[PPT] - Production of the D s meson in proton-proton collisions at 13 TeV PowerPoint Presentation

SLIDE 1

Arthur Gal University of Strasbourg Institut Pluridisciplinaire Hubert Curien

Production of the Ds± meson in proton-proton collisions at 13 TeV as a function of multiplicity

Rencontres QGP France 2019

SLIDE 2

Outline

Part II : Presentation of my current analysis work Part I : Physics motivations

→ Small systems versus heavy ion → What are the interests in proton-proton at high multiplicity ? → Heavy fmavour production as a function of multiplicity in proton-proton collisions → ALICE detector → Extraction of the Ds production yield → Production yield as a function of the event multiplicity in pp collisions

SLIDE 3

Three main collision systems : pp, p-Pb and Pb-Pb

chemical freeze-out kinetic freeze-out Pre- equilibrium QGP phase Hadronic gaz 0.5 - 1 7 10 20 fm/c (10-24 s)

Proton-proton Pb-Pb

→ quasi-perfect fmuid → hydrodynamic description → kinematically and chemically equilibrated → statistical physics principles → interplay between hard and soft QCD processes

hard scattering
multi parton interaction
fragmentation of beam remnants
initial and fjnal state radiation

→ relative contributions of these processes spatial distributions

f hard partons (x ≥ 10-3)

At LHC, three main collision systems available → small systems : pp, p-Pb → heavy ion : Pb-Pb

3

SLIDE 4

Proton-proton collision system

Why studying proton-proton ?

Historically pp is a reference system

→ no QGP in pp ⇒ reference for p-A and AA systems

Recently typical efgect of heavy-ion phenomenology has been observed in pp high multiplicity

→ test of the QCD → two-particle angular correlations ⇒ ridge observed (∆휙 ≃ 0, |∆휂| > 2 ) → azimuthal anisotropy harmonics ⇒ “elliptic fmow” harmonic v2

1 Ntrig dNpair d∆φ α 1 + X

n

2Vn∆cos(n∆φ)

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Expansion in Fourier series :

10.1007/JHEP09(2010)091 10.1016/j.physletb.2016.12.009

4

SLIDE 5

Proton-proton collision system

→ strangeness enhancement ⇒ originally proposed as a QGP signature

ALI-PUB-106886

10.1038/nphys4111

훺 (s s s) m ≃ 1.7 GeV/c2 훯 (d s s) m ≃ 1.3 GeV/c2 훬 (u d s) m ≃ 1.1 GeV/c2 K0s (d s) m ≃ 0.5 GeV/c2

strangeness content

→ enhancement increases with strangeness content rather than with mass or baryon number → similar to the patterns seen in p–Pb and Pb–Pb collisions at the LHC → behaviour not reproduced by any of the MC models commonly used

|< 0.5 η |

〉 η /d

ch

N d 〈 10

2

10

3

10

4

10 )

−

π +

+

π Ratio of yields to (

3 −

10

2 −

10

1 −

10

12) × (

+

Ω +

−

Ω 3) × (

+

Ξ +

−

Ξ Λ + Λ 2) × ( φ 2

S

2K 6) × ( p p+

ALICE = 7 TeV s pp, = 5.02 TeV

NN

s p-Pb, ALICE Preliminary = 13 TeV s pp, = 5.02 TeV

NN

s Pb-Pb, = 5.44 TeV

NN

s Xe-Xe,

ALI−PREL−159147

→ continuity between pp, pPb and PbPb

5

SLIDE 6

Heavy fmavour quarks to heavy fmavour hadrons

Fragmentation process in “PYTHIA”-like Monte Carlo models

Heavy fmavour hadrons

pen heavy fmavours : c → D0, D±, Ds±, D*±, Λc± … b → B0, B±, Bs± …

hidden heavy fmavours : c → J/Ψ, Ψ(2S) … b → γ(1S, 2S, 3S) …

→ non perturbative process → fragmentation model (Lund string model) → colour reconnection : colour connections between partons in the fjnal state coming from difgerent hard scattering processes → colour rope : string close in space can interact and form ropes ⇒ hadron production is afgected by the whole system evolution → possible perturbative QCD calculation of the production cross section down to low pT → difgerent heavy quarks ⇒ difgerent Q2 probed

Produced in hard scattering processes (high Q2)

6

Heavy fmavour quarks : mc ≃ 1.3 GeV/c2 , mb ≃ 4.2 GeV/c2 >> ΛQCD ≃ 0.2 GeV

SLIDE 7

Heavy fmavour as a function of multiplicity in proton-proton collision

〉

T

p d y /d N

2

d 〈 ) /

T

p d y /d N

2

(d

5 10 15 20 25

c <4 GeV/

T

p |<0.5, 2< y meson |

+

, D*

+

, D Average D >0

T

p |<0.9, y , |

e

+

e → ψ Prompt J/

= 7 TeV s ALICE, pp

not shown 〉 η /d N d 〈 ) / η /d N 6% unc. on (d ± +6%/-3% normalization unc. not shown

〉 η /d

ch

N d 〈 ) / η /d

ch

N (d

1 2 3 4 5 6 7 8 9

B feed-down unc. 0.4 − 0.2 − 0.2 0.4

1/2 (2) at low (high) multiplicity × B fraction hypothesis:

ALI−PUB−95849

→ heavy-fmavour relative yield enhancement qualitatively described by :

PYTHIA 8.157 calculations including the MPI contributions to particle production
percolation model (exchange of colour sources between the projectiles)
EPOS 3 event generator

ALICE paper pp 7 TeV (10.1007/JHEP09(2015)148)

〉

T

p d y /d N

2

d 〈 ) /

T

p d y /d N

2

(d

2 4 6 8 10 12 14 16 18 20 ALICE = 7 TeV s pp

B feed-down and normalization uncertainties not shown

c < 2 GeV/

T

p 1 <

D meson 2 4 6 8 10 12 14 16 18 20

c < 4 GeV/

T

p 2 <

>0

T

p Percolation, EPOS 3.099 EPOS 3.099 + Hydro PYTHIA 8.157

〉 η /d

ch

N d 〈 ) / η /d

ch

N (d

1 2 3 4 5 6 7 8 9

〉

T

p d y /d N

2

d 〈 ) /

T

p d y /d N

2

(d

2 4 6 8 10 12 14 16 18 20

c < 8 GeV/

T

p 4 <

〉 η /d

ch

N d 〈 ) / η /d

ch

N (d

1 2 3 4 5 6 7 8 9 2 4 6 8 10 12 14 16 18 20

c < 12 GeV/

T

p 8 <

ALI−PUB−92985

→ open vs hidden heavy fmavour production ⇒ the behaviour is most likely related to cc and bb production ⇒ not signifjcantly infmuenced by hadronisation

7

〉

T

p d y /d N

2

d 〈 ) /

T

p d y /d N

2

(d

5 10 15 20 25

c <4 GeV/

T

p |<0.5, 2< y meson |

+

, D*

+

, D Average D >0

T

p |<0.9, y , |

e

+

e → ψ Non-prompt J/

= 7 TeV s ALICE, pp

not shown 〉 η /d N d 〈 ) / η /d N 6% unc. on (d ± +6%/-3% normalization unc. not shown

〉 η /d

ch

N d 〈 ) / η /d

ch

N (d

1 2 3 4 5 6 7 8 9

B feed-down unc. 0.4 − 0.2 − 0.2 0.4

1/2 (2) at low (high) multiplicity × B fraction hypothesis:

ALI−PUB−92971

SLIDE 8

Ds meson

Motivation Ds meson measurement

ALICE paper pPb 5.02 TeV (arXiv:1906.03425)

10

2

10

3

10

|<0.5 η |

〉 η /d

ch

N d 〈

1

+

/ D

+ s

D

0.5 c < 8 GeV/

T

p 6 <

10

2

10

3

10

|<0.5 η |

〉 η /d

ch

N d 〈

1

+

/ D

+ s

D

0.5 c < 6 GeV/

T

p 4 < 10

2

10

3

10

|<0.5 η |

〉 η /d

ch

N d 〈

1

+

/ D

+ s

D

0.5 c < 4 GeV/

T

p 2 <

ALICE Preliminary

4.3% BR uncertainty not shown ± = 5.02 TeV s pp Minimum Bias, = 5.02 TeV

NN

s Pb, − p SPD multiplicity classes = 5.02 TeV

NN

s Pb, − Pb arXiv:1804.09083 V0 multiplicity classes

10

2

10

3

10

|<0.5 η |

〉 η /d

ch

N d 〈

1

+

/ D

+ s

D

0.5 c < 16 GeV/

T

p 12 < 10

2

10

3

10

|<0.5 η |

〉 η /d

ch

N d 〈

1

+

/ D

+ s

D

0.5 c < 12 GeV/

T

p 8 <

ALI−PREL−149859

→ within uncertainties, diffjcult to argue for a modifjcation of the Ds/D

+ yield ratios

in pp and p–Pb collisions Goal of my current work → Ds composed by a charm and a strange quark ⇒ study strangeness enhancement in conjunction with charm production → reach the overlap between pp and pPb, PbPb on the heavy fmavour side

8

⇒ Ds analysis as a function of multiplicity in pp ⇒ using the high statistics available in pp at √s = 13 TeV ⇒ complete the picture

SLIDE 9

Outline

Part II : Presentation of my current analysis work Part I : Physics motivations

→ Small systems versus heavy ion → What is are the interests in proton-proton at high multiplicity ? → Heavy fmavour production as a function of multiplicity in proton-proton collisions → ALICE detector → Extraction of the Ds production yield → Production yield as a function of the event multiplicity in pp collisions

SLIDE 10

10

Inner Tracking System Time Projection Chamber

Particle trajectories reconstruction

0.1 < pT < 50 - 80 GeV/c

Momentum measurement
Vertex reconstruction
Particle identifjcation

Key roles Time Of Flight

26 x 16m 10 000 tons

Particularities

“low” material budget (12-13% X0, ITS+TPC)
“low” B fjeld (∼ 0.5 T)
identifjed particles down to pT ∼ 100 MeV/c

ALICE detector

V0 (trigger, centrality, multiplicity)

SLIDE 11

20 40 60 80 100 120 140

tracklets

N 0.01 0.02 0.03 0.04 0.05 0.06 0.07

events

normalised N

11

Production yield

Corrected yield Data

→ proton-proton collision at √s = 13 TeV (2016, 2017, 2018) → 2 triggers : Minimum bias : ∼ 1.8 109 events High multiplicity : ∼ 330 106 events (HM-SPD) ∼ 900 106 events (HM-V0) → multiplicity estimator : SPD tracklets tracklets : segment built with clusters in the two layers of SPD → pT and multiplicity difgerential analysis

pT bins : [2, 4], [4, 6], [6, 8], [8, 12], [12, 16] GeV/c Ntracklets classes : [1, 10], [11, 20], [21, 30], [31, 45], [46, 150] MB trigger

Ncorr(Ds)||y|<0.5 = 1 ∆pT ∆y fprompt(pT ) . 1

2N D+

s +D− s

raw

(pT , Ntrk) Nevent(Ntrk) . [Acc.Eff]prompt(pT , Ntrk) . BR

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HMSPD MB

→ tracklets to density of charged particles ⇒ use correlations

Work in progress

SLIDE 12

12

Ds+ → 휙(1020)휋+ → K+ K- 휋+ BR = 2.27 ± 0.08 %

pp √s = 13 TeV

Topological reconstruction

K- 휋+ K+ c휏 ≃151.2 휇m 휙(1020) Exploiting the displaced Ds decay vertex, topological cuts and PID to extract the Ds Lxy pT(Ds) 휃p,xy d0,xy DCA

n paper :

experimentally :

|m(K+K-) - m(휙)|

SLIDE 13

13

) c (GeV/ p 1 10 in TPC (arb. units) x /d E d

2

10 π e K p d t

ALICE performance = 13 TeV s pp,

ALI−PERF−101240

Particle identifjcation

In TPC In TOF Two PID strategies → “conservative” : n = 3 in TPC and TOF when possible applied to each Ds daughter tracks

|Smesured − Sπ,K,p

expected| < nσ

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→ “strong” : TPC + TOF n = 3 TPC n = 2 or n = 1 if 600<pT<800 MeV TOF n = 3

SLIDE 14

2 4 6 8 10 12 14 16 ) c (GeV/

T

p 2 4 6 8 10 12 14 16 18 20 ) σ 3 ± Significance (

10 ≤

tracklets

N ≤ 1 20 ≤

tracklets

N ≤ 11 30 ≤

tracklets

N ≤ 21 45 ≤

tracklets

N ≤ 31 150 ≤

tracklets

N ≤ 46

Raw yield extraction

1.75 1.8 1.85 1.9 1.95 2 2.05 2.1 2.15

)

2

c ) (GeV/

±

π

±

K

±

Invariant mass (K

10 20 30 40 50 60

2

c Raw counts / 6.0 MeV/

0.7 ± ) = 10.9 σ 3 ± Significance ( 15 (9.57 %) ± ) = 157 σ 3 ± S ( 2 ± ) = 52 σ 3 ± B ( ) = 3.0165 σ 3 ± S/B (

2

c 0.001 GeV/ ± = 1.971

mass

µ

2

c 0.001 GeV/ ± = 0.011

mass

σ /ndf = 1.19

2

χ (+ c.c.)

+

π φ →

s +

D c ) < 8 GeV/

s ±

(D

T

p 6 <

N D+

s +D− s

raw

(pT , Ntrk)

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→ extracted from invariant mass histograms for each pT and Ntracklet bins

11 ≤ Ntrk ≤ 20

Signal extraction quality (for MB data) : → Ds and D+ peaks fjtted with a double gaussian background fjtted with an exponential function

14

5휎 3휎 → in most cases, the signal extracted has a signifjcance > 4휎

ALICE pp at √s = 13 TeV MB-V0 triggers ALICE pp at √s = 13 TeV MB-V0 triggers

Work in progress Work in progress

SLIDE 15

2 4 6 8 10 12 14 16 ) c (GeV/

T

p

2 −

10

1 −

10 1 prompt)

s

Acc x Eff (D

10 ≤

tracklets

N ≤ 1 20 ≤

tracklets

N ≤ 11 30 ≤

tracklets

N ≤ 21 45 ≤

tracklets

N ≤ 31 150 ≤

tracklets

N ≤ 46

Acceptance and effjciency corrections

[Acc.Eff]prompt(pT , Ntrk)

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correction needed to take into account : → the limited acceptance of the detector → the reconstruction effjciency of the Ds

(vertex, tracks and candidate selection + PID)

→ Monte Carlo simulations ⇒ Acc : toy MC ⇒ Efg : generation + transport MC

15

ALICE pp at √s = 13 TeV MB-V0 triggers

Work in progress

SLIDE 16

2 4 6 8 10 12 14 16 ) c (GeV/

T

p

6 −

10

5 −

10

4 −

10

3 −

10

2 −

10

y<|0.5|

)|

s

(D

corr

N

10, MB trigger ≤

trk

N ≤ 1 20, MB trigger ≤

trk

N ≤ 11 30, MB trigger ≤

trk

N ≤ 21 45, MB trigger ≤

trk

N ≤ 31 150, MB trigger ≤

trk

N ≤ 46

Production yield

→ increase of the production yield with multiplicity as expected

16

→ hierarchy between results in difgerent Ntracklet classes as a function of pT → consistent with other charm meson measurements

ALICE pp at √s = 13 TeV MB-V0 triggers

Work in progress

SLIDE 17

10 20 30 40 50 60 >

tracklets

y<|0.5|

)|

s

(D

corr

<N

y<|0.5|

)|

s

(D

corr

N

, MB trigger c < 4 GeV/

T

p 2 <

Production yield

Production yield divided by its MB quantity

17

ALICE pp at √s = 13 TeV MB-V0 triggers

Work in progress

SLIDE 18

10 20 30 40 50 60 >

tracklets

y<|0.5|

)|

s

(D

corr

<N

y<|0.5|

)|

s

(D

corr

N

, MB trigger c < 4 GeV/

T

p 2 < , MB trigger c < 6 GeV/

T

p 4 <

Production yield

18

ALICE pp at √s = 13 TeV MB-V0 triggers

Production yield divided by its MB quantity

Work in progress

SLIDE 19

10 20 30 40 50 60 >

tracklets

y<|0.5|

)|

s

(D

corr

<N

y<|0.5|

)|

s

(D

corr

N

, MB trigger c < 4 GeV/

T

p 2 < , MB trigger c < 6 GeV/

T

p 4 < , MB trigger c < 8 GeV/

T

p 6 <

Production yield

19

ALICE pp at √s = 13 TeV MB-V0 triggers

Production yield divided by its MB quantity

Work in progress

SLIDE 20

10 20 30 40 50 60 >

tracklets

y<|0.5|

)|

s

(D

corr

<N

y<|0.5|

)|

s

(D

corr

N

, MB trigger c < 4 GeV/

T

p 2 < , MB trigger c < 6 GeV/

T

p 4 < , MB trigger c < 8 GeV/

T

p 6 < , MB trigger c < 12 GeV/

T

p 8 <

Production yield

20

ALICE pp at √s = 13 TeV MB-V0 triggers

Production yield divided by its MB quantity

Work in progress

SLIDE 21

10 20 30 40 50 60 >

tracklets

y<|0.5|

)|

s

(D

corr

<N

y<|0.5|

)|

s

(D

corr

N

, MB trigger c < 4 GeV/

T

p 2 < , MB trigger c < 6 GeV/

T

p 4 < , MB trigger c < 8 GeV/

T

p 6 < , MB trigger c < 12 GeV/

T

p 8 < , MB trigger c < 16 GeV/

T

p 12 <

Production yield

21

→ do the ratios : Ds/D+ ⇒ strange/non-strange and D+/D0 ⇒ non strange/non-strange (analysis ongoing) What’s next ? → use the high multiplicity triggers to complete the study ⇒ strangeness enhancement ?

ALICE pp at √s = 13 TeV MB-V0 triggers

Production yield divided by its MB quantity

Work in progress

SLIDE 22

Conclusion

Outlook Conclusion → Similarity between efgects seen in heavy-ion and high-multiplicity pp collisions → Complete the high multiplicity part of the study with HM-SPD and HM-V0 triggers → Extract the Ds over D+ ratio → Confront the results with MC models → Motivation for the extension of light-fmavour to heavy-fmavour production → Ds production yield as a function of multiplicity in pp collisions

22