Preliminary version Heavy Ion Physics the ALICE program

Preliminary version Heavy Ion Physics: the ALICE program Raimond Snellings 1. Physics motivation and the focus of our group 2. The NIKHEF hardware contribution to ALICE 3. Current status and our ambitions at NIKHEF Raimond Snellings

QCD at extreme conditions • Lattice QCD predicts a phase transition to a quark gluon plasma at energy densities of about 1 Ge. V/fm 3 and at a temperature of about 170 Me. V • The quark gluon plasma is a state of matter expected to have existed in the early universe about 1 microsecond after the Big Bang • Heavy-ion collisions provide experimental access to the properties of QCD matter at extreme temperature and density (the equation of state at the QGP phase transition and in the QGP phase) – Spontaneous chiral symmetry restoration • The origin of our mass – deconfinement • The building blocks of QCD, quarks and gluons, become quasi free 11/27/2020 Raimond Snellings 2

The focus of our group • The properties of the QCD Equation of State above Tc – dp/de calculable in lattice QCD – observables: collective motion of low transverse momentum particles as function of mass • The color density of hot and dense QCD matter – Induced soft gluon radiation by partons traversing the medium – observables: medium modifications of jets and heavy particle production 11/27/2020 Raimond Snellings 3

Heavy ion physics needs a reference… • QGP properties are calculable from first principles in lattice QCD • However currently our observables are not completely calculable from first principles (i. e. contributions from “cold” hadronic matter) • A reference measurement is needed and can be provided by elementary collisions (p+p and p+A) – p+A certainly not before 2010 • Or by collision geometry – Centrality dependence – Azimuthal dependence 11/27/2020 Raimond Snellings 4

Non central A-A collisions Non central collisions break the azimuthal symmetry! Observables, like the collective motion and the medium modification of jets, become azimuthally dependent. These are currently studied at STAR by our group 11/27/2020 Raimond Snellings 5

Azimuthal dependence of particle yield (elliptic flow) Phys. Rev. Lett. 86: 402 -407, 2001 e-Print Archive: nucl-ex/0009011 TOPCITE = 100+ Cited 265 times • • Strong elliptic flow observed at RHIC Agreement with hydrodynamic model calculations for non-peripheral collisions Mass dependence shows sensitivity to the Eo. S, heavy mass particles are particularly sensitive Day 1 measurement 11/27/2020 Raimond Snellings 6

Big impact! 11/27/2020 Raimond Snellings 7

Parton energy loss in hot and dense matter Radiated gluons decohere due to multiple interactions with the medium This energy loss depends on the path length and gluon density at the early phase 11/27/2020 Raimond Snellings 8

High-pt azimuthal correlations • Clear back to back azimuthal correlation in p+p and d+Au collisions • Disappearance of the back to back correlation in central Au+Au collisions • Color density more than 50 times larger than in cold nuclear matter! 11/27/2020 Raimond Snellings 9

“Jets” versus the reaction plane • Energy loss dependence on path length! 11/27/2020 Raimond Snellings 10

The analysis of elliptic flow and jet correlations are closely connected • Elliptic flow and jets, both sources of azimuthal correlations between the particles – Azimuthal correlations due to jets need to be understood in order to study flow – Azimuthal correlations due to flow need to be understood to study jets • At large transverse momenta largest contribution to azimuthal correlations still due to elliptic flow • After flow correction jet like signature clearly visible • Sophisticated analysis of multiparticle correlations allow to disentangle the flow component from the jets 11/27/2020 Raimond Snellings 11

The QGP observables we study versus the reaction plane in ALICE • Collective motion of low pt particles versus the reaction plane (elliptic flow) – Test of quark gluon plasma Equation of State properties, dp/de (calculable in lattice QCD) – Order of the phase transition – Open charm particularly interesting: test if heavy masses participate in the hydrodynamic behavior • Jet correlations versus the reaction plane – Detailed test of medium induced parton energy loss, jet quenching mechanism (length and gluon density dependence) – Open charm particularly interesting: detailed test of jet quenching mechanism (dead cone effect) 11/27/2020 Raimond Snellings 12

Why heavy-ions at the LHC? d. Nch/dy e[Ge. V/fm 3] (t 0 = 1 fm/c) Vf [fm 3] t. QGP [fm/c] t 0 SPS(17) 400 RHIC(200) 700 LHC(5500) 3000 -8000 ≈ 2. 5 ≈ 3. 5 - 7. 5 ≈ 15 – 40 ≈ 103 ≤ 1 ≥ 1 ≈ 7*103 1. 5 – 4 ≈ 0. 5 ≈ 2*104 4 – 10 ≤ 0. 2 • Larger, longer lived QGP phase – Observables get largest contribution from the QGP phase • Higher energies provide access to abundant hard probes (high-pt jets, charm, . . ) 11/27/2020 Raimond Snellings 13

Calculated elliptic flow and the QGP properties at the LHC Hirano, private communication 11/27/2020 Raimond Snellings • (black line) QGP contribution to the observable, increases with colliding energy • (red dots) total observed signal: QGP + hadron phase • At the LHC about 80% of the integrated flow signal generated in the QGP phase! 14

The best suited detector at the LHC for heavy-ions: ALICE • Ideally suited for these correlation with the reaction plane measurements – Full azimuthal coverage – Particle reconstruction and identification from 100 Me. V/c to tens of Ge. V/c – The key detectors are the TPC and the ITS (with the NIKHEF SSD contribution) 11/27/2020 Raimond Snellings 15

The Alice ITS • Strong contribution to outer layers (SSD) • project leader SSD (6 labs) • Main vertex 15 µm in central Pb. Pb • Vertex charm, strange decays 50 µm • Δp/p (p. T>1 Ge. V, with TPC) 14%->3% • Particle ID (d. E/dx) • FE module • Support and cooling • Endcap • ADC SSD 11/27/2020 • DAQ Raimond Snellings 16

NIKHEF ALICE hardware activities (SSD) • • • Design of SSD support (with Turin) Design ladder frames (with St. Petersburg) Design of SSD cooling system (with CERN) Design of front-end modules (with Kharkov and Strasbourg) Design ladder cabling (with Kharkov) • • Design SSD cabling (industrial production) Design and production of front-end module test equipment Design and production of End. Cap electronics Design and production of read-out modules • • Ladder assembly (with Nantes) Final SSD assembly • Bottom line: ITS project on schedule and NIKHEF SSD contribution will finish on time (2006) 11/27/2020 Raimond Snellings 17

ALICE group: current manpower • Utrecht and NIKHEF Amsterdam • Amsterdam manpower: – Staff physicist: 3 – Ph. D students: 2 • Amsterdam infrastructure: – Fraction of mechanical and electronics workshop – Ladder assembly room • Utrecht manpower: – – Staff physicist: 4 Post-doc: 1 Ph. D students: 5 Students: 2 • Utrecht infrastructure: – Fraction of the faculty mechanical and electronics workshop – mechanical and electronic workshop of the SAP department (4 fte) – Assembly room 11/27/2020 Raimond Snellings 18

ALICE group: current physics activities • Have strong role in STAR EMC analysis – 1 fte staff, 1 post-doc, 3 Ph. D's (until 2009) and 2 students • Had a leading role in correlation analysis with the reaction plane in STAR – Effort is scaled down to 1 Ph. D (until 2007) and 0. 2 fte staff • Have a coordinating role in correlation analysis with the reaction plane in ALICE (Physics Performance Report) – Effort 4 fte staff and 2 Ph. D – Will increase further with 3 Ph. D’s and 1 post-doc 11/27/2020 Raimond Snellings 19

Summary • NIKHEF ALICE hardware effort on track for timely delivery! • NIKHEF had and has a big impact in STAR physics program – Important preparation for the ALICE physics program • NIKHEF has a strong effort in physics analysis in ALICE, – observables identified which test the initial gluon density of the created system and the QCD Langrangian at the phase transition and in the quark gluon plasma phase – observables have in common correlations with the reaction plane – observables like elliptic flow and first jet correlations with the reaction plane are day one physics with big impact – observables like charm flow and charm energy loss provide more detailed constrains and are a longer term effort 11/27/2020 Raimond Snellings 20

Extra 11/27/2020 Raimond Snellings 21

ALICE: neutral Kaon flow E. Simili • Full simulations, using charged particle tracks from ITS and TPC to determine reaction plane and calculate neutral Kaon elliptic flow 11/27/2020 Raimond Snellings 22

Flow in non-central collisions: elliptic flow • Different flow in and out of the reaction plane: the main component elliptic flow • Unambiguous signature of collective motion • The driving force of elliptic flow dominates at “early” times (self quenching) – Largest contribution comes from QGP phase P. F. Kolb and U. Heinz, in Quark Gluon Plasma, nucl-th/0305084 11/27/2020 • Large magnitude of elliptic flow signature of hydrodynamic behavior (local thermalization -> LQCD) Raimond Snellings 23