source: HiSusy/trunk/Pythia8/pythia8170/phpdoc/Tunes.php @ 1

Last change on this file since 1 was 1, checked in by zerwas, 11 years ago

first import of structure, PYTHIA8 and DELPHES
File size: 16.9 KB
Line 
1<html>
2<head>
3<title>Tunes</title>
4<link rel="stylesheet" type="text/css" href="pythia.css"/>
5<link rel="shortcut icon" href="pythia32.gif"/>
6</head>
7<body>
8
9<script language=javascript type=text/javascript>
10function stopRKey(evt) {
11var evt = (evt) ? evt : ((event) ? event : null);
12var node = (evt.target) ? evt.target :((evt.srcElement) ? evt.srcElement : null);
13if ((evt.keyCode == 13) && (node.type=="text"))
14{return false;}
15}
16
17document.onkeypress = stopRKey;
18</script>
19<?php
20if($_POST['saved'] == 1) {
21if($_POST['filepath'] != "files/") {
22echo "<font color='red'>SETTINGS SAVED TO FILE</font><br/><br/>"; }
23else {
24echo "<font color='red'>NO FILE SELECTED YET.. PLEASE DO SO </font><a href='SaveSettings.php'>HERE</a><br/><br/>"; }
25}
26?>
27
28<form method='post' action='Tunes.php'>
29
30<h2>Tunes</h2>
31
32Since some physics aspects cannot be derived from first principles,
33this program contains many parameters that represent a true
34uncertainty in our understanding of nature. Particularly afflicted
35are the areas of hadronization and multiparton interactions, which both
36involve nonperturbative QCD physics.
37
38<p/>
39Technically, PYTHIA  parameters can be varied independently of each
40other, but the physical requirement of a sensible description of a set
41of data leads to correlations and anticorrelations between the
42parameters. Hence the need to produce tunes, not of one parameter at 
43a time, but simultaneously for a group of them. A well-known (separate)
44such example is parton densities, where combined tunes to a wide range
45of data have been produced, that can then be obtained prepackaged. 
46
47<p/>
48Given the many PYTHIA parameters to be tuned, it is convenient to
49divide the task into subtasks. Firstly, if we assume jet universality,
50hadronization and final-state parton showers should be tuned to
51<i>e^+e^-</i> annihilation data, notably from LEP1, since this
52offers the cleanest environment. Secondly, with such parameters fixed,
53hadron collider data should be studied to pin down multiparton interactions
54and other further aspects, such as initial-state radiation. Ideally this
55would be done separately for diffractive and non-diffractive events,
56although it is not possible to have a clean separation. (Thirdly
57would come anything else, such as physics with photon beams, which
58involve further parameters, but that is beyond the current scope.)
59
60<p/>
61The first step in this program has now been taken, with a tune to LEP1
62data by Hendrik Hoeth, using the Rivet + Professor framework. Starting
63with version 8.125 it defines the default values for hadronization
64parameters and timelike showers.
65
66<p/>
67The situation is more complicated for hadronic interactions in general
68and multiparton interactions in particular, where PYTHIA 8 is more
69different from PYTHIA 6, and therefore more work is needed. Specifically,
70it is <i>not</i> possible to "port" a PYTHIA 6 tune to PYTHIA 8.
71
72<p/>
73A first simple tune, appropriately called "Tune 1", became default
74starting with version 8.127. It was noted, in particular by Hendrik
75Hoeth, that this tune had a tension between parameters needed to
76describe minimum-bias and underlying-event activity. Therefore some
77further physics features were introduced in the code itself
78[<a href="Bibliography.php" target="page">Cor10a</a>], which were made default as of 8.140. This version
79also included two new tunes, 2C and 2M, based on the CTEQ 6L1 and the
80MRST LO** PDF sets, respectively. These have been made by hand, as a
81prequel to complete Professor-style tunings.
82
83<p/>
84The very first data to come out of the LHC showed a higher rapidity
85plateau than predicted for current PYTHIA 6 tunes, also for the lower
86energies. This may suggest some tension in the data. Two alternatives,
873C and 3M, were produced by a few brute-force changes of 2C and 2M.
88These were introduced in 8.140, but discontinued in 8.145 in favour of
89the new 4C tune, that is based on a more serious study of some early
90LHC data, see [<a href="Bibliography.php" target="page">Cor10a</a>]. Following the comparative studies in
91[<a href="Bibliography.php" target="page">Buc11</a>], which independently confirmed a reasonable agreement
92with LHC data, tune 4C was made the default as of 8.150. A variant is
93tune 4Cx, where the Gaussian matter profile has an <i>x</i>-dependent
94width [<a href="Bibliography.php" target="page">Cor11</a>].
95
96<p/>
97Several ATLAS tunes have now been included, obtained with different PDFs
98and with different emphasis on minimum-bias and underlying-event data
99[<a href="Bibliography.php" target="page">ATL12</a>]. These typically require LHAPDF to be linked, but this
100can be avoided in cases where the same PDF set is implemented internally.
101
102<p/>
103Central diffraction is a recent addition to the "soft QCD" process palette,
104and is thus not yet included in tunes; indeed its cross section is actively
105zeroed. You can switch it back on <i>after</i> you have selected your tune,
106with <code>SigmaTotal:zeroAXB = off</code>. But note that, since the
107total cross section is assumed unchanged, the minbias cross section
108is reduced and thus also the MPI machinery affected, even if effects
109should not be big (for a small central diffractive cross section).
110
111<p/>
112Note that comparisons with data also require that other aspects agree,
113such as that decay chains are stopped at an agreed-on level. For instance,
114in the ATLAS tunes all particles with a lifetime above 10 mm
115are considered stable, <code>ParticleDecays:limitTau0 = on</code>,
116<code>ParticleDecays:tau0Max = 10</code>. We have chosen not to
117include this as part of the tune settings itself, since the tune as
118such could still be used with any other choice of stable and
119unstable particles.
120
121<p/>
122Further comparisons have been posted on the
123<a href="http://mcplots.cern.ch/">MCPLOTS</a> pages.
124They have been produced with help of the
125<a href="http://projects.hepforge.org/rivet/">Rivet</a> package
126[<a href="Bibliography.php" target="page">Buc10</a>].
127
128<p/>
129In the future we hope to see further PYTHIA 8 tunes appear. Like with
130parton distributions, there is likely to be several tunes, because
131different sets of data will pull in different directions, by imperfections   
132in the model or in the data, and by differences in the chosen
133tuning strategies. We therefore propose to collect some of these tunes
134here, in a prepackaged form. Of course, in all cases it is a matter
135of setting values for parameters already defined elsewhere, so the
136tunes offer no new functionality, only a more convenient setup.
137
138<p/>
139You should be aware that the evolution of the program will not guarantee
140complete backwards compatibility between versions. Most obviously this
141concerns bug fixes. But also for some other major changes, like the
142introduction of the new diffractive machinery, the default behaviour
143of old tunes has been changed retroactively. (Which should be fine for
144diffraction, since previous tunes were not based on data strongly
145influenced by diffraction.) 
146
147<p/>
148The setup of the tunes is special, in that the choice of a tune forces
149the change of several different flags, modes and parameters. Furthermore
150a design principle has been that it should be possible to start out
151from a tune and then change a few of its settings. This gives power
152and flexibility at the expense of requiring a more careful ordering
153of commands. We therefore here sketch the order in which operations
154are carried out.
155<ol>
156<li>The constructor of a <code>Pythia</code> instance will read in
157all settings, and initialize them with their default values.
158</li>
159<li>At the end of this operation, the <code>Tune:ee</code> and
160<code>Tune:pp</code> modes (see further below) are checked. If either
161of them are positive the methods <code>Settings::initTuneEE(...)</code>
162and <code>Settings::initTunePP(...)</code>, respectively, are called
163to overwrite the whole collection of settings in the relevant tune.
164Zero (or negative) means that nothing will be done.
165</li>
166<li>After the <code>Pythia</code> constructor all the relevant values
167for the default tune(s) have thus been set up.
168</li>
169<li>You as a user can now start to overwrite the values at will,
170using <code>Pythia::readFile(...)</code> to read a configuration file,
171or a list of <code>Pythia::readString(...)</code> commands,
172or the lower-level <code>Settings</code> methods. All changes
173are made in the order in which the commands are encountered during
174the execution. A given variable can be changed multiparton times,
175but it is the latest change that sets the current value.
176</li>
177<li>The two <code>Tune:ee</code> and <code>Tune:pp</code> modes can also
178be changed in exactly the same way as described for all other settings
179above. Unique for them, however, is that when one of them is encountered
180it also initiates a call to the <code>initTuneEE(...)</code> or
181<code>initTunePP(...)</code> method, respectively. In such cases all
182settings affected by the <i>e^+e^-</i> or <i>pp/ppbar</i> tune
183are first reset to the default values (the <code>-1</code> options)
184and thereafter the relevant tune is set up.
185</li>
186<li>It is possible to mix commands of type 4 and 5 in any order; it
187is always the last change that counts. That is, any changes you have
188made to variables of a tune <i>before</i> a <code>Tune:ee</code> or
189<code>Tune:pp</code> command are overwritten by it, while variables
190you set <i>after</i> will overwrite the tune values. As a rule,
191therefore, you want to begin with the tune choice, and thereafter
192modify only a small part of its settings.
193</li>
194<li>Needless to say, the flexibility can lead to unwanted setups if
195you do not exercise some discipline. It is therefore recommended that
196you always check the listing obtained with
197<code>Pythia::settings.listChanged()</code> to confirm that the
198final set of changes is the intended one.
199</li>
200</ol>
201
202<br/><br/><table><tr><td><strong>Tune:ee </td><td>  &nbsp;&nbsp;(<code>default = <strong>0</strong></code>; <code>minimum = -1</code>; <code>maximum = 3</code>)</td></tr></table>
203Choice of tune to <ei>e^+e^-</ei> data, mainly for the hadronization
204and timelike-showering aspects of PYTHIA. You should study the
205<code>Settings::initTuneEE(...)</code> method to find exactly which
206are the settings for the respective tune.
207<br/>
208<input type="radio" name="1" value="-1"><strong>-1 </strong>: reset all values that are affected by any of the <ei>e^+e^-</ei> tunes to the default values. This option can be used  on its own, but is also automatically used as a first step for either  of the positive tune values below, to undo the effect of previous tune settings.  <br/>
209<input type="radio" name="1" value="0" checked="checked"><strong>0 </strong>: no values are overwritten during the initial setup, step 2 above. Note that changing to <code>0</code> in the user code has no effect; if you want to restore the individual settings you  should instead use <code>-1</code>.  <br/>
210<input type="radio" name="1" value="1"><strong>1 </strong>: the original PYTHIA 8 parameter set, based on some very old flavour studies (with JETSET around 1990) and a simple tune <ei>of alpha_strong</ei> to three-jet shapes to the new  <ei>pT</ei>-ordered shower. These were the default values before version 8.125.  <br/>
211<input type="radio" name="1" value="2"><strong>2 </strong>: a tune by Marc Montull to the LEP 1 particle composition, as published in the RPP (August 2007). No related (re)tune  to event shapes has been performed, however.   <br/>
212<input type="radio" name="1" value="3"><strong>3 </strong>: a tune to a wide selection of LEP1 data by Hendrik  Hoeth within the Rivet + Professor framework, both to hadronization and timelike-shower parameters (June 2009). These are the default values  starting from version 8.125, so currently there is no need for this option. <br/>
213
214<br/><br/><strong>Tune:preferLHAPDF</strong>  <input type="radio" name="2" value="on" checked="checked"><strong>On</strong>
215<input type="radio" name="2" value="off"><strong>Off</strong>
216 &nbsp;&nbsp;(<code>default = <strong>on</strong></code>)<br/>
217Tunes made by experimental collaborations typically use the LHAPDF
218package to obtain their PDF values, and so PYTHIA has to be linked
219accordingly. For PDFs implemanted natively in PYTHIA it is possible
220to use the respective tunes, without having to link to LHAPDF, if you
221set <code>Tune:preferLHAPDF = off</code> <i>before</i> the
222<code>Tune:pp</code> choice.
223 
224
225<br/><br/><table><tr><td><strong>Tune:pp </td><td>  &nbsp;&nbsp;(<code>default = <strong>5</strong></code>; <code>minimum = -1</code>; <code>maximum = 11</code>)</td></tr></table>
226Choice of tune to <ei>pp/ppbar</ei> data, mainly for the
227initial-state-radiation, multiparton-interactions and  beam-remnants
228aspects of PYTHIA. Note that the previous crude (non-)tunes
2293C and 3M are removed as of 8.145, superseded by the 4C tune.
230You should study the <code>Settings::initTunePP(...)</code> method
231to find exactly which are the settings for the respective tune.
232<br/>
233<input type="radio" name="3" value="-1"><strong>-1 </strong>: reset all values that are affected by any of the <ei>pp/ppbar</ei> tunes to the default values. This option can be used  on its own, but is also automatically used as a first step for either  of the positive tune values below, to undo the effect of previous tune settings.  <br/>
234<input type="radio" name="3" value="0"><strong>0 </strong>: no values are overwritten during the initial setup, step 2 above. Note that changing to <code>0</code> in the user code has no effect; if you want to restore the individual settings you  should instead use <code>-1</code>.  <br/>
235<input type="radio" name="3" value="1"><strong>1 </strong>: default used up to version 8.126, based on  some early and primitive comparisons with data. <br/>
236<input type="radio" name="3" value="2"><strong>2 </strong>: "Tune 1", default in 8.127 - 8.139, based on some  data comparisons by Peter Skands. Largely but not wholly overlaps with the default option 0. <br/>
237<input type="radio" name="3" value="3"><strong>3 </strong>: "Tune 2C", introduced with 8.140 <ref>Cor10a</ref>.  It uses the CTEQ 6L1 PDF, and is intended to give good agreement with  much of the published CDF data. <br/>
238<input type="radio" name="3" value="4"><strong>4 </strong>: "Tune 2M", introduced with 8.140 <ref>Cor10a</ref>. It is uses the MRST LO** PDF, which has a momentum sum somewhat above unity, which is compensated by a smaller <ei>alpha_s</ei> than in the previous tune. Again it is intended to give good agreement with much of  the published CDF data. <br/>
239<input type="radio" name="3" value="5" checked="checked"><strong>5 </strong>: "Tune 4C", new tune, introduced with 8.145  <ref>Cor10a</ref>. Starts out from tune 2C, but with a reduced cross  section for diffraction, plus modified multiparton interactions parameters  to give a higher and more rapidly increasing charged pseudorapidity  plateau, for better agreement with some early key LHC numbers.  See also the comparative study in <ref>Buc11</ref>. <br/>
240<input type="radio" name="3" value="6"><strong>6 </strong>: "Tune 4Cx", based on tune 4C, but using the x-dependent matter profile, <code>MultipartonInteractions:bProfile = 4</code> and an increased <code>MultipartonInteractions:pT0Ref</code> <ref>Cor11</ref>. <br/>
241<input type="radio" name="3" value="7"><strong>7 </strong>: "ATLAS MB Tune A2-CTEQ6L1", a minimum-bias tune based  on tune 4Cx, but without rapidity-ordered spacelike emissions <ref>ATL12</ref>. Uses CTEQ 6L1, by default  from LHAPDF.  <br/>
242<input type="radio" name="3" value="8"><strong>8 </strong>: "ATLAS MB Tune A2-MSTW2008LO", as above, but uses MSTW 2008 LO, by default from LHAPDF.  <br/>
243<input type="radio" name="3" value="9"><strong>9 </strong>: "ATLAS UE Tune AU2-CTEQ6L1", an underlying-event tune based on tune 4Cx, but without rapidity-ordered spacelike emissions <ref>ATL12</ref>. Uses CTEQ 6L1, by default from LHAPDF.  <br/>
244<input type="radio" name="3" value="10"><strong>10 </strong>: "ATLAS UE Tune AU2-MSTW2008LO", as above,  but uses MSTW 2008 LO, by default from LHAPDF.  <br/>
245<input type="radio" name="3" value="11"><strong>11 </strong>: "ATLAS UE Tune AU2-CT10", as above,  but uses CT 10, which is not currently implemented in PYTHIA,  so you must link LHAPDF.  <br/>
246<input type="radio" name="3" value="12"><strong>12 </strong>: "ATLAS UE Tune AU2-MRST2007LO*", as above,  but uses MRST 2007 LO*, by default from LHAPDF.  <br/>
247<input type="radio" name="3" value="13"><strong>13 </strong>: "ATLAS UE Tune AU2-MRST2007LO**", as above,  but uses MRST 2007 LO**, by default from LHAPDF.  <br/>
248
249<input type="hidden" name="saved" value="1"/>
250
251<?php
252echo "<input type='hidden' name='filepath' value='".$_GET["filepath"]."'/>"?>
253
254<table width="100%"><tr><td align="right"><input type="submit" value="Save Settings" /></td></tr></table>
255</form>
256
257<?php
258
259if($_POST["saved"] == 1)
260{
261$filepath = $_POST["filepath"];
262$handle = fopen($filepath, 'a');
263
264if($_POST["1"] != "0")
265{
266$data = "Tune:ee = ".$_POST["1"]."\n";
267fwrite($handle,$data);
268}
269if($_POST["2"] != "on")
270{
271$data = "Tune:preferLHAPDF = ".$_POST["2"]."\n";
272fwrite($handle,$data);
273}
274if($_POST["3"] != "5")
275{
276$data = "Tune:pp = ".$_POST["3"]."\n";
277fwrite($handle,$data);
278}
279fclose($handle);
280}
281
282?>
283</body>
284</html>
285
286<!-- Copyright (C) 2012 Torbjorn Sjostrand -->
Note: See TracBrowser for help on using the repository browser.