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Azimuthal Correlations within Exclusive Dijets with Large Momentum Transfer in Photon-Lead Collisions
A Tumasyan1, W Adam2, T Bergauer2
1Yerevan Physics Institute, Yerevan, Armenia.
Physical Review Letters
|August 18, 2023
Summary
This study measured azimuthal angular correlations in photon-lead interactions, revealing insights into nuclear gluon polarization. Results suggest current models need refinement to explain observed correlations in high-energy collisions.
Area of Science:
- High-energy particle physics
- Quantum chromodynamics
- Nuclear physics
Background:
- Nucleon structure is complex, depending on parton transverse momenta, spatial geometry, and polarization.
- High-energy photons from ultraperipheral heavy-ion collisions offer a unique probe for studying this structure.
- Understanding nuclear gluon polarization is crucial for a complete picture of nucleon structure.
Purpose of the Study:
- To present the first measurement of azimuthal angular correlations for exclusive dijet production in photon-lead interactions.
- To investigate the sensitivity of this process to underlying nuclear gluon polarization.
- To compare experimental results with theoretical models.
Main Methods:
- Analysis of ultraperipheral lead-lead collisions at sqrt[s_{NN}]=5.02 TeV using a 0.38 nb^{-1} integrated luminosity dataset.
- Data collected with the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC).
- Measurement of the azimuthal angular correlations between the transverse momentum vectors of two jets.
Main Results:
- The second harmonic of the azimuthal angular correlation between the sum and difference of jet transverse momentum vectors was measured.
- This harmonic was found to be positive and exhibits a rising trend with increasing dijet transverse momentum.
- A widely used theoretical model, successful for proton scattering data, failed to reproduce the observed correlations.
Conclusions:
- The observed azimuthal angular correlations in photon-lead interactions provide evidence for nuclear gluon polarization effects.
- The discrepancy with the standard model suggests the need for refined theoretical frameworks incorporating gluon polarization.
- This measurement opens new avenues for exploring the multidimensional structure of nucleons.
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