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Using Z Boson Events to Study Parton-Medium Interactions in Pb-Pb Collisions
A M Sirunyan1, A Tumasyan1, W Adam2
1Yerevan Physics Institute, Yerevan, Armenia.
Physical Review Letters
|April 8, 2022
Summary
Measurements of charged hadrons in Z boson events reveal modifications in lead-lead (Pb-Pb) collisions compared to proton-proton (pp) collisions. These findings indicate changes in the parton shower and medium response within heavy ion interactions.
Area of Science:
- High-energy physics
- Nuclear physics
- Particle physics
Background:
- Investigating the properties of the quark-gluon plasma (QGP) is crucial for understanding the strong nuclear force.
- Z bosons provide a clean probe to study parton interactions within the QGP due to their well-defined production mechanism and decay.
Purpose of the Study:
- To measure the spectra of charged hadrons produced in association with Z bosons in lead-lead (Pb-Pb) and proton-proton (pp) collisions.
- To investigate modifications of parton showers and medium response in heavy-ion collisions by comparing Pb-Pb data to pp reference data.
Main Methods:
- Analysis of data from the CMS experiment at the Large Hadron Collider (LHC).
- Selection of hadronic collision events with a reconstructed Z boson candidate (pT > 30 GeV/c).
- Measurement of azimuthal angular distributions and fragmentation functions of charged hadrons relative to the Z boson direction.
Main Results:
- Observed modifications in the azimuthal angular correlations of charged hadrons in central Pb-Pb collisions compared to pp collisions.
- Significant changes in fragmentation functions and transverse momentum (pT) spectra of charged particles in central Pb-Pb events relative to the pp reference.
- These modifications suggest alterations in the longitudinal structure of the parton shower within the QGP.
Conclusions:
- The study provides evidence for the modification of parton showers and the medium's response in heavy-ion collisions.
- Z boson tagged jets offer a powerful tool to probe the properties of the QGP.
- The results highlight the sensitivity of these measurements to the in-medium effects experienced by partons.
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