| | Jhana can be a tricky thing, if you are mixing your approaches, i.e. noting, but tend to get more concentrated on your breath and wish to cultivate Jhana, this would be what Buddha regarded as Right Concentration and a full mastery is required for the higher paths (3-4), according to the Sutras, but vipassana, has based on Buddha's method, typically taught after Jhana has been obtained, so if you are now getting Jhana Factors, it may be worthwhile to cultivate a bit of concentration and build from there.
Full absorption in Jhana, will be known only really after the fact, since you can't really observe the Jhana factors (one-pointedness, rapture, bliss, etc) while fully absorbed, due to the level of one-pointed concentration required for full absorption to take place, but the Jhana factors do arise prior to full absorption, for me Piti, is a regular occurrence during meditation, even if I am not aiming for absorption, for instance. Although a Jhana factor or factors are present, the only thing this signifies is the purification of the Hindrance that offsets the factor, it doesn't not imply full Jhana (http://www.dhammacenter.org/the_3_trainings/training_in_mentality/jhana_factors - I.e. Ill Will is offset by Piti) - Although with them arising it does indicate you are close to Jhana.
In order to get full Jhana, continue to concentrate one pointedly and when it's ready, you should get pulled into Jhana, if you chase factors or shift your object of meditative focus, you will lose concentration and may not get fully absorbed.
Longer sessions might help you with some of your session dedicated to building concentration, you might want to instead of doing 2x20 minutes sessions, do a 40 minute, 20 minutes pure concentration then switch to insight. If you indeed get to first Jhana, fully absorbed, then take time to stay there and master it before moving on, typically if you do not do this and try to hit the 2nd Jhana (which involves the dropping of the more coarse Jhana factors - a greater refinement), both will fade and you will be back in access concentration.
Now in order to keep Jhana you need to maintain concentration on your meditation object, any application of momentary concentration or directing will create your attention to be lost and bump you out of Jhana.
Best of luck |