Monte Carlo Event Generators

1
Monte Carlo Event Generators
LEMC Workshop, Fermilab, February 2007

• for HEP Studies

Peter Skands
2
Physics at the IP
Primary Vertex

• Philosophy of this talk Mail-order two (2) ACME
  muon guns
• ? Physics Studies at the Interaction Point
• This talk is meant to give an update on HEP event
  generators, with special focus on µµ-? HEP

3
The Event Generator Position
Collider
Detector
Reconstruction Framework

• Detailed Simulations prerequisite for
• Serious physics studies
• Detector design studies
• Design reports

4
The Monte Carlo Method
Hadronization 1 GeV 10-15 m
Parton Showers Multi-GeV
Hard Part Hundreds of GeV ? Ecm
Hadron Decays
shard process, Pres
PISR, PFSR
Phadronization
Pdecays
5
Bremsstrahlung Parton Showers

• Starting observation photon forward brems
  singularity is process-independent. Fundamental
  property of gauge theory ? also applies to gluon
  brems.
• Leading contributions to both QED (photon
  radiation) QCD (quark, gluon radiation) can be
  worked out to all orders once and for all
• ? exponentiated (Altarelli-Parisi) integration
  kernels
• Iterative (Markov chain) formulation parton
  shower
• can be used to generate the forward singular
  (collinear) parts of QED and QCD corrections to
  any process to infinite order in the coupling
• ordered in a measure of resolution ? a series of
  successive factorizations the lower end of which
  can be matched to a hadronization description at
  some fixed low hadronization scale
• Limitations
• misses interference terms relevant in the deep
  non-singular region
• kinematic ambiguities and double counting between
  fixed order part and resummed part

6
Pre-LEP Event Generators

• ARIADNE, HERWIG, and PYTHIA

• Seated on a tripod above a crack in the earth,
  she went into a trance by the stupefying vapors
  rising from the earth and by chewing laurel
  leaves. From the incoherent babbling which the
  priestess spoke in her ecstasy, the temple
  priests formulated the oracle.

T. Sjöstrand, S. Mrenna, PS, JHEP 05 (2006) 026
The Pythia

• There was a certain amount of voodoo involved
• Still, an impressive amount of data could be
  accounted for
• We now have much better voodoo

7
Developments since LEP

• Hard Bremsstrahlung (additional jets, e.g.
  Z?3,4,5 jets)
• Parton shower approximation breaks down ? large
  uncertainties
• Lots of progress in last 5 years matching to
  matrix elements
• Jet Broadening (soft/collinear parton
  bremsstrahlung)
• New generation of theoretical models
• Improved parton showers implemented in both
  general-purpose generators (HERWIG() and
  PYTHIA)
• work here at Fermilab VINCIA a
  next-generation antenna shower
• The Final Femtometer Hadronization
• With short-distance parts better under control ?
  non-perturbative side has less wiggle room ? also
  here improved possibility for studies
• Current studies at hadron colliders ? feed back
  to lepton collider physics

8
VINCIA
virtual numerical collider with integrated
antennae
Giele, Kosower, PS in progress
1

• VINCIA Dipole shower
• C code for gluon showers running
• Can evolve in either of 2 different shower
  evolution variables
• pT-ordering ( ARIADNE)
• Virtuality-ordering ( Pythia 6.2 SHERPA)
• For each evolution type, an infinite family of
  radiation functions implemented, all with
  correct collinear and soft behaviour
  ( antenna functions)

Dipoles a dual description of QCD
2
3

• First parton shower with systematic possibility
  of variation of shower variable and shower
  functon ? control uncertainties
• To any fixed order, these variations can be
  absorbed by a new type of matching to matrix
  elements

9
VINCIA Example H ? gg ? ggg
Giele, Kosower, PS in progress

• First Branching first order in perturbation
  theory
• Unmatched shower varied from soft to hard
  soft shower has radiation hole. Filled in by
  matching.

VINCIA 0.008 Unmatched soft A2
VINCIA 0.008 Matched soft A2
y23
y23
Expect public code and long writeup before summer
radiation hole in high-pT region
Next Quarks and leptons ? lepton colliders
y23
y23
VINCIA 0.008 Unmatched hard A2
VINCIA 0.008 Matched hard A2
Later plug-in for Pythia 8 ?
y12
y12
10
The Move to C (from F77)

• HERWIG complete reimplementation
• Improved parton shower and decay algorithms
• Eventually to include CKKW-style matching ?
• B.R. Webber S. Gieseke, D. Grellscheid, A.
  Ribon, P. Richardson, M. Seymour, P. Stephens, .
  . .
• SHERPA complete implementation, has CKKW
  matching
• ME generator wrappers to / adaptations of
  PYTHIA, HERWIG
• F. Krauss T. Fischer, T. Gleisberg, S. Hoeche,
  T. Laubrich, A. Schaelicke, S. Schumann, C.
  Semmling, J. Winter
• PYTHIA 8 selective reimplementation
• Improved PS and UE, limited number of hard
  subprocesses
• Many obsolete features not carried over ?
  simpler, less parameters
• T. Sjöstrand, S. Mrenna, P. Skands

11
PYTHIA for the Muon Collider

• Instructive Examples

12
Z Radiative Return
Standard PC ? 1M evts / hr.

• Z with mass 1 TeV, with invisible decays (here
  neutrinos)
• MC running at 1.5 TeV. Radiative return via
  photon bremsstrahlung

Event listing (summary) I particle/jet KS
KF orig p_x p_y p_z E
m 1 !mu! 21 -13 0 0.000
0.000 750.000 750.000 0.106 2 !mu-!
21 13 0 0.000 0.000 -750.000
750.000 0.106

3 !mu! 21 -13 1 0.000 0.000
750.000 750.000 0.000 4 !mu-! 21
13 2 0.000 0.000 -750.000 750.000
0.000 5 !mu! 21 -13 3
35.339 66.868 627.465 632.007 0.000 6
!mu-! 21 13 4 0.549 2.140
-388.502 388.509 0.000 7 !Z'0! 21
32 0 35.888 69.007 238.963 1020.516
989.090 8 !nu_e! 21 12 7
-162.336 -426.971 135.508 476.466 0.000
9 !nu_ebar! 21 -12 7 198.224 495.978
103.455 544.050 0.000

10 (Z'0) 11 32 7 35.888
69.007 238.963 1020.516 989.090 11 gamma
1 22 3 -35.320 -66.793 108.367
132.107 0.000 12 gamma 1 22
4 0.514 -1.099 -16.725 16.769 0.000
13 gamma 1 22 4 -1.082 -1.115
-330.605 330.608 0.000 14 nu_e 1
12 8 -162.336 -426.971 135.508 476.466
0.000 15 nu_ebar 1 -12 9
198.224 495.978 103.455 544.050 0.000 16
gamma 1 22 1 0.000 0.000
0.000 0.000 0.000 17 gamma 1
22 2 0.000 0.000 0.000 0.000
0.000

sum 0.00 0.000 0.000 0.000
1500.000 1500.000
Examples using PYTHIA 6.410 T. Sjöstrand, S.
Mrenna, PS, JHEP 05 (2006) 026 http//projects.hep
forge.org/pythia6/
Note also handles full ?/Z0/Z0 interference for
SM channels
13
SM Higgs Factory
Standard PC ? 1M evts / hr.
Event listing (summary) I particle/jet KS
KF orig p_x p_y p_z E
m 1 !mu! 21 -13 0 0.000
0.000 60.000 60.000 0.106 2 !mu-!
21 13 0 0.000 0.000 -60.000
60.000 0.106

3 !mu! 21 -13 1 0.000 0.000
60.000 60.000 0.000 4 !mu-! 21
13 2 0.000 0.000 -60.000 60.000
0.000 5 !mu! 21 -13 3 0.000
0.000 60.000 60.000 0.000 6 !mu-!
21 13 4 0.000 0.000 -60.000
60.000 0.000 7 !h0! 21 25
0 0.000 0.000 0.000 120.000 120.000
8 !b! 21 5 7 -27.886 6.281
52.534 60.000 4.800 9 !bbar! 21
-5 7 27.886 -6.281 -52.534 60.000
4.800
10 (h0)
11 25 7 0.000 0.000 0.000
120.000 120.000 11 gamma 1 22
1 0.000 0.000 0.000 0.000 0.000
12 gamma 1 22 2 0.000 0.000
0.000 0.000 0.000 13 (ubar) A 12
-2 8 -0.243 -0.347 0.397 0.668
0.330 14 (g) I 12 21 8
0.173 -0.630 0.658 0.927 0.000 15
(g) I 12 21 8 -0.887 -0.091
1.462 1.712 0.000 16 (b) V 11
5 8 -9.565 10.722 44.056 46.587
4.800 17 (u) A 12 2 8 -12.758
-3.627 -0.934 13.300 0.330 18 (g)
I 12 21 8 -1.441 -0.459 0.931
1.775 0.000 19 (g) I 12 21
9 0.620 0.004 -0.189 0.648 0.000
20 (g) I 12 21 9 -0.081 1.305
-1.532 2.014 0.000 21 (g) I 12
21 9 -0.101 0.355 -0.413 0.554
0.000 22 (g) I 12 21 9
0.773 -0.305 -0.065 0.834 0.000 23
(g) I 12 21 9 0.332 0.059
-0.228 0.407 0.000 24 (bbar) V 11
-5 9 23.177 -6.986 -44.142 50.572
4.800
25 (string)
11 92 13 -10.522 9.654 46.573
49.895 10.799 26 (omega) 11 223
25 -0.253 -0.461 1.549 1.812 0.778
27 (pi0) 11 111 25 -0.480
-0.281 0.321 0.656 0.135 28 (pi0)
11 111 25 -1.442 2.077 7.957
8.350 0.135 29 (rho-) 11 -213 25
-1.077 1.453 5.978 6.291 0.754
30 (Bbar0) 11 -513 25 -7.270 6.866
30.767 32.786 5.325 31 (string) 11
92 17 10.522 -9.654 -46.573 70.105
50.416 32 (rho0) 11 113 31
-5.421 -1.084 -0.402 5.565 0.492 33
(K) 11 323 31 -4.307 -1.543
0.409 4.674 0.870 34 K- 1
-321 31 -1.770 -0.800 -0.443 2.052
0.494 35 p 1 2212 31 -2.323
-0.381 -0.291 2.551 0.938 36 (eta')
11 331 31 -0.351 0.200 0.439
1.128 0.958 37 (Deltabar-) 11 -2214
31 1.141 1.009 -1.561 2.513 1.248
38 pi 1 211 31 0.105
-0.415 -1.261 1.339 0.140 39 (rho-)
11 -213 31 5.155 -1.570 -8.550
10.137 0.790 40 pi 1 211
31 0.981 0.012 -2.262 2.469 0.140
41 (B0) 11 511 31 17.310
-5.083 -32.651 37.676 5.279
Examples using PYTHIA 6.410 T. Sjöstrand, S.
Mrenna, PS, JHEP 05 (2006) 026 http//projects.hep
forge.org/pythia6/
14
A0 (from 2HDM)
H (from LR Symmetry)
Event listing (summary) I particle/jet KS
KF orig p_x p_y p_z 1
!mu! 21 -13 0 0.000 0.000
300.000 2 !mu-! 21 13 0
0.000 0.000 -300.000
3 !mu!
21 -13 1 0.000 0.000 300.000
4 !mu-! 21 13 2 0.000
0.000 -300.000 5 !mu! 21 -13 3
0.000 0.000 300.000 6 !mu-! 21
13 4 0.000 0.001 -299.999 7 !A0!
21 36 0 0.000 0.001
0.001 8 !Z0! 21 23 7 -121.255
37.370 250.912 9 !h0! 21 25
7 121.255 -37.369 -250.911 10 !d!
21 1 8 -124.900 34.235 257.398 11
!dbar! 21 -1 8 3.645 3.135
-6.485 12 !tau-! 21 15 9
133.239 -9.141 -163.468 13 !tau! 21
-15 9 -11.985 -28.227 -87.444

14 (A0) 11 36 7
0.000 0.001 0.001 15 gamma 1
22 4 0.000 -0.001 -0.001 16 (Z0)
11 23 8 -121.255 37.370 250.912
17 (h0) 11 25 9 121.255
-37.369 -250.911 18 (tau) 11 -15
13 -11.983 -28.224 -87.433 19 (tau-)
11 15 12 131.583 -9.121 -161.287 20
gamma 1 22 12 1.655 -0.023
-2.192 23 (d) A 12 1 10
-86.461 23.971 171.287 24 (g) I 12
21 10 -20.973 4.898 39.060 25 (g)
I 12 21 10 -4.846 1.556
10.350 26 (g) I 12 21 10
-2.985 1.077 6.514 27 (g) I 12
21 10 -1.208 0.094 11.716 28 (g)
I 12 21 10 -1.148 0.894 3.534
29 (g) I 12 21 11 -0.829
-0.584 2.033 30 (g) I 12 21
11 -3.152 1.114 7.427 31 (g) I
12 21 11 -1.286 -0.891 2.165 32
(g) I 12 21 11 -0.322 -0.945
1.215 33 (g) I 12 21 11 -0.390
-0.326 -0.317 34 (g) I 12 21
11 0.284 0.117 0.004 35 (g) I
12 21 11 0.497 2.252 -0.578 36
(g) I 12 21 11 1.241 3.958
-3.508 37 (dbar) V 11 -1 11
0.324 0.184 0.009
38
nu_taubar 1 -16 18 -8.239 -19.736
-62.376 39 (rho) 11 213 18
-3.745 -8.488 -25.057 40 nu_tau 1
16 19 0.376 -0.010 -0.335 41 (rho-)
11 -213 19 131.207 -9.111 -160.951
42 (string) 11 92 23 -121.255
37.370 250.912 43 (omega) 11 223
42 -54.820 14.763 107.817
Event listing (summary) I particle/jet KS
KF orig p_x p_y p_z 1 !mu!
21 -13 0 0.000 0.000 1000.000
2 !mu-! 21 13 0 0.000
0.000-1000.000
3 !mu! 21
-13 1 0.000 0.000 1000.000 4
!mu-! 21 13 2 0.000
0.000-1000.000 5 !mu! 21 -13 3
0.097 0.092 991.468 6 !mu-! 21
13 4 0.000 0.000 -999.999 7
!H_L! 21 9900041 0 622.421 -441.228
603.501 8 !H_L--! 21-9900041 0
-622.324 441.320 -612.033 9 !tau! 21
-15 7 390.204 -216.443 455.416 10
!tau! 21 -15 7 232.217 -224.785
148.085 11 !tau-! 21 15 8
-620.412 420.784 -541.234 12 !tau-! 21
15 8 -1.912 20.536 -70.799

13 (H_L) 11 9900041 7
622.421 -441.228 603.501 14 (H_L--)
11-9900041 8 -622.324 441.320 -612.033 15
gamma 1 22 3 -0.097 -0.092
8.530 16 gamma 1 22 3 0.000
0.000 0.002 17 (tau-) 11 15
11 -620.412 420.784 -541.234 18 (tau-)
11 15 12 -1.912 20.536 -70.799 19
(tau) 11 -15 9 390.194 -216.438
455.405 20 (tau) 11 -15 10
226.721 -219.279 144.594 21 gamma 1
22 10 5.506 -5.511 3.502 22 gamma
1 22 1 0.000 0.000
0.000 23 gamma 1 22 2 0.000
0.000 0.000
24 nu_tau
1 16 17 -348.492 235.606 -302.953 25
pi- 1 -211 17 -271.921 185.179
-238.281 26 nu_tau 1 16 18
-0.933 4.425 -15.491 27 pi- 1
-211 18 -0.214 3.391 -10.885 28 (rho0)
11 113 18 -0.765 12.720 -44.422
29 nu_taubar 1 -16 19 101.142
-55.537 116.914 30 pi 1 211
19 289.052 -160.900 338.491 31 nu_e
1 12 20 3.975 -3.877 2.430 32
e 1 -11 20 216.486 -209.065
137.898 33 nu_taubar 1 -16 20
6.260 -6.337 4.267 34 pi- 1
-211 28 -0.794 12.176 -42.192 35 pi
1 211 28 0.029 0.544 -2.230

sum 0.00
0.000 0.000 0.000
Examples using PYTHIA 6.410 T. Sjöstrand, S.
Mrenna, PS, JHEP 05 (2006) 026 http//projects.hep
forge.org/pythia6/
15
Technicolor
Standard PC ? 250k evts / hr.
Event listing (summary) I particle/jet KS
KF orig p_x p_y p_z E
m 1 !mu! 21 -13 0 0.000
0.000 1000.000 1000.000 0.106 2 !mu-!
21 13 0 0.000 0.000-1000.000
1000.000 0.106

3 !mu! 21 -13 1 0.000
0.000 1000.000 1000.000 0.000 4 !mu-!
21 13 2 0.000 0.000-1000.000
1000.000 0.000 5 !mu! 21 -13
3 0.000 0.000 1000.000 1000.000 0.000
6 !mu-! 21 13 4 0.000
0.000-1000.000 1000.000 0.000 7 !pi_tc!
21 3000211 0 330.799 -763.014 -241.681
1000.025 500.022 8 !pi_tc-! 21-3000211
0 -330.799 763.014 241.681 999.975 499.920
9 !u! 21 2 7 -63.162
-482.381 -111.969 499.218 0.330 10 !bbar!
21 -5 7 393.961 -280.633 -129.712
500.808 4.800 11 !ubar! 21 -2
8 44.437 520.715 107.332 533.516 0.330
12 !b! 21 5 8 -375.236 242.299
134.349 466.459 4.800

13 (pi_tc) 11 3000211 7
330.799 -763.014 -241.681 1000.025 500.022 14
(pi_tc-) 11-3000211 8 -330.799 763.014
241.681 999.975 499.920 15 gamma 1
22 1 0.000 0.000 0.000 0.000
0.000 16 gamma 1 22 2 0.000
0.000 0.000 0.000 0.000 17 (u)
A 12 2 9 -50.238 -373.883 -84.036
386.489 0.330 18 (g) I 12 21
9 -10.115 -94.777 -23.332 98.130 0.000
19 (g) I 12 21 9 -0.365 -1.610
-0.077 1.653 0.000 20 (g) I 12
21 9 -1.459 -5.564 0.547 5.778
0.000 21 (g) I 12 21 9
0.991 -6.413 -5.097 8.252 0.000 22
(g) I 12 21 9 1.065 -1.928
-0.883 2.373 0.000 23 (g) I 12
21 10 0.511 -1.018 -0.464 1.230
0.000 24 (g) I 12 21 10 0.608
-0.218 -0.132 0.659 0.000 25 (g)
I 12 21 10 1.588 -0.970 -0.384
1.900 0.000 26 (g) I 12 21
10 13.555 -10.109 -4.320 17.453 0.000
27 (bbar) V 11 -5 10 374.657
-266.523 -123.505 476.108 4.800 28 (ubar)
A 12 -2 11 15.212 201.143 42.628
206.173 0.330 29 (g) I 12 21
11 17.753 214.099 42.291 218.957 0.000
30 (g) I 12 21 11 9.279
104.465 21.247 107.007 0.000 31 (g)
I 12 21 11 1.138 1.929 0.646
2.331 0.000 32 (g) I 12 21 11
-1.868 0.865 1.543 2.573 0.000
33 (g) I 12 21 12 -1.611 1.425
0.882 2.325 0.000 34 (g) I 12
21 12 -0.409 0.207 0.208 0.504
0.000 35 (g) I 12 21 12
-1.694 1.075 0.416 2.049 0.000 36
(b) V 11 5 12 -368.599 237.806
131.820 458.057 4.800

37 (string) 11 92 17 330.799
-763.014 -241.681 1000.025 500.022 38 p
1 2212 37 -28.471 -214.162 -48.494
221.424 0.938 39 (rho) 11 213
37 -6.754 -52.209 -11.786 53.955 0.925
40 pbar- 1 -2212 37 -16.097
-119.073 -27.000 123.156 0.938 41 (pi0)
11 111 37 -1.194 -13.408 -2.850
13.760 0.135 42 (pi0) 11 111
37 -2.712 -26.468 -6.257 27.333 0.135
43 (rho0) 11 113 37 -4.398
-33.030 -7.997 34.277 0.767

• Technicolor Strawman model
• Lowest-lying bound states of lightest
  Techni-fermion doublet
• Can be used for studies of a wide range of
  non-perturbative New Physics models
• Topcolor, walking Technicolor, extended
  Technicolor,

Mrenna, Lane Phys.Rev.D67115011,2003
Examples using PYTHIA 6.410 T. Sjöstrand, S.
Mrenna, PS, JHEP 05 (2006) 026 http//projects.hep
forge.org/pythia6/
16
The Generator Outlook

• MC Generators in state of continuous development
• Not much done (yet) specifically for muon
  colliders, but whats there is already pretty
  useful
• As physics studies pick up, interactions likely
  to foster more developments ? more studies ? more
  developments
• Get yours today its free

? more precise, more reliable theoretical
predictions
µ
µ-
http//projects.hepforge.org/pythia6/