I synchronized the zoom and the pan of the charts. However I would like to improve it

When I zoom in in a chart, I would like to sync the zoom the other charts only in the X direction.

Is it possible with the Chart.zoom() method, or there is some zoomX() function for this?

I would like to be able to zoom/pan the charts in both directions.
BUT I want to synchronize the zoom/pan only on the X axis.

When you bind the zoom/pan from one chart to another you can fix the Y parameter.
Have a look at this sample: https://play.data2viz.io/sketches/EYOmdg/edit/

Note that:

chart1.onZoom { evt -> 
    chart2.zoom(evt.zoomOriginX, evt.zoomOriginY, evt.zoomFactorX, 100.pct) 
chart1.onPan { evt -> 
    chart2.pan(evt.panX, 0.pct) 

The zoom Y ratio is set to 100% (no zoom no unzoom)
The pan Y offset is set to 0% (no pan up or down)

By doing this, you only synchronize the X movement and zoom from the first chart to the second.

Check this how-to for more information: How-to synchronize charts display