mjhjmtu

How could I make the picture:

using FeynMF?

You mention feynmf in the title but are tagging the question with almost everything... Here a feynmf working start point, to run with latex + mf + latex. (There is surely room for improvement.) It works the same way with feynmp and METAPOST, of course.

documentclassarticle

usepackagefeynmf

begindocument

beginfmffilediagram
beginfmfgraph*(100,80)
fmfstraight
fmfleftni5
fmfrightno5
fmffermioni5,vt,o5
fmfphantomi1,vb,o1
fmfphoton,label=$W$vt,vb
fmffreeze
fmffermioni1,vb
fmffermion,label=$Delta^++$vb,vr
fmffermionvr,o2
fmffermionvr,o1
fmflabel$nu_1$i5
fmflabelpi1
fmflabelpo1
fmflabel$mu^-$o5
fmflabel$pi^+$o2
endfmfgraph*
endfmffile
enddocument

Very similar to campa's nice answer but with a scalar propagator for the pion. I only post the code of the Feynman diagram.

beginfmfgraph*(50,40)
fmflefti1,i2
fmfrightf1,f2
fmffermion,label=i1,v1,f1
fmffermion,label=i2,v2,f2
fmfphoton,label=$W$v1,v2
fmffreeze
fmfphantomf1,f3,h1,h2,h3,f2
fmfphantomv1,h4,h5,v3,f1
fmffreeze
fmfphantomh1,pi,f3
fmfphantom,label=$Delta^++$v1,v3
fmfdashesv3,f3
fmflabel$p$i1
fmflabel$nu_1$i2
fmflabel$p$f1
fmflabel$pi^+$pi
fmflabel$mu^-$f2
endfmfgraph*

Using usepackagefeynman, https://ctan.org/tex-archive/macros/latex209/contrib/feynman

documentclass[a4paper,12pt]article

usepackagemathtools
usepackagefeynman
usetikzlibrarypatterns, arrows, decorations.pathreplacing, decorations.markings
begindocument

beginfeynman 
 fermion6.20, 1.207.20, 2.20
 fermion0.20, 5.203.20, 4.20
 electroweak3.20, 2.203.20, 4.20
 fermion3.20, 2.206.20, 1.20
 fermion3.20, 4.206.20, 5.20
 fermion[lineWidth=2]6.20, 1.207.20, 2.20
 fermion0.20, 1.203.20, 2.20
 fermion[showArrow=true, flip=true]7.20, 0.206.20, 1.20
 text5.00,2.20Delta^++
 text1.00,0.90p
 text5.60,4.60mu^-
 text6.60,0.20p
 text0.90,4.50v_1
 text6.70,2.20pi^+
endfeynman

enddocument

Here I have added feynman.sty (to save as .sty).

NeedsTeXFormatLaTeX2e
ProvidesPackagefeynman
 [2015/02/01 v0.8 LaTeX package for drawing feynman diagrams with an interface similar to the one found at feynman.aivazis.com]

RequirePackagexcolor
RequirePackagetikz
RequirePackagexifthen
RequirePackagekvoptions
RequirePackagefp

usetikzlibrarypatterns, arrows, decorations.pathreplacing, decorations.markings

% turn off the fp messages
FPmessagesfalse

% treat @ like a normal letter
makeatletter


%------------------------------------------------------------------------------
% configuration parameters
%------------------------------------------------------------------------------

% define the diagram configuration settings family
SetupKeyvalOptionsfamily=diagram, prefix=diagram@
DeclareStringOption[in]unit
DeclareStringOption[An Example Feynman Diagram]title

% define the propagator configuration settings family
SetupKeyvalOptionsfamily=style, prefix=style@
DeclareStringOption[000000]color
DeclareStringOption[2]lineWidth
DeclareBoolOption[true]endcaps
DeclareStringOption[1/3]gluonWidth
DeclareStringOption[center]location
DeclareStringOptionlabel
DeclareStringOption[0.5]labelDistance
DeclareStringOption[0.5]labelLocation
DeclareBoolOption[true]showArrow
DeclareBoolOption[false]flip


%------------------------------------------------------------------------------
% the feynman diagram environment
%------------------------------------------------------------------------------

% define an enviroment to encompass a single diagram
newenvironmentfeynman[1]
% before the content

 % load the diagram configuration settings
 setkeysdiagram#1
 % start the tikz environment
 begintikzpicture[x=1diagram@unit, y=1diagram@unit]

% after the content

 % close the tikz environment
 endtikzpicture



%------------------------------------------------------------------------------
% utility macros
%------------------------------------------------------------------------------

% convert a particular length to the designated unit
% i.e. converttomm1pt
newcommand*convertto[2]strip@ptdimexpr #2*65536/numberdimexpr 1#1

% compute the length between two points
defcalcLength(#1,#2)#3
 % compute the delta between two points
 pgfpointdiffpgfpointanchor#1center
 pgfpointanchor#2center
 pgf@xa=pgf@x
 pgf@ya=pgf@y
 % cast the deltas in the appropriate unit system
 FPeval@temp@apgfmath@tonumberpgf@xa/72.27
 FPeval@temp@bpgfmath@tonumberpgf@ya/72.27

 % store the sum of the squares
 FPeval@temp@sum(@temp@a*@temp@a+@temp@b*@temp@b)
 % take the square root of the result
 FProotFPMathLen@temp@sum2
 % cut off at 5 decimal places
 FProundFPMathLenFPMathLen9relax
 % set the value of the macro we were given
 expandafteredefcsname #3endcsnameFPMathLen


% compute the angle between two points
defcalcAngle(#1,#2)#3
 % compute the difference between the two points
 pgfpointdiffpgfpointanchor#1center
 pgfpointanchor#2center
 % extract the delta between the two points
 pgf@xa=pgf@x
 pgf@ya=pgf@y
 % cast the deltas as numbers
 FPevaldeltaXpgfmath@tonumberpgf@xa
 FPevaldeltaYpgfmath@tonumberpgf@ya
 % use pgf to compute atan2
 pgfmathparseatan2(deltaY, deltaX)
 % set the angle to the result
 FPevalangleround(pgfmathresult , 5)

 % set the value of the macro we were given
 expandafteredefcsname #3endcsnameangle


% shortcut macro to print an expression to the console
newcommand*print[1]typeout#1


%------------------------------------------------------------------------------
% patterns and colors
%------------------------------------------------------------------------------

% declare the parameters for the pattern
tikzset
 hatch distance/.store in=hatchdistance,
 hatch distance=10pt,
 hatch thickness/.store in=hatchthickness,
 hatch thickness=1pt

% define the parton fill pattern
pgfdeclarepatternformonly[hatchdistance,hatchthickness]parton
% declare the origin
pgfqpoint0pt0pt
% define the variables in this coordinate system
pgfqpointhatchdistancehatchdistance
pgfpointhatchdistance-1pthatchdistance-1pt
% set up the pattern

 pgfsetcolortikz@pattern@color
 pgfsetlinewidthhatchthickness
 pgfpathmovetopgfqpoint0pt0pt
 pgfpathlinetopgfqpointhatchdistancehatchdistance
 pgfusepathstroke



% define the arrow style
tikzset
 arrow/.style=
 decoration=
 markings,
 mark=at position .5 with 
 arrow[#1, scale=1.5]latex
 
 ,
 postaction=decorate,
 

tikzset
 arrow flipped/.style=
 decoration=
 markings,
 mark=at position .5 with 
 arrow[#1, scale=1.5]latex reversed
 
 ,
 postaction=decorate,
 



% define a light gray to be used as a fill color for partons
definecolorlight-graygray.7

%------------------------------------------------------------------------------
% text macros
%------------------------------------------------------------------------------

% overline with variable width (the second brace)
newcommand*anti[2][1.0]
 overline#2


% overline with variable width (the second brace)
newcommand*txt[1]
 textrm#1


%------------------------------------------------------------------------------
% propagator styles
%------------------------------------------------------------------------------

% fermions
newcommand*fermion[3]
 % scope the configuration options
 begingroup
 % load the configuration parameters
 setkeysstyle#1

 % parse the color of the line
 definecolorlineColorHTMLstyle@color

 % if they asked to draw the arrow
 ifstyle@showArrow
 ifstyle@flip
 % draw the line with an arrow
 draw[color=lineColor, line width = style@lineWidth, arrow flipped] (#2) -- (#3);
 else
 % draw the line with an arrow
 draw[color=lineColor, line width = style@lineWidth, arrow] (#2) -- (#3);
 fi
 % otherwise they did not ask to draw the arrow
 else
 % draw the line
 draw[color=lineColor, line width = style@lineWidth] (#2) -- (#3);
 fi

 % draw the label
 drawLabel#2#3
 endgroup



% dashed propagators
newcommand*dashed[3]
 % scope the configuration options
 begingroup
 % load the configuration parameters
 setkeysstyle#1

 % parse the color of the line
 definecolorlineColorHTMLstyle@color

 % if they asked to draw the arrow
 ifstyle@showArrow
 ifstyle@flip
 % draw the line with an arrow
 draw[dashed, color=lineColor, line width = style@lineWidth, arrow flipped=lineColor] (#2) -- (#3);
 else
 % draw the line with an arrow
 draw[dashed, color=lineColor, line width = style@lineWidth, arrow=lineColor] (#2) -- (#3);
 fi
 % otherwise they did not ask to draw the arrow
 else
 % draw the line
 draw[dashed, color=lineColor, line width = style@lineWidth] (#2) -- (#3);
 fi

 % draw the label
 drawLabel#2#3
 endgroup



% gluons
newcommand*gluon[3]
 % scope the configuration options
 begingroup
 % load the configuration parameters
 setkeysstyle#1

 % create TikZ coordinates at the end points
 coordinate (start) at (#2);
 coordinate (finish) at (#3);
 % store the distance between the two points
 calcLength(start,finish)length % stores it in a macro called length
 % store the angle between the two points
 calcAngle(start,finish)angle % stores it in a macro called angle

 % turn the start coordinate into a pgf point
 pgfpointanchorstartcenter
 FPevalstartXpgfmath@tonumberpgf@x
 FPevalstartYpgfmath@tonumberpgf@y

 FPevalgluonWidthstyle@gluonWidth
 % store a value for half of the gluonWidth
 FPevalhalfWidthgluonWidth/2
 % store the closest whole number of full periods
 FPevalnLoopsround((length / gluonWidth ) - 1, 0)
 FPevaltotalLength(nLoops+1) * gluonWidth
 FPevalscalelength / totalLength
 % parse the color of the line
 definecolorlineColorHTMLstyle@color

 % if we dont fit a whole loop between the two points
 ifthenelseequalnLoops0
 % use a fermion line instead
 fermion#2#3

 % we fit at least one loop between the two points
 

 % if they want the end caps (to draw the right kind of line)
 ifstyle@endcaps
 % if they asked to flip the loops
 ifstyle@flip
 % set the maximum value to be positive
 FPevalymaxhalfWidth
 FPevalymin0-halfWidth
 % otherwise draw the loops right side up
 else
 % set the maximum value to be negative
 FPevalymax0-halfWidth
 FPevalyminhalfWidth
 fi

 % style the opening end cap
 draw[color=lineColor, line width = style@lineWidth, yshift=startY, xshift=startX,
 rotate=angle, xscale=scale, yscale=scale]
 % draw the opening end cap
 (0,0) .. controls (halfWidth, 0) and (0, ymin) .. (halfWidth, ymin);
 % for each loop that we have to draw
 foreach loopNumber in 1,...,nLoops
 % compute the starting location of the loop
 FPevalxloopNumber * gluonWidth - halfWidth
 % compute the half way point of the loop
 FPevalxMidhalfWidth + x
 % compute the endpoint of the loop
 FPevalxFinalgluonWidth + x

 % style the first half of the loop
 draw[color=lineColor, line width = style@lineWidth, yshift=startY, xshift=startX,
 rotate=angle, xscale=scale, yscale=scale]
 % draw the first half of the loop
 (x, ymin) .. controls (xFinal, ymin) and (xFinal, ymax) .. (xMid, ymax);
 % style the second half of the loop
 draw[color=lineColor, line width = style@lineWidth, yshift=startY, xshift=startX,
 rotate=angle, xscale=scale, yscale=scale]
 % draw the second half of the loop
 (xMid, ymax) .. controls (x, ymax) and (x, ymin) .. (xFinal, ymin);
 

 % compute the locations for the closing end cap
 FPevalfinalStart(nLoops+1) * gluonWidth - halfWidth
 FPevalfinalHalffinalStart + halfWidth
 FPevalfinalStopfinalStart + halfWidth
 % style the closing end cap
 draw[color=lineColor, line width = style@lineWidth, yshift=startY, xshift=startX,
 rotate=angle, xscale=scale, yscale=scale]
 % draw the closing end cap
 (finalStart, ymin) .. controls (finalStop, ymin) and (finalStart, 0) .. (finalStop, 0);

 % they did not want end caps
 else
 % if they asked for the gluons to be flipped
 ifstyle@flip
 % store a value for the height of the gluon loop
 FPevalheight0-gluonWidth
 else
 % store a value for the height of the gluon loop
 FPevalheightgluonWidth
 fi

 % for each loop that we have to draw
 foreach loopNumber in 0,...,nLoops
 % compute the starting location of the loop
 FPevalxloopNumber * gluonWidth
 % compute the midpoint of the loop
 FPevalxMidhalfWidth + x
 % compute the endpoint of the loop
 FPevalxFinalgluonWidth + x
 % style the first half of the loop
 draw[color=lineColor, line width = style@lineWidth, yshift=startY, xshift=startX,
 rotate=angle, xscale=scale, yscale=scale]
 % draw the first half of the loop
 (x,0) .. controls (xFinal, 0) and (xFinal, height) .. (xMid, height);
 % style the second half of the loop
 draw[color=lineColor, line width = style@lineWidth, yshift=startY, xshift=startX,
 rotate=angle, xscale=scale, yscale=scale]
 % draw the second half of the loop
 (xMid,height) .. controls (x, height) and (x, 0) .. (xFinal, 0);
 
 fi
 
 % draw the label
 drawLabel#2#3
 endgroup



% electroweak lines
newcommand*electroweak[3]
 % scope the configuration options
 begingroup
 % load the configuration parameters
 setkeysstyle#1

 % create TikZ coordinates at the end points
 coordinate (start) at (#2);
 coordinate (finish) at (#3);
 % store the distance between the two points
 calcLength(start,finish)length % stores it in a macro called length
 % store the angle between the two points
 calcAngle(start,finish)angle % stores it in a macro called angle

 % turn the start coordinate into a pgf point
 pgfpointanchorstartcenter
 FPevalstartXpgfmath@tonumberpgf@x
 FPevalstartYpgfmath@tonumberpgf@y

 FPevalperiodstyle@gluonWidth
 % store a value for half of the gluonWidth
 FPevalhalfPeriodperiod/2
 % store the closest whole number of full periods
 FPevalnLoopsround((length / period ) - 1, 0)
 FPevaltotalLength(nLoops+1) * period
 FPevalscalelength / totalLength
 % parse the color of the line
 definecolorlineColorHTMLstyle@color

 % if we dont fit a whole loop between the two points
 ifthenelseequalnLoops0
 % use a fermion line instead
 fermion#2#3

 % we fit at least one loop between the two points
 
 % store the amplitude of the curve
 FPevalamplitudeperiod * 3 / 2

 % if they asked for the gluons to be flipped
 ifstyle@flip
 % save the maximum height of the curve
 FPevalymaxamplitude
 % save the minimum value of the curve
 FPevalymin0-amplitude
 else
 % save the maximum height of the curve
 FPevalymax0-amplitude
 % save the minimum value of the curve
 FPevalyminamplitude
 fi

 % store the minimum height
 % for each period that we have to draw
 foreach loopNumber in 0,...,nLoops
 % compute the starting location
 FPevalxloopNumber * period
 % compute the midpoint
 FPevalxMidhalfPeriod + x
 % compute the endpoint
 FPevalxFinalperiod + x
 % style the period
 draw[color=lineColor, line width = style@lineWidth, yshift=startY, xshift=startX,
 rotate=angle, xscale=scale, yscale=scale]
 % place the period
 (x,0) .. controls (xMid, ymin) and (xMid, ymax) .. (xFinal, 0);
 
 
 % draw the label
 drawLabel#2#3
 endgroup



% gluinos
newcommand*gluino[3]
 % scope the configuration options
 begingroup
 % load the configuration parameters
 setkeysstyle#1
 % enforce that endcaps is true
 setkeysstyleendcaps=true
 % draw a fermion between the two points
 fermion#2#3
 % draw a gluon between the two points
 gluon#2#3
 % draw the label
 drawLabel#2#3
 endgroup



% sfermions
newcommand*sfermion[3]
 % scope the configuration options
 begingroup
 % load the configuration parameters
 setkeysstyle#1
 % enforce that endcaps is true
 setkeysstyleendcaps=true
 % draw a fermion between the two points
 fermion#2#3
 % draw a gluon between the two points
 electroweak#2#3
 % draw the label
 drawLabel#2#3
 endgroup



%------------------------------------------------------------------------------
% other objects
%------------------------------------------------------------------------------

% circle centered at #2 with radius #3
newcommand*parton[3]
 % scope the configuration options
 begingroup
 % load the configuration parameters
 setkeysstyle#1
 % parse the color of the line
 definecolorlineColorHTMLstyle@color
 % style the circle
 draw[color=lineColor, line width = style@lineWidth, pattern=parton,
 pattern color=light-gray]
 % draw the circle
 (#2) circle (#3 diagram@unit);
 endgroup



% text a located at #2 with content #3
newcommand*text[3]
 % scope the configuration options
 begingroup
 % load the configuration parameters
 setkeysstyle#1
 % parse the color of the line
 definecolorcolorHTMLstyle@color
 % create a node at the location with the given contents
 draw[text=color, anchor=style@location] (#2) node huge #3;
 endgroup



% draw a label using the coordinate system along the line joining #1 and #2
newcommand*drawLabel[2]

 % if they provided a value for the label
 ifthenelseequalstyle@label

 % create TikZ coordinates at the end points
 coordinate (start) at (#1);
 coordinate (finish) at (#2);

 % compute the difference between the two points
 pgfpointdiffpgfpointanchorstartcenter
 pgfpointanchorfinishcenter
 pgf@xa=pgf@x
 pgf@ya=pgf@y
 % cast the deltas in the appropriate unit system
 FPevaldXpgfmath@tonumberpgf@xa/72.27
 FPevaldYpgfmath@tonumberpgf@ya/72.27

 % compute the location of the starting coordinate
 pgfpointanchorstartcenter
 pgf@xa=pgf@x
 pgf@ya=pgf@y
 FPevalstartXround(pgfmath@tonumberpgf@xa/72.27, 5)
 FPevalstartYround(pgfmath@tonumberpgf@ya/72.27, 5)

 % store local copies of the target position
 FPevallabelLocationstyle@labelLocation
 FPevallabelDistance0+style@labelDistance

 % compute the location along the line where we belong
 FPeval@temp@locXround(startX + labelLocation * dX, 5)
 FPeval@temp@locYround(startY + labelLocation * dY, 5)

 % if the change in y is zero (infinite slope)
 ifthenelseequaldY0
 FPevallabelX@temp@locX
 FPevallabelY@temp@locY+labelDistance
 % otherwise we are safe to compute the slope
 
 % compute the slope of the perpendicular line
 FPevalperpSlope0 - dX/dY

 % the points that are perpedicular to the line a distance r away satisfy
 % y = mx
 % x^2 + y^2 = r

 % compute the x that satisfies this equation
 % note: macro can start with because it can never be negative
 FPevalx2(0+labelDistance) * (0+labelDistance) / (1 + (perpSlope * perpSlope))
 FProotxx22
 % compute the y that satisfies this equation
 FPevalyx * perpSlope

 newdimen distance
 distance = labelDistance pt
 newdimen slope
 slope = perpSlope pt

 % if the perpendicular line has positive slope
 ifthenelseslope > 0 pt OR slope = 0 pt
 % if they are a positive distance away
 ifthenelsedistance > 0 pt
 FPevallabelX@temp@locX + x
 FPevallabelY@temp@locY + y
 % otherwise they are a negative distance away
 
 FPevallabelX@temp@locX - x
 FPevallabelY@temp@locY - y
 
 % otherwise the perpendicular line as negative slope
 
 % if the label is a positive distance away
 ifthenelsedistance > 0 pt
 FPevallabelX@temp@locX - x
 % note: the y is negative so we subtract even though we want to add
 FPevallabelY@temp@locY - y
 % otherwise the label is a negative distance from the line
 
 FPevallabelX@temp@locX + x
 % note: the y is negative so we add even though we want to subtract
 FPevallabelY@temp@locY + y
 
 
 

 % place the label on the right of the coordinates
 deflocright

 % draw the label
 draw[loc] (labelX,labelY) node huge style@label;
 


%------------------------------------------------------------------------------
% cleanup
%------------------------------------------------------------------------------

% turn @ back into a special character
makeatother

endinput


% end of file