1 / 15

The Double Ridge Phenomenon in p-Pb Collisions Measured with ALICE

The Double Ridge Phenomenon in p-Pb Collisions Measured with ALICE. Jan Fiete Grosse-Oetringhaus, CERN for the ALICE Collaboration Moriond QCD 2013. 0-20% 60-88% pp. Motivation.

chaka
Télécharger la présentation

The Double Ridge Phenomenon in p-Pb Collisions Measured with ALICE

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. The Double Ridge Phenomenon in p-Pb Collisions Measured with ALICE Jan Fiete Grosse-Oetringhaus, CERN for the ALICE Collaboration Moriond QCD 2013

  2. 0-20% 60-88%pp Motivation • Proton-nucleus collisions are studied to access cold nuclear matter effects and assess a baseline for heavy-ion studies • At RHIC d-Au collisions, a modification of the away side is seen in mid-forward correlations for central collisions (PRL 107 (2011) 172301) • CMS has observed a near side ridge in high-multiplicity pp and p-Pb collisions (PLB718 (2013) 795) PHENIX, PRL 107 (2011) 172301 CMS, PLB718 (2013) 795 The Double-Ridge in p–Pb Collisions Measured with ALICE – Jan Fiete Grosse-Oetringhaus

  3. L3 Magnet T0/VZEROTrigger/Centrality ACORDE Cosmic trigger EMCAL γ, π0, jets HMPID PID (RICH) @ high pT TRD Electron ID (TR) TOF PID PMD γ multiplicity TPC Tracking, PID (dE/dx) ITS Low pT tracking PID + Vertexing MUON μ-pairs FMD Charged multiplicity PHOS γ, π0, jets ALarge Ion Collider Experiment Dipole Not shown: ZDC (at ±114m) The Double-Ridge in p–Pb Collisions Measured with ALICE – Jan Fiete Grosse-Oetringhaus

  4. Two-Particle Correlations • Correlation between a trigger and an associated particle in certain pT intervals (pT,assoc < pT,trig) • Signal S contains correlation within same event • Background B contains "correlation" between different events • 1.7M p-Pb events from 4 hour test run in Sep/2012 • sNN = 5.02 TeV [4 TeV p beam / 1.58 TeV per nucleon Pb beam] • Rapidity shift of 0.465 in p direction • Quantities given here in the lab system trigger particle associated particle Mixed event Dh Dj (rad) The Double-Ridge in p–Pb Collisions Measured with ALICE – Jan Fiete Grosse-Oetringhaus

  5. Event Classes • Centrality in "heavy-ion terms" of impact parameter is not used  separate, non-trivial, topic in p-A collisions • We define four multiplicity event classes in multiplicity ranges with a forward scintillator detector (VZERO) • 2.8 < h < 5.1 and -3.7 < h < -1.7 • Denoted by 0-20% (highest multiplicity), 20-40%, 40-60%, 60-100% (lowest multiplicity) The Double-Ridge in p–Pb Collisions Measured with ALICE – Jan Fiete Grosse-Oetringhaus

  6. The Ridge 2 < pT,trig < 4 GeV/c1 < pT,assoc < 2 GeV/c20% highest multiplicity • The near-side long-range ridge observed by CMS in pp and p-Pb can also be seen with ALICE [JHEP 09 (2010) 091, PLB718 (2013) 795] (zoomed) Near-side jet(Dj ~ 0, Dh ~ 0) 1/Ntrig d2Nassoc/dDhdDj Away-side jet(Dj ~ p, elongated in Dh) Near-side ridge(Dj ~ 0, elongated in Dh) Dh Dj (rad) The Double-Ridge in p–Pb Collisions Measured with ALICE – Jan Fiete Grosse-Oetringhaus

  7. Projection to Dj 0-20%20-40%40-60%60-100%pp • Shifted to same baseline by subtracting the value at Dj = 1.3 • Low multiplicity class agrees with results from pp collisions • Increase of the yield on the near-side and away-side towards higher event multiplicity classes The Double-Ridge in p–Pb Collisions Measured with ALICE – Jan Fiete Grosse-Oetringhaus

  8. Subtraction Procedure • Can we separate the jet and ridge components? • No ridge seen in 60-100% and similar to pp what remains if we subtract 60-100%? • A double ridge! 0-20% 60-100% – = Dh Dh Dj (rad) Dj (rad) Dj (rad) Dh The Double-Ridge in p–Pb Collisions Measured with ALICE – Jan Fiete Grosse-Oetringhaus

  9. The Double RidgeProjections to Dh • Ridges are flat in |Dh| < 2 • Slight excess on the near side around Dh ~ 0 • Could be residual jet: change of jet contribution as a function of multiplicity (fragmentation bias)? • Exclude |Dh| < 0.8 on near side • Away side? Bias evaluated and added to the systematic uncertainty by • Subtracting near side excess also from away side • Scaling 60-100% such that no near side excess remains Dh Dj (rad) |Dj| < p/3 |Dj - p| < p/3 Remaining Dj 1/Ntrig d2Nassoc/dDhdDj Dh The Double-Ridge in p–Pb Collisions Measured with ALICE – Jan Fiete Grosse-Oetringhaus

  10. The Double RidgeProjections to Dj • Modulation mostly of cos 2Dj type • Small but significant cos 3Dj term needed • Fit allows to extract vn coefficient • Baseline from 0-20% event class to be used! • Same procedure applied on HIJING simulated events  no significant modulation remains Dh Dj (rad) 1/Ntrig d2Nassoc/dDhdDj Dj (rad) The Double-Ridge in p–Pb Collisions Measured with ALICE – Jan Fiete Grosse-Oetringhaus

  11. v2 and v3 Coefficients • v2 and v3 as a function of pT for different event classes (each 60-100% subtracted) • v2 • Strong increase with pT • Mild increase with multiplicity • v3 • Increase with pTwithin large uncertainties v2 v3 The Double-Ridge in p–Pb Collisions Measured with ALICE – Jan Fiete Grosse-Oetringhaus

  12. Ridge Yields • Integrating near side and away side above baseline allows to extract ridge yields • Increase with trigger pT and multiplicity • Despite significant change in absolute values, remarkable agreement of near side and away side ridge yields • Common underlying physical origin for near side and away side ridge? line = diagonal (no fit!) Near sideAway side The Double-Ridge in p–Pb Collisions Measured with ALICE – Jan Fiete Grosse-Oetringhaus

  13. Symmetric Ridge? • What would the assumption of a symmetric ridge give us? • Determine near-side ridge in 1.2 < |Dh| < 1.8 • Mirror to away side and subtract 0-20%20-40%40-60%60-100%pp Dj (rad) Dj (rad) In addition to symmetric double ridge, no significant other structures The Double-Ridge in p–Pb Collisions Measured with ALICE – Jan Fiete Grosse-Oetringhaus

  14. Flow? 3+1 viscous hydro (arXiv:1112.0915) Saturation? Color glass condensate (arXiv:1302.7018) Interpretation Band: Calculation Points: ALICE data arXiv:1112.0915 Ridge Yields per Dh arXiv:1302.7018 0-20% 20-40% 40-60% Boxes: our values for 0-20% The Double-Ridge in p–Pb Collisions Measured with ALICE – Jan Fiete Grosse-Oetringhaus

  15. Summary • An intriguing double ridge structure in high-multiplicity p-Pb collisions has been observed • The ridge on near side and away side has identical yield and is mostly symmetric (plus a v3 component) regardless of pT and multiplicity • Qualitative agreement of the pT and multiplicity dependence of the observed ridges with hydrodynamic calculations and color-glass condensate models Thank you for your attention! Find more details in PLB719 (2013) 29 The Double-Ridge in p–Pb Collisions Measured with ALICE – Jan Fiete Grosse-Oetringhaus

More Related