[R] Fit Gaussian curve on my data ?

[varin sacha]

Dear R-experts,

I am trying to fit a gaussian density curve. More precisely, I would like to obtain the fitted "Gaussian curve". 
"m" is the gaussian mean, "sd" is the standard deviation and "k" is an arbitrary scaling parameter (since the gaussian density is constrained to integrate to 1, whereas my data isn't). 
There is no error message. In my opinion, the last command of my reproducible R script is not doing its job !

Many thanks for your lights.

############################################################
a <- as.Date(c("2020-02-25", "2020-02-26","2020-02-27","2020-02-28","2020-03-1","2020-03-2","2020-03-3","2020-03-4","2020-03-5","2020-03-6","2020-03-7","2020-03-8","2020-03-9","2020-03-10","2020-03-11","2020-03-12","2020-03-13","2020-03-14","2020-03-15","2020-03-16"))

b<- c(20,28,45,68,89,123,154,190,245,302,460,379,298,300,245,189,165,100,90,78)

d <-as.numeric(a)

m<-11.84

sd<-3.93

k<-359.77

plot(b~d)

plot(function(d) k*exp(-0.5*(d-m)^2/sd^2),col=2,add=TRUE,xlim=range(d))
############################################################