Flow measurements from CMS Julia Velkovska for the CMS - - PowerPoint PPT Presentation

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Flow measurements from CMS Julia Velkovska for the CMS - - PowerPoint PPT Presentation

Aug 01, 2023 237 likes •457 views

Flow measurements from CMS Julia Velkovska for the CMS Collaboration CMS flow measurements: LHC flow WG, August 2011 Publically available documents CMS PAS HIN-10-002 preliminary v 2 results CMS PAS HIN-11-005 preliminary v

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CMS flow measurements: LHC flow WG, August 2011

Flow measurements from CMS

Julia Velkovska for the CMS Collaboration

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Publically available documents

  • CMS PAS HIN-10-002

– preliminary v2 results

  • CMS PAS HIN-11-005

– preliminary vn results from cumulants and LYZ

  • Not covered in this talk are vn from di-hadron correlations
  • arXiv:1105.2438 ; CMS-HIN-11-001 ; CERN-PH-EP-2011-056 ; to

be published in: J. High Energy Phys – di-hadron correlations v1-v5 from central events

  • CMS PAS HIN-11-006

– preliminary di-hadron correlations v1-v5 : centrality dependence

Julia Velkovska (Vanderbilt) CMS flow measurements: LHC flow WG, August 2011

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The CMS detectors used in the analyses

  • Additional EP defined in HF to be included in the final results

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2.9 < |η| < 5.2 3.23 < |η| < 4.65 |η| < 2.4

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Event selection and centrality determination

Additional centrality bins in the final analysis

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Vertex cut |zvtx |< 10 cm Trigger efficiency : 97+/- 3%

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Track reconstruction

Efficiency and fake rate also estimated from sim pions embedded in real events

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Mid-rapidity Forward rapidity HYDJET BASS

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Track selection

  • Improved

“standard cuts” for final analysis

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Preliminary results: 0.3 < pT < 12 GeV/c

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vn preliminary measurements from CMS

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n = 6 n = 2 n = 3 n = 4 n = 5

Julia Velkovska (Vanderbilt) CMS flow measurements: LHC flow WG, August 2011

Add EP in final results Add EP in final results Add EP in final results Add EP in final results

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EP v2

  • HF EP in final results : larger rapidity gap ∆η ≥ 2

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EP efficiency corrections

  • No efficiency correction for the differential v2(pt)
  • To obtain integrated v2 at mid rapidity and v2(η), first the

differential v2(pt) is measured in bins of ∆η = 0.4 – then integrated in the range 0.3 < pt < 3 GeV/c

  • No fake track v2 correction in preliminary v2(pt) results – a

correction is being implemented for the final results to reduce the low-pt systematic uncertainty

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Cumulants (I)

  • Cumulants are obtained using generating functions

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Differential gen function are evaluated using several interpolation points in the complex plane

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Cumulants details of analysis (II)

  • Results obtained in 5% centrality bins : averaged to get 40-50%,etc
  • Fixed multiplicity: M = <M> -2σ : σ is r.m.s. of the multiplicity

distribution for that centrality interval

  • 21 Interpolation points in the complex plane 3 values for r0 and 7 for

the phase, p:

r0 – radius determined from the multiplicity and the number of events in each centrality class. Varied for systematic studies

  • To avoid auto-correlations , the particles used for determining

differential flow are excluded from the integrated flow calculation

  • Track-by-track efficiency correction applied as a weight in

the gen function

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Cumulants (III)

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Lee-Yang Zeros

  • Flow vector Q projected onto an arbitrary direction wrt x axis : 5 values of θ used
  • weight used in gen function to correct for efficiency
  • Differential v2, v4 and v6 reconstructed from V2

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Systematic studies

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Summary of systematic uncertainties: EP

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Systematics EP : v2(η)

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Summary of changes for final results

  • Vn from EP
  • Using HF EP with large rapidity gap
  • Rapidity gaps in cumulant analysis
  • Improved track selections + corrections for fake

track v2 at low-pt

  • Improved statistics ( ~ factor of 10)
  • Reduced systematic uncertainties

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