1/10 Boris Tomášik: Contribution of hard processes to elliptic flow Boris Tomášik Univerzita Mateja Bela, Banská Bystrica, Slovakia and Czech Technical University, Prague, Czech Republic Workshop on High pt at the LHC Tokaj, Hungary March 17, 2008 Contribution of hard processes to elliptic flow

2/10 Boris Tomášik: Contribution of hard processes to elliptic flow Motivation: the elliptic flow Azimuthal variation of momentum spectra Collective effect - more expansion in the reaction plane Due to different pressure gradients Early signal, IMPORTANT conclusions => rapid thermalisation => (near) perfect fluid dynamics => need to understand very details of v 2

3/10 Boris Tomášik: Contribution of hard processes to elliptic flow One jet in medium, and further... Momentum is being transferred to the bulk => expect collective response of the bulk Proposed Mach cones -> possible signals seen in correlation data -> cones correlated to leading particle (not primarily correlated to elliptic flow) LHC (and maybe RHIC): more than one (mini)jet in single event What is the influence of two or more (pairs of) jets which transfer momentum on the bulk?

4/10 Boris Tomášik: Contribution of hard processes to elliptic flow Jets in medium One pair of jets Contribution to v 2 Two pairs of jets Momenta cancel out - energy deposition => less v 2 generation => decrease of flow in direction

5/10 Boris Tomášik: Contribution of hard processes to elliptic flow More jets in medium Question: If - we have ellipsoidal fireball, - jets are produced isotropically, in which direction will most of the collisions happen? In that direction we shall have less flow. This will give contribution to v 2.

6/10 Boris Tomášik: Contribution of hard processes to elliptic flow Some considerations 1: position Easy for jets to “pass by”. Hard to “pass by”. More likely collisions out-of-plane – in-plane elliptic flow

7/10 Boris Tomášik: Contribution of hard processes to elliptic flow Some considerations 2: direction Less likely to find another jet if flying out-of-plane More likely to find another jet if flying in-plane More likely collisions in-plane – out-of-plane elliptic flow

8/10 Boris Tomášik: Contribution of hard processes to elliptic flow A toy model Jets are represented by droplets of matter Jet pt spectrum Droplets evaporate pions If they are close, droplets collide and merge into a heavier droplet

9/10 Boris Tomášik: Contribution of hard processes to elliptic flow A toy model: results Negative contribution to v 2 on per cent level What would be the result of hydrodynamic simulation?

10/10 Boris Tomášik: Contribution of hard processes to elliptic flow Summary......outlook  At LHC, it may be interesting to look at contributions to elliptic flow from the action of more jets.  Expect effect on per cent level – needs to be understood for the extraction of bulk properties.  How to recognise this contribution? (v 2 fluctuations?)  Do hydro + jets!