1 / 21

Patricia Fachini for the STAR collaboration

ρ 0 Production in Cu+Cu Collisions at √s NN = 200 and 62.4 GeV in STAR. Motivation Measurements Results Conclusions. Patricia Fachini for the STAR collaboration. π -. ρ 0. π +. ρ 0. ρ 0. ρ 0. π -. π +. π -. ρ 0. +. +. +. π +. -. -. -. Motivation - I. π +. π -.

nyssa-garrison
Download Presentation

Patricia Fachini for the STAR collaboration

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. ρ0 Production in Cu+Cu Collisions at √sNN = 200 and 62.4 GeV in STAR Motivation Measurements Results Conclusions Patricia Fachini for the STAR collaboration QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  2. π- ρ0 π+ ρ0 ρ0 ρ0 π- π+ π- ρ0 + + + π+ - - - Motivation - I π+ π- • In-medium modification of mass and/or width  Chiral Symmetry Restoration? • Leptonic decay channel probes all stages of the collision. • Hadronic decay channel probes only late stages of the collision. ρ0 π+ π- ρ0 c = 1.3 fm QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  3. Motivation - II • Hadrons scale number constituent quarks  v2/n • ρ0 v2 scale number constituent quarks? • ρ0(770) production mechanism  scale NCQ  v2/n • ππρ0  n = 4 • qq ρ0  n = 2 • Difference between two limiting cases  30% C. Nonaka et al., Phys.Rev. C69 (2004) 031902 Hadron Gas Hadron Gas + QGP QGP QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  4. Motivation - III • Ifρ0 decays before kinetic freeze-out  not reconstructed due to rescattering of daughters • Chemical freeze-out elastic interactionsπ+π- ρ0π+π-regenerateρ0until kinetic freeze-out • Is the regeneration and rescattering driven by the hadron cross-sections? π- ρ0 π- π+ ρ0 measured ρ0 ρ0 lost π- π+ ρ0 π- π+ ρ0 π+ π+ π- ρ0 measured Chemical freeze-out Kinetic freeze-out QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  5. σ(πp) σ(ππ) π p Δ++ π π p π Δ++ ρ π π π π π ρ π p π Δ++ K* π K π K* π π ρ K π π σ(Kπ) σ(ππ) Motivation - IV • ρ0 regeneration  σ(ππ) • ρ0 daughter rescattering σ(πp)andσ(Kπ) • σ(ππ)>> σ(Kπ) • σ(πp)>σ(ππ) Chemical freeze-out Kinetic freeze-out  Probe dynamics between chemical and kinetic freeze-outs QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  6. K0Sπ+π- ω(782) (π+π-) π0and π+ π- K0S ω η (π+π-) π0 and (π+π-) η’ (π+π-)ηand (π+π-) ρ0 η + η’ K*(892)0 Kπwith K misidentified as π K*0 + K*0misidentified π+π- Invariant Mass Distribution from Monte Carlo • HIJING events with a realistic simulation of detector response STAR Preliminary ρ0(770)  π+π- sNN= 200 GeV ρ0 • Use ωandK*0shape from HIJING to fit the data • K*0signal is fixed using STAR measurement QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  7. Invariant Mass Distribution - Cocktail • Background subtracted  like-sign technique. • ρ0 and f0 widths  fixed according PDG. QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  8. Phase Space = π+ ρ0 π+ π- π- -  M2 + pT2 M e T  M2 + pT2 3 Γ(M) Mρ M2– 4mπ2 2 BW(M) = Γ(M) = Γρ (M2 – M2)2+ M2Γ(M)2 Mρ2– 4mπ2 M Phase Space • M = Invariant Mass; pT = transverse momentum; T = Temperature • Chemical and kinetic freeze-out  resonances formed until particles too far apart  resonances emitted T = 120 MeV • E.V. Shuryak and G.E. Brown, Nucl. Phys. A 717 (2003) 322 P. Braun-Munzinger et.al., CERES Int. Note, March 2000, unpublished; E.V. Shuryak and G.E. Brown, Nucl. Phys. A 717 (2003) 322; P.K. Kolb and M. Prakash, nucl-th/0301007; H.W. Barz et al., Phys. Lett. B 265, 219 (1991); R. Rapp, hep-ph/0305011. QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  9. Mass J. Adams et al., Phys. Rev. Lett. 92 (2004) 92301 Statistical errors only Statistical errors only • Mass shift ~45 MeV/c2 observed  possible explanations • Medium modifications • Bose-Einstein correlations R. Rapp, Nucl.Phys. A725, 254 (2003), E.V. Shuryak and G.E. Brown, Nucl. Phys. A 717 (2003) 322 G.D. Lafferty, Z. Phys. C 60, 659 (1993); R. Rapp, Nucl.Phys. A725 (2003) 254-268 S. Pratt et al., Phys.Rev. C68 (2003) 064905 QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  10. Spectra • ρ0measured in four different centralities in Cu+Cu. • Statistical and systematic errors added in quadrature. • Small signal to background ratio prevents the measurement in central collisions (~1/1000). • Solid lines  exponentialfits. QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  11. Mean pT J. Adams et al., Phys. Rev. Lett. 92 (2004) 92301 J. Adams et al., Phys. Rev. C 71 (2005) 64902 B. I. Abelev et al., Phys. Rev. C 78 (2008) 44906 • Statistical and systematic errors added in quadrature. • ρ0mean pT slightly increases with Npart. • ρ0mean pT comparable with proton mean pT. QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  12. Particle Ratios M. Bleicher et al. J. Phys. G 25 (1999) 1859 σ(Kπ) σ(ππ) σ(πp) • Cross-section regeneration or rescattering. • K*  rescattering of the daughters. • ρ0 regeneration compensating rescattering of the daughters. QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  13. Particle Ratios M. Bleicher et al. J. Phys. G 25 (1999) 1859 σ(Kπ) σ(ππ) σ(πp) • Cross-section regeneration or rescattering. • K*  rescattering of the daughters. • ρ0 regeneration compensating rescattering of the daughters. QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  14. Particle Ratios – Transport Model M. Bleicher et al. J. Phys. G 25 (1999) 1859 σ(Kπ) σ(ππ) σ(πp) • UrQMD long expansion time  π+π- scattering will not have enough energy to produce ρ0. QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  15. Elliptic Flow • Significant ρ0v2 measured  pT > 1.2 GeV/c  v2 ~ 13 ± 4%. QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  16. Elliptic Flow n=4 n=2 • Resonance v2 ρ0(770) production mechanism  scale NCQ  v2/n • ππρ0  n = 4 orqq ρ0  n = 2 • a, b, c, and d constants extracted using KS0and Λ v2ρ0 v2n= 4.7 ± 2.9 • pT range covered not sufficient for conclusive statement on the ρ0production mechanism. X. Dong et al., Phys.Lett. B597 (2004) 328 an v2(pT,n) = - dn 1 + exp[-(pT/n – b)/c] QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  17. Conclusions • Significant ρ0production measured in Cu+Cu collisions at √sNN= 200 and 62.4 GeV. • Production measured in 20-60% of hadronic cross-section. • Mass shift ~45 MeV/c2 observed • Medium modifications. • Bose-Einstein correlations. • Regeneration and rescattering  driven by hadron cross-sections. • K* rescattering of the daughters. • ρ0 regeneration compensating rescattering of the daughters. • First measurement of the ρ0v2  significantρ0v2measured. • pT range covered not sufficient for conclusive statement on the ρ0 production mechanism. See the poster by Prabhat Pujahari for details on the analysis of the results presented in this talk. QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  18. Elliptic Flow QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  19. Elliptic Flow • Significant ρ0v2 measured  pT > 1.2 GeV/c  v2 ~ 13 ± 4%. QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  20. Possible Explanations for Mass Shift - I R. Rapp, hep-ph/0305011 • 1. Dynamical effectρ0interactions at late stages of the collision • nucleons, hyperons and baryon resonances • pions, kaons and ρ0-mesons • t-channel exchanges • Distortion of the ρ0 spectral shape mass shift and/or broadening E.V. Shuryak and G.E. Brown, Nucl. Phys. A 717 (2003) 322 -23 MeV/c2 shift in the ρ0 mass -38 MeV/c2 shift in the ρ0mass due to t-channel attraction QM2009, Knoxville, March 30 - April 4 Patricia Fachini

  21. π+ π+ π+ ρ0 ρ0 A A D π- π- π- Possible Explanations for Mass Shift - II • 2. Interference between various π+π- scattering channels can effectively distort the line shape of resonances R. Longacre, nucl-exp/0305015 • 3. Bose-Einstein correlations between ρ0decay daughters and pions in the surrounding matter can also distort the resonance shape G.D. Lafferty, Z. Phys. C 60, 659 (1993); R. Rapp, hep-ph/0305011; S. Pratt et al., nucl-th/0308087. Interference QM2009, Knoxville, March 30 - April 4 Patricia Fachini

More Related