New PHOBOS results on event-by-event fluctuations

Alver, B.; Back, B. B.; Baker, M. D.; Ballintijn, M.; Barton, D. S.; Betts, R. R.; Bickley, A. A.; Bindel, R.; Budzanowski, A.; Busza, W.; Carroll, A.; Chai, Z.; Chetluru, V.; Decowski, M. P.; Garcia, E. Oliver; Gburek, T.; George, N.; Gulbrandsen, K.; Gushue, S.; Halliwell, C.; Hamblen, J.; Heintzelman, G. A.; Henderson, C.; Harnarine, I.; Hofman, D. J.; Hollis, R. S.; Hołyński, R.; Holzman, B.; Iordanova, A.; Johnson, E.; Kane, J. L.; Khan, Naeem; Kucewicz, W.; Kulinich, P.; Kuo, C. M.; Li, W.; Lin, W.; Loizides, Constantinos; Manly, S.; Mignerey, A. C.; Nouicer, R.; Olszewski, A.; Pak, R.; Park, I. C.; Reed, Corey James; Remsberg, L. P.; Reuter, M.; Richardson, E.; Roland, C.; Roland, G.; Rosenberg, L.; Sagerer, J.; Sarin, P.; Sawicki, P.; Sedykh, I.; Skulski, W.; Smith, Christopher; Stankiewicz, M. A.; Steinberg, P.; Stephans, G. S. F.; Суханов, А.; Szostak, A.; Tang, J. L.; Tonjes, M. B.; Trzupek, A.; Vale, C.; Nieuwenhuizen, G. J. van; Vaurynovich, S. S.; Verdier, R.; Veres, G. I.; Walters, Patrick; Wenger, E. A.; Willhelm, D.; Wolfs, F. L. H.; Wosiek, B. K.; Woźniak, K. W.; Wuosmaa, A. H.; Wyngaardt, S.; Wysłouch, B.

doi:10.1063/1.2197387

Cited by 142 publications

(273 citation statements)

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“…A quantitatively meaningful comparison of the elliptic flow values measured in Cu+Cu and Au+Au collisions requires dividing out the difference in the eccentricity of the nuclear overlap zone since, for a given centrality, the average eccentricity depends on the size of the colliding nuclei. For the same size of the overlap zone, similar densities are achieved in the two collision systems [27,28], but the Cu+Cu system exhibits a significantly smaller spatial eccentricity. If one scales the measured v 2 by this eccentricity, using its conventional definition in terms of the spatial deformation of the average transverse distribution of participating nucleons at a given impact parameter, one is led to the paradoxical finding that the smaller Cu+Cu system translates the initial spatial deformation more efficiently into a final momentum anisotropy than the larger Au+Au system [27,28].…”

Section: Introductionmentioning

confidence: 62%

Importance of correlations and fluctuations on the initial source eccentricity in high-energy nucleus-nucleus collisions

Alver¹,

Back²,

Baker³

et al. 2008

Phys. Rev. C

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263

198

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In relativistic heavy-ion collisions, anisotropic collective flow is driven, event by event, by the initial eccentricity of the matter created in the nuclear overlap zone. Interpretation of the anisotropic flow data thus requires a detailed understanding of the effective initial source eccentricity of the event sample. In this paper, we investigate various ways of defining this effective eccentricity using the Monte Carlo Glauber (MCG) approach. In particular, we examine the participant eccentricity, which quantifies the eccentricity of the initial source shape by the major axes of the ellipse formed by the interaction points of the participating nucleons. We show that reasonable variation of the density parameters in the Glauber calculation, as well as variations in how matter production is modeled, do not significantly modify the already established behavior of the participant eccentricity as a function of collision centrality. Focusing on event-by-event fluctuations and correlations of the distributions of participating nucleons, we demonstrate that, depending on the achieved event-plane resolution, fluctuations in the elliptic flow magnitude v 2 lead to most measurements being sensitive to the root-mean-square rather than the mean of the v 2 distribution. Neglecting correlations among participants, we derive analytical expressions for the participant eccentricity cumulants as a function of the number of participating nucleons, N part , keeping nonnegligible contributions up to O(1/N 3 part ). We find that the derived expressions yield the same results as obtained from mixed-event MCG calculations which remove the correlations stemming from the nuclear collision process. Most importantly, we conclude from the comparison with MCG calculations that the fourth-order participant eccentricity cumulant does not approach the spatial anisotropy obtained assuming a smooth nuclear matter distribution. In particular, for the Cu+Cu system, these quantities deviate from each other by almost a factor of 2 over a wide range in centrality. This deviation reflects the essential role of participant spatial correlations in the interaction of two nuclei.

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Section: Introductionmentioning

confidence: 62%

Importance of correlations and fluctuations on the initial source eccentricity in high-energy nucleus-nucleus collisions

Alver¹,

Back²,

Baker³

et al. 2008

Phys. Rev. C

Self Cite

263

198

View full text Add to dashboard Cite

show abstract

“…In a more-recent strategy "higher harmonic flows" were invoked to explain all aspects of the η-elongated SS peak or "soft ridge" [11]. The various harmonic flows were attributed to fluctuations in the initial-state A-A geometry coupled to radial expansion of the bulk medium [12,13]. In an alternative scheme the elongated SS 2D peak was explained in terms of glasma flux tubes coupled to radial flow [14,15].…”

Section: Introductionmentioning

confidence: 99%

Challenging claims of nonjet “higher harmonic” components in 2D angular correlations from high-energy heavy-ion collisions

2012

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Background: Possible evidence for triangular flow and other "higher harmonic flows" in high energy nucleus-nucleus collisions has received much attention recently. It is conjectured that several higher harmonic flows vm may result from initial-state geometry fluctuations in A-A collisions coupled to a radially-expanding medium. But as with "elliptic flow" v2 measurements, nonhydrodynamic mechanisms such as jet production may contribute to other higher azimuth multipoles vm as biases. Purpose: Careful distinctions should be maintained between jet-related and nonjet (possibly hydrodynamic) contributions to vm (e.g., "nonflow" and "flow"). In this study we consider several questions: (a) To what extent do jet-like structures in two-dimensional (2D) angular correlations contribute to azimuth multipoles inferred from various vm methods? (b) If a multipole element is added to a 2D fit model is a nonzero amplitude indicative of a corresponding flow component? and (c) Can 2D correlations establish the necessity of nonjet contributions to some or all higher multipoles? Method: Model fits to 2D angular correlations are used to establish the origins of azimuth multipoles inferred from 1D projections onto azimuth or from nongraphical numerical methods. Results: We find that jet-like angular correlations, and specifically a 2D peak at the angular origin consistent with jet production, constitute the dominant contribution to inferred higher multipoles, and the data do not require higher multipoles in isolation from the jet-like 2D peak. Conclusions: Inference of "higher harmonic flows" results from identifying certain nominally jetlike structure as flow manifestations through unjustified application of 1D Fourier series analysis. Although the peak structure at the angular origin is strongly modified in more-central collisions some properties remain compatible with relevant pQCD theory expectations for jet production.

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“…In two-particle correlations, a pronounced near-side (small relative azimuthal angle |∆φ| ∼ 0) long-range (large relative pseudorapidity ∆η) structure, also known as the "ridge-like" structure, has been observed and extensively explored in relativistic high energy nucleus-nucleus (AA) collisions at both the Relative Heavy Ion Collider (RHIC) [1,2,3,4,5] and the Large Hadron Collider (LHC) [6,7,8,9,10], over a wide range of energies and system sizes. These long-range correlations can be interpreted as hydrodynamic collective flow of the strongly interacting and expanding medium.…”

Section: Introductionmentioning

confidence: 99%

Azimuthal anisotropy of charged particles from multiparticle correlations in pPb and PbPb collisions with CMS

Wang

2014

Nuclear Physics A

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Motivated by two-and four-particle azimuthal correlation measurements that suggest possible collective flow for charged particles emitted in pPb collisions at √ s N N =5.02 TeV, we extend the correlation results for these collisions using the six-and eight-particle cumulant methods, and the Lee-Yang Zeros method. CMS has an extensive program studying azimuthal harmonic coefficients for both PbPb and pPb collisions using various methods. The current pPb results will be presented in this context. The data were collected by the CMS experiment at the LHC using both minimum bias and highmultiplicity collision triggers over a wide range in pseudorapidity. The results are compared to 2.76 TeV semi-peripheral PbPb collision data collected in 2011 covering a similar range of particle multiplicities. The second-order azimuthal anisotropy Fourier harmonic (v 2 ) is shown for the different methods. A comparison of the six-and greater particle correlations to the previously published twoand four-particle correlation results sheds light on the multiparticle nature of the azimuthal anisotropy. The results are also discussed in terms of recent calculations that explore the role of participant fluctuations on measurements of higher-order particle correlations in pPb collisions. AbstractMotivated by two-and four-particle azimuthal correlation measurements that suggest possible collective flow for charged particles emitted in pPb collisions at √ s NN = 5.02 TeV, we extend the correlation results for these collisions using the six-and eight-particle cumulant methods, and the Lee-Yang Zeros method. CMS has an extensive program studying azimuthal harmonic coefficients for both PbPb and pPb collisions using various methods. The current pPb results will be presented in this context. The data were collected by the CMS experiment at the LHC using both minimum bias and high-multiplicity collision triggers over a wide range in pseudorapidity. The results are compared to 2.76 TeV semi-peripheral PbPb collision data collected in 2011 covering a similar range of particle multiplicities. The second-order azimuthal anisotropy Fourier harmonic (v 2 ) is shown for the different methods. A comparison of the six-and greater particle correlations to the previously published two-and four-particle correlation results sheds light on the multiparticle nature of the azimuthal anisotropy. The results are also discussed in terms of recent calculations that explore the role of participant fluctuations on measurements of higher-order particle correlations in pPb collisions.

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New PHOBOS results on event-by-event fluctuations

Cited by 142 publications

References 0 publications

Importance of correlations and fluctuations on the initial source eccentricity in high-energy nucleus-nucleus collisions

Importance of correlations and fluctuations on the initial source eccentricity in high-energy nucleus-nucleus collisions

Challenging claims of nonjet “higher harmonic” components in 2D angular correlations from high-energy heavy-ion collisions

Azimuthal anisotropy of charged particles from multiparticle correlations in pPb and PbPb collisions with CMS

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