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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>∆φ</title>
<!--
In order to write latex-style equations, i.e. <span lang=latex>\sqrt{s}</span>.
(see https://www.codecogs.com/latex/integration/htmlequations.php)
-->
<script type="text/javascript" src="http://latex.codecogs.com/latexit.js"></script>
</head>
<body>
<div align='center' style='padding:10px;background-color:#DC143C11'>
<strong>
Measurement of the azimuthal decorrelation angle<br>
between the leading jet and scattered lepton<br>
in deep inelastic scattering at HERA
</strong>
</div>
<hr>
web page meintained by Ivan Pihdurskyi <[email protected]><br>
last eddited: 12.06.2020
<hr>
<div>
<h2>Introduction</h2>
Azimuthal angular decorrelation measurements have been extensively studied because it
is one of the preferred channels to study perturbative QCD, soft-gluon radiation and its
implications looking for physics beyond the standard model. Several decorrelation meas-
urements of two jets have been performed in hadron collisions at a large center-of-mass
energy [1–3]. In these collisions, the azimuthal decorrelation angle ∆φ is equal to π (back-
to-back events) in the extreme case when the two jets are produced with equal transverse
momenta and there is no soft-gluon radiation. Recent pQCD calculations have been able
to provide excellent description of the data in high-energy hadron collisions [4]. Theoret-
ical calculations of lepton-jet decorrelation rely on simplified calculation compared to the
counterpart in hadron collision [5]. New azimuthal angular decorrelation measurements
with the HERA collider in deep inelastic scattering (DIS) are presented in this analysis.
In this lepton-proton type of collider, events will deviate from ∆φ ∼ π due to higher order
gluon radiation and the intrinsic transverse momentum of the struck parton in the proton,
providing a way to study transverse momentum distribution (TMDs) and its evolution in
squared four-momentum transfer Q2. Additionally, the kinematic coverage at HERA
is capable to reach lower values of Bjorken-x (xBj ), which provide valuable information in
the study of the nucleon structure and will complement previous measurements at large
center-of-mass energy, where pQCD calculation has shown good agreement with the data.
The relative low energy measurements at HERA will test the limits and/or reach of the
perturbative calculation. With the possible construction of a new electron ion collider
(EIC) in USA, the interest looking into lepton-proton collision data have been growing
both from the theory and experimental community.
<h2>Event selection</h2>
This analysis was performed with data taken during HERA II period with electron collision
in the years 2004-2006, corresponding to an integrated luminosity of 189 pb−1,
and during the years 2006-2007 for the positron period with 143 pb−1.
During these periods, the lepton energy was Ee = 27.5 GeV collided with protons of an energy 920 GeV,
corresponding to a centre-of-mass energy √s = 318 GeV.
The selection of neutral current (NC) events was perform in a similar manner that previous
ZEUS analysis of jets in DIS [6, 7]. The cuts used in this analysis are the following:
<ul>
<li>10 GeV<sup>2</sup> < Q<sup>2</sup> < 350 GeV<sup>2</sup></li>
<li>y<sub>jb</sub> > 0.04</li>
<li>y<sub>el</sub> < 0.7</li>
<li>|z<sub>vtx</sub>| < 40 cm</li>
<li>45 < E − p<sub>z</sub> < 65 (both calorimeter and Zufo)</li>
<li>p<sub>T</sub> / √E<sub>T</sub> < 2.5 (of the calorimeter)</li>
<li>Lepton Energy E > 10 GeV</li>
<li>140<sup>⚬</sup> < θ<sub>lepton</sub> < 180<sup>⚬</sup></li>
<li>Lepton position x<sup>2</sup> + y<sup>2</sup> > 20 cm<sup>2</sup></li>
<li>Hadronic energy inside cone centred on electron has to be smaller than 10% of total energy in cone</li>
<li>Use lepton with highest probability and Prob > 0.9</li>
<li>Trigger SPP02 for 0405e</li>
<li>Trigger SPP09 for 06e and 0607p</li>
<li>Jet transverse energy and momentum E<sub>T</sub> > 2.5 GeV and P<sub>T</sub> < 30 GeV</li>
<li>Jet |η| < 1</li>
</ul>
The same analysis procedure and cuts were used with ARIADNE Monte Carlo (MC) sample.
<!--Comparison of the data and MC at the detector level for the vertex, Q<sup>2</sup>, Bjorken-x and lepton inelasticity (electron method), is presented in fig. 1.-->
This analysis uses jets clustered with massive kt-jet algorithm [8], with jet resolution parameter R = 1.
<h2>Monte Carlo Simulation</h2>
The NC DIS events were generated with DJANGOH 1.6 [9].
The ARIADNE 4.12 colour-dipole model [10] was used for parton showering.
The Lund string model was used for hadronization, as implemented in JETSET 7.4.1 [11].
Diffration processes were included in the simulation.
<h2>Control plots</h2>
<ul>
<li>
<a href="absetale1/control-plots/index.html">|η<sup>Jet</sup>| < 1</a>
<font color=green>✓</font>
</li>
<li>
<a href="widereta/control-plots/index.html">-1.5 < η<sup>Jet</sup> < 1.8</a>
<font color=green>✓</font>
</li>
</ul>
<h2>Bin migration matrices</h2>
<table>
<tr>
<th>|η<sup>Jet</sup>| < 1</th>
<th>-1.5 < η<sup>Jet</sup> < 1.8</th>
</tr>
<tr>
<td style="text-align:center">
<img width="90%" src="absetale1/xsections/images/mig-integral.png">
</td>
<td style="text-align:center">
<img width="90%" src="widereta/xsections/images/mig-integral.png">
</td>
</tr>
</table>
<h2>Unfolding</h2>
<font color=red>TODO: add correlation matrices with statistical uncertainties only</font>
<h2>Systematics</h2>
<ul>
<li>
The energy of the measured scattered lepton was varied by its known scale uncertainty of ±2% [6].
<ul>
<li>
<a href="absetale1/sys/siecorr/index.html">|η<sup>Jet</sup>| < 1</a>
<font color='green'>✓</font>
</li>
<li>
<a href="widereta/sys/siecorr/index.html">-1.5 < η<sup>Jet</sup> < 1.8</a>
<font color='green'>✓</font>
</li>
</ul>
</li>
<li>
The jet energy scale was varied ±4% for values of E<sub>T</sub><sup>jet</sup> < 10 GeV
and ±2.5% for E<sub>T</sub><sup>jet</sup> > 10 GeV [6]
<ul>
<li>
<a href="absetale1/sys/etjet/index.html">|η<sup>Jet</sup>| < 1</a>
<font color='green'>✓</font>
</li>
<li>
<a href="widereta/sys/etjet/index.html">-1.5 < η<sup>Jet</sup> < 1.8</a>
<font color='green'>✓</font>
</li>
</ul>
</li>
<!--<li>Add statistical error of theory curve ✓</li>-->
<li>
Difference between Ariadne and Lepto.
<ul>
<li>
<a href="absetale1/sys/lepto/index.html">|η<sup>Jet</sup>| < 1</a>
<font color='green'>✓</font>
</li>
<li>
<a>-1.5 < η<sup>Jet</sup> < 1.8</a>
<font color='red'>✗</font>
</li>
</ul>
</li>
<li>Breit frame <font color='red'>✗</font></li>
<li>
The uncertainty due to the lepton selection cuts was estimated by varying the values of
the cuts within the resolution of each variable (Not shown in this study).
<ul>
<li>
|η<sup>Jet</sup>| < 1
<ul>
<li><a href="absetale1/sys/eprob/index.html">Lepton probability</a> <font color='green'>✓</font></li>
<li><a href="absetale1/sys/y/index.html">Inelasticity</a> <font color='green'>✓</font></li>
<li><a href="absetale1/sys/empz/index.html">E - p<sub>z</sub></a> <font color='green'>✓</font></li>
</ul>
</li>
<li>
-1.5 < η<sup>Jet</sup> < 1.8
<ul>
<li><a href="widereta/sys/eprob/index.html">Lepton probability</a> <font color='green'>✓</font></li>
<li><a>Inelasticity</a> <font color='red'>✗</font></li>
<li><a href="widereta/sys/empz/index.html">E - p<sub>z</sub></a> <font color='green'>✓</font></li>
</ul>
</li>
</ul>
</li>
</ul>
<h2>Final plots and conclusions</h2>
<ul>
<li><a href="absetale1/xsections/index.html">|η<sup>Jet</sup>| < 1</a></li>
<li><a href="widereta/xsections/index.html">-1.5 < η<sup>Jet</sup> < 1.8</a></li>
</ul>
<h2>References</h2>
<ul>
<li>
[1] Abazov, V. M. and others, Measurement of dijet azimuthal decorrelations at central
rapidities in <span lang="latex">p\bar{p}</span> collisions at <span lang=latex>\sqrt{s}</span> = 1.96 TeV, Phys. Rev. Lett.94, 221801 (2005).
<br>
<a href='http://dx.doi.org/10.1103/PhysRevLett.94.221801'>doi:10.1103/PhysRevLett.94.221801</a>.
<a href='http://arxiv.org/abs/hep-ex/0409040'>arXiv:hep-ex/0409040</a>.
</li>
<li>
[2] Khachatryan, Vardan and others, Dijet Azimuthal Decorrelations inppCollisions at
<span lang=latex>\sqrt{s}</span> = 7 TeV, Phys. Rev. Lett.106, 122003 (2011).
<br>
<a href='http://dx.doi.org/10.1103/PhysRevLett.106.122003'>doi:10.1103/PhysRevLett.106.122003</a>.
<a href='http://arxiv.org/abs/1101.5029'>arXiv:1101.5029</a>.
</li>
<li>
[3] Aad, Georges and others, Measurement of Dijet Azimuthal Decorrelations in pp Collisions at √s = 7 TeV, Phys. Rev. Lett.106, 172002 (2011).
<br>
<a href='http://dx.doi.org/10.1103/PhysRevLett.106.172002'>doi:10.1103/PhysRevLett.106.172002.</a>
<a href='http://arxiv.org/abs/1102.2696'>arXiv:1102.2696</a>.
</li>
<li>
[4] Sun, Peng and Yuan, C. -P. and Yuan, Feng, Transverse Momentum Resummation for Dijet Correlation in Hadronic Collisions, Phys. Rev.D92, 094007 (2015).
<br>
<a href='http://dx.doi.org/10.1103/PhysRevD.92.094007'>doi:10.1103/PhysRevD.92.094007</a>.
<a href='http://arxiv.org/abs/1506.0617'>arXiv:1506.0617</a>.
</li>
<li>
[5] Liu, Xiaohui and Ringer, Felix and Vogelsang, Werner and Yuan, Feng, Lepton-jet correlations in deep inelastic scattering at the electron-ion collider, Phys. Rev. Lett.126122, 192003 (2019).
<br>
<a href='http://dx.doi.org/10.1103/PhysRevLett.122.192003'>doi:10.1103/PhysRevLett.122.192003</a>
</li>
<li>
[6] Abramowicz, H. and others, Measurement of isolated photons accompanied by jets in deep inelastic ep scattering, Phys. Lett.B715, 88 (2012).
<br>
<a href='http://dx.doi.org/10.1016/j.physletb.2012.07.031'>doi:10.1016/j.physletb.2012.07.031</a>.
<a href='http://arxiv.org/abs/1206.2270'>arXiv:1206.2270</a>.
</li>
<li>
[7] <a href='https://zeusdp.desy.de/ZEUS_ONLY/analysis/primer/DIS/index.html'>https://zeusdp.desy.de/ZEUS_ONLY/analysis/primer/DIS/index.html</a>
</li>
<li>
[8] Ellis, Stephen D. and Soper, Davison E., Successive combination jet algorithm for hadron collisions, Phys. Rev. D48, 3160 (1993).
<br>
<a href='http://dx.doi.org/10.1103/PhysRevD.48.3160'>doi:10.1103/PhysRevD.48.3160</a>
</li>
<li>
[9] Spiesberger, H, Django 1.6 Version 4.6.6 A Monte Carlo Generator for Deep Inelastic Lepton Proton Scattering Including QED and QCD Radiative Effects (2005).
<br>
<a href='http://wwwthep.physik.uni-mainz.de/~hspiesb/djangoh/djangoh.html'>http://wwwthep.physik.uni-mainz.de/~hspiesb/djangoh/djangoh.html</a>.
</li>
<li>
[10] Lonnblad, Leif, ARIADNE version 4: A Program for simulation of QCD cascades implementing the color dipole model, Comput. Phys. Commun.71, 15 (1992).
<br>
<a href='http://dx.doi.org/10.1016/0010-4655(92)90068-A'>doi:10.1016/0010-4655(92)90068-A</a>.
</li>
<li>
[11] Sjostrand, Torbjorn, High-energy physics event generation with PYTHIA 5.7 and JETSET 7.4, Comput. Phys. Commun.82, 74 (1994).
<br>
<a href='http://dx.doi.org/10.1016/0010-4655(94)90132-5'>doi:10.1016/0010-4655(94)90132-5</a>.
</li>
<li>
[12] Schmitt, Stefan, TUnfold: an algorithm for correcting migration effects in high energy physics, JINST7, T10003 (2012).
<br>
<a href='http://dx.doi.org/10.1088/1748-0221/7/10/T10003'>doi:10.1088/1748-0221/7/10/T10003</a>.
<a href='http://arxiv.org/abs/1205.6201'>arXiv:1205.6201</a>.
</li>
</ul>
<h2>HOWTO</h2>
<ol>
<li>
To apply event selection and generate intermediate root-files see <a href='https://www.desy.de/~pidhii/code/runner/README.txt'>README</a>.
All needed files can be found in the <a href='https://www.desy.de/~pidhii/code/runner/'>"runner"-direcory</a>.<br>
Whole directory in a single archive: <a href='https://www.desy.de/~pidhii/code/runner.tar.gz'>runner.tar.gz</a>.
</li>
<li>
To produce control plots use <a href='https://www.desy.de/~pidhii/code/ControlPlots.cpp'>ControlPlots.cpp</a>.<br>
usage: <code>./ControlPlots -d <path-to-data.root> -m <path-to-mc> [--bin <ibin>]</code><br>
where pathes specify root-file generated with desired multiplicity, and <b>optional</b> parameter <em><code>ibin</code></em> specifies a bin to do the plots for; otherwize plots will be made for integrated kinematic range.<br>
You can also check out <code>./ControlPlots -h</code> for more information on command line options.
</li>
<li>
In order to produce plots for normalized cross sections (with unfolding) use <a href='https://www.desy.de/~pidhii/code/CrossSection.C'>CrossSection.C</a>.<br>
compilation: <code>g++ `root-config --cflags --libs` -lUnfold -lconfig++ -o CrossSection CrossSection.C</code><br>
usage: <code>./CrossSection --pt|q2 -d <path-to-data.root> -m <path-to-MC.root> -t <path-to-MC-had.root> --sys <list-of-systematics></code><br>
where <em><code>list-of-systematics</code></em> is the list of pathes (separated with spaces) to mc-root-files generated with, e.g., biased cuts.<br>
You can also check out <code>./CrossSections -h</code> for more information on command line options.
</li>
</ol>
</div>
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</body>
</html>