Background fluctuations in jet studies in heavy ion

Background fluctuations in jet studies in heavy ion collisions Antonio Da Silva Charles Hughes Antonio Da Silva, Charles Hughes, Christine Nattrass University of Tennessee, Knoxville Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 1

Motivation Want to study jets in heavy ion collisions ALICE Random cones compared to Tenn. Gen background generator PYTHIA Angantyr JHEP 03 (2012) 053 But there’s a large background. We need to understand it. Signal Background Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 2

Tenn. Gen background generator Track properties Event properties ε 1 ε 3 Blast Wave Fit d. N/dy ε 2 , ε 4 , ε 6 Momentum spectra Random p. T ALICE PLB 720 (2013) 52 -62 p. T Even event planes fixed at Ψ=0 Odd planes at random φ Multiplies from ALICE PRC 88 (2013) 044910 No jets! No resonances Emulates hydro correlations vn ε 5 Polynomial Fit vn ALICE JHEP 1609 (2016) 164 Azimuthal asymmetries p. T Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 Random φ 3

PYTHIA Angantyr JHEP (2018) 2018: 134 Based on PYTHIA 8 Sjöstrand, Mrenna & Skands, JHEP 05 (2006) 026 Comput. Phys. Comm. 178 (2008) 852. Based on Fritiof & wounded nucleons N-N collisions w/fluctuating radii → Lots of jets! And resonances! fluctuating σ No hydrodynamics, no jet quenching Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 4

Area-based background subtraction k. T algorithm For all i, j calculate: Combine smallest dij. If di. B smallest, di. B→ jet Repeat until no particles left Energy (arb. units) Particles, clusters Cacciari & Salam, PLB 659: 119– 126, 2008 Cacciari DIS 2006 Cacciari & Salam Phys. Lett. B 641: 57 -61, 2006 Jet candidates Median ρ=p. T/A Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 5

Random cones X Excluded R=0. 4 Real jets Excluded Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 6

Random cones JHEP 03 (2012) 053 ALICE This work Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 7

Shape of width of the distribution Single particle spectra Σp. T of N particles→N-fold convolution: Tannenbaum, PLB(498), 1– 2, Pg. 29 -34(2001) Add Poissonian fluctuations in N: Add non-Poissonian fluctuations in N due to flow Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 8

Width vs multiplicity Tenn. Gen ALICE Deviations Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 9

Width vs multiplicity Angantyr ALICE Discrepancy not from an excess of jets! Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 10

Width vs multiplicity Angantyr ALICE Doesn’t go away with random track orientation! Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 11

Shape of width of the distribution Single particle spectra Σp. T of N particles→N-fold convolution: Tannenbaum, PLB(498), 1– 2, Pg. 29 -34(2001) Assumes shape Add Poissonian fluctuations in N: Add non-Poissonian fluctuations in N due to flow Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 Assumes uncorrelated number fluctuations 12

Conclusions Comparisons with Tenn. Gen and Angantyr broadly support ALICE conclusions: random background Both studies indicate sensitivity to shape of spectrum Tenn. Gen studies indicate trivial flow correlations also import Important for model studies to treat background Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 13

Width vs multiplicity Consistent with random fluctuations Slight deviations Other sources of correlations. . . ? ALICE Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 14

Background density ρ ALICE ` This work Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 15

Random cones in ALICE Estimate ρ k. T jet finder→jet candidates ρ = Median(p. T/A) JHEP 03 (2012) 053 Draw Random cone Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 16

Width vs multiplicity Angantyr ALICE Little difference with collision energy! Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 17

Signal vs Background: the standard paradigm Background Combinatorial jet Christine Nattrass, University of Tennessee, Knoxville, 19 April 2020 Signal 18