# TwoParticle Correlation in e e Collisions at 91

- Slides: 37

+ Two-Particle Correlation in e e Collisions at 91. 2 Ge. V with ALEPH Archived Data Anthony Badea, Austin Baty, Yen-Jie Lee, Christopher Mc. Ginn, Michael Peters, Jesse Thaler Massachusetts Institute of Technology Gian Michele Innocenti CERN Paoti Chang, Tzu-An Sheng National Taiwan University Marcello Maggi Universita degli Studi di Bari 2 nd JETSCAPE Winter School and Workshop 2019 Texas A&M University Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 1

Motivation pp e+ e- p. Pb Pb. Pb ? • Ridge observed in small systems, possible explanations: QGP Escape • • • Initial state effect (CGC) Final state effect due to mini-QGP MPIs Escape mechanism … • Similarity between e+e-, pp and AA • Event multiplicity per participant • d. N/dη(y) • Study of high multiplicity event with well-defined initial condition: • No complication from hadron structure, Gluon ISR • No multi-parton interaction Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 2

Remarkable similarity between e+e- and AA collisions Charged Hadron d. N/dη Total Charged Particle Multiplicity Per Participant e+ e- pp Au. Au Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 3

ΔΦ correlation with large η gap JHEP 09 (2010) 091 2<|Δη|<4. 8 Small N (Event Multiplicity) ΔΦ Projection > 35 particles ΔΦ Projection Large Event Multiplicity Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 4

Modeling e+e- collisions with AMPT J. L Nagle et. al PRC 97, 024909 (2018) Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 5

Modeling two strings configuration with AMPT J. L Nagle et. al PRC 97, 024909 (2018) Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 6

The ALEPH Detector Hadron Calorimeter Electromagnetic Superconducting Calorimeter Magnet (1. 5 T) Charged Particle Multiplicity Muon Chamber >30 10 -20 Time Projection Chamber <10 20 -30 Inner Tracking Chamber Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 7 >35

Hadronic Event Selection • Track Selection: • Number of TPC hits for a charged tracks >= 4 • |d 0| < 2 cm • |z 0|< 10 cm • |cosθ|<0. 94 (corresponding to |η|<1. 74) • p. T> 0. 2 Ge. V (p. T with respect to beam axis) • NTPC >=4 • x 2/ndf < 1000. • Neutral Hadron Selection: • ECAL / HCAL objects • E> 0. 4 Ge. V • |cosθ|<0. 98 Charged Particle Multiplicity >30 10 -20 <10 20 -30 • Event Selection: • Number of good charged particles >= 5 (including charged hadrons and leptons) • Number of good ch+neu. Particles >= 13 • Echarged > 15 Ge. V • |cos(θsphericity)|<0. 82 Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 8 >35

Event Shape: Thrust e+ Yen-Jie Lee (MIT) e- Two-Particle Correlation in e+e- with ALEPH archived data 9

Unfolded Thrust Distribution Pencil-like: T~1 Thrust (T) Spherical: T~0. 5 Typical e+e- annihilation events are more pencil-like Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 10

High Multiplicity Event in e+e- Collisions (1) Highest multiplicity event in ALEPH LEP 1 data Yen-Jie Lee (MIT) 55 Tracks T=0. 71 Two-Particle Correlation in e+e- with ALEPH archived data 11

High Multiplicity Event in e+e- Collisions (2) 44 Tracks T=0. 57 Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 12

High Multiplicity Event in e+e- Collisions (3) 39 Tracks T=0. 98 Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 13

Charged Particle Multiplicity • PYTHIA 6 (dots) gives reasonable description of multiplicity distribution in the ALEPH LEP 1 archived data • Slight under-predicting the high multiplicity tail • Note that PYTHIA 8 (default) significantly under-predict the high multiplicity tail (not shown) Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 14

Uncorrected Thrust Distributions Inclusive N 20≤N<30 N<10 N≥ 30 10≤N<20 N≥ 35 N: # of charged particles with p. T>0. 2 Ge. V and |η|<1. 74 High multiplicity events are more spherical Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 15

Uncorrected Thrust Distributions Inclusive N 20≤N<30 N<10 N≥ 30 10≤N<20 N≥ 35 N: # of charged particles with p. T>0. 2 Ge. V and |η|<1. 74 High multiplicity events are more spherical, reasonable description from PYTHIA Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 16

Beam Axis Analysis Soft radiation e+ e- Identical measurement as performed in pp, p. A and AA collisions in various experiments Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 17

Beam Axis Analysis η Φ e+ e- Pseuodorapidity (η) and azimuthal angle (Φ) are calculated with respect to the beam pipe Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 18

Beam Axis Analysis Φ 2 Δη=η 1 -η 2 Φ 1 e+ e- • Search for ridge signal with beam axis: enhance number of charged particle pairs with large Δη gap and similar Φ (small ΔΦ=Φ 1 -Φ 2) • Ex: Sensitive to “pressure driven expansion” of the medium in the direction perpendicular to the beam axis New results since QM 2018 will be presented in Anthony’s talk Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 19

Beam Axis Analysis e+ e- See Anthony’s talk No ridge signal is found in beam axis analysis, which is mainly sensitive to perturbative physics (+ parton shower) Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 20

Thrust Axis Analysis e+ e- Thrust axis analysis to follow the “direction of color string” Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 21

Thrust Axis Analysis Φ η e+ e- Thrust axis analysis to follow the “direction of color string” Pseuodorapidity (η) and azimuthal angle (Φ) are calculated with respect to the Thrust Axis Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 22

Thrust Axis Analysis Φ 1 e+ Δη=η 1 -η 2 e- Φ 2 Search for ridge signal with thrust axis: enhance number of charged particle pairs with large Δη gap and similar Φ (small ΔΦ=Φ 1 -Φ 2) Thrust axis analysis to follow the “direction of color string” Pseuodorapidity (η) and azimuthal angle (Φ) are calculated with respect to the Thrust Axis Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 23

Event Mixing in Thrust Axis Analysis Signal Event Matched Event Thrust axis of the signal event e+ e- e+ Thrust axis of the signal event e- • Use the signal event Thrust axis to calculate the particle (η, Φ) distributions. • Problem: (η, Φ) distributions of the mixed event will not match with the spectra in the signal events in the multiplicity bin • Idea: Reweight the mixed event (η, Φ) distribution to match the average (η, Φ) distributions in the multiplicity bin Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 24

Two-Particle Correlation Function Signal pair distribution: Beam Axis Background pair distribution: Event 1 same event pairs mixed event pairs Event 2 Reweight the mixed event to match the signal event η-Φ distributions Δη = η 1 -η 2 Δφ = φ1 -φ2 Associated hadron yield per trigger: Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 25

Correlation Function with Thrust Axis ALEPH e+e 10≤N<20 Thrust axis CMS pp Inclusive Beam axis Correlation function with Thrust Axis as reference become much more similar to the beam axis result in pp collisions (with many caveats / differences) Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 26

Correlation Function with Thrust Axis ALEPH e+e 10≤N<20 Thrust axis ALEPH e+e. N≥ 35 Thrust axis Narrower away side peak in high multiplicity events Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 27

LEP 1 Data vs PYTHIA 6 N≥ 30 Projection 1. 6<|Δη|<3. 0 (Long range) (ZYAM subtracted) • Hint of near-side peak in data • Consistent with PYTHIA 6 without final state effects • Contribution from multi-jet correlation and reconstruction effects • PYTHIA 6 reference limited by archive MC statistics Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 28

LEP 1 Data vs PYTHIA 6 N≥ 35 Projection 1. 6<|Δη|<3. 0 (Long range) (ZYAM subtracted) • Hint of near-side peak in data • Consistent with PYTHIA 6 without final state effects • Contribution from multi-jet correlation and reconstruction effects • PYTHIA 6 reference limited by archive MC statistics Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 29

Thrust Axis Analysis e+ e- • “Perturbative QCD physics” still comes in the Thrust axis analysis (Jets) • One possibility to suppress jet component is to apply a |η| selection Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 30

Thrust Axis Analysis with “Barrel Particles” soft radiation Jet Veto e+ e • Remove particles at large η (in the leading and subleading jet) by requiring |η| < 1. 6 • Enhance the contribution of soft radiation • “Perturbative QCD physics” still comes in the Thrust axis analysis (Jets) • One possibility to suppress jet component is to apply a |η| selection Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 31

LEP 1 Data vs LEP 1 MC N≥ 35 Projection • Hint of near-side peak in data • Consistent with PYTHIA 6 w/o final state effects • Contribution from multi-jet correlation and reconstruction effect • PYTHIA 6 reference limited by archive MC statistics Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 32

LEP 1 Data vs LEP 1 MC N≥ 35 Projection |η| < 1. 6 • Hint of near-side peak in data • Consistent with PYTHIA 6 w/o final state effects • Contribution from multi-jet correlation and reconstruction effect • PYTHIA 6 reference limited by archive MC statistics Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 33

Future plan • Near term: • ZYAM: Change to fit (as opposite to the current local minimum) • Correct for the Thrust reco effects • Extract associated yield upper limit from data (See Anthony Badea’s talk) • New ideas: • Collinear drop algorithm for correlation analysis • Re-analyze large thrust region (jet core) • Possibility to have a more detail look at the jet structure fluctuation in e+e • Azimuthal angle correlation of particles inside the jet cone • Fragmentation function vs. multiplicity • D and B meson measurement vs. multiplicity • …Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data D 0→KK D 0→Kπ M(Kπ) (Ge. V)

Summary Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 35

MIT Team Demonstrating the value of open data Anthony Badea Austin Baty Gian Michele Innocenti Yen-Jie Lee Christopher Mc. Ginn Michael Peters Jesse Thaler Looking forward to LEP 2 data analysis! Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 36

Acknowledgement We would like to thank Roberto Tenchini and Guenther Dissertori from the ALEPH collaboration for the useful comments and suggestions on the use of ALEPH archived data. We would like to thank Wei Li, Maxime Guilbaud, Wit Busza and Yang-Ting Chen for the useful discussions on the analysis. The MIT group's work was supported by US DOE-NP Yen-Jie Lee (MIT) Two-Particle Correlation in e+e- with ALEPH archived data 37

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