This study focuses on the path-length dependent parton energy loss in lead-lead collisions at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The researchers analyze the azimuthal anisotropies of dijets with high transverse momentum to understand the behavior of partons within the dense partonic medium created in these collisions. The data used for the analysis were collected by the CMS experiment in 2018 and correspond to an integrated luminosity of 1.69 nb$^{-1}$. To investigate correlations between jets and hadrons, as well as between two hadrons, relative azimuthal angles and pseudorapidities ($\eta$) are constructed. These anisotropies are expressed using Fourier expansion coefficients $v_n$, where $n$ ranges from 2 to 4, representing different harmonics of the azimuthal distributions. To suppress background contributions from jet fragmentation processes, dijet $v_n$ values are extracted from long-range components (1.5 $\lt$ $\vert\Delta\eta\vert$ $\lt$ 2.5) of these correlations. It is observed that positive dijet $v_2$ values increase from central to more peripheral events, indicating a stronger path-length dependence for more peripheral collisions. However, they find that the $v_3$ and $v_4$ values are consistent with zero within experimental uncertainties. To evaluate possible deviations arising from imperfect acceptance correction, an analysis is performed by extracting long-range correlation distributions only from either negative or positive sides of $\Delta\eta$. Any differences observed compared to the nominal result are assigned as systematic uncertainties. Overall, this study provides valuable insights into parton energy loss and its dependence on path length within a dense partonic medium created in lead-lead collisions at high energies. The findings contribute to our understanding of quark-gluon plasma and the properties of the strong nuclear force.
- The study looked at how energy is lost by particles called partons in collisions between lead atoms at a very high energy of 5.02 TeV.
- Parton: A particle that makes up protons and neutrons.
- Energy loss: When particles lose some of their energy during a collision.
- The researchers analyzed the patterns of two high-energy jets that were produced in the collisions.
- Jets: Streams of particles produced when high-energy particles collide.
- The data used in the study was collected by an experiment called CMS in 2018, and it had a total amount of 1.69 nb$^{-1}$.
- Experiment: A scientific test or investigation to gather information.
- Luminosity: A measure of how many collisions happened during the experiment.
- The researchers investigated how these jets and other particles are related to each other using angles and positions.
- Correlations: Connections or relationships between different things.
- Azimuthal angles: Angles that describe the direction of a particle's motion around a central point.
- Pseudorapidities ($\eta$): A way to measure the position of a particle within an experiment.
- They expressed these relationships using numbers called Fourier expansion coefficients, which ranged from 2 to 4.
- Fourier expansion coefficients: Numbers used to describe patterns or shapes.
- To get rid of unwanted effects, they only looked at certain parts of the data, specifically when the difference in
Path-Length Dependent Parton Energy Loss in Lead-Lead Collisions at 5.02 TeV
The Large Hadron Collider (LHC) at CERN is the world’s most powerful particle accelerator, capable of producing lead-lead collisions with nucleon-nucleon center-of-mass energies up to 5.02 TeV. These high energy collisions create a dense partonic medium, which can be studied to gain insights into quark–gluon plasma and the properties of the strong nuclear force. In this study, researchers analyze azimuthal anisotropies of dijets with high transverse momentum to understand the behavior of partons within this medium and their path length dependent energy loss.
Data Collection and Analysis
The data used for this analysis were collected by the CMS experiment in 2018 and correspond to an integrated luminosity of 1.69 nb$^{-1}$. To investigate correlations between jets and hadrons, as well as between two hadrons, relative azimuthal angles ($\Delta \phi$) and pseudorapidities ($\eta$) are constructed. These anisotropies are expressed using Fourier expansion coefficients $v_n$, where $n$ ranges from 2 to 4, representing different harmonics of the azimuthal distributions. To suppress background contributions from jet fragmentation processes, dijet $v_n$ values are extracted from long-range components (1.5 $\lt$ $\vert\Delta\eta\vert$ $\lt$ 2.5) of these correlations.
Results
It is observed that positive dijet $v_2$ values increase from central to more peripheral events, indicating a stronger path-length dependence for more peripheral collisions. However, they find that the $v_3$ and $v_4$ values are consistent with zero within experimental uncertainties. To evaluate possible deviations arising from imperfect acceptance correction, an analysis is performed by extracting long-range correlation distributions only from either negative or positive sides of $\Delta\eta$. Any differences observed compared to the nominal result are assigned as systematic uncertainties..
Conclusion
Overall, this study provides valuable insights into parton energy loss and its dependence on path length within a dense partonic medium created in lead–lead collisions at high energies The findings contribute to our understanding of quark–gluon plasma and the properties of the strong nuclear force
The path-length dependent parton energy loss within the dense partonic medium created in lead-lead collisions at a nucleon-nucleon center-of-mass energy of $\sqrt{s_\mathrm{NN}}$ = 5.02 TeV is studied by determining the azimuthal anisotropies for dijets with high transverse momentum. The data were collected by the CMS experiment in 2018 and correspond to an integrated luminosity of 1.69 nb$^{-1}$. For events containing back-to-back jets, correlations in relative azimuthal angle and pseudorapidity ($\eta$) between jets and hadrons, and between two hadrons, are constructed. The anisotropies are expressed as the Fourier expansion coefficients $v_n$, $n = $ 2-4 of these azimuthal distributions. The dijet $v_n$ values are extracted from long-range (1.5 $\lt$ $\vert\Delta\eta\vert$ $\lt$ 2.5) components of these correlations, which suppresses the background contributions from jet fragmentation processes. Positive dijet $v_2$ values are observed which increase from central to more peripheral events, while the $v_3$ and $v_4$ values are consistent with zero within experimental uncertainties.
