MonChER: Monte-Carlo generator for CHarge Exchange Reactions. Version 1.1. Physics and Manual
aa r X i v : . [ h e p - ph ] J un CERNJune 2011 M ONCHER: M ONte Carlo generator for CHarge Exchange ReactionsVersion 1.1Physics and Manual
R.A. Ryutin, A.E. Sobol, V.A. Petrov
Institute for High Energy Physics
142 281
Protvino, Russia
Abstract
Moncher is a Monte Carlo event generator for simulation of single and doublecharge exchange reactions in proton-proton collisions at energies from 0.9 to 14 TeV.Such reactions, pp → n + X and pp → n + X + n , are characterized by leadingneutron production. They are dominated by π + exchange and could provide us withmore information about total and elastic π + p and π + π + cross sections and partondistributions in pions in the still unexplored kinematical region. Keywords
Single Charge Exchange – Double Charge Exchange – pion-proton – pion-pion – crosssections – event generator ontents π , ρ and a reggeons. . . . . . . . . . . . . . . . . 8 Introduction
In the paper we present a new Monte-Carlo event generator
Moncher . The generatoris devoted to the simulation of single and double charge exchange reactions in proton-proton collisions at energies from 0.9 to 14 TeV. This region of energies covers the presentcapabilities of the LHC. Charge exchange reactions, pp → n + X and pp → n + X + n , arecharacterized by the leading neutron production. They can be studied with LHC detec-tors incorporated with forward neutron calorimeters like the ZDC (Zero Degree Calorime-ter) [1] in the CMS [2].Reactions with the leading neutron production are dominated by π + exchange [3]-[6].At the LHC they could provide us with information about π + p and π + π + interactions inthe region of energies 1-5 TeV in the c.m.s. Using indirect methods [7]-[8] we could extracttotal and elastic π + p and π + π + cross sections at these energies. It is worth mentioningthat the total cross-section of π + p interaction is measured only at energies up to 25 GeVby direct methods in the fixed target experiments [9] and total and elastic cross sections of π + π + interactions are extracted from the data at energies 1.5-18.4 GeV only (see Ref. [10]-[12]). Moreover, a study of charge exchange reactions with hard scattering π + p and π + π + followed by dijet production at the LHC, could provide us with parton distributions in thepion in the unexplored kinematical domain. So, we had weighty motivations to develop amodel and to create a generator for charge exchange simulation which could be used athigh energies of the LHC.An important point is that at high energies we have to take into account effects ofsoft rescattering which can be calculated as corrections to the Born approximation. Inthe calculations of such absorptive effects we use the Regge-eikonal approach [13]. For π + p and π + π + interactions several models which predict different cross sections havebeen applied. In addition to the dominant π + exchange we have calculated contributionsof two other important Reggeons, ρ + and a +2 , to the charge exchange cross section [14]and implemented both Reggeons to the generation. Pythia
Moncher . Moncher has the same format of events, parameters andcommon blocks as
Pythia . Pythia subroutines are used also for the simulation of π + p and π + π + interactions and for the subsequent hadronization and decays. The diagram of the Single pion Exchange (S π E) process p + p → n + X is presented inFig. 1a. The momenta are p , p , p n , p X respectively. In the center-of-mass frame thesecan be represented as follows (boldface letters denote transverse momenta): p = √ s , √ s β, ! , p = √ s , − √ s β, ! . (1)With this notation, the momentum of the π is p π = ξ √ s β + t + m p − m n √ s , ξ √ s β, q ! , (2)and p n = p − p π , (3) p X = M , (4)1igure 1: Amplitudes of the processes: a) p + p → n + X (S π E), b) p + p → n + X + n (D π E). S and S represent soft rescattering corrections. ξ = M − m n − t + m p − m n ) sβ ≃ M s , (5) − t = q + ξ β m p + ( m n − m p ) (cid:18) ξβ − m n − m p s (cid:19) − ξβ + m n − m p ) s ≃ q + ξ m p − ξ , (6) β = s − m p s . (7)As a Born approximation for π exchange we use the familiar triple-Regge formula.This formula can be rewritten as dσ X, S π E dξdt d Φ X = G π + pn π − t ( t − m π ) F ( t ) ξ − α π ( t ) × dσ X,π + p ( ξs ) d Φ X S ( s/s , ξ, t ) , (8)where Φ X is the phase space for the system X produced in the π + p scattering, the piontrajectory is α π ( t ) = α ′ π ( t − m π ). The slope α ′ ≃ . − , ξ = 1 − x L , were x L isthe fraction of the initial proton longitudinal momentum carried by the neutron, and G π pp / (4 π ) = G π + pn / (8 π ) = 13 .
75 [16, 17]. The form factor F ( t ) is usually expressed asan exponential F ( t ) = exp( bt ) , (9)where, from recent data [18],[19], we expect b ≃ . − . We are interested in thekinematical range 0 .
01 GeV < | t | < . , ξ < . , (10)where formula (8) dominates according to [20] and [21]. At high energies we can use anyadequate parametrizations of different π + p cross-sections. The suppression factor S arises from absorptive corrections [3]. We estimate absorptionin the initial state for inclusive reactions and for both initial and final states in exclusive2xchanges. For this task we use our model with 3 Pomeron trajectories [13]: α IP ( t ) − . ± . . ± . t ,α IP ( t ) − . ± . . ± . t , (11) α IP ( t ) − . ± . . ± . t . These trajectories are the result of a 20 parameter fit of the total and differential cross-sections in the region0 .
01 GeV < | t | <
14 GeV , < √ s < . Although the χ /d.o.f. = 2 .
74 is rather large, the model gives good predictions for theelastic scattering (especially in the low-t region with χ /d.o.f. ∼ dσ ( s/s , ξ, q ) dξd q = S ( s/s , ξ, q ) dσ ( ξ, q ) dξd q , (12) dσ ( ξ, q ) dξd q == ( m p ξ + q ) | Φ B ( ξ, q ) | ξ (1 − ξ ) σ π + p ( ξ s ) , (13) S = m p ξ | Φ ( s/s , ξ, q ) | + q | Φ s ( s/s , ξ, q ) | ( m p ξ + q ) | Φ B ( ξ, q ) | . (14)The functions Φ and Φ s arise from different spin contributions to the amplitude A p → n = 1 √ − ξ ¯Ψ n (cid:16) m p ξ ˆ σ · Φ + q ˆ ~σ · Φ s (cid:17) Ψ p (15)and both are equal to Φ B in the Born approximation. Here ˆ σ i are Pauli matrices and¯Ψ n , Ψ p are neutron and proton spinors. All the above functions can be calculated by thefollowing set of formulae:Φ B ( ξ, q ) = N ( ξ )2 π q + ǫ + ı πα ′ π − ξ ) ! exp( − β q ) ≃≃ N ( ξ )2 π q + ǫ
11 + β q , q → , (16) N ( ξ ) = (1 − ξ ) G π + pn ξ α ′ πǫ − ξ exp " − b m p ξ − ξ , (17) β = b + α ′ π ln ξ − ξ , ǫ = m p ξ + m π (1 − ξ ) , (18)Θ ( b, ξ, | q | ) = b J ( b | q | ) (cid:16) K ( ǫ b ) − K (cid:16) bβ (cid:17)(cid:17) − β ǫ , (19)Θ s ( b, ξ, | q | ) = b J ( b | q | ) (cid:16) ǫ K ( ǫ b ) − β K (cid:16) bβ (cid:17)(cid:17) − β ǫ , (20)Φ = N ( ξ )2 π ∞ Z db Θ ( b, ξ, | q | ) V ( b ) , (21) | q | Φ s = N ( ξ )2 π ∞ Z db Θ s ( b, ξ, | q | ) V ( b ) , (22)3 c i . ± . . ± .
16 1 . ± . r i (GeV − ) 6 . ± . . ± . . ± . V ( b ) = exp ( − Ω el ( s/s , b )) , (23)Ω el = X i =1 Ω i , (24)Ω i = 2 c i πB i (cid:18) ss e − ı π (cid:19) α IPi (0) − exp " − b B i , (25) B i = α ′ IP i ln (cid:18) ss e − ı π (cid:19) + r i . (26)The values of parameters c i and r i are derived in (11) and listed in Table 1. Figs. 2demonstrate function S ( s/s , ξ, q t ) calculated for two values of energies a) √ s = 62 . √ s = 10 TeV for different ξ values: ξ = 0 . ξ = 0 . ξ = 10 − (solid). (a) t2 ,GeV (b) t2 ,GeV Figure 2: Function S ( s/s , ξ, q t ) at a) √ s = 62 . √ s = 10 TeV for different ξ values: ξ = 0 . ξ = 0 . ξ = 10 − (solid). π + p cross section In the present version of generator we use 4 parametrizations for π + p cross section. The Donnachie-Landshoff (DL) parametrization [22]: σ totπ + p ( s ) = 13 . s . + 25 . s − . , (mb) . (27) The COMPETE parametrization [23]: σ totπ + p ( s ) = Z πp + B ln (cid:18) ss (cid:19) + ( Y + s α + − Y − s α − ) /s, (mb) . (28)4 c ′ m m m π f π a π f a Z πp = 21 . ± .
33 mb ,B = 0 . ± . ,s = 34 ± . ,Y + = 17 . ± . , α + = 0 . ± . ,Y − = 5 . ± . , α − = 0 . ± . . In the next two parametrizations total cross-section can be obtained thorough theoptical theorem σ totπ + p = 1 s ℑ m T ( s, t ) | t =0 . (29) The Bourrely-Soffer-Wu (BSW) parametrization [24]: T( s, t p ) = ı ∞ Z b db J ( b q − t p )(1 − e − Ω ( s,b ) ) , (30)Ω ( s, b ) = Ω IP + X i Ω i , (31)Ω IP ≃ s c ln c ′ s ıπc (cid:16) ıπ ln s (cid:17) c ′ F BSW ( b ) for s ≫ m p , | t | . (32)For the π + p we have i = ρ in (31) and F π + pBSW ( b ) = ∞ Z q dq J ( qb ) f π a π − q a π + q × q m )(1 + q m )(1 + q m π ) , (33)Ω ρ ≃ C ρ (1 + ı ) (cid:18) ss (cid:19) α ρ (0) − e − b Bρ B ρ , (34) B ρ = b ρ + α ′ ρ (0) ln ss , b ρ = 4 . , (35) α ρ ( t ) = 0 . t, C ρ = 4 . , (36)where values of parameters are listed in Table 2. The Godizov-Petrov (GP) parametrization [25],[26].
In this parametrization the scattering amplitude is represented in the usual eikonal form T ( s, b ) = e iδ ( s,b ) − i (37)(here T ( s, b ) is the amplitude in the impact parameter b space, s is the invariant masssquared of colliding particles and δ ( s, b ) is the eikonal function). Amplitudes in the impactparameter space and momentum one are related thorough the Fourier-Bessel transforms f ( s, b ) = 116 πs Z ∞ d ( − t ) J ( b √− t ) f ( s, t ) , (38) f ( s, t ) = 4 πs Z ∞ db J ( b √− t ) f ( s, b ) . (39)5ikonal function in the momentum space is δ ( s, t ) = δ P ( s, t ) + δ f ( s, t ) == i + tg π ( α P ( t ) − ! β P ( t ) (cid:18) ss (cid:19) α P ( t ) ++ i + tg π ( α f ( t ) − ! β f ( t ) (cid:18) ss (cid:19) α f ( t ) . (40)The parametrization for the pomeron residue is β P ( t ) = B P e b P t (1 + d t + d t + d t + d t ) , (41)which is approximately (at low values of d , d , d d ) an exponential at low t values.Residues of secondary reggeons we set as exponentials: β f ( t ) = B f e b f t . (42) Pomeron f -reggeon ω -reggeon p . c f . c ω . p .
58 GeV − p . B P . B f B ω b P . − b f . − b ω . − d .
43 GeV − d .
39 GeV − d .
051 GeV − d .
035 GeV − α P (0) 1 . α f (0) 0 . α ω (0) 0 . α ′ P (0) 0 .
28 GeV − α ′ f (0) 0 .
63 GeV − α ′ ω (0) 0 .
07 GeV − Table 3: Values of parameters of the model [25],[26] for pp scattering.Phenomenological parametrization for the ”soft” pomeron trajectory is set to α P ( t ) = 1 + p (cid:20) − p t (cid:18) arctg( p − p t ) − π (cid:19)(cid:21) . (43)Trajectories of secondary reggeons f and ω are parametrized by functions α R ( t ) = (cid:18) π α s ( √− t + c R ) (cid:19) / , R = f, ω, (44)where α s ( µ ) = 4 π − n f µ Λ + 11 − µ Λ (45)is the one-loop analytic QCD running coupling [27], n f = 3 is the number of flavours,Λ ≡ Λ (3) = 0 .
346 GeV [28]. Parameters c f , c ω > ππ , πp and pp are assumed to be β ππP ( t ) = β πpP ( t ) β πpP ( t ) β ppP ( t ) , (46) β ππf ( t ) = β πpf ( t ) β πpf ( t ) β ppf ( t ) . (47)Parameters of the model are listed in Tables 3.6 .2 Double Pion Exchange The diagram of the Double Pion Exchange (D π E) process p + p → n + X + n is presentedin Fig. 1b. The momenta are p , p , p n , p X , p n respectively. In the center-of-mass framethese can be represented as follows p π i ≃ ξ i √ s , ( − i − ξ i √ s , q i ! , (48) p n i = p i − p π i , (49) p X = M = ξ ξ sβ β − ( q + q ) − m p β ( ξ + ξ ) ++( t + t + 2( m p − m n )) · β ( ξ + ξ ) + t + t + 2( m p − m n ) s ! ≃ ξ ξ s, (50) − t i ≃ q i + ξ i m p − ξ i . (51)The cross-section can be evaluated as follows: dσ = S ( s/s , ξ , , q , ) dσ , (52) dσ ( ξ , ξ , q , q ) dξ dξ d q d q = Y i =1 " ( m p ξ i + q i ) | Φ B ( ξ i , q i ) | ξ i (1 − ξ i ) · σ π + π + ( ξ ξ s ) , (53) S = P i,j =0 ,s ρ ij | ¯Φ ij ( s/s , ξ , , q , ) | Q i =1 h ( m p ξ i + q i ) | Φ B ( ξ i , q i ) | i , (54)¯Φ ij = N ( ξ ) N ( ξ )(2 π ) · ∞ Z db db Θ i ( b , ξ , | q | )Θ j ( b , ξ , | q | ) I φ ( b , b ) , (55) I φ ( b , b ) = π Z dφπ V (cid:18)q b + b − b b cos φ (cid:19) , (56) ρ = m p ξ ξ , ρ s = m p ξ , ρ s = m p ξ , ρ ss = 1 . (57)For low t i the function S is approximately equal to F ( ξ , ξ ) ≡ S ( s/s , ξ , ξ , , ≃≃ (cid:18)q S ( s/s , ξ ,
0) + q S ( s/s , ξ , − q S ( s/s , ξ , S ( s/s , ξ , (cid:19) . (58)Figs. 3 demonstrates 2D projections of function S ( s/s , ξ , , | q , | ) and function F ( ξ , ξ )at √ s = 10 TeV.To obtain π + π + cross-sections we use parametrizations described in the subsec-tion 2.1.2 with the following approximations: σ totπ + π + ≃ (cid:16) σ totπ + p (cid:17) σ totpp (59)for the DL and COMPETE ones, quantities F π + π + BSW ( b ) ≃ ∞ Z q dq J ( qb ) f ππ a ππ − q a ππ + q q m π ) , (60)7 a) (cid:143) (cid:143) (cid:143) (b) Ξ Ξ Ξ ( ) Ξ Ξ Ξ Figure 3: The function S ( s/s , ξ , , | q , | ) at √ s = 10 TeV: a) for fixed ξ , = 0 .
01 b) forfixed | q , | ∼
0. c) The function F ( ξ , ξ ) at √ s = 10 TeV.Ω ≃ Ω IP , f ππ = f π f , a ππ = 2 a π − a . (61)for the BSW one, which should be substituted to (32), and equations (46),(47) for the GP one. π , ρ and a reggeons. For ρ and a contributions formulae are similar to ones described in the chapters (2.1)and (2.2). dσ SIRE dξdt = F IR ( ξ, t ) S IR ( s/s , ξ, t ) σ IR + p ( ξs ) , (62) dσ DIR π E dξ dξ dt dt = F IR π ( ξ , ξ , t , t ) S IR , ( s/s , { ξ i } , { t i } ) × σ IR + π + ( ξ ξ s ) , (63) F IR ( ξ, t ) = | η IR | ˜ G + pn π e b R t ξ − α IR ( t ) κ q m p ! , (64) F IR π ( { ξ i } , { t i } ) = F (1) F IR (2) + F (2) F IR (1) ++2 vuut F (1) F (2) F IR (1) F IR (2) t t (1 − ξ )(1 − ξ ) × (cid:16) m p ξ + q κ IR m p (cid:17) (cid:16) m p ξ + q κ IR m p (cid:17)(cid:18) q κ m p (cid:19) (cid:18) q κ m p (cid:19) , (65) F , IR ( i ) = F , IR ( ξ i , t i ) , q i ≃ − t i (1 − ξ i ) − m p ξ i . (66)Here κ IR = 8 is the ratio of spin-flip to nonflip amplitude, α IR ( t ) ≃ . . t and param-eters for ρ , a mesons are [29] η ρ = − ı + 1 , η a = ı + 1 , (67) b ρ = 2 GeV − , b a = 1 GeV − , (68)˜ G ρ + pn π = 0 .
18 GeV − , ˜ G a pn π = 0 .
405 GeV − . (69)Rescattering corrections S IR and S IR , are calculated by the method used in [7],[8]. Basicassumptions in our calculations are: • ρ ρ , ρ a and a a contributions are small;8 interference terms of the type T ∗ S π E T SIRE , T ∗ DIR π E T DIR ′ π E are small [19], IR , IR ′ = π, ρ, a , IR = IR ′ , where T are amplitudes of the corresponding processes; • approximate relations σ IR + p ≃ σ π + p , σ IR + π + ≃ σ π + π + [19].Figs. 4 demonstrates 3D plots for cross sections of the Single and Double ReggeonExchange reactions for the different reggeons (S π E a), S ρ E+S a E b), D π E c) andD ρπ E+D a π E d)) at √ s = 7 TeV.Figure 4: Cross-sections dσdξdr in mb · cm − at √ s = 7 TeV for: a) S π E; b) S ρ E+S a E; c)D π E; d) D ρπ E+D a π E. r is the transverse distance from the beam.9 Program Overview
The kinematics of SIRE and DIRE reactions, pp → n + (IR p ) → n + X (70)and pp → n + (IRIR) + n → n + X + n, (71)are defined by the relative energy loss of ξ n and the square of the transverse momentum t n of the leading neutron. The vertex p IR n is generated on the basis of the modelsdescribed above. The differential cross sections for the generated neutron and reggeonare calculated according the selected models for absorptive corrections and for IR p (IRIR)interactions. Then, PYTHIA 6.420 [15] is called for the IR p → X generation in the caseof SIRE and IRIR → X generation in the case of DIRE. Parameters of the all generatedparticles, including beam protons, leading neutrons, reggeons and X, products of IR p (IRIR) interaction, are stored in Pythia common blocks.
SUBROUTINE MONINIT
Purpose: to initialize the generation procedure. In particulary,- to show program title;- to read control parameters from the file moncher.par ;- to set default
Moncher parameters;- to initilize
Pythia ;- to initilize LHE format output.
Status of call: should be called obligatory, one time, in the begining of the mainprogram before calling of
MONEVEN . Calling by: main program
Calling of: MONTITL , MONPARA , MONMBDF , MONUPIN , PYINITSUBROUTINE MONTITL
Purpose: to print title of
Moncher on the screen. Namely, ********************************** ** MON-te-carlo generator for ** CH-arge ** E-xchange ** R-eactions ** ** Version 1.1.0.(12/03/2011) ** ** ** ** R.Ryutin,A.Sobol,V.Petrov ** (IHEP,Protvino) ** **********************************Status of call: should be called OBLIGATORY.
Calling by: MONINIT UBROUTINE MONPARA
Purpose: to read control parameters for the
Moncher and
Pythia generation fromthe file moncher.par
Control parameters for
Moncher are called
MONPAR ,they are stored to the common block /MONGLPA/ . Any
Pythia parameterscan be defined for
Pythia common blocks /PYJETS/,/PYDAT1/,/PYDAT2/,/PYDAT3/,/PYDAT4/,/PYDATR/,/PYSUBS/,/PYPARS/,/PYINT1/,/PYINT2/,/PYINT3/,/PYINT4/,/PYINT5/,/PYINT6/,/PYINT7/,/PYINT8/,/PYMSSM/,/PYMSRV/,/PYTCSM/,/PYPUED/ (see [15]).
Status of call: can be called if you like to define some control parameters from the moncher.par . By default,
Moncher initilizes a generation of minimum biasevents by
Pythia with some default parameters.
Calling by: MONINITCalling of: MONGIVESUBROUTINE MONMBDF
Purpose: to define default parameters for the generation. By default,
Moncher and
Pythia parameters are defined to generate 10 minimum bias events at c.m.s.energy 7 TeV.
Status of call: to be called at initialization. Default parameters are redefined by thecall of the
MONPARA reading parameters from the file moncher.par . Calling by: MONINITCalling of: MONGIVESUBROUTINE MONEVEN
Purpose: call subroutines for the single event generation
MONPAR(7)= 1 : call
MONSPEG for Single Charge Exchange (SCE) generation.
MONPAR(8)= 1 : call
MONDPEG for Double Charge Exchange (DCE) generation.
MONPAR(7)= 0 and MONPAR(8)= 0 : call
PYEVNT for the
Pythia event generation.
Status of call: should be be called in the user main program, in the cycle of events.
Calling by: main program
Calling of: MONSPEG , MONDPEG , PYEVNTSUBROUTINE MONSPEG
Purpose: to generate single SCE event, p beam p beam → n ( π + virt p beam ) → nX , in the follow-ing sequence:- the vertex p beam nπ + virt is generated by MONSPEM ;- Pythia is initialized for the generation of π + virt p beam interaction;- Pythia is called for the generation, hadronization and decays;- the
Pythia output is rewriting to include beam protons and neutronto the final state of the reaction with the particles from X .Simulation of π + virt p beam interaction is controled by Pythia parameters. It canbe elastic, minimum bias or diffractive interaction. Number of the correspond-ing SCE process is equal to the number of the
Pythia process + 500.
Status of call: called if
MONPAR(7)=1 . Calling by: MONEVENCalling of: MONSPEM , MONSHPY , PYINIT , PY1ENT , PYANGL UBROUTINE MONDPEG
Purpose: to generate single DCE event, p beam p beam → n ( π + virt π + virt ) n → nXn , in thefollowing sequence:- the vertexes p beam nπ + virt and p beam nπ + virt are generated by MONDPEM ;- Pythia is initialized for the generation of π + virt π + virt interaction;- Pythia is called for the generation, hadronization and decays;- the
Pythia output is rewriting to include beam protons and neutronsto the final state of the reaction with the particles from X .Simulation of π + virt π + virt interaction is controled by Pythia parameters. It canbe elastic, minimum bias or diffractive interaction. Number of the correspond-ing DCE process is equal to the number of the
Pythia process + 600.
Status of call: called if
MONPAR(8)=1 . Calling by: MONEVENCalling of: MONDPEM , MONSHPY , PYINIT , PY1ENT , PYANGLSUBROUTINE MONSPEM(NO,PN,PR,M2)
Purpose: to generate momentums and energies of neutron n and virtual exchangereggeon IR + in the reaction of Single Charge Exchange: p beam p beam → n (IR + p beam ) → nX INTEGER NO ( input ) : type of exchange reggeon IR; = 1 : π + = 2 : ρ + = 3 : a +2 DOUBLE PRECISION PN(5) ( output ) : kinematical parameters of the neutron n . PN(1) : p x , momentum of neutron in the x direction, in GeV/ c . PN(2) : p y , momentum of neutron in the y direction, in GeV/ c . PN(3) : p z , momentum of neutron in the z direction, in GeV/ c . PN(4) : E , energy of neutron, in GeV. PN(5) : m , mass of neutron, in GeV/ c . DOUBLE PRECISION PR(5) ( output ) : kinematical parameters of the reggeon IR + . PR(1) : p x , momentum of reggeon in the x direction, in GeV/ c . PR(2) : p y , momentum of reggeon in the y direction, in GeV/ c . PR(3) : p z , momentum of reggeon in the z direction, in GeV/ c . PR(4) : E , energy of reggeon, in GeV. PR(5) : m , mass of reggeon, in GeV/ c . DOUBLE PRECISION M2 ( output ) : invariant mass of the system (IR + p beam ), in GeV/ c . Calling by: MONSPEGCalling of: MONGE2DSUBROUTINE MONDPEM(NO,PN1,PN2,PR1,PR2,M2)
Purpose: to generate momentums and energies of neutrons n and virtual exchangereggeons IR + in the reaction of Double Charge Exchange: p beam p beam → n (IR +1 IR +2 ) n → nXn INTEGER NO ( input ) : type of exchange reggeons IR +1 IR +2 ; = 1 : π + π + = 2 : π + ρ + = 3 : π + a +2 DOUBLE PRECISION PN1(5),PN2(5) ( output ) : kinematical parameters of the neu-12ron n . PN1(1),PN2(1) : p x , momentum of neutrons in the x direction, in GeV/ c . PN1(2),PN2(2) : p y , momentum of neutrons in the y direction, in GeV/ c . PN1(3),PN2(3) : p z , momentum of neutrons in the z direction, in GeV/ c . PN1(4),PN2(4) : E , energy of neutrons, in GeV. PN1(5),PN2(5) : m , mass of neutrons, in GeV/ c . DOUBLE PRECISION PR1(5),PR2(5)( output ) : kinematical parameters of thereggeons IR +1 , . PR(1),PR2(1) : p x , momentum of reggeons in the x direction, in GeV/ c . PR(2),PR2(2) : p y , momentum of reggeons in the y direction, in GeV/ c . PR(3),PR2(3) : p z , momentum of reggeons in the z direction, in GeV/ c . PR(4),PR2(4) : E , energy of reggeons, in GeV. PR(5),PR2(5) : m , mass of reggeons, in GeV/ c . DOUBLE PRECISION M2 ( output ) : invariant mass of the system (IR +1 IR +2 ), in GeV/ c . Calling by: MONDPEGCalling of: MONGE2D , MONGE2D4SUBROUTINE MONSHPY(NSHIFT)
Purpose: to shift data of arrays of the
Pythia common block /PYJETS/ for
NSHIFT positions. It should be done to fill first
NSHIFT positions of /PYJETS/ arraysby the parameters of the beam protons and neutrons in the final state ofreaction.
Calling by: MONSPEG , MONDPEGSUBROUTINE MONGIVE(CHIN)
Purpose: modification of the
Pythia subroutine
PYGIVE to set the value of any variableresiding in the commmonblocks
PYJETS , PYDAT1 , PYDAT2 , PYDAT3 , PYDAT4 , PYDATR , PYSUBS , PYPARS , PYINT1 , PYINT2 , PYINT3 , PYINT4 , PYINT5 , PYINT6 , PYINT7 , PYINT8 , PYMSSM , PYMSRV , PYTCSM or MONGLPA . This is done in a morecontrolled fashion than by directly including the common blocks in your pro-gram, in that array bounds are checked and the old and new values for the vari-able changed are written to the output for reference. In the following example,”
CALL MONGIVE(’MONPAR(3)=14000’) ”, we have changed pp c.m.s. energy to14 TeV. More detail explanation see in Ref. [15] for subroutine
PYGIVE . CHARACTER CHIN*(*) ( input ) : character expression of length at most 100 characters,with requests for variables to be changed.
Calling by: MONPARA , MONMBDFSUBROUTINE MONUPEV
Purpose: to write information about generated processes to the file moncher.lhe usingspecial LHE record format. For more detail information about LHE formatsee Ref. [30].
Status of call: called if
MONPAR(2)=1 . Calling by: MONINITSUBROUTINE MONUPIN
Purpose: to save information about all stable particles generated in the event to the file13 oncher.lhe using special LHE record format. For more detail informationabout LHE format see Ref. [30].
Status of call: should be called for each generated event if
MONPAR(2)=1 . Calling by: user main program
These subroutines are used for internal calculations and should not be changed.
SUBROUTINE MONGE2D(FF,X1,X2,N1,N2,FF1,FF2,FF3,RG,XG,IG)
Purpose: to generate two variables according to the 2D distribution from the table.
DOUBLE PRECISION FF(N1,N2)( input ) : N1 × N2 dimensional interpolation table of 2Ddistribution. DOUBLE PRECISION X1(N1),X2(N2))( input ) : arrays of variables corresponding to thetable FF . INTEGER N1,N2( input ) : dimensions of the 2D table.
DOUBLE PRECISION FF1(N1),FF2(N1)( input ) : auxiliary integrated tables for 2D dis-tribution.
DOUBLE PRECISION FF3(2,N1,N2)( input ) : auxiliary sums from the table for 2D distri-bution.
DOUBLE PRECISION RG(2)( input ) : array for generated random numbers from 0 to 1.
DOUBLE PRECISION XG(2)( output ) : array for generated variables according to the 2Ddistribution.
INTEGER IG(2)( output ) : auxiliary numbers of the nearest to the
XG(2) discrete point.
Calling by: MONSPEM , MONDPEMSUBROUTINE MONG2D4(FF,X1,X2,N1,N2,FF1,FF2,FF3,II,XX,RG,XG)
Purpose: to generate four variables according to the 4D distribution from the table.
DOUBLE PRECISION FF(N1,N1,N2,N2)( input ) : N1 × N1 × N2 × N2 dimensional interpola-tion table of 4D distribution. DOUBLE PRECISION X1(N1),X2(N2))( input ) : arrays of variables corresponding to thetable FF . INTEGER N1,N2( input ) : dimensions of the 4D table.
DOUBLE PRECISION FF1(4,N1,N1,N2),FF2(4,N1,N1,N2)( input ) : auxiliary integratedtables for the 4D distribution.
DOUBLE PRECISION FF3(8,N1,N1,N2,N2)( input ) : auxiliary sums from the table for the4D distribution.
INTEGER II(2)( input ) : auxiliary numbers for multidimensional calculations.
DOUBLE PRECISION XX(2)( input ) : auxiliary points for multidimensional calculations.
DOUBLE PRECISION RG(4)( input ) : array for generated random numbers from 0 to 1.
DOUBLE PRECISION XG(4)( output ) : array for generated variables according to the 4Ddistribution.
Calling by: MONDPEMSUBROUTINE MONCUBI(FF,VS,FUN)
Purpose: cubic spline interpolation for a function in the variable ln s . DOUBLE PRECISION FF(6)( input ) : table of the function at six values of variable s storedin the array XSQ(6) (see below the commonblock MONTAB1 ).14
OUBLE PRECISION VS( input ) : input value of s . DOUBLE PRECISION FUN( output ) : output value of the function.
Calling by: MONDATASUBROUTINE MONLI2D(FDT,X1,X2,N1,N2,XV,FUN)
Purpose:
Linear 2D interpolation from the table of any function.
DOUBLE PRECISION FDT(N1,N2)( input ) : N1 × N2 dimensional table of values for the in-put function. DOUBLE PRECISION X1(N1),X2(N2)( input ) : arrays for discrete points corresponding tothe values of the input function.
INTEGER N1,N2( input ) : dimensions of the 2D interpolation table.
DOUBLE PRECISION XV(2)( input ) : input values for two variables of the function.
DOUBLE PRECISION FUN( output ) : output value of the function.
Calling by: MONDATASUBROUTINE MONLI4D(FDT,X1,X2,X3,X4,N1,N2,N3,N4,XV,FUN)
Purpose:
Linear 4D interpolation from the table of any function.
DOUBLE PRECISION FDT(N1,N2,N3,N4)( input ) : N1 × N2 × N3 × N4 dimensional table ofvalues for the input function. DOUBLE PRECISION X1(N1),X2(N2),X3(N3),X4(N4)( input ) : arrays for discrete pointscorresponding to the values of the input function.
INTEGER N1,N2,N3,N4( input ) : dimensions of the 4D interpolation table.
DOUBLE PRECISION XV(4)( input ) : input values for four variables of the function.
DOUBLE PRECISION FUN( output ) : output value of the function.
Calling by: MONDATASUBROUTINE MONIN2D(FF,X1,X2,N1,N2,FF1,FF2,FF3)
Purpose: calculations of additional integrated tables used in the generation subroutine
MONGE2D , MONG2D4 . DOUBLE PRECISION FF(N1,N2)( input ) : input table of 2D function.
DOUBLE PRECISION X1(N1),X2(N2)( input ) : arrays for discrete points corresponding tothe values of the input function.
INTEGER N1,N2( input ) : dimensions of the 2D interpolation table.
DOUBLE PRECISION FF1(N1),FF2(N1),FF3(2,N1,N2)( output ) : generated auxiliary ta-bles.
Calling by: MONDATA , MONIN4DSUBROUTINE MONIN4D(FF,X1,X2,N1,N2,FF1,FF2,FF3)
Purpose: calculations of additional integrated tables used in the generation subroutine
MONG2D4 . DOUBLE PRECISION FF(N1,N1,N2,N2)( input ) : input table of 4D function.
DOUBLE PRECISION X1(N1),X2(N2)( input ) : arrays for discrete points corresponding tothe values of the input function.
INTEGER N1,N2( input ) : dimensions of the 4D interpolation table.
DOUBLE PRECISION FF1(2,N1,N1,N2),FF2(2,N1,N1,N2),FF3(8,N1,N1,N2,N2)( output ) : generated auxiliary tables. 15 alling by: MONDATASUBROUTINE MONDATA
Purpose: to read tables for absorptive corrections and for pRn form factors from theexternal files
Spi 1 , Sro 1 , Sa2 1 , S2pi 1 , S2ro 1 , S2a2 1 , FFpi 1 , FFro 1 , FFa2 1 . These tables are used for calculation of the differential cross sectionsfor SCE and DCE reactions at given energy (defined by parameter
MONPAR(3) )by interpolation methods.
Status of call: is called if
MONPAR(7)=1 or MONPAR(8)=1 . Calling by: MONINITCalling of: MONCUBI , MONLI2D , MONLI4D , MONIN2D , MONIN4D
DOUBLE PRECISION FUNCTION MONCSEC(KP,KR)
Purpose: to give the value of the total cross section of SCE ( pp → nX ) or DCE ( pp → nXn ) reaction for the given reggeon exchange at the c.m.s. energy definedby parameter MONPAR(3) for the model defined by parameters
MONPAR(4) and
MONPAR(5) . INTEGER KP ( input ) : single or double exchange = 1 : for SCE cross section = 2 : for DCE cross section
INTEGER KR ( input ) : type of the reggeon exchange = 1 : for SCE define π + exchange, for DCE π + π + one. = 2 : for SCE ρ + exchange, for DCE π + ρ + . = 3 : for SCE a +2 exchange, for DCE π + a +2 . Calling by: MONINITDOUBLE PRECISION FUNCTION MONCSCE(NO,XI,QT)
Purpose: to give the value of cross section of SCE ( pp → nX ) reaction for the givenreggeon exchange at given ξ n of neutron and Q t of reggeon at the c.m.s. en-ergy defined by parameter MONPAR(3) for the model defined by parameters
MONPAR(4) and
MONPAR(5) . INTEGER NO ( input ) : type of the reggeon exchange = 1 : for π + exchange. = 2 : for ρ + exchange. = 3 : for a +2 exchange. DOUBLE PRECISION XI ( input ) : ξ n = | p beam − p n | p beam , relative momentum loss of the neu-tron. DOUBLE PRECISION QT ( input ) : Q t , transverse momentum of the exchange reggeon. Calling by: MONCDCE , MONDATADOUBLE PRECISION FUNCTION MONCDCE(NO,XI1,XI2,QT1,QT2) urpose: to give the value of cross section of the DCE ( pp → nXn ) reaction for the givenreggeon exchange at given ξ , n of neutron and Q , t of reggeons at the c.m.s.energy defined by parameter MONPAR(3) for the model defined by parameters
MONPAR(4) and
MONPAR(5) . INTEGER NO ( input ) : type of the reggeon exchange = 1 : for π + π + exchange. = 2 : for π + ρ + exchange. = 3 : for π + a +2 exchange. DOUBLE PRECISION XI ( input ) : ξ , n = | p , beam − p , n | p , beam , relative momentum loss of the neu-trons. DOUBLE PRECISION QT ( input ) : Q , t , transverse momentum of the exchange reggeons. Calling by: MONCDCE , MONDATADOUBLE PRECISION FUNCTION MONCSRP(NO,NCSMOD,SVAR)
Purpose: to give the value of the total reggeon-proton cross section
INTEGER NO ( input ) : type of the reggeon exchange = 1 : for π + exchange. = 2 : for ρ + exchange. = 3 : for a +2 exchange. INTEGER NCSMOD ( input ) : type of model for the reggeon-proton cross section calcula-tion = 1 :
Donnachie-Landshoff parametrization [22]. = 2 :
COMPETE parametrization [23]. = 3 :
Bourrely-Soffer-Wu parametrization [24]. = 4 :
Godizov-Petrov parametrization [25].
DOUBLE PRECISION SVAR ( input ) : invariant mass of reggeon-proton system
Calling by: MONCSRR , MONCSCE , MONCDCEDOUBLE PRECISION FUNCTION MONCSRR(NO,NCSMOD,SVAR)
Purpose: to give the value of the total reggeon-reggeon cross section
INTEGER NO ( input ) : type of the reggeon-reggeon exchange = 1 : for π + π + exchange. = 2 : for π + ρ + exchange. = 3 : for π + a +2 exchange. INTEGER NCSMOD ( input ) : type of model for the reggeon-reggeon cross section calcu-lation = 1 :
Donnachie-Landshoff parametrization [22]. = 2 :
COMPETE parametrization [23]. = 3 :
Bourrely-Soffer-Wu parametrization [24]. = 4 :
Godizov-Petrov parametrization [25].
DOUBLE PRECISION SVAR ( input ) : invariant mass of reggeon-reggeon system
Calling by: MONDATA , MONCDCE .4 Main Commonblocks and Parameters PARAMETER (MXGLPAR=200)REAL MONPARCOMMON/MONGLPA/ MONPAR(MXGLPAR)
Purpose: to give access to the main
Moncher switches and parameters
MONPAR(1) : number of events for the generation.
MONPAR(2) : switch for LHE output. = 0 :
LHE output is switched off. = 1 :
LHE output is switched on.
MONPAR(3) : pp centre mass energy, in GeV, (from 900 to 14000 GeV).
MONPAR(4) : kod of model for pR and RR interaction. = 1 :
Donnachie-Landshoff parametrization [22]. = 2 :
COMPETE parametrization [23]. = 3 :
Bourrely-Soffer-Wu parametrization [24]. = 4 :
Godizov-Petrov parametrization [25].
MONPAR(5) : kod of model for absorptive corrections. = 1 :
MONPAR(6) : type of exchange reggeon. = 1 : for SCE define π + exchange, for DCE π + π + one. = 2 : for SCE ρ + exchange, for DCE π + ρ + . = 3 : for SCE a +2 exchange, for DCE π + a +2 . MONPAR(7) : switch for SCE generation. = 0 :
SCE is switched off. = 1 :
SCE is switched on.
MONPAR(8) : switch for DCE generation. = 0 :
DCE is switched off. = 1 :
DCE is switched on.
Note 1: if MONPAR(7)=0 and
MONPAR(8)=0 , minimum bias events are generatedby
Pythia . Note 2: in the present version of
Moncher , v.1.1, the simultaneous generationof SCE and DCE is impossible.
DOUBLE PRECISION SINTEGER NMODPP,NMODRR,ITYPRCOMMON/MONTAB0/S,NMODPP,NMODRR,ITYPR
Purpose: to give access to some important
Moncher parameters.
S : pp c.m.s. energy, in GeV.
NMODPP : kod of model for absorptive corrections. = 1 :
NMODRR : kod of model for pR and RR interaction. = 1 :
Donnachie-Landshoff parametrization [22]. = 2 :
COMPETE parametrization [23]. = 3 :
Bourrely-Soffer-Wu parametrization [24]. = 4 :
Godizov-Petrov parametrization [25].
ITYPR : type of exchange reggeon. = 1 : for SCE define π + exchange, for DCE π + π + one.18 for SCE ρ + exchange, for DCE π + ρ + . = 3 : for SCE a +2 exchange, for DCE π + a +2 . DOUBLE PRECISION XSQ,PI,MPI,MP,MN,MRHO,MA2COMMON/MONTAB1/XSQ(6),PI,MPI,MP,MN,MRHO,MA2
Purpose: to give access to some important
Moncher parameters.
XSQ : six values of √ s for the interpolation subroutine MONCUBI . PI : 3.141592653589793D0MPI : pion mass.
MP : proton mass.
MN : neutron mass.
MRHO : ρ meson mass. MA2 : a meson mass. DOUBLE PRECISION XIMIN,XIMAX,QTMIN,QTMAXCOMMON/MONTAB2/XIMIN,XIMAX,QTMIN,QTMAX
Purpose: to give access to some important
Moncher parameters.
XIMIN : minimal value of the variable ξ . XIMAX : maximal value of the variable ξ . QTMIN : minimal value of the variable | q | (transverse momentum of the neutron). QTMAX : maximal value of the variable | q | (transverse momentum of the neutron). DOUBLE PRECISION API,ARHO,AA2,R2PI,R2RHO,R2A2COMMON/MONTAB3/API,ARHO,AA2,R2PI,R2RHO,R2A2
Purpose: to give access to some important
Moncher parameters.
API : slope of the pion regge trajectory.
ARHO : slope of the ρ meson regge trajectory. AA2 : slope of the a meson regge trajectory. R2PI : slope of the exponent in the residue of the pion trajectory.
R2RHO : slope of the exponent in the residue of the ρ meson trajectory. R2A2 : slope of the exponent in the residue of the a meson trajectory. DOUBLE PRECISION GPI,GRHO,GA2,SIGRSQ,KARHO,KAA2COMMON/MONTAB4/GPI,GRHO,GA2,SIGRSQ,KARHO,KAA2
Purpose: to give access to some important
Moncher parameters.
GPI,GRHO,GA2 : constants G π + pn / (8 π ), ˜ G ρ + pn / (8 π ) and ˜ G a +2 pn / (8 π ). SIGRSQ : | η R | . KARHO, KAA2 : κ ρ , κ a . 19 OUBLE PRECISION SSPI,SSRHO,SSA2,SDPIS,SDPIA,& SDRHOS,SDRHOA,SDA2S,SDA2A,FFDPI,FFDRHO,FFDA2COMMON/MONDGET/SSPI(6,53,41),SSRHO(6,53,51),& SSA2(6,53,51),SDPIS(6,10,8,9,8),SDPIA(6,10,8,9,8),& SDRHOS(6,10,8,9,8),SDRHOA(6,10,8,9,8),SDA2S(6,10,8,9,8),& SDA2A(6,10,8,9,8),FFDPI(6,60,16),FFDRHO(6,60,16),& FFDA2(6,60,16)
Purpose: to give access to the input tables.
DOUBLE PRECISION XSSPI,XSSRHO,XSSA2,XSDPIS,XSDPIA,& XSDRHOS,XSDRHOA,XSDA2S,XSDA2A,XFFDPI,XFFDRHO,XFFDA2COMMON/MONDFIX/XSSPI(53,41),XSSRHO(53,51),& XSSA2(53,51),XSDPIS(10,8,9,8),XSDPIA(10,8,9,8),& XSDRHOS(10,8,9,8),XSDRHOA(10,8,9,8),XSDA2S(10,8,9,8),& XSDA2A(10,8,9,8),XFFDPI(60,16),XFFDRHO(60,16),& XFFDA2(60,16)
Purpose: to give access to the additional tables obtained from the input files.
DOUBLE PRECISION SPI,SRHO,SA2,DPI,DRHO,DA2,FDPI,FDRHO,FDA2COMMON/MONDMOD/SPI(41,41),SRHO(41,41),SA2(41,41),& DPI(17,17,17,17),DRHO(17,17,17,17),DA2(17,17,17,17),& FDPI(17,17),FDRHO(17,17),FDA2(17,17)
Purpose: to give access to the tables for 2D and 4D generations.
DOUBLE PRECISION SPIX1,SPIX2,SPIXQ,SROX1,SROX2,SROXQ,& SA2X1,SA2X2,SA2XQ,DPIX1,DPIX2,DPIXX,& DROX1,DROX2,DROXX,DA2X1,DA2X2,DA2XXCOMMON/MONDGE1/SPIX1(41),SPIX2(41),SPIXQ(2,41,41),& SROX1(41),SROX2(41),SROXQ(2,41,41),& SA2X1(41),SA2X2(41),SA2XQ(2,41,41),& DPIX1(17),DPIX2(17),DPIXX(2,17,17),& DROX1(17),DROX2(17),DROXX(2,17,17),& DA2X1(17),DA2X2(17),DA2XX(2,17,17)
Purpose: to give access to the auxiliary tables for 2D and 4D generations.
DOUBLE PRECISION DDPI1,DDPI2,DDPI3,DDRO1,DDRO2,DDRO3,& DDA21,DDA22,DDA23COMMON/MONDGE2/& DDPI1(4,17,17,17),DDPI2(4,17,17,17),DDPI3(8,17,17,17,17),& DDRO1(4,17,17,17),DDRO2(4,17,17,17),DDRO3(8,17,17,17,17),& DDA21(4,17,17,17),DDA22(4,17,17,17),DDA23(8,17,17,17,17)
Purpose: to give access to the auxiliary tables for 2D and 4D generations.20
OUBLE PRECISION VXIR,VFIS,VFIA,VQTR,& VXIRF,VFIF,VXI,VQT,SVXI,SVQT,DVXI,DVQTCOMMON/MONDVAR/VXIR(10),VFIS(8),VFIA(8),VQTR(9),& VXIRF(60),VFIF(16),VXI(53),VQT(41),& SVXI(41),SVQT(41),DVXI(17),DVQT(17)
Purpose: to give access to the arrays of variables for the input and auxiliary tables.21
Program Installation
Some materials related to the
Moncher physics and generator is the one found on theweb page http://rioutine.web.cern.ch/rioutine in the section ”Generators”. To get the code of the generator one should download thefile http://rioutine.web.cern.ch/rioutine/gencode/moncher1.1.tar.gz
The program is written essentially entirely in standard Fortran 77, and should run on anyplatform with such a compiler.The following installation procedure is suggested for the Linux users, it was testedwith CERN SLC5. $ gunzip moncher1.1.tar.gz$ tar -cvf moncher1.1.tar$ cd moncher/1.1.0$ ls
Now you can see some files:
README contains brief description of the files in the current directory; moncher.f is the code of the generator; moncher.par defines switch keys and parameters for the simulation;
Spi 1 Sro 1 Sa2 1 contain data for the calculations of absorptive corrections for SCE;
Sp2i 1 S2ro 1 S2a2 1 contain data for absorptive corrections for DCE;
FFpi 1 FFro 1 FFa2 1 contain data for form-factors; mkmoncher is the executable file to compile and link moncher.f ; rmoncher is the executable file to run moncher created by mkmoncher . $ ./mkmoncher compiles moncher.f by g
77 compiler and link the generator with
Pythia moncher should be run by $ ./rmoncher
Result of the simulation should be the
Pythia standard listing of one generated event ofthe SCE reaction pp → nX at c.m.s. energy 7 TeV. The listing should be printed on thescreen. If you have passed successfully all above, get start with the next step.22 Getting Started with the Simple Example
The Simple Example could look as following:
PROGRAM MAINIMPLICIT DOUBLE PRECISION(A-H, O-Z)IMPLICIT INTEGER(I-N)c...global MONCHER parametersINTEGER MXGLPARREAL MONPARPARAMETER (MXGLPAR=200)COMMON/MONGLPA/ MONPAR(MXGLPAR)c...initializationCALL MONGIVE(’MONPAR(1)=1000’) ! number of eventsCALL MONGIVE(’MONPAR(2)=1’) ! switch for LHE savingCALL MONGIVE(’MONPAR(3)=7000’) ! pp centre mass energy in GeVCALL MONGIVE(’MONPAR(4)=1’) ! code of model for pR/RR interactionCALL MONGIVE(’MONPAR(5)=1’) ! code of model for absorptionCALL MONGIVE(’MONPAR(6)=1’) ! type of ReggeonCALL MONGIVE(’MONPAR(7)=1’) ! switch for SCE generationCALL MONGIVE(’MONPAR(8)=0’) ! switch for DCE generationCALL MONGIVE(’MSEL=2’) ! pythia: mb+sd+dd+elastic+lowptCALL MONINITNTOT=MONPAR(1)KLHE=MONPAR(2)c...generationDO NEV=1,NTOTCALL MONEVENIF(NEV.EQ.1) CALL PYLIST(1)CALL ANALYZER(IOUT)IF(KLHE.EQ.1.AND.IOUT.EQ.1) CALL MONUPEVENDDOc...final statisticsCALL PYSTAT(1)c...produce final Les Houches Event File.IF(KLHE.EQ.1) CALL PYLHEFSTOPEND
First, we set some values for elements of array
MONPAR which control a process of gen-eration. Then, we should initialize the generator calling
MONINIT . In this example we aregoing to generate 1000 events of Single Pion Exchange, pp → n ( π + p ) → nX , at c.m.s. en-ergy 7 TeV. The ( π + p ) interaction is controlled by Pythia and it includes minimum bias,single and double diffraction, elastic scattering and low-pt scattering. Filling of
MONPAR elements can be done also from the external file moncher.par . Subroutine
MONPARA call-ing by
MONINIT checks the presence of the moncher.par in the current directory and, ifit exists, reads parameters
MONPAR , see chapter 6.23n the next step, we generate some number of events, defined by
MONPAR(2) . Everyevent is generated by
MONEVEN . User’s subroutine
ANALYZER(IOUT) is called after everyevent generation, analyses the event and sets some value to the integer variable
IOUT If IOUT is equal to unity, we save this event in the LHE format using the subroutine
MONUPEV .Here you can see example of the Simple Analyzer:
SUBROUTINE ANALYZER(IOUT)IMPLICIT DOUBLE PRECISION(A-H, O-Z)IMPLICIT INTEGER(I-N)c...HEPEVT commonblock.PARAMETER (NMXHEP=4000)COMMON/HEPEVT/NEVHEP,NHEP,ISTHEP(NMXHEP),IDHEP(NMXHEP),&JMOHEP(2,NMXHEP),JDAHEP(2,NMXHEP),PHEP(5,NMXHEP),VHEP(4,NMXHEP)DOUBLE PRECISION PHEP,VHEPSAVE /HEPEVT/c IOUT =0ISIGN =1NEUTRONS=0c CALL PYHEPC(1)c DO I=1,NHEPKP =IDHEP(I)ETA =PYP(I,19)IF(KP.EQ.2112.AND.DABS(ETA).GE.8.5) THENNEUTRONS=NEUTRONS+1ISIGN=ISIGN*ETAENDIFENDDOc IF(NEUTRONS.EQ.2.AND.ISIGN.LT.0) IOUT=1c RETURNEND
In this example, we analyse all particles in the generated event and look for the neutrons(code 2112) in the region of pseudorapidity | η | ≥ . IOUT is set to unity.Finally, we print the
Pythia statistics by
PYSTAT and produce the final LHE file whichhas the name moncher.lhe by default.This example has a concrete physical meaning. We have selected SCE events with 2leading neutrons moving in the opposite directions which imitate a DCE process. So, wehave saved background for the DCE from the SCE.24
Program Control Parameters
All parameters that control the generation can be defined in the external file moncher.par .For example, the set of parameters for the generation of the S π E process, described inthe chapter 5, can look as follows: c--------------------- MONCHER v.1.1.0 card filecc----------------------------------------------- MONCHER control keyscMONPAR(1)=1000 ! number of events to generatecMONPAR(2)=1 ! key for Les Houches data(1-save,0-no)cMONPAR(3)=7000 ! pp centre mass energy in GeV (900 -> 14000)cMONPAR(4)=1 ! code of model for pR and RR interactionc NMODRR=1 -> Donnachie-Landshoff model (default)c NMODRR=2 -> COMPETE (PDG) modelc NMODRR=3 -> Bourreli-Sopfer-Wu modelc NMODRR=4 -> Godizov-Petrov modelcMONPAR(5)=1 ! code of model for absorptionc NMODPP=1 3 IP eikonal model (default)c not now NMODPP=2 -> Godizov-Petrov modelc not now NMODPP>2 -> other models...cMONPAR(6)=1 ! type of Reggeon (1-pi+, 2-rho+, 3-a2+)c (for DCE only pi-pi, pi-rho and pi-a2 survive)cMONPAR(7)=1 ! key for SCE generationcMONPAR(8)=0 ! key for DCE generationcc----------------------------------------------- PYTHIA control keysccMSEL =0 ! full user controlcMSUB(11)=1 ! f + f’ -> f + f’ (QCD)cMSUB(12)=1 ! f + fbar -> f’ + fbar’cMSUB(13)=1 ! f + fbar -> g + gcMSUB(28)=1 ! f + g -> f + gcMSUB(53)=1 ! g + g -> f + fbarcMSUB(68)=1 ! g + g -> g + gcMSUB(91)=1 ! Elastic scatteringcMSUB(92)=1 ! Single diffractive (AX)cMSUB(93)=1 ! Single diffractive (XB)cMSUB(94)=1 ! Double diffractivecMSUB(95)=1 ! Low-pT scatteringcMSEL =1 ! mbMSEL =2 ! mb+sd+dd+elastic+lowptcMRPY(1)=12031967 ! start point of random number generator
MONPARA reads lines from moncher.par . All lines begining with a letter”c” are ignored by the program, all others lines are processed by subroutine
MONGIVE ,which can recognize any variables from the
Moncher common block /MONGPGL/ andthe
Pythia common blocks /PYJETS/, /PYDAT1/, /PYDAT2/, /PYDAT3/, /PYDAT4/,/PYDATR/, /PYSUBS/, /PYPARS/, /PYINT1/, /PYINT2/, /PYINT3/, /PYINT4/,/PYINT5/, /PYINT6/, /PYINT7/, /PYINT8/, /PYMSSM/, /PYMSRV/, /PYTCSM/,/PYPUED/ , (see [15]). Parameters
MONPARA are described in detail in the section 3,page 18.Using parameters from the common blocks listed above, one can define wide spectrumof SCE (
MONPAR(7)=1 ) and DCE ((
MONPAR(8)=1 ) processes or any processes existing in
Pythia (if (
MONPAR(7)=0 and
MONPAR(8)=0 ). Some examples are described in the nextchapter.
N Process Type of π + p interactions Picture of the process The Moncher parameters1 pp → nX minimum bias: π + p → X MONPAR(7)=1MONPAR(8)=0MSEL=1 pp → nπ + p elastic scattering: π + p → π + p MONPAR(7)=1MONPAR(8)=0MSEL=0MSUB(91)=1 pp → nXY doublediffraction: π + p → X + Y MONPAR(7)=1MONPAR(8)=0MSEL=0MSUB(94)=1 pp → nXp single diffraction( π + dissociation): π + p → X + p MONPAR(7)=1MONPAR(8)=0MSEL=0MSUB(92)=1 pp → nXπ + single diffraction( p dissociation): π + p → X + π + MONPAR(7)=1MONPAR(8)=0MSEL=0MSUB(93)=1
Table 4: Some S π E processes which can be generated with
Moncher .It was mentioned already in Chapter 3 that the
Moncher generates p IR n verticesand, then, IR p (for SIRE) or IRIR (for DIRE) interactions are generated by Pythia . Thetype of these interactions can be controled by the
Pythia parameters. We can defineelastic or inelastic interactions, diffractive or non-diffractive processes, different types of26iffraction, hard scattering, etc. Some of the basic processes for S π E and D π E, which canbe generated by the
Moncher , are presented in the tables 4 and 5 respectively.Let us consider one more simple example, how to generate process number 2 fromTable 4. This is a Single Pion Exchange with elastic scattering of the virtual pion by theproton of the beam. This reaction, pp → nπ + p , has very clear signature: neutron, proton,single π + meson and nothing else in the final state. Initial particles are scattered at verysmall angles and, thereof, there are no any detector signals in the region of pseudorapidity | η | <
7. An experimental possibility of such measurements has been analysed in Ref. [8]with prereleased version of
Moncher .File moncher.par with parameters for the generation of pp → nπ + p can look as follows: MONPAR(1)=1 ! number of events to generateMONPAR(2)=0 ! key for Les Houches data(1-save,0-no)MONPAR(3)=7000 ! pp centre mass energy in GeV (900 -> 14000)MONPAR(4)=1 ! code of model for pR and RR interactionMONPAR(5)=1 ! code of model for absorptionMONPAR(6)=1 ! type of Reggeon (1-pi+, 2-rho+, 3-a2+)MONPAR(7)=1 ! key for SCE generationMONPAR(8)=0 ! key for DCE generationMSEL =0 ! full user controlMSUB(91)=1 ! elastic scattering
Parameter
MONPAR(7)=1 defines the generation of the SIRE process. Exchange reggeon is apion (
MONPAR(6)=1 ). Pythia parameters
MSEL=0 and
MSUB(91)=1 set elastic π + p scatter-ing. Parameter MONPAR(4)=1 sets Donnachie-Landshoff parametrization for π + p interac-tion, see subsection 2.1.2. Parameter MONPAR(5)=1 specifies 3 Pomeron model for absorp-tive correcttions, see subsection 2.1.1. Parameters
MONPAR(1)=1 and
MONPAR(3)=7000 setthe generation of 1 event at 7 TeV pp c.m.s. energy. We don’t ask to save any events(
MONPAR(2)=0 ) and the only result of the generation is the
Pythia listing of the generatedevent:
Event listing (summary)I particle/jet KS KF orig p_x p_y p_z E m1 !p+! 21 2212 0 0.000 0.000 3500.000 3500.000 0.9382 !p+! 21 2212 0 0.000 0.000-3500.000 3500.000 0.938===========================================================================3 n0 1 2112 2 0.114 0.216-2296.804 2296.804 0.9404 !pi+! 21 211 2 -0.114 -0.216-1203.196 1203.196 0.140===========================================================================5 !p+! 21 2212 3 -0.019 -0.001 3500.000 3500.000 0.9386 !pi+! 21 211 4 -0.095 -0.215-1203.196 1203.196 0.140===========================================================================7 p+ 1 2212 5 -0.019 -0.001 3500.000 3500.000 0.9388 pi+ 1 211 6 -0.095 -0.215-1203.196 1203.196 0.140sum: 2.00 0.000 0.000 0.000 7000.000 7000.000
In this listing lines 1 and 2 correspond to the protons of the beams. Lines 3, 7 and 8relate to the neutron, proton and pion, respectively, in the final state of the reaction.The proton is deflected at angle ≈ − rad., neutron and pion are scattered in thedirection opposite to proton, as it is shown on the diagram of the process in the table 4,with polar angles ≈ − and ≈ − rad. 27 Process Type of π + π + interactions Picture of the process The Moncher parameters1 pp → nXn minimum bias: π + π + → X MONPAR(7)=0MONPAR(8)=1MSEL=1 pp → nπ + π + n elastic scattering: π + π + → π + π + MONPAR(7)=0MONPAR(8)=1MSEL=0MSUB(91)=1 pp → nXY n doublediffraction: π + π + → X + Y MONPAR(7)=0MONPAR(8)=1MSEL=0MSUB(94)=1 pp → nXπ + n single diffraction: π + π + → X + π + MONPAR(7)=0MONPAR(8)=1MSEL=0MSUB(92)=1 or MSUB(93)=1
Table 5: Some D π E processes which can be generated with
Moncher . Aknowledgements
This work is supported by the grant RFBR-10-02-00372-a.
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MONTITL subroutine 10
MONPARA subroutine 11
MONMBDF subroutine 11
MONEVEN subroutine 11
MONSPEG subroutine 11
MONDPEG subroutine 12
MONSPEM subroutine 12
MONDPEM subroutine 12
MONSHPY subroutine 13
MONGIVE subroutine 13
MONUPEV subroutine 13
MONUPIN subroutine 13
MONGE2D subroutine 14
MONG2D4 subroutine 14
MONCUBI subroutine 14
MONLI2D subroutine 15
MONLI4D subroutine 15
MONIN2D subroutine 15
MONIN4D subroutine 15
MONDATA subroutine 16
MONCSEC function 16
MONCSCE function 16
MONCDCE function 16
MONCSRP function 17
MONCSRR function 17
MONGLPA common block 18
MONTAB0 common block 18
MONTAB1 common block 19
MONTAB2 common block 19
MONTAB3 common block 19
MONTAB4 common block 19
MONDGET common block 20
MONDFIX common block 20
MONDMOD common block 20
MONDGE1 common block 20
MONDGE2 common block 20
MONDVAR common block 21
MONPAR in /MONGLPA/ S in /MONTAB0/ NMODPP in /MONTAB0/ NMODRR in /MONTAB0/ ITYPR in /MONTAB0//MONTAB0/