Stefan's Pythia 8 Working Page

Everything official is available here: Pyhita

Everything on this page is only for internal use and not official Pythia 8 code!

Private Test Versions

Known Errors

  1. Since not all process are possible/available for all model parameter values an Error occurs if an unavailable value have been specified, e.g.
     Error in Sigma2xxxx2yyyyyyyy::initProc : Incorrect spin value (turn process off)! 
    The cross section should then be set to zero, except for processes which include interference with the SM ( like ffbar->G*->gammagamma ) where the SM result should be obtained.
  2. The following error happens in rare cases for the Z+U/G process (corner of phase space where uHat or tHat << mU^2),
     PYTHIA Negative minimum for xxxxxx process changed to yyyyy 
    and it can be removed for example by requiring (if the analysis allows),
     pythia.readString("PhaseSpace:pTHatMin = 50."); 

Quark Compositeness


  1. E. Eichten, K. D. Lane and M. E. Peskin, New Tests for Quark and Lepton Substructure , Phys. Rev. Lett. 50 (1983) 811.
  2. P. Chiappetta and M. Perrottet, Large Hadron Collider Workshop eds. G. Jarlskog and D. Rein, CERN Yellow Reports 90-10, Vol. II, p.806.
  3. C. Berger, P. Fuhrmann, F. Raupach, M. Spira and P. Zerwas, Large Hadron Collider Workshop eds. G. Jarlskog and D. Rein, CERN Yellow Reports 90-10, Vol. II, p.1014.


  • Quark contact interactions based on [1] and [2]. (included in Pythia8)
  • Same contact interactions between ffbar and charged llbar.
  • Angular distributions for decay, f*->f+V, in process, f+f->f+f*, based on [3].

Large Extra Dimension and Unparticle Processes

(Real Emission and Virtual Exchange of Unparticles/Gravitons)


  1. S. Ask et al., Real Emission and Virtual Exchange of Gravitons and Unparticles in Pythia8 , Comp. Phys. Comm. 181 (2010) 1593, arXiv:0912.4233v2 [hep-ph].
    (Main documentation of the U/G + jet, gammagamma and llbar processes)
  2. S. Ask, Simulation of Z plus Graviton/Unparticle Production at the LHC , Eur. Phys. J. C60 (2009) 509, arXiv:0809.4750v2 [hep-ph].
    (Main documentation of the U/G + Z/gamma process)
  3. R. Franceschini, G. F. Giudice, P. P. Giardino, P. Lodone and A. Strumia, LHC bounds on large extra dimensions , JHEP 1105 (2011) 092;
    G. F. Giudice, T. Plehn and A. Strumia, Graviton collider effects in one and more large extra dimensions , Nucl. Phys. B706 (2005) 455.
    (Cross section and S(x) formulae for di-jets)
  4. J.L Hewett, Indirect Collider Signals for Extra Dimensions , Phys. Rev. Lett. 82 (1999) 4765.
  5. M. C. Kumar et al., Unparticle physics in diphoton production at the CERN LHC , Phys. Rev. D77 (2008) 055013, arXiv:0709.2478v2 [hep-ph]
    (MEs taken from this paper: di-photon)
  6. K. Cheung, W.Y. Keung and T.C. Yuan, Collider Phenomenology of Unparticle Physics , Phys. Rev. D76 (2007) 055003, arXiv:0706.3155v2 [hep-ph].
    (MEs taken from this paper: mono-Z/gamma, mono-jets, di-leptons)
  7. T. G. Rizzo, Identification of the Origin of Monojet Signatures at the LHC , Phys. Lett. B665 (2008) 361, arXiv:0805.0281 [hep-ph]
    (MEs taken from this paper: mono-jet complement)
  8. G. F. Giudice, R. Rattazzi and J. D. Wells, Quantum Gravity and Extra Dimensions at High-Energy Colliders , Nucl. Phys. B544 (1999) 3, arXiv:hep-ph/9811291v2
    (MEs taken from this paper: mono-jet complement)
  9. J. Hewett and T. G. Rizzo, Collider Signals of Gravitational Fixed Points , JHEP 0712 (2007) 009, arXiv:0707.3182v1 [hep-ph]
    (Form factor taken from this paper)
  10. G Azuelos, P-H Beauchemin and C P Burgess, Phenomenological constraints on extra-dimensional scalars , J. Phys. G: Nucl. Part. Phys. (2005) 31 1.
    (MEs taken from this paper: mono-jet complement)


  • Di-jet production. (In progress)
    • Based on [3] above.
    • Implemented amplitude function, S(x), AmpLedS.pdf.
  • Di-photon production. (Included in Pythia8)
    • The virtual graviton exchange processes share the same implementation, but corresponds to the special case, spin-2, dU = 2, lambda^2 x Chi --> 4 pi. This reproduce the graviton formulas in hep-ph/9811291v2 and hep-ph/0408320v1.
  • Di-lepton production. (Included in Pythia8)
    • The same di-lepton graviton formulas as in hep-ph/9811291v2 and hep-ph/0408320v1 could be reproduced by the same model parameter translation as used for the di-photon process. The implementation does not include the t-channel contributions relevant for e+e- ->e+e-.
  • Monojets. (Included in Pythia8)
    • All unparticle processes (spin-0 and spin-1) have a universal unparticle-SM coupling, lambda, implemented according to the effective operators in (2). Also include posibility of scalar graviton emission, which have different amplitudes wrt scalar unparticle.
    • GravScalar.tgz
  • Mono - Z / gamma. (Included in Pythia8)
    Spin-2 U with r .NE. 1 issue: (see also attached plots below)
    • Point 102 corresponds to the case lambda = lambdaprime, i.e. unparticle = graviton apart from constants
      In this case the events are generated with resonable speed and the graviton/unparticle mass spectrum looks good.
    • Point 101 and 103 has a small deviation from lambda = lambdaprime (see below).
      The event generation becomes in both cases very slow and the unparticle mass spectrum has a very large zero-bin ?
    • This is the text output for point 101: output_101.txt
    • Points (Spin, dU, Lambda U, lambda, r, N_evt, sigma):
    • 101: (2, 2.0, 2000., 1.0, 1.01, 10k, 5.053 fb)
    • 102: (2, 2.0, 2000., 1.0, 1.00, 10k, 0.501 fb)
    • 103: (2, 2.0, 2000., 1.0, 0.99, 10k, 5.034 fb)
    • Explanation:
    • r = 1 imply cancelation between ME terms which have no U-mass in nominator but do have in the denominator, giving an IR divergence.
    • GG: This looks similar to the van Dam - Veltman disconinuity (m=0 .NE. m->0 for gravity theory)
    • Two IR divergencies which normaly cancels becomes unbalanced by r .NE. 1, like if setting different couplings in tripple and quartice gauge interactions.

Small Extra Dimension (RS) Resonances


  1. S. Ask et al., Identifying the colour of TeV-scale resonances , arXiv:1108.2396v1 [hep-ph]
    (Main documentation of the gluon resonance)
  2. J. Bijnens et al., QCD Signatures of Narrow Graviton Resonances in Hadron Colliders , Phys. Lett. B503 (2001) 341, arXiv:hep-ph/0101316v1
    (Main documentation of the graviton resonance)
  3. H. Davoudiasl, J.L. Hewett, T.G. Rizzo, Experimental probes of localized gravity: On and off the wall , Phys. Rev. D63 (2001) 075004, arXiv:hep-ph/0006041v1
  4. K. Agashe, A. Delgado, M. J. May, R. Sundrum, RS1, Custodial Isospin and Precision Tests , JHEP 0308 (2003) 050, arXiv:hep-ph/0308036v2
  5. A. L. Fitzpatrick et al., Searching for the Kaluza-Klein Graviton in Bulk RS Models , JHEP 0709 013 2007, arXiv:hep-ph/0701150v2
  6. K. Agashe et al., Warped Gravitons at the LHC and Beyond , Phys. Rev. D76 (2007) 036006, arXiv:hep-ph/0701186v3
  7. B. Lillie, L. Randall, L.-T. Wang, The Bulk RS KK-gluon at the LHC , JHEP 0709 074 2007, arXiv:hep-ph/0701166v1
  8. K. Agashe et al., LHC Signals from Warped Extra Dimensions , Phys. Rev. D77 (2008) 015003, arXiv:hep-ph/0612015v1


  • Gluon resonance. (Included in Pythia8)
  • Graviton resonance. (update to be included)
    • Old pythia graviton resonance extended to flavour dependent couplings.
    • Couplings follow convention in (3).
    • Currently missing scalar decays (Higgs and longitudinal W/Z).
    • Analytically the Pythia 8 implementation is identical to the cross section and width formulas of (2) and (5).
      Apart from the coupling constant kappaMG and some phase space factors (in the width) neglected in (5) and (6).

Dark Sector Processes


  • Four gamma

Photon Collisions


  1. A.D. Martin, R.G. Roberts, W.J. Stirling and R.S. Thorne, Parton distributions incorporating QED contributions , Eur. Phys. J. C39 (2005) 155, arXiv:hep-ph/0411040 (MRST 2004 QED).
  2. V.M. Budnev, I.F. Ginzburg, G.V. Meledin and V.G. Serbo, The Two photon particle production mechanism. Physical problems. Applications. Equivalent photon approximation_ , Phys.Rept.15 (1975) 181 (Equivalent Photon Spectrum).
  3. V.A. Khoze, A.D. Martin, R. Orava and M.G. Ryskin, Luminosity monitors at the LHC , Eur. Phys. J. C19 (2001) 313, arXiv:hep-ph/0010163v1 (Survival Probability).
  4. J. de Favereau de Jeneret et al., High energy photon interactions at the LHC , arXiv:0908.2020v1 [hep-ph].
  5. M.G. Albrow, T.D. Coughlin and J.R. Forshaw, Central Exclusive Particle Production at High Energy Hadron Colliders , arXiv:1006.1289v1 [hep-ph].


-- StefanAsk - 24 Jun 2008

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf AmpLedS.pdf r1 manage 242.9 K 2011-11-11 - 17:03 UnknownUser  
Compressed Zip archivetgz GamGam_160210.tgz r1 manage 4.4 K 2010-02-16 - 14:44 UnknownUser  
Compressed Zip archivetgz GravScalar.tgz r1 manage 3.7 K 2010-05-04 - 09:59 UnknownUser  
Compressed Zip archivetar MC4BSM12_140312.tar r1 manage 8970.5 K 2012-03-14 - 18:41 UnknownUser  
Compressed Zip archivetgz gravkk_030908.tgz r1 manage 9.6 K 2008-09-03 - 18:17 UnknownUser  
Compressed Zip archivetgz gravunp100.tgz r1 manage 7.7 K 2008-07-30 - 09:11 UnknownUser  
PDFpdf hmll.pdf r1 manage 14.3 K 2009-06-19 - 15:37 UnknownUser  
Texttxt kkres_notes_100609.txt r1 manage 1.1 K 2009-06-10 - 14:00 UnknownUser  
Compressed Zip archivetgz pythia8130_A_UE_180909.tgz r1 manage 4642.5 K 2009-09-28 - 10:31 UnknownUser  
Compressed Zip archivetgz pythia8135_sa_180210.tgz r1 manage 4976.2 K 2010-02-18 - 14:36 UnknownUser  
Compressed Zip archivetgz pythia8135_sa_260310.tgz r1 manage 5041.8 K 2010-03-26 - 13:59 UnknownUser  
Compressed Zip archivetgz pythia8142_GamGam_190810.tgz r1 manage 4745.3 K 2010-08-19 - 15:49 UnknownUser  
Compressed Zip archivetgz pythia8142_sa_071010.tgz r1 manage 4738.2 K 2010-10-07 - 09:57 UnknownUser  
Compressed Zip archivetgz pythia81_sa040312.tgz r1 manage 10378.7 K 2012-03-05 - 15:33 UnknownUser  
Unknown file formatgz pythia81_sa081211.tar.gz r1 manage 10871.2 K 2011-12-08 - 10:13 UnknownUser  
Unknown file formatgz pythia81_sa100112.tar.gz r1 manage 10852.5 K 2012-01-10 - 13:40 UnknownUser  
Unknown file formatgz pythia81_sa211211.tar.gz r1 manage 10872.4 K 2011-12-21 - 18:29 UnknownUser  
Compressed Zip archivetgz pythia81_sa_260711.tgz r1 manage 10257.3 K 2011-07-26 - 10:04 UnknownUser  
Compressed Zip archivetgz pythia_plot_190609.tgz r1 manage 6012.3 K 2009-06-19 - 15:37 UnknownUser  
PDFpdf virtGravUnp_6.pdf r1 manage 100.1 K 2009-06-19 - 15:47 UnknownUser  
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