I created the following plot in `R` with `ggplot2`

```
KL_tot_RM = c(19.95814, 19.82527, 19.59050, 19.54873, 19.52221, 19.51316, 20.69058,
  20.40126, 19.85393, 19.70881, 19.59630, 19.55224, 21.07645, 20.75875,
  20.09839, 19.88498, 19.69226, 19.60695, 21.87141, 21.53600, 20.77132,
  20.46374, 20.10521, 19.89015, 22.15567, 21.82590, 21.05127, 20.72808,
  20.33150, 20.07257, 22.43661, 22.12112, 21.33892, 21.00751, 20.58678,
  20.29487, 22.66943, 22.37502, 21.66856, 21.33899, 20.90636, 20.59057,
  22.58487, 22.11511, 21.80200, 21.36871, 21.03423, 22.33055, 22.06044,
  21.75075, 22.45573, 22.17089, 20.63523)
KL_tot_BM = c(19.39840, 19.44582, 19.50268, 19.50384, 19.50405, 19.50406, 19.39609,
  19.51611, 19.51505, 19.51001, 19.50653, 19.50530, 19.73257, 19.69439,
 19.55838, 19.53254, 19.51575, 19.50994, 21.00110, 20.71141, 20.07691,
 19.87026, 19.68416, 19.60225, 21.48362, 21.18844, 20.47549, 20.19863,
 19.90049, 19.74088, 21.92624, 21.65443, 20.92355, 20.61059, 20.23113,
 19.99025, 22.26873, 22.11128, 21.42642, 21.10224, 20.68051, 20.38133,
 22.31634, 22.00143, 21.69530, 21.26701, 20.94143, 22.37260, 22.04097,
 21.73265, 19.70630, 22.23376, 19.32922)
df_plot = data.frame(KL = c(KL_tot_RM,KL_tot_BM), x= 1:53, 
                     data_set = c(rep('RM',53),rep('BM',53)) )
ggplot(df_plot, aes(x = x, y = KL, colour = data_set)) +
  geom_point(size = 1.8)

```

[![enter image description here](https://i.stack.imgur.com/h4L8A.png)](https://i.stack.imgur.com/h4L8A.png)

what I would like to do it to discard the x-axis, i.e. remove the value 0, 20, 40 and let it blank. And then somehow create the following plot

[![enter image description here](https://i.stack.imgur.com/muvDQ.png)](https://i.stack.imgur.com/muvDQ.png)

The dotted vertical lines indicate the groups. What I would like to do is at the middle of each group to place a factor `p_{1}, p_{2}, p_{3},....,p_{11}` is there a way to do that?