QCD prediction of jet structure in 2D trigger-associated momentum correlations and implications for multiple parton interactions

Thomas A Trainor,F Fabbri,P Giacomelli

doi:10.1051/epjconf/20159002003

Abstract

The expression "multiple parton interactions" (MPI) denotes a conjectured QCD mechanism representing contributions from secondary (semi)hard parton scattering to the transverse azimuth region (TR) of jet-triggered p-p collisions. MPI is an object of underlying-event (UE) studies that consider variation of TR $n_{ch}$ or $p_t$ yields relative to a trigger condition (leading hadron or jet $p_t$). An alternative approach is 2D trigger-associated (TA) correlations on hadron transverse momentum $p_t$ or rapidity $y_t$ in which all hadrons from all p-p events are included. Based on a two-component (soft+hard) model (TCM) of TA correlations a jet-related TA hard component is isolated. Contributions to the hard component from the triggered dijet and from secondary dijets (MPI) can be distinguished, including their azimuth dependence relative to the trigger direction. Measured $e^+$-$e^-$ and p-\=p fragmentation functions and a minimum-bias jet spectrum from 200 GeV p-\=p collisions are convoluted to predict the 2D hard component of TA correlations as a function of p-p collision multiplicity. The agreement between QCD predictions and TA correlation data is quantitative, confirming a dijet interpretation for the TCM hard component. The TA azimuth dependence is inconsistent with conventional UE assumptions.

Highlights

In a high-energy physics (HEP) context dijet production has long been accepted as an important mechanism for hadron formation by parton fragmentation [1,2,3]
The spectrum hard component for p-p spectra has been described quantitatively by a pQCD calculation [12] based on a MB jet spectrum [18] and measured parton fragmentation functions (FFs) [9]. Those results establish that the spectrum and angular-correlation hard components in p-p collisions are jet related [10, 12], The present study extends that program with a method to predict 2D trigger-associated (TA) hadron correlations arising from dijets produced in high-energy p-p collisions based on measured FFs and a large-angle-scattered parton spectrum [19,20,21]
The two-component (soft+hard) model (TCM) for 2D TA correlations is based on the TCM for 1D yt spectra from p-p collisions which we briefly summarize here

Summary

Introduction

In a high-energy physics (HEP) context dijet production has long been accepted as an important mechanism for hadron formation by parton fragmentation [1,2,3]. Previously-accepted contributions from minimum-bias (MB) dijets to high energy collisions are displaced by the claimed presence of strong collective motion (flows) in a thermalized bulk medium or quark-gluon plasma to explain spectrum and correlation structure Such claims are based in part on the a priori assumption that all hadrons with transverse momentum pt < 2 GeV/c emerge from a thermalized bulk medium [8]. To establish a direct comparison between the system of fragmentation functions conditional on MB dijet spectrum and 2D TA correlations the FF system must be partitioned into trigger and associated components.

The importance of low-energy jets

How well does the TCM describe nuclear data?

Findings

Isolation of triggered dijets from secondaries

Summary