Increasingly, with the data collected at the LHC we are confronted with the possible existence of flow in pp collisions. In this work, we show that PYTHIA 8 produces flowlike effects in events with ...multiple hard subcollisions due to color string formations between final partons from independent hard scatterings, the so-called color reconnection. We present studies of different identified hadron observables in pp collisions at 7 TeV. Studies have been done both for minimum bias and multiplicity intervals in events with and without color reconnection to isolate the flowlike effect.
QCD challenges from pp to A–A collisions Adolfsson, J.; Andronic, A.; Bierlich, C. ...
The European physical journal. A, Hadrons and nuclei,
2020, Volume:
56, Issue:
11
Journal Article
Peer reviewed
Open access
This paper is a write-up of the ideas that were presented, developed and discussed at the third International Workshop on QCD Challenges from pp to A–A, which took place in August 2019 in Lund, ...Sweden (Workshop link:
https://indico.lucas.lu.se/event/1214/
). The goal of the workshop was to focus on some of the open questions in the field and try to come up with concrete suggestions for how to make progress on both the experimental and theoretical sides. The paper gives a brief introduction to each topic and then summarizes the primary results.
The study and understanding of the details of proton-proton collisions is important since they are the benchmark for the comparison with heavy ion results. In the present work we have studied the ...ΔηΔφ correlations as a function of the event multiplicity and transverse sphericity in pp collisions at 7 TeV using the PYTHIA 8.180 generator. The results show large variation in the shape of the correlation as function of the sphericity and multiplicity indicating the importance of slicing the data in bins of both observables to better understand the complexity of the interactions. Motivated by the flow like patterns originated by color reconnection (CR), results with and without CR together with dihadron correlations are discussed.
At the LHC very interesting similarities among different colliding systems (p-p, p-Pb and Pb-Pb) where observed in the multiplicity evolution of the transverse momentum spectra. This has prompted a ...number of analyses that have explained the results in terms of collective hydrodynamic flow. The explanation in terms of hydrodynamics has recognized problems with the smallness of the interaction volume in the systems created in p-p and p- Pb collisions. On the other hand, some event generators based on QCD produce a reasonable qualitative, and sometimes quantitative, agreement with the data. Those results can be achieved introducing in the hadronisation model the so-called color reconnection which produces flowlike patterns via boosted strings. In this work we present the behavior of the various color reconnection (CR) schemes compared to those without the CR case for different center-of-mass energies at the LHC (0.9, 7 and 13 TeV).
A small-size prototype of a new Ring Imaging Cherenkov (RICH) detector using for the first time pressurized C4F8O radiator gas and a photon detector consisting of MWPC equipped with a CsI ...photocathode has been built and tested at the PS accelerator at CERN. It contained all the functional elements of the detector proposed as Very High Momentum Particle Identification (VHMPID) upgrade for the ALICE experiment at LHC to provide charged hadron track-by-track identification in the momentum range starting from 5 potentially up to 25GeV/c. In the paper the equipment and its elements are described and some characteristic test results are shown.
The proton-proton collisions at LHC energies reveals important new phenomena observed in heavy ions collisions and not completely understood in small systems. Different approaches and techniques have ...been implemented to study those processes, but still the details of the underlying event, which correspond at certain level to soft processes remains unknown. Here we present a study of proton-proton collisions using the event shape variable sphericity for identified particles combined with multiplicity bins. The results allow us to get important features of collisions, which could be used to explore in more details and extract phenomena of QCD processes.
The correlation multiplicity in forward-backward pseudorapidity is really important for the overall event characterization and to extract information on non-pertubative hadronic processes. In this ...work we present a study of the correlation conditions at LHC. Subsequently, the study is extended using p + p simulations of events to different energies, the correlations in multiplicity are studied with different initial conditions of the events in order to show how it is related to the mechanisms of hadronization, as well as concerning multiple partonic interactions, and consequently the degree of hardness of the collision. The sensitivity to the QCD color reconnection strength is reported.
Modifications of the structure of jets produced in ion-ion collisions represent a very sensitive tool to study the interactions of partons with the medium. Partonic energy loss manifests itself as a ...decrease of the number of particles carrying a high fraction of the jet energy and, the additional radiated energy, increases the number of low-energy particles. We present and analysis of jets produced in ion-ion collisions at LHC energies. Predictions with two different Monte Carlo simulation models (PYQUEN and Q-PYTHIA) for the parton energy loss, are analyzed together with modification of the jet structure.
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