Abstract
Abstract Subtraction of the large background in reconstruction is a key ingredient in jet studies in high-energy heavy-ion collisions at RHIC and the LHC. Here we address the question to which extent the most commonly used subtraction techniques are able to eliminate the effects of the background on the most commonly discussed observables at present: single inclusive jet distributions, dijet asymmetry and azimuthal distributions. We consider two different background subtraction methods, an area-based one implemented through the FastJet package and a pedestal subtraction method, that resemble the ones used by the experimental collaborations at the LHC. We also analyze different ways of defining the optimal parameters in the second method. We use a toy model that easily allows variations of the background characteristics: average background level and fluctuations and azimuthal structure, but cross-checks are also done with a Monte Carlo simulator. Furthermore, we consider the influence of quenching using Q-PYTHIA on the dijet observables with the different background subtraction methods and, additionally, we examine the missing momentum of particles. The average background level and fluctuations affect both single inclusive spectra and dijet asymmetries, although differently for different subtraction setups. A large azimuthal modulation of the background has a visible effect on the azimuthal dijet distributions. Quenching, as implemented in Q-PYTHIA, substantially affects the di-jet asymmetry but little the azimuthal dijet distributions. Besides, the missing momentum characteristics observed in the experiment are qualitatively reproduced by Q-PYTHIA.
Highlights
Final estimation-1 η (a) Transverse energy ETtower(η) .(b) Dispersion σTtower(η) .that may come from an underestimation of the background due to the zeroing of negative cells in steps 2, 5 in subsection 2.3.1.the dijet asymmetry is shown for different values of T
We consider the influence of quenching using Q-PYTHIA on the dijet observables with the different background subtraction methods and, we examine the missing momentum of particles
We focus on the effects of two ingredients: background fluctuations in a given event and quenching, on several jet observables like the dijet energy imbalance, the azimuthal distributions and the single jet spectra
Summary
In order to study jets in a heavy-ion environment, we will assume that they√are fully decoupled from the medium. We have checked that this minimum pT offers a compromise between minimizing the CPU time required for the simulations and minimizing the biases in the distributions (observed in [40]) for the minimum ET of the leading jet that we will use, see below. For the hardest and next-to-hardest jets in the event, with transverse energies ET 1 and ET 2 respectively, the distribution in azimuthal angle between them,. Where the sum runs over all charged particles in the event with transverse momenta piT and azimuthal angle φi. Note that the expression above has a sign that sets the projection of particles on the hemisphere of the leading jet to give a negative contribution to the sum
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