Given that Processing sketches are GUI programs, I am a bit dubious of the interest of such operation...
There was a similar thread from somebody wanting to run a sketch on a Web server.
Perhaps your best bet is to make a Java program, perhaps using Processing as a library (but the PApplet might go in the way).

What is demonize?

demonize means run a program in "backgraund". You know the program run but, you don't wath it Even though you go to the task menager.

Give me  a way to understand how I can do!!

Please

I agree with Phil that there is probably a better way to accomplish the thing you are try to accomplish.  

The & detaches the process from the console, but doesn't hide it.
And daemon processes can be found, they are not totally stealth.
Again, I wonder why you are trying to do. What is the interest of making a graphic program not visible?

Perhaps you could answer the questions asked...

Apparently somebody posted a solution to run Processing without GUI at https://forum.processing.org/topic/embedding-processing-without-threading