Two-particle Bose-Einstein correlations in $pp$ collisions at $\mathbf {\sqrt{s} =}$ 0.9 and 7 TeV measured with the ATLAS detector

The
ATLAS
collaboration

Eur.Phys.J.C 75 (2015) 466, 2015.

CERN-LHC. Studies of Bose-Einstein Correlations (BEC) for pairs of like-sign charged particles measured in the kinematic range $p_{T} > 100\ MeV$ and $|\eta| < 2.5$ in proton-proton collisions at centre-of-mass energies of $0.9$ and $7\ TeV$ with the ATLAS detector at the CERN Large Hadron Collider are presented. In addition to minimum-bias data, high-multiplicity data recorded at $7\ TeV$ using a dedicated trigger are investigated. The integrated luminosities are approximately $7\ \mu$$b^{-1}$ (2009), $190\ \mu$$b^{-1}$ (2010) and $12.4\ nb^{-1}$ (2010) for $0.9\ TeV$, $7\ TeV$ minimum-bias and $7\ TeV$ high-multiplicity (HM) data samples, respectively.
Bose-Einstein correlations are measured in terms of a two-particle correlation function. The density function is parameterized in terms of the Lorentz-invariant four-momentum difference squared, $Q^{2}$, of the two particles. The studies were performed using the double-ratio correlation function $R_{2}(Q)$. In the double-ratio method, the single-ratio correlation function $C_{2}(Q)$ obtained from the data is divided by a similar single-ratio calculated using Monte Carlo events, which do not have BEC effects. The reference sample for each of the two single-ratios is constructed from unlike-sign charged-particle pairs.
A clear signal of Bose-Einstein correlations is observed in the region of small four-momentum difference. The BEC effect is usually described by a function with two parameters: the effective radius $R$ and the strength parameter $\lambda$ (incoherence or chaoticity parameter). To quantitatively characterize the BEC effect, the Gaussian $\Omega^{(G)}$ and the Exponential $\Omega^{(E)} $parametrizations are fit to the measured correlation functions. As the Gaussian parametrization provides a poor description of the BEC-enhanced region and hence the Exponential parametrization is used for the final results. The fits are performed in the $Q$ range $0.02\ GeV$ to $2\ GeV$ and with a bin width of $0.02\ GeV$. Around $Q \sim 0.7\ GeV$ there is a visible bump which is due to an overestimate of $\rho \to \pi^{+}\pi^{-}$ decays in the Monte Carlo simulation. Therefore the region $0.5 \le Q \le 0.9\ GeV$ is excluded from the fits.
The BEC parameters characterizing the correlation strength $\lambda$ and the correlation source size $R$ are measured for $0.9\ TeV$, $7\ TeV$ minimum-bias charged-particle events and $7\ TeV$ high-multiplicity charged-particle events with multiplicities $n_{ch} \ge 2$, $n_{ch} \ge 2$ and $n_{ch} \ge 150$, respectively. The average transverse momentum $k_{T}$ and the multiplicity $n_{ch}$ dependences of the BEC parameters are investigated for charged-particle multiplicities of up to $240$. A saturation effect in the multiplicity dependence of the correlation source size is observed using the high-multiplicity $7\ TeV$ data samples.
See Eur. Phys. J. C75 (2015) 466 for more details.

Loading Data...

Please try again later, or email info@hepdata.net if this error persists.

This table is too large to load automatically.

The table size is MB, which is greater than our threshold of MB.

Loading Data...

Please try again later, or email info@hepdata.net if this error persists.