Abstract
γ-Jet production is considered one of the best probes of the hot quark–gluon plasma in high-energy heavy-ion collisions since the direct γ can be used to gauge the initial energy and momentum of the associated jet. This is investigated within the Linear Boltzmann Transport (LBT) model for jet propagation and jet-induced medium excitation. With both parton energy loss and medium response from jet-medium interaction included, LBT can describe experimental data well on γ-jet correlation in Pb+Pb collisions at the Large Hadron Collider. Multiple jets associated with direct γ production are found to contribute significantly to γ-jet correlation at small pTjet<pTγ and large azimuthal angle relative to the opposite direction of γ. Jet medium interaction not only suppresses the leading jet at large pTjet but also sub-leading jets at large azimuthal angle. This effectively leads to the narrowing of γ-jet correlation in azimuthal angle instead of broadening due to jet-medium interaction. The γ-jet profile on the other hand will be broadened due to jet-medium interaction and jet-induced medium response. Energy flow measurements relative to the direct photon is illustrated to reflect well the broadening and jet-induced medium response.
Highlights
Though the Sudakov form factor from initial state radiation dominates the azimuthal angle correlation of di-jets and γ-jets with large transverse momentum, especially at Large Hadron Collider (LHC) [37, 38], it has been proposed that the large angle correlation could be influenced by large angle scattering between jet shower and medium partons that can provide insight into the emergence of strongly interacting fluid from an asymptotically weakly interaction theory [39]
To further investigate the contribution of sub-leading jets in γ-jet correlation, we show in Fig. 6 the γ-jet correlation in azimuthal angle ∆φγJ = |φγ − φjet| from Linear Boltzmann Transport (LBT) simulations and CMS experiment√data for p+p and 030% central Pb+Pb collisions at s = 2.76 TeV
Within the LBT Monte Carlo model for jet propagation in hot quark-gluon plasma (QGP) medium, we have studied γ-jet produc- tion and modification in high-energy heavy-ion collisions at LHC
Summary
Parton energy loss during jet propagation in dense medium can lead to suppression of the single inclusive hadron spectra at large transverse momentum [1,2,3,4,5,6,7,8,9,10], large transverse momentum γ-hadron [11,12,13,14,15,16] and dihadron correlations [17, 18] in high-energy heavy-ion collisions. We should note that this value of αs is only the effective strong coupling constant in the jet-medium interaction within the LBT model which employs the perturbative estimate of Debye screening mass as a cut-off in the transverse momentum transfer in the elastic scattering between jet-shower/recoil and medium partons.
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