1 0 1 2

0.6

0.8

1

1.2

1.4

MC

/D

ata


Fritiofˆ

Results

Outlook

bb

bbbb b b

bbbbbb

b

b

b

b

bb

b

b

b

b

b

b

b

b

b

b

b

b

b

b

Datab

FritiofP8

Absorptive

10−5

10−4

10−3

10−2

10−1

1

10 1

pPb @ 5.02 TeV, Inclusive charged 1.3 < η < 1.81

/(2

πp⊥)d

2N

/d

p⊥

/d

η(G

eV2c2

)

1 10 1 10 2

0.6

0.8

1

1.2

1.4

p⊥ [GeV]

MC

/D

ata


Fritiofˆ

Results

Outlook

bb

bb b b b b

bbbbbb

b

b

b

b

bb

b

b

b

b

b

b

b

b

b

b

b

b

b

b

Datab

FritiofP8

Absorptive

10−5

10−4

10−3

10−2

10−1

1

10 1

pPb @ 5.02 TeV, Inclusive charged −1.3 < η < −0.81

/(2

πp⊥)d

2N

/d

p⊥

/d

η(G

eV2c2

)

1 10 1 10 2

0.6

0.8

1

1.2

1.4

p⊥ [GeV]

MC

/D

ata


DIPSY, ropes and shoving

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