a pythia simulation study of - cyclotron institute · a&m cyclotron reu presentation thaug. 7 ,...
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A PYTHIA Simulation Study of Direct-Photon and π0-Triggered
Hadron Correlations in p+p Collisions at 𝑠𝑁𝑁 = 200 GeV
By Chris Marble (REU Student, Tarleton State University)
Advisor: Dr. Saskia Mioduszewski (Texas A&M University)
A&M Cyclotron REU Presentation
Aug. 7th, 2015
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Outline
• Background and Motivation
• PYTHIA Simulation Conditions and Analysis
• Comparison of Simulation vs. STAR Data
• Study of pT trigger/pT parton distribution
• Future Work
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Background
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• Relativistic Heavy Ion Collider (RHIC) collides Au+Au at 0.99995 c.
• The collision is believed to temporarily create a new state of matter called Quark Gluon Plasma.
• Early collisions of quarks and gluons (within protons and neutrons) in the Au nuclei can result in hard scattering. However in Au+Au collisions hard scattered partons must pass through QGP.
Image from: http://www.staff.science.uu.nl/~misch101/research.htm
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Motivation • Simulation of photon + jet versus jet + jet production
– How well are per-trigger yields measured in p+p reproduced by simulation?
– What can simulation tell us about how much of the jet energy is carried by the trigger particle?
Image 1 from: http://inspirehep.net/record/853601/plots
Image 2 from: http://www-cdf.fnal.gov/physics/new/qcd/run2/ue/chgjet/
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Motivation • Simulation of photon + jet versus jet + jet production
– How well are per-trigger yields measured in p+p reproduced by simulation?
– What can simulation tell us about how much of the jet energy is carried by the trigger particle?
Image 1 from: http://inspirehep.net/record/853601/plots
Image 2 from: http://www-cdf.fnal.gov/physics/new/qcd/run2/ue/chgjet/
π0
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Motivation • Simulation of photon + jet versus jet + jet production
– How well are per-trigger yields measured in p+p reproduced by simulation?
– What can simulation tell us about how much of the jet energy is carried by the trigger particle?
Image 1 from: http://inspirehep.net/record/853601/plots
Image 2 from: http://www-cdf.fnal.gov/physics/new/qcd/run2/ue/chgjet/
Photon
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Simulation Parameters
•Using the PYTHIA 8.185 event generator •Kept events with a photon or π0 with a high transverse momentum (pT) > 5 GeV/c and pseudorapidity ( 𝜂 ) < 1. •Kept associated hadrons that were charged with a pT > 1 GeV/c and 𝜂 < 1.
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Image from: http://www.quantumdiaries.org/tag/heavy-ion-physics/
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Analysis
• Analyzed events with transverse trigger momentum 8 < pT < 16 GeV/c (previous publication) or 12 < pT < 20 GeV/c (current paper draft)
• Studied pT of associated particles in away jet and near jet (π0 case).
• Made separate histograms for different zT cuts
• 𝑧𝑇 ≡ 𝑝𝑇assc/𝑝𝑇trig
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8-16 GeV/c Histograms Analyzed: 1. Fit two Gaussians and a
uniform background. 2. Took background value
and uncertainty from the fit
3. Integrated histogram peaks (-0.63, 0.63) and (π – 0.63, π + 0.63)
4. Subtracted the background
5. Normalized by dividing by the number of trigger particles.
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12-20 GeV/c Histograms Analyzed: 1. Integrated peaks (-1.4,
1.4) and (π - 1.4, π + 1.4) 2. Subtracted the
background calculated as the average value over (-1.4 , -0.8) and (0.8 ,1.4)
3. Normalized by dividing by the number of trigger particles.
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Compare Sim. to Exp. blue to brown (8-16 GeV/c), red to black (12-20 GeV/c)
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12 Reasonable agreement for both pT ranges
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Compare Sim. to Exp. for the away side jet with π0 triggers Note: blue to brown (8-16 GeV/c) is not in agreement at high zT
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Simulation underestimates yield for 8-16 GeV/c pT range Reasonable agreement for 12-20 GeV/c pT range
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Compare Sim. to Exp for the away side jet for photon triggers Reasonable agreement for simulation and experiment
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Note: Large uncertainties caused by large uncertainties in the experimental data points
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Simulation Verification
• 12-20 GeV/c simulation appears to be in agreement with the STAR Data
• 8-16 GeV/c simulation is also in agreement with STAR Data except for high-zT π0 away jet values
• Reason is undetermined.
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Now lets compare the away side jet zT yields for photon triggers versus π0 triggers.
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*where pT Parton is the pT of the away-side jet parton
8-16 GeV/c Pi0 Peak: 0.77 ± 0.02
12-20 GeV/c Pi0 Peak: 0.78 ± 0.02
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π0 simulation data unshifted
π0 pT 8-16 GeV/c shifted 0.77*zT π0 pT 12-20 GeV/c shifted 0.78*zT
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Future Work •Understand pT π0 Trigger/pT Parton > 1 •Look at the effect of removing kT (intrinsic parton pT) from the π0 simulation •Look at the effects of removing Initial and Final State Radiation from the π0 simulation.
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Photon vs. π0 summary •π0 triggers have on average approximately 80% of the pT of the scattered parton •Correcting for this results in yields for π0 and photon triggering that are close to agreement
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Acknowledgements • My advisor: Dr. Saskia Mioduszewski
• Dr. Nihar Sahoo - for providing guidance as well as the pT 12-20 GeV/c experimental data
• Derek Anderson - for helping me learn Root and PYTHIA as well as providing the initial simulation code
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8-16 GeV/c data from: Abelev et al. (STAR Collaboration), Phys. Rev. C 82 (2010)
12-20 GeV/c data from: STAR Preliminary data, STAR manuscript to be submitted for publication
NSF Grant No. 1263281 DOE Grant No. DE-FG02-07ER41485
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Extra Slides
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Additional Information
• Initial and Final State Radiation Enabled • pTHatMin = 4 GeV/c (minimum invariant pT
considered) • 500M HQCD events simulated:
– 86502 8-16 GeV/c Pi0 Triggers • 307358 Associated Particles
– 6447 12-20 GeV/c Pi0 Triggers • 30764 Associated Particles
• 1M Prompt Photon events simulated: – 45512 8-16 GeV/c Photon Triggers
• 93292 Associated Particles
– 6677 12-20 GeV/c Photon Triggers • 18432 Associated Particles
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From Primary Hard Scatter: -23
From Secondary Hard Scatter: -33
From Other (Decay, Baryogenesis of quarks not involved in the hard scatter, etc.): -500
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*where pT Parton is the pT of the away-side jet parton
8-16 GeV/c Pi0 Peak: 0.78 ± 0.02
12-20 GeV/c Pi0 Peak: 0.79 ± 0.02
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*where pT Parton is the pT of the away-side jet parton
8-16 GeV/c Photon Peak: 1.07 ± 0.02
12-20 GeV/c Photon Peak: 1.04 ± 0.02
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From Primary Hard Scatter: -23
From Secondary Hard Scatter: -33
From Other (Decay, Baryogenesis of quarks not involved in the hard scatter, etc.): -500
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Photon Simulation without Initial and Final State Radiation (ISR and FSR), Multi-Parton Interactions (MPI) and Initial Parton pT (kT) Note: The red line completely overlaps the blue line