Observation of Multiplicity Dependent Prompt χ_{c1}(3872) and ψ(2S) Production in pp Collisions

Area of Science:

• High Energy Physics
• Particle Physics
• Quantum Chromodynamics

Background:

• The χ_{c1}(3872) is an exotic hadron whose internal structure remains under investigation.
• Understanding its properties can provide insights into non-perturbative Quantum Chromodynamics.
• Previous studies have explored its production mechanisms, but dependence on event multiplicity is less understood.

Purpose of the Study:

• To investigate the production of χ_{c1}(3872) and ψ(2S) hadrons as a function of charged particle multiplicity in proton-proton collisions.
• To test theoretical models, particularly the compact tetraquark hypothesis for χ_{c1}(3872), by examining production ratios.
• To probe the influence of the collision environment on the production mechanisms of these charmonium states.

Main Methods:

• Analysis of proton-proton collision data at a center-of-mass energy of 8 TeV.
• Measurement of χ_{c1}(3872) and ψ(2S) hadron production cross sections as a function of charged particle multiplicity.
• Separation of prompt production from production in b-hadron decays.
• Comparison of experimental results with theoretical predictions, including those based on the tetraquark model.

Main Results:

• The fraction of promptly produced χ_{c1}(3872) and ψ(2S) hadrons decreases with increasing charged particle multiplicity.
• The ratio of prompt χ_{c1}(3872) to ψ(2S) cross sections decreases with multiplicity.
• No significant multiplicity dependence was observed for the ratio of χ_{c1}(3872) to ψ(2S) produced in b-hadron decays.

Conclusions:

• The observed multiplicity dependence of prompt production is consistent with the χ_{c1}(3872) being a compact tetraquark state.
• The results provide constraints on theoretical models and shed light on the binding energy of the χ_{c1}(3872).
• The study highlights the importance of event multiplicity as a variable in understanding hadron production dynamics at the LHC.