Abstract
Measurements of two-particle correlation functions and the first five azimuthal harmonics, v(1) to v(5), are presented, using 28 nb(-1) of p + Pb collisions at a nucleon-nucleon center-of-mass energy of root s(NN) = 5.02 TeV measured with the ATLAS detector at the LHC. Significant long-range ridgelike correlations are observed for pairs with small relative azimuthal angle (|Delta phi| 2 pi/3) over the transverse momentum range 0.4 4 GeV. The v(2)(p(T)), v(3)(p(T)), and v(4)(p(T)) are compared to the v(n) coefficients in Pb + Pb collisions at root s(NN) = 2.76 TeV with similar event multiplicities. Reasonable agreement is observed after accounting for the difference in the average p(T) of particles produced in the two collision systems.
Highlights
One striking observation in high-energy nucleus-nucleus (A + A) collisions is the large anisotropy of particle production in the azimuthal angle φ [1,2]
The event activity is characterized by either ETPb, the sum of transverse energy measured on the Pb-fragmentation side of the forward calorimeters (FCals) with −4.9 < η < −3.2, or Ncrhec, the off-line-reconstructed track multiplicity in the inner detector (ID) with |η| < 2.5 and pT > 0.4 GeV
The correlation functions are compared to the distributions of the recoil component, αYpceorrir( φ) in Eq (6), estimated from the peripheral event class defined by ETPb < 10 GeV
Summary
One striking observation in high-energy nucleus-nucleus (A + A) collisions is the large anisotropy of particle production in the azimuthal angle φ [1,2]. This anisotropy is often studied via a two-particle correlation of particle pairs in relative pseudorapidity ( η) and azimuthal angle ( φ) [3,4]. The data correspond to an energy of integrated luminosity of approximately 28 nb−1, recorded in 2013 by the ATLAS experiment at the LHC This measurement benefits from a dedicated high-multiplicity trigger (see Sec. II B). The analysis technique follows closely the previous ATLAS study of v2 and v3 based on a much smaller dataset from a short p + Pb run in 2012 [24]
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