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+<html>
+<head>
+<title>R-hadrons</title>
+<link rel="stylesheet" type="text/css" href="pythia.css"/>
+<link rel="shortcut icon" href="pythia32.gif"/>
+</head>
+<body>
+
+<h2>R-hadrons</h2>
+
+When a coloured SUSY particle is longer-lived than typical
+hadronization scales, i.e. around c*tau > 1 fm, or equivalently
+width Gamma < 0.2 GeV, it will have time to hadronize into a colour
+singlet hadronic state, a R-hadron. Currently a set of such
+R-hadrons have been implemented for the case of a long-lived
+gluino, stop or sbottom. Needless to say, the normal case would be
+that only one of them will be long-lived enough to form R-hadrons.
+
+<p/>
+For simplicity all gluino-mesons are assumed to have light-flavour
+spin 1, since those are the lightest and favoured by spin-state
+counting. Further, all gluino-baryons are bookkept as having
+light-flavour spin 3/2, and flavours are listed in descending order.
+This is more for convenience of notation, however, since the normal
+baryon octet e.g. has no uuu = "p++" state. When a diquark is
+extracted, a mixture of spin 0 and spin 1 is allowed. Names and codes
+are essentially in agreement with the PDG conventions, e.g.
+<br/>1000993 <code>R0(~g g)</code> (or gluinoball)
+<br/>1009213 <code>R+(~g u dbar)</code> (or gluino-rho+)
+<br/>1092214 <code>R+(~g uud)</code> (or gluino-Delta+)
+<br/>For internal bookkeeping of momenta, the code 1009002,
+<code>Rtemp(~g q)</code>, is used to denote the intermediate
+state formed when only one of the two string peices attached to
+the gluino has broken.
+
+<p/>
+For the stop- and sbottom-hadrons the spin counting is simpler,
+since it is entirely given by the constituent quark or diquark spin.
+Again names and codes follow PDG conventions, e.g.
+<br/>1000612 <code>R+(~t dbar)</code>
+<br/>1006211 <code>R+(~t ud0)</code>
+
+<p/>
+The spin and electromagnetic charge of the new particle plays only
+a minor role in the hadronization process, that can be neglected
+to first approximation. Therefore it is possible to use the same
+R-hadrons framework instead for other BSM scenarios with long-lived
+coloured particles, e.g. with massive extra-dimensions copies
+of gluons and quarks, or with leptoquarks. This can be regulated by
+the switches below. Note that the codes and names of the R-hadrons
+is not changed when the heavy particle involved is switched, for
+reasons of administrative simplicity. R-hadron mass spectra and
+other relevant particle data is automatically updated to reflect
+the change, however.
+
+<p/><code>flag </code><strong> RHadrons:allow </strong>
+ (<code>default = <strong>off</strong></code>)<br/>
+Allows the gluino, stop and sbottom to hadronize if their respective
+widths are below the limit <code>RHadrons:maxWidth</code>.
+
+
+<p/><code>parm </code><strong> RHadrons:maxWidth </strong>
+ (<code>default = <strong>0.2</strong></code>; <code>minimum = 0.0</code>; <code>maximum = 1.0</code>)<br/>
+The maximum width of the gluino for which it is possible to form
+R-hadrons, provided that <code>RHadrons:allow</code> is on.
+
+
+<p/><code>mode </code><strong> RHadrons:idGluino </strong>
+ (<code>default = <strong>1000021</strong></code>)<br/>
+The gluino identity code. For other scenarios than SUSY this code
+could be changed to represent another long-lived uncharged colour
+octet particle, that then would be treated in the same spirit.
+Could be set to 0 to forbid any gluino R-hadron formation even when
+the above two criteria, <code>RHadrons:allow</code>
+and <code>RHadrons:maxWidth</code>, are met.
+
+
+<p/><code>mode </code><strong> RHadrons:idStop </strong>
+ (<code>default = <strong>1000006</strong></code>)<br/>
+The lightest stop identity code. For other scenarios than SUSY this
+code could be changed to represent another long-lived charge 2/3
+colour triplet particle, that then would be treated in the same
+spirit. As above it could be set to 0 to forbid any stop R-hadron
+formation.
+
+
+<p/><code>mode </code><strong> RHadrons:idSbottom </strong>
+ (<code>default = <strong>1000005</strong></code>)<br/>
+The lightest sbottom identity code. For other scenarios than SUSY this
+code could be changed to represent another long-lived charge -1/3
+colour triplet particle, that then would be treated in the same
+spirit. As above it could be set to 0 to forbid any sbottom R-hadron
+formation.
+
+
+<p/><code>flag </code><strong> RHadrons:allowDecay </strong>
+ (<code>default = <strong>on</strong></code>)<br/>
+Allows the R-hadrons to decay or not. If the gluino/stop/sbottom is
+stable or too long-lived to decay inside the detector this switch
+has no real function, since then no decays will be performed anyway.
+If the sparticle is so short-lived that it decays before reaching
+the beam pipe then having the decay on is the logical choice.
+So the interesting region is when the decays happens after the
+R-hadron has passed through part of the detector, and changed its
+momentum and quite possibly its flavour content before it is to
+decay. Then normal decays should be switched off, and the R-hadron
+tracked through matter by a program like GEANT
+[<a href="Bibliography.html" target="page">Kra04,Mac07</a>]. After that, the new R-hadron info can be
+overwritten into the event record and the
+<code>Pythia::forceRHadronDecay()</code> method can be called
+to force this modified R-hadron to decay.
+
+
+<p/><code>flag </code><strong> RHadrons:setMasses </strong>
+ (<code>default = <strong>on</strong></code>)<br/>
+Use simple mass formulae to construct all available R-hadron masses
+based on the currently initialized gluino/squark masses and the
+constituent masses of the other partons in the hadron. If you switch
+this off, it is your responsibility to set each of the R-hadron masses
+on your own, and set them in an internally consistent way. If you
+mess up on this you may generate accordingly crazy results.
+Specifically, it is to be assumed that none of the R-hadrons has a
+mass below its constituent sparticle, i.e. that the light degrees
+of freedom and the additional confinement gluon field gives a net
+positive contribution to the R-hadron mass.
+
+
+<p/><code>parm </code><strong> RHadrons:probGluinoball </strong>
+ (<code>default = <strong>0.1</strong></code>; <code>minimum = 0.0</code>; <code>maximum = 1.0</code>)<br/>
+The fraction of produced gluino R-hadrons that are contain a "valence"
+gluon, with the rest containing a meson or baryon quark flavour content.
+
+
+<p/><code>parm </code><strong> RHadrons:mOffsetCloud </strong>
+ (<code>default = <strong>0.2</strong></code>; <code>minimum = 0.0</code>)<br/>
+Extra mass (in GeV) added to each of the one or two extra constituent
+masses in an R-hadron, to calculate the mass of a R-hadron. The same
+offset is also used when the R-hadron momentum and mass is split
+between the squark or gluino and the one or two light (di)quarks,
+one for a squark and two for a gluino. Thus once or twice this amount
+represents a part of the nominal squark or gluino mass that will not
+decay weakly, since it is taken to correspond to the cloud of gluons
+that surround the squark or gluino.
+
+
+<p/><code>parm </code><strong> RHadrons:mCollapse </strong>
+ (<code>default = <strong>1.0</strong></code>; <code>minimum = 0.0</code>)<br/>
+A colour singlet system with an invariant mass less than this amount,
+above the R-hadron mass with the given flavour content, is assumed to
+collapse to this single R-hadron, whereas a full fragmentation handling
+is applied above this mass.
+
+
+<p/><code>parm </code><strong> RHadrons:diquarkSpin1 </strong>
+ (<code>default = <strong>0.5</strong></code>; <code>minimum = 0.0</code>; <code>maximum = 1.0</code>)<br/>
+Probability that a diquark extracted from the flavour code of a gluino
+R-hadron should be assigned spin 1, with the rest being spin 0. Does
+not apply for two identical quarks, where spin 1 is only possibility.
+Note that gluino R-hadron codes for simplicity are assigned as if spin
+is 1 always, and so give no guidance. For stop and sbottom the diquark
+spin is preserved in the particle code, so there is no corresponding
+issue.
+
+
+</body>
+</html>
+
+<!-- Copyright (C) 2012 Torbjorn Sjostrand -->
+
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