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1	<html>
2	<head>
3	<title>PDF Selection</title>
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28	<form method='post' action='PDFSelection.php'>
29
30	<h2>PDF Selection</h2>
31
32	This page contains five subsections. The first deals with how to
33	pick the parton distribution set for protons, including from LHAPDF,
34	to be used for all proton and antiproton beams. The second is a special
35	option that allows a separate PDF set to be used for the hard process
36	only, while the first choice would still apply to everything else.
37	The third and fourth give access to pion and Pomeron PDF's, respectively,
38	the latter being used to describe diffractive systems.
39	The fifth gives the possibility to switch off the lepton
40	"parton density". More information on PDF classes is found
41	<?php $filepath = $_GET["filepath"];
42	echo "<a href='PartonDistributions.php?filepath=".$filepath."' target='page'>";?>here</a>.
43
44	<h3>Parton densities for protons</h3>
45
46	The selection of parton densities is made once and then is propagated
47	through the program. It is essential to make an informed choice,
48	for several reasons [<a href="Bibliography.php" target="page">Kas10</a>]:
49	<br/><b>Warning 1:</b> the choice of PDF set affects a number of
50	properties of events. A change of PDF therefore requires a complete
51	retuning e.g. of the multiparton-interactions model for minimum-bias and
52	underlying events.
53	<br/><b>Warning 2:</b> People often underestimate the differences
54	between different sets on the market. The sets for the same order are
55	constructed to behave more or less similarly at large <i>x</i> and
56	<i>Q^2</i>, while the multiparton interactions are dominated by the
57	behaviour in the region of small <i>x</i> and <i>Q^2</i>. A good
58	PDF parametrization ought to be sensible down to <i>x = 10^-6</i>
59	(<i>x = 10^-7</i>) and <i>Q^2 = 1</i> GeV^2 for Tevatron (LHC)
60	applications. Unfortunately there are distributions on the market that
61	completely derail in that region. The <code>main51.cc</code> and
62	<code>main52.cc</code> programs in the <code>examples</code>
63	subdirectory provide some examples of absolutely minimal sanity checks
64	before a new PDF set is put in production.
65	<br/><b>Warning 3:</b> NLO and LO sets tend to have quite different
66	behaviours, e.g. NLO ones have less gluons at small x, which then is
67	compensated by positive corrections in the NLO matrix elements.
68	Therefore do not blindly assume that an NLO tune has to be better than
69	an LO one when combined with the LO matrix elements in PYTHIA. There are
70	explicit examples where such thinking can lead you down the wrong alley,
71	especially if you study low-<i>pT</i> physics. In the list below you
72	should therefore be extra cautious when using set 6 or set 9.
73
74	<p/>
75	The simplest option is to pick one
76	of the distributions available internally:
77
78	<br/><br/><table><tr><td><strong>PDF:pSet </td><td>   (<code>default = <strong>2</strong></code>; <code>minimum = 1</code>; <code>maximum = 12</code>)</td></tr></table>
79	Parton densities to be used for proton beams (and, by implication,
80	antiproton ones):
81	<br/>
82	<input type="radio" name="1" value="1"><strong>1 </strong>: GRV 94L, LO <ei>alpha_s(M_Z) = 0.128</ei> (this set is out of date, but retained for historical comparisons).<br/>
83	<input type="radio" name="1" value="2" checked="checked"><strong>2 </strong>: CTEQ 5L, LO <ei>alpha_s(M_Z) = 0.127</ei> (this set is also out of date, but not badly so, and many tunes are based on it).<br/>
84	<input type="radio" name="1" value="3"><strong>3 </strong>: MRST LO* (2007), NLO <ei>alpha_s(M_Z) = 0.12032</ei>.<br/>
85	<input type="radio" name="1" value="4"><strong>4 </strong>: MRST LO** (2008), NLO <ei>alpha_s(M_Z) = 0.11517</ei>.<br/>
86	<input type="radio" name="1" value="5"><strong>5 </strong>: MSTW 2008 LO (central member), LO <ei>alpha_s(M_Z) = 0.13939</ei>.<br/>
87	<input type="radio" name="1" value="6"><strong>6 </strong>: MSTW 2008 NLO (central member), NLO <ei>alpha_s(M_Z) = 0.12018</ei> (NLO, see Warning 3 above).<br/>
88	<input type="radio" name="1" value="7"><strong>7 </strong>: CTEQ6L, NLO <ei>alpha_s(M_Z) = 0.1180</ei>.<br/>
89	<input type="radio" name="1" value="8"><strong>8 </strong>: CTEQ6L1, LO <ei>alpha_s(M_Z) = 0.1298</ei>.<br/>
90	<input type="radio" name="1" value="9"><strong>9 </strong>: CTEQ66.00 (NLO, central member), NLO <ei>alpha_s(M_Z) = 0.1180</ei> (NLO, see Warning 3 above).<br/>
91	<input type="radio" name="1" value="10"><strong>10 </strong>: CT09MC1, LO <ei>alpha_s(M_Z) = 0.1300</ei>.<br/>
92	<input type="radio" name="1" value="11"><strong>11 </strong>: CT09MC2, NLO <ei>alpha_s(M_Z) = 0.1180</ei>.<br/>
93	<input type="radio" name="1" value="12"><strong>12 </strong>: CT09MCS, NLO <ei>alpha_s(M_Z) = 0.1180</ei>.<br/>
94	<br/><b>Note:</b> the <i>alpha_s(M_Z)</i> values and the order of the
95	running in the description above is purely informative, and does not
96	affect any other parts of the program. Instead you have the freedom to
97	set <i>alpha_s(M_Z)</i> value and running separately for
98	<?php $filepath = $_GET["filepath"];
99	echo "<a href='CouplingsAndScales.php?filepath=".$filepath."' target='page'>";?>hard processes</a>
100	(including resonance decays),
101	<?php $filepath = $_GET["filepath"];
102	echo "<a href='MultipartonInteractions.php?filepath=".$filepath."' target='page'>";?>multiparton interactions</a>,
103	<?php $filepath = $_GET["filepath"];
104	echo "<a href='SpacelikeShowers.php?filepath=".$filepath."' target='page'>";?>initial-state radiation</a>, and
105	<?php $filepath = $_GET["filepath"];
106	echo "<a href='TimelikeShowers.php?filepath=".$filepath."' target='page'>";?>final-state radiation</a>.
107
108	<p/>
109	This is a reasonably complete list of recent LO fits, both
110	ones within the normal LO context and ones with modifications for better
111	matching to event generators. In addition two older sets are
112	included for backwards reference (most studies to date are based on
113	CTEQ 5L). If you link to the
114	<a href="http://projects.hepforge.org/lhapdf/" target="page">LHAPDF
115	library</a> [<a href="Bibliography.php" target="page">Wha05</a>] you get access to a much wider selection.
116	<br/><b>Warning 1:</b> owing to previous problems with the behaviour
117	of PDF's beyond the <i>x</i> and <i>Q^2</i> boundaries of a set,
118	you should only use LHAPDF <b>version 5.3.0 or later</b>.
119	<br/><b>Warning 2:</b> the behaviour of the LHAPDF sets need not be
120	identical with the implementation found in PYTHIA. Specifically we
121	are aware of the following points that may influence a comparison.
122	<br/>(a) CTEQ 5L in PYTHIA is the parametrization, in LHAPDF the grid
123	interpolation.
124	<br/>(b) MRST LO* and LO** in PYTHIA is based on an updated edition,
125	where one makes use of the expanded MSTW grid format, while LHAPDF
126	is based on the original smaller grid.
127	<br/>(c) The CTEQ 6 and CT09MC sets in PYTHIA are frozen at the
128	boundaries of the grid, by recommendation of the authors, while
129	LHAPDF also offers an option with a smooth extrapolation outside
130	the grid boundaries.
131
132	<br/><br/><strong>PDF:useLHAPDF</strong> <input type="radio" name="2" value="on"><strong>On</strong>
133	<input type="radio" name="2" value="off" checked="checked"><strong>Off</strong>
134	(<code>default = <strong>off</strong></code>)<br/>
135	If off then the choice of proton PDF is based on <code>PDF:pSet</code>
136	above. If on then it is instead based on the choice of
137	<code>PDF:LHAPDFset</code> and <code>PDF:LHAPDFmember</code> below.
138	<br/><b>Note:</b> in order for this option to work you must have
139	compiled PYTHIA appropriately and have set the <code>LHAPATH</code>
140	environment variable to provide the data-files directory of your local
141	LHAPDF installation. See the README file in the <code>examples</code>
142	directory for further instructions.
143
144
145	<br/><br/><table><tr><td><strong>PDF:LHAPDFset </td><td></td><td> <input type="text" name="3" value="MRST2004FF4lo.LHgrid" size="20"/>   (<code>default = <strong>MRST2004FF4lo.LHgrid</strong></code>)</td></tr></table>
146	Name of proton PDF set from LHAPDF to be used. You have to choose
147	from the
148	<a href="http://projects.hepforge.org/lhapdf/pdfsets" target="page">
149	list of available sets</a>. Examples of some fairly recent ones
150	(but still less recent than found above) would be
151	cteq61.LHpdf, cteq61.LHgrid, cteq6l.LHpdf, cteq6ll.LHpdf,
152	MRST2004nlo.LHpdf, MRST2004nlo.LHgrid, MRST2004nnlo.LHgrid and
153	MRST2004FF3lo.LHgrid. If you pick a LHpdf set it will require some
154	calculation the first time it is called.
155	<br/><b>Technical note:</b> if you provide a name beginning with a
156	slash (/) it is assumed you want to provide the full file path and then
157	<code>initPDFsetM(name)</code> is called, else the correct path is assumed
158	already set and <code>initPDFsetByNameM(name)</code> is called.
159
160
161	<br/><br/><table><tr><td><strong>PDF:LHAPDFmember </td><td></td><td> <input type="text" name="4" value="0" size="20"/>   (<code>default = <strong>0</strong></code>; <code>minimum = 0</code>)</td></tr></table>
162	Further choice of a specific member from the set picked above. Member 0
163	should normally correspond to the central value, with higher values
164	corresponding to different error PDF's somewhat off in different
165	directions. You have to check from set to set which options are open.
166	<br/><b>Note:</b> you can only use one member in a run, so if you
167	want to sweep over many members you either have to do many separate
168	runs or, as a simplification, save the
169	<?php $filepath = $_GET["filepath"];
170	echo "<a href='EventInformation.php?filepath=".$filepath."' target='page'>";?>pdf weights</a> at the hard scattering
171	and do an offline reweighting of events.
172
173
174	<br/><br/><strong>PDF:extrapolateLHAPDF</strong> <input type="radio" name="5" value="on"><strong>On</strong>
175	<input type="radio" name="5" value="off" checked="checked"><strong>Off</strong>
176	(<code>default = <strong>off</strong></code>)<br/>
177	Parton densities have a guaranteed range of validity in <i>x</i>
178	and <i>Q^2</i>, and what should be done beyond that range usually is
179	not explained by the authors of PDF sets. Nevertheless these boundaries
180	very often are exceeded, e.g. minimum-bias studies at LHC may sample
181	<i>x</i> values down to <i>10^-8</i>, while many PDF sets stop
182	already at <i>10^-5</i>. The default behaviour is then that the
183	PDF's are frozen at the boundary, i.e. <i>xf(x,Q^2)</i> is fixed at
184	its value at <i>x_min</i> for all values <i>x < x_min</i>,
185	and so on. This is a conservative approach. Alternatively, if you
186	switch on extrapolation, then parametrizations will be extended beyond
187	the boundaries, by some prescription. In some cases this will provide a
188	more realistic answer, in others complete rubbish. Another problem is
189	that some of the PDF-set codes will write a warning message anytime the
190	limits are exceeded, thus swamping your output file. Therefore you should
191	study a set seriously before you run it with this switch on.
192
193
194	<p/>
195	If you want to use PDF's not found in LHAPDF, or you want to interface
196	LHAPDF another way, you have full freedom to use the more generic
197	<?php $filepath = $_GET["filepath"];
198	echo "<a href='PartonDistributions.php?filepath=".$filepath."' target='page'>";?>interface options</a>.
199
200	<h3>Parton densities for protons in the hard process</h3>
201
202	The above options provides a PDF set that will be used everywhere:
203	for the hard process, the parton showers and the multiparton interactions
204	alike. As already mentioned, therefore a change of PDF should be
205	accompanied by a <b>complete</b> retuning of the whole MPI framework,
206	and maybe more. There are cases where one may want to explore
207	different PDF options for the hard process, but would not want to touch
208	the rest. If several different sets are to be compared, a simple
209	reweighting based on the <?php $filepath = $_GET["filepath"];
210	echo "<a href='EventInformation.php?filepath=".$filepath."' target='page'>";?>originally
211	used</a> flavour, <i>x</i>, <i>Q^2</i> and PDF values may offer the
212	best route. The options in this section allow a choice of the PDF set
213	for the hard process alone, while the choice made in the previous section
214	would still be used for everything else. The hardest interaction
215	of the minimum-bias process is part of the multiparton-interactions
216	framework and so does not count as a hard process here.
217
218	<p/>
219	Of course it is inconsistent to use different PDF's in different parts
220	of an event, but if the <i>x</i> and <i>Q^2</i> ranges mainly accessed
221	by the components are rather different then the contradiction would not be
222	too glaring. Furthermore, since standard PDF's are one-particle-inclusive
223	we anyway have to 'invent' our own PDF modifications to handle configurations
224	where more than one parton is kicked out of the proton [<a href="Bibliography.php" target="page">Sjo04</a>].
225
226	<p/>
227	The PDF choices that can be made are the same as above, so we do not
228	repeat the detailed discussion.
229
230	<br/><br/><strong>PDF:useHard</strong> <input type="radio" name="6" value="on"><strong>On</strong>
231	<input type="radio" name="6" value="off" checked="checked"><strong>Off</strong>
232	(<code>default = <strong>off</strong></code>)<br/>
233	If on then select a separate PDF set for the hard process, using the
234	variables below. If off then use the same PDF set for everything,
235	as already chosen above.
236
237
238	<br/><br/><table><tr><td><strong>PDF:pHardSet </td><td>   (<code>default = <strong>2</strong></code>; <code>minimum = 1</code>; <code>maximum = 12</code>)</td></tr></table>
239	Parton densities to be used for proton beams (and, by implication,
240	antiproton ones):
241	<br/>
242	<input type="radio" name="7" value="1"><strong>1 </strong>: GRV 94L, LO <ei>alpha_s(M_Z) = 0.128</ei> (out of date).<br/>
243	<input type="radio" name="7" value="2" checked="checked"><strong>2 </strong>: CTEQ 5L, LO <ei>alpha_s(M_Z) = 0.127</ei> (slightly out of date; many tunes are based on it).<br/>
244	<input type="radio" name="7" value="3"><strong>3 </strong>: MRST LO* (2007), NLO <ei>alpha_s(M_Z) = 0.12032</ei>.<br/>
245	<input type="radio" name="7" value="4"><strong>4 </strong>: MRST LO** (2008), NLO <ei>alpha_s(M_Z) = 0.11517</ei>.<br/>
246	<input type="radio" name="7" value="5"><strong>5 </strong>: MSTW 2008 LO (central member), LO <ei>alpha_s(M_Z) = 0.13939</ei>.<br/>
247	<input type="radio" name="7" value="6"><strong>6 </strong>: MSTW 2008 NLO (central member), LO <ei>alpha_s(M_Z) = 0.12018</ei>.<br/>
248	<input type="radio" name="7" value="7"><strong>7 </strong>: CTEQ6L, NLO <ei>alpha_s(M_Z) = 0.1180</ei>.<br/>
249	<input type="radio" name="7" value="8"><strong>8 </strong>: CTEQ6L1, LO <ei>alpha_s(M_Z) = 0.1298</ei>.<br/>
250	<input type="radio" name="7" value="9"><strong>9 </strong>: CTEQ66.00 (NLO, central member), NLO <ei>alpha_s(M_Z) = 0.1180</ei>.<br/>
251	<input type="radio" name="7" value="10"><strong>10 </strong>: CT09MC1, LO <ei>alpha_s(M_Z) = 0.1300</ei>.<br/>
252	<input type="radio" name="7" value="11"><strong>11 </strong>: CT09MC2, NLO <ei>alpha_s(M_Z) = 0.1180</ei>.<br/>
253	<input type="radio" name="7" value="12"><strong>12 </strong>: CT09MCS, NLO <ei>alpha_s(M_Z) = 0.1180</ei>.<br/>
254
255	<br/><br/><strong>PDF:useHardLHAPDF</strong> <input type="radio" name="8" value="on"><strong>On</strong>
256	<input type="radio" name="8" value="off" checked="checked"><strong>Off</strong>
257	(<code>default = <strong>off</strong></code>)<br/>
258	If off then the choice of proton PDF is based on <code>hardpPDFset</code>
259	above. If on then it is instead based on the choice of
260	<code>hardLHAPDFset</code> and <code>hardLHAPDFmember</code> below.
261	Note that if you want to use LHAPDF here, and you also use LHAPDF
262	for the "normal" PDF set, then LHAPDF must have been compiled so as to
263	handle (at least) two concurrent sets, with the configure statement
264	<code>--with-max-num-pdfsets=2</code>.
265
266
267	<br/><br/><table><tr><td><strong>PDF:hardLHAPDFset </td><td></td><td> <input type="text" name="9" value="MRST2004FF4lo.LHgrid" size="20"/>   (<code>default = <strong>MRST2004FF4lo.LHgrid</strong></code>)</td></tr></table>
268	Name of proton PDF set from LHAPDF to be used.
269
270
271	<br/><br/><table><tr><td><strong>PDF:hardLHAPDFmember </td><td></td><td> <input type="text" name="10" value="0" size="20"/>   (<code>default = <strong>0</strong></code>; <code>minimum = 0</code>)</td></tr></table>
272	Further choice of a specific member from the set picked above.
273
274
275	<p/>
276	Note that there is no separate equivalent of the
277	<code>PDF:extrapolateLHAPDF</code> flag specifically for the hard
278	PDF. Since LHAPDF only has one global flag for extrapolation or not,
279	the choice for the normal PDF's also applies to the hard ones.
280
281	<h3>Parton densities for pions</h3>
282
283	The parton densities of the pion are considerably less well known than
284	those of the proton. There are only rather few sets on the market,
285	and none particularly recent. Only one comes built-in, but others can
286	be accessed from LHAPDF. Input parametrizations are for the <i>pi+</i>.
287	>From this the <i>pi-</i> is obtained by charge conjugation and the
288	<i>pi0</i> from averaging (half the pions have <i>d dbar</i>
289	valence quark content, half <i>u ubar</i>.
290
291	<p/>
292	Much of the switches are taken over from the proton case, with obvious
293	modifications; therefore the description is briefer. Currently we have
294	not seen the need to allow separate parton densities for hard processes.
295	When using LHAPDF the <code>PDF:extrapolateLHAPDF</code> switch of the
296	proton also applies to pions.
297
298	<br/><br/><table><tr><td><strong>PDF:piSet </td><td>   (<code>default = <strong>1</strong></code>; <code>minimum = 1</code>; <code>maximum = 1</code>)</td></tr></table>
299	Internal parton densities that can be used for pion beams, currently with
300	only one choice.
301	<br/>
302	<input type="radio" name="11" value="1" checked="checked"><strong>1 </strong>: GRV 92 L.<br/>
303
304	<br/><br/><strong>PDF:piUseLHAPDF</strong> <input type="radio" name="12" value="on"><strong>On</strong>
305	<input type="radio" name="12" value="off" checked="checked"><strong>Off</strong>
306	(<code>default = <strong>off</strong></code>)<br/>
307	If off then the choice of proton PDF is based on <code>PDF:piSet</code>
308	above. If on then it is instead based on the choice of
309	<code>PDF:piLHAPDFset</code> and <code>PDF:piLHAPDFmember</code> below.
310
311
312	<br/><br/><table><tr><td><strong>PDF:piLHAPDFset </td><td></td><td> <input type="text" name="13" value="OWPI.LHgrid" size="20"/>   (<code>default = <strong>OWPI.LHgrid</strong></code>)</td></tr></table>
313	Name of pion PDF set from LHAPDF to be used. You have to choose from the
314	<a href="http://projects.hepforge.org/lhapdf/pdfsets" target="page">
315	list of available sets</a>.
316
317
318	<br/><br/><table><tr><td><strong>PDF:piLHAPDFmember </td><td></td><td> <input type="text" name="14" value="0" size="20"/>   (<code>default = <strong>0</strong></code>; <code>minimum = 0</code>)</td></tr></table>
319	Further choice of a specific member from the set picked above.
320
321
322	<h3>Parton densities for Pomerons</h3>
323
324	The Pomeron is introduced in the description of diffractive events,
325	i.e. a diffractive system is viewed as a Pomeron-proton collision at a
326	reduced CM energy. Here the PDF's are even less well known.
327	Most experimental parametrizations are NLO, which makes them less
328	well suited for Monte Carlo applications. Furthemore note that
329	the momentum sum is arbitrarily normalized to a non-unity value.
330
331	<br/><br/><table><tr><td><strong>PDF:PomSet </td><td>   (<code>default = <strong>6</strong></code>; <code>minimum = 1</code>; <code>maximum = 6</code>)</td></tr></table>
332	Parton densities that can be used for Pomeron beams.
333	<br/>
334	<input type="radio" name="15" value="1"><strong>1 </strong>: <ei>Q^2</ei>-independent parametrizations <ei>xf(x) = N_ab x^a (1 - x)^b</ei>, where <ei>N_ab</ei> ensures unit momentum sum. The <ei>a</ei> and <ei>b</ei> parameters can be set separately for the gluon and the quark distributions. The momentum fraction of gluons and quarks can be freely mixed, and production of <ei>s</ei> quarks can be suppressed relative to that of <ei>d</ei> and <ei>u</ei> ones, with antiquarks as likely as quarks. See further below how to set the six parameters of this approach. <br/>
335	<input type="radio" name="15" value="2"><strong>2 </strong>: <ei>pi0</ei> distributions, as specified in the section above. <br/>
336	<input type="radio" name="15" value="3"><strong>3 </strong>: the H1 2006 Fit A NLO <ei>Q^2</ei>-dependent parametrization, based on a tune to their data <ref>H1P06</ref>, rescaled by the factor <code>PomRescale</code> below. <br/>
337	<input type="radio" name="15" value="4"><strong>4 </strong>: the H1 2006 Fit B NLO <ei>Q^2</ei>-dependent parametrization, based on a tune to their data <ref>H1P06</ref>, rescaled by the factor <code>PomRescale</code> below. <br/>
338	<input type="radio" name="15" value="5"><strong>5 </strong>: the H1 2007 Jets NLO <ei>Q^2</ei>-dependent parametrization, based on a tune to their data <ref>H1P07</ref>, rescaled by the factor <code>PomRescale</code> below. <br/>
339	<input type="radio" name="15" value="6" checked="checked"><strong>6 </strong>: the H1 2006 Fit B LO <ei>Q^2</ei>-dependent parametrization, based on a tune to their data <ref>H1P06</ref>, rescaled by the factor <code>PomRescale</code> below. <br/>
340
341	<br/><br/><table><tr><td><strong>PDF:PomGluonA </td><td></td><td> <input type="text" name="16" value="0." size="20"/>   (<code>default = <strong>0.</strong></code>; <code>minimum = -0.5</code>; <code>maximum = 2.</code>)</td></tr></table>
342	the parameter <i>a</i> in the ansatz <i>xg(x) = N_ab x^a (1 - x)^b</i>
343	for option 1 above.
344
345
346	<br/><br/><table><tr><td><strong>PDF:PomGluonB </td><td></td><td> <input type="text" name="17" value="3." size="20"/>   (<code>default = <strong>3.</strong></code>; <code>minimum = 0.</code>; <code>maximum = 10.</code>)</td></tr></table>
347	the parameter <i>b</i> in the ansatz <i>xg(x) = N_ab x^a (1 - x)^b</i>
348	for option 1 above.
349
350
351	<br/><br/><table><tr><td><strong>PDF:PomQuarkA </td><td></td><td> <input type="text" name="18" value="0." size="20"/>   (<code>default = <strong>0.</strong></code>; <code>minimum = -0.5</code>; <code>maximum = 2.</code>)</td></tr></table>
352	the parameter <i>a</i> in the ansatz <i>xq(x) = N_ab x^a (1 - x)^b</i>
353	for option 1 above.
354
355
356	<br/><br/><table><tr><td><strong>PDF:PomQuarkB </td><td></td><td> <input type="text" name="19" value="3." size="20"/>   (<code>default = <strong>3.</strong></code>; <code>minimum = 0.</code>; <code>maximum = 10.</code>)</td></tr></table>
357	the parameter <i>b</i> in the ansatz <i>xq(x) = N_ab x^a (1 - x)^b</i>
358	for option 1 above.
359
360
361	<br/><br/><table><tr><td><strong>PDF:PomQuarkFrac </td><td></td><td> <input type="text" name="20" value="0.2" size="20"/>   (<code>default = <strong>0.2</strong></code>; <code>minimum = 0.</code>; <code>maximum = 1.</code>)</td></tr></table>
362	the fraction of the Pomeron momentum carried by quarks
363	for option 1 above, with the rest carried by gluons.
364
365
366	<br/><br/><table><tr><td><strong>PDF:PomStrangeSupp </td><td></td><td> <input type="text" name="21" value="0.5" size="20"/>   (<code>default = <strong>0.5</strong></code>; <code>minimum = 0.</code>; <code>maximum = 1.</code>)</td></tr></table>
367	the suppression of the <i>s</i> quark density relative to that of the
368	<i>d</i> and <i>u</i> ones for option 1 above.
369
370
371	<br/><br/><table><tr><td><strong>PDF:PomRescale </td><td></td><td> <input type="text" name="22" value="1.0" size="20"/>   (<code>default = <strong>1.0</strong></code>; <code>minimum = 0.5</code>; <code>maximum = 5.0</code>)</td></tr></table>
372	Rescale the four H1 fits above by this uniform factor, e.g. to bring
373	up their momentum sum to around unity. By default all three have
374	a momentum sum of order 0.5, suggesting that a factor around 2.0
375	should be used. You can use <code>examples/main51.cc</code> to get
376	a more precise value. Note that also other parameters in the
377	<?php $filepath = $_GET["filepath"];
378	echo "<a href='Diffraction.php?filepath=".$filepath."' target='page'>";?>diffraction</a> framework may need to
379	be retuned when this parameter is changed.
380
381
382	<h3>Parton densities for leptons</h3>
383
384	For electrons/muons/taus there is no need to choose between different
385	parametrizations, since only one implementation is available, and
386	should be rather uncontroversial (apart from some technical details).
387	However, insofar as e.g. <i>e^+ e^-</i> data often are corrected
388	back to a world without any initial-state photon radiation, it is
389	useful to have a corresponding option available here.
390
391	<br/><br/><strong>PDF:lepton</strong> <input type="radio" name="23" value="on" checked="checked"><strong>On</strong>
392	<input type="radio" name="23" value="off"><strong>Off</strong>
393	(<code>default = <strong>on</strong></code>)<br/>
394	Use parton densities for lepton beams or not. If off the colliding
395	leptons carry the full beam energy, if on part of the energy is
396	radiated away by initial-state photons. In the latter case the
397	initial-state showers will generate the angles and energies of the
398	set of photons that go with the collision. In addition one collinear
399	photon per beam carries any leftover amount of energy not described
400	by shower emissions. If the initial-state showers are switched off
401	these collinear photons will carry the full radiated energy.
402
403
404	<p/>
405	Neutrinos are always taken pointlike. Do note that the phase space
406	selection machinery currently does not allow one resolved and one
407	unresolved beam. For lepton-neutrino collisions to work you must
408	therefore set <code>PDF:lepton = off</code>.
409
410	<h3>Incoming parton selection</h3>
411
412	There is one useful degree of freedom to restrict the set of incoming
413	quark flavours for hard processes. It does not change the PDF's as such,
414	only which quarks are allowed to contribute to the hard-process cross
415	sections. Note that separate but similarly named modes are available
416	for multiparton interactions and spacelike showers.
417
418	<br/><br/><table><tr><td><strong>PDFinProcess:nQuarkIn </td><td></td><td> <input type="text" name="24" value="5" size="20"/>   (<code>default = <strong>5</strong></code>; <code>minimum = 0</code>; <code>maximum = 5</code>)</td></tr></table>
419	Number of allowed incoming quark flavours in the beams; a change
420	to 4 would thus exclude <i>b</i> and <i>bbar</i> as incoming
421	partons, etc.
422
423
424	<input type="hidden" name="saved" value="1"/>
425
426	<?php
427	echo "<input type='hidden' name='filepath' value='".$_GET["filepath"]."'/>"?>
428
429	<table width="100%"><tr><td align="right"><input type="submit" value="Save Settings" /></td></tr></table>
430	</form>
431
432	<?php
433
434	if($_POST["saved"] == 1)
435	{
436	$filepath = $_POST["filepath"];
437	$handle = fopen($filepath, 'a');
438
439	if($_POST["1"] != "2")
440	{
441	$data = "PDF:pSet = ".$_POST["1"]."\n";
442	fwrite($handle,$data);
443	}
444	if($_POST["2"] != "off")
445	{
446	$data = "PDF:useLHAPDF = ".$_POST["2"]."\n";
447	fwrite($handle,$data);
448	}
449	if($_POST["3"] != "MRST2004FF4lo.LHgrid")
450	{
451	$data = "PDF:LHAPDFset = ".$_POST["3"]."\n";
452	fwrite($handle,$data);
453	}
454	if($_POST["4"] != "0")
455	{
456	$data = "PDF:LHAPDFmember = ".$_POST["4"]."\n";
457	fwrite($handle,$data);
458	}
459	if($_POST["5"] != "off")
460	{
461	$data = "PDF:extrapolateLHAPDF = ".$_POST["5"]."\n";
462	fwrite($handle,$data);
463	}
464	if($_POST["6"] != "off")
465	{
466	$data = "PDF:useHard = ".$_POST["6"]."\n";
467	fwrite($handle,$data);
468	}
469	if($_POST["7"] != "2")
470	{
471	$data = "PDF:pHardSet = ".$_POST["7"]."\n";
472	fwrite($handle,$data);
473	}
474	if($_POST["8"] != "off")
475	{
476	$data = "PDF:useHardLHAPDF = ".$_POST["8"]."\n";
477	fwrite($handle,$data);
478	}
479	if($_POST["9"] != "MRST2004FF4lo.LHgrid")
480	{
481	$data = "PDF:hardLHAPDFset = ".$_POST["9"]."\n";
482	fwrite($handle,$data);
483	}
484	if($_POST["10"] != "0")
485	{
486	$data = "PDF:hardLHAPDFmember = ".$_POST["10"]."\n";
487	fwrite($handle,$data);
488	}
489	if($_POST["11"] != "1")
490	{
491	$data = "PDF:piSet = ".$_POST["11"]."\n";
492	fwrite($handle,$data);
493	}
494	if($_POST["12"] != "off")
495	{
496	$data = "PDF:piUseLHAPDF = ".$_POST["12"]."\n";
497	fwrite($handle,$data);
498	}
499	if($_POST["13"] != "OWPI.LHgrid")
500	{
501	$data = "PDF:piLHAPDFset = ".$_POST["13"]."\n";
502	fwrite($handle,$data);
503	}
504	if($_POST["14"] != "0")
505	{
506	$data = "PDF:piLHAPDFmember = ".$_POST["14"]."\n";
507	fwrite($handle,$data);
508	}
509	if($_POST["15"] != "6")
510	{
511	$data = "PDF:PomSet = ".$_POST["15"]."\n";
512	fwrite($handle,$data);
513	}
514	if($_POST["16"] != "0.")
515	{
516	$data = "PDF:PomGluonA = ".$_POST["16"]."\n";
517	fwrite($handle,$data);
518	}
519	if($_POST["17"] != "3.")
520	{
521	$data = "PDF:PomGluonB = ".$_POST["17"]."\n";
522	fwrite($handle,$data);
523	}
524	if($_POST["18"] != "0.")
525	{
526	$data = "PDF:PomQuarkA = ".$_POST["18"]."\n";
527	fwrite($handle,$data);
528	}
529	if($_POST["19"] != "3.")
530	{
531	$data = "PDF:PomQuarkB = ".$_POST["19"]."\n";
532	fwrite($handle,$data);
533	}
534	if($_POST["20"] != "0.2")
535	{
536	$data = "PDF:PomQuarkFrac = ".$_POST["20"]."\n";
537	fwrite($handle,$data);
538	}
539	if($_POST["21"] != "0.5")
540	{
541	$data = "PDF:PomStrangeSupp = ".$_POST["21"]."\n";
542	fwrite($handle,$data);
543	}
544	if($_POST["22"] != "1.0")
545	{
546	$data = "PDF:PomRescale = ".$_POST["22"]."\n";
547	fwrite($handle,$data);
548	}
549	if($_POST["23"] != "on")
550	{
551	$data = "PDF:lepton = ".$_POST["23"]."\n";
552	fwrite($handle,$data);
553	}
554	if($_POST["24"] != "5")
555	{
556	$data = "PDFinProcess:nQuarkIn = ".$_POST["24"]."\n";
557	fwrite($handle,$data);
558	}
559	fclose($handle);
560	}
561
562	?>
563	</body>
564	</html>
565
566	<!-- Copyright (C) 2012 Torbjorn Sjostrand -->

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