1 / 24

Eccentricity and v2 in proton-proton collisions at the LHC

Eccentricity and v2 in proton-proton collisions at the LHC. Yoshitaka Hatta (U. Tsukuba). in collaboration with. E. Avsar, C. Flensburg, J.-Y. Ollitrault, T. Ueda. arXiv:1009.5643 v2 [hep-ph]. Contents. High-multiplicity events at the LHC Flow in pp? Dipole model & DIPSY

thor
Download Presentation

Eccentricity and v2 in proton-proton collisions at the LHC

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Eccentricity and v2 in proton-proton collisions at the LHC Yoshitaka Hatta (U. Tsukuba) in collaboration with E. Avsar, C. Flensburg, J.-Y. Ollitrault, T. Ueda arXiv:1009.5643v2 [hep-ph]

  2. Contents • High-multiplicity events at the LHC • Flow in pp? • Dipole model & DIPSY • Eccentricity and v2 in pp • Nonflow correlations • Signatures of flow

  3. The first data from the LHC

  4. High-multiplicity pp events

  5. Like an AA collision ! CMS PHOBOS high multiplicity pp 7TeV comparable to ~18 nucleon pairs, each colliding at 62.4GeV in CuCu pT>0.1GeV/c h -2 +2 Phenomena usually discussed in the context of AA collisions may be observed in pp collisions.

  6. Ridge in pp CMS Collaboration, arXiv:1009.4122 near-side, long-range rapidity correlation First unexpected result from the LHC !

  7. Elliptic flow at RHIC Hallmark of collective expansion, widely regarded as a signal of the QGP.

  8. Elliptic flow in pp? Luzum,Romatschke 0901.4588 Prasad, Roy, Chattopadhyay 0910.4844 d’Enterria, et al. 0910.3029 Bozek 0911.2392 Bautista, Cunqueiro, de Deus, Pajares 0905.3058 Pierog, Porteboeuf, Karpenko, Werner, 1005.4526 Casalderrey-Solana, Wiedemann 0911.4400 Toy models : Woods-Saxon, Glauber, Hard Sphere…. Partons + flux tube model “Hot spot” model

  9. Participant eccentricity Event plane may be different from the reaction plane. Can be nonzero even at vanishing impact parameter due to fluctuations. AA  fluctuation of nucleons pp  fluctuation of small-x gluons

  10. QCD dipole model Mueller (1994~) Coordinate space formulation of the BFKL evolution.  Strong fluctuation in the gluon multiplicity  Strong correlation in impact parameter space These correlations are important to study correlations observables.

  11. Multiplicity fluctuation Probability distribution of the number of dipoles (gluons) Salam (1995)

  12. Correlation in impact parameter space For an initially dilute system (like a proton), the double dipole scattering amplitude does not factorize at least at the onset of unitarity corrections. YH and Mueller (2007) Avsar and YH (2008)

  13. DIPSY Full-fledged Monte Carlo event generator for pp based on the dipole model. Flensburg, Gustafson, Lonnblad, COMING SOON extension of Avsar, Gustafson, Lonnblad (2005~) “Lund gang” Featuring: BFKL Running coupling (NLO) Energy conservation ( ) Saturation effects Confinement effects Multiple scattering, Underlying events, Parton shower (ARIADNE) Hadronization (Pythia)

  14. Some sample results from DIPSY Flensburg, 1009.5323 Adjust (a few) parameters to fit the total cross section. No ad hoc re-tuning of the parameters at different energies.

  15. Multiple parton-parton collisions In high-multiplicity pp events, there are >10 subcollisions ! (high-multiplicity events) = (upward fluctuation in the gluon number) +(multiple gluon collisions)

  16. Eccentricity in pp at 7 TeV Shape of the area occupied by the “liberated” gluons. ~40% eccentricity, comparable to AA collisions at RHIC

  17. Nature of eccentricity in pp The conventional definition of the eccentricity at fixed b is negative, in stark contrast to AA ! y x “Overlapping area of the two protons”…largely irrelevant.

  18. Elliptic flow at 7 TeV Use the empirical formula Drescher et al. (2007) 6-7% Comparable to Au-Au at RHIC

  19. “Nonflow” effects “flow” “nonflow” Nonflow correlations from 22 hard collisions, resonance decays. Suppressed like if subcollisions are uncorrelated, which is the case in AA. In pp, nonflow effects are very large due to jets, etc. BUT, they have never been estimated before. We’ll do it !

  20. Nonflow correlations in pp All pairs within One particle from the other from Do NOT decrease as Nch increases ! It’s even increasing a bit.

  21. Nonflow correlations get replaced by flow correlations. Approach the flow limit either from above, or from below. Signature of flow in pp 100% nonflow 100% flow 100% nonflow

  22. We find Negative ! Four-particle correlations corresponding to

  23. Signature of flow in pp (cont’d) real and positive Low-Nch High-Nch

  24. Conclusions • High-multiplicity events : important to understand the low-x structure of the proton. Well simulated by DIPSY. • Fluctuations in the transverse plane lead to a large (40%) eccentricity. • Challenging to distinguish from non-flow correlations. First (serious) quantitative estimates and proposal of signatures.

More Related