Andrzej Olszewski
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Andrzej Olszewski

practices to children when possible, as this has been found to be predictive ofchildren’s behaviour.Parent Knowledge about ConcussionsConcussion is a specific type of head injury that has recently received agreat deal of research and media attention due to the high risk of injury amongchildren and youth involved in sports, and the link between repeatedconcussions and chronic complications such as chronic traumaticencephalopathy (CTE). Recent research looking at the incidence of concussionson a Canadian minor hockey team suggests that the rate of injury is as much asseven times greater than was previously thought (Echlin et al., 2010). Given thehigh risk of concussion and the influence parents have on risk-taking behaviour,research has begun to examine parents’ knowledge and attitudes towardconcussion.In terms of parents’ knowledge about concussions, studies have shownmixed results. Some research suggests parents generally understand what aconcussion is and can accurately identify the symptoms (Coghlin, Myles &Howitt, 2009; Sullivan et al., 2009; Koo, 2013). For example, parents of highschool rugby players in New Zealand were correctly able to recognizeconcussion symptoms as stated in the Sport Concussion Assessment Tool (SCAT)(Sullivan et al., 2009). However, it was also suggested that while parents wereable to properly identify symptoms, they often identified incorrect symptoms atthe same time (Coghlin et al., 2009). Other research looking at hockey parents inthe Toronto area supports this disconnect in parental knowledge (Cusimano,Chipman, Volpe, & Donnelly 2009). Overall, more research is needed todetermine if parents are able to accurately recognize concussion symptoms. In

Harmonic Flow MeasurementsEvent Plane (EP) Method• Event plane is determined by flow vectorQn calculated from energy depositions inthe first two layers of FCal detector• Flow magnitude v n is measured bycorrelation of tracks with respect to eventplane, corrected by a resolution factor nthat accounts for the smearing of themeasured Ψn around true angle Ψ RP,n• Sub-event method cross-correlatessubdetector sides in order to ensure largepseudorapidity gap between FCal and ID(||>3.2) to reduce non-flow correlations• Full FCal method for determining eventplane is used when high resolution isrequired with low multiplicity (pt, cent) binsParticle Correlation (2PC) Method• The correlations are using tracks from theInner Detector which has an coverage of(-2.5,+2.5) and full f coverage. This allowsto build correlations with max ±5.0• The correlations density is calculated bydividing foreground pairs by mixedbackground pairs accounting for detectoracceptance effects• It can be expanded into Fourier seriesdNdΔφ~ 1 2cos(nΔφ)• v n,n can be calculated via Discrete FourierTransform (DFT)• If the anisotropy is driven by collectiveexpansion, v n,n should factorize to productof single particle harmonic coefficientsna bvn, n(pT,pT) vvnn,n(paT)vn(pbT)April 16, 2012 QNP20126

EP: v n vs Centrality• Variation of the magnitude of the n-th typeharmonic flow v n with collision centrality forseveral p T ranges• Using full FCal event for EP determinationto improve resolution for higher harmonics• Going from central to more peripheralcollisions magnitude of the elliptic flow v 2first increases, reaching a maximum in the30–50% centrality range, and thendecreases• In agreement with a change in the ellipticgeometry with centrality• The higher-order coefficients v 3 –v 6 showmuch weaker centrality dependence• This behavior is consistent with ananisotropy related to the fluctuations in theinitial geometryApril 16, 2012 QNP20127

EP: v n vs • Variation of the magnitude of the n-thtype harmonic flow v n with pseudorapidityin several centrality intervals• For particles in the 2–3 GeV p T range• Using FCalP(N) EP method• Very weak dependence is observed• Flow values decrease by less than 5%towards large || for central and midcentralevents, and the decrease ismore pronounced both for n ≥ 3 andfor peripheral events• Similar behavior is observed in otherp T rangesApril 16, 2012 QNP20128

Two-Particle Correlationsjet+resonanceridgedouble hump• Pair distributions at low p T have a „jet like”,“ridge” & “double hump” structures• Make Fourier decomposition in slices of and determine v n,n correlation parametersdNdΔφ~ 1 2ncos(nΔφ)• Measure v n,n (p Ta , p Tb , Δη,cent,n) with ||cut, and calculate v n flow using relationvn,n(paT,pbTv) vnn,n(paT)vn(pbT)• Check properties of Fourier parameters,v n,n in slices of in order to find regionwhere flow dominates correlations• In the „jet” region v n,n parameters varyquickly while in the region of ridge theyare almost flat, as expected from singleparticle flow behavior• Suggesting to use cut at 2 < || < 5 incalculation of flow parameters in order toremove the „jet” region biasApril 16, 2012 QNP201210

2PC vs EP: p T Dependence• Compare flow v n obtained from thecorrelations to the EP values, as afunction of p T• The two methods agree within 5%–15% for v 2 and 5%–10% for v 3 –v 5 forpT < 4 GeV• Significant deviations are observedfor pT > 4–5 GeV when using 2PCfixed p T method, presumably due tocontributions from the away-side jet• In order to reduce contributions fromhigh p T jet particles EP results arecompared to 2PC mixed p T methodwith low p T reference particles• In this case agreement is very goodindicating that v n = v n,n factorizationholds as it should in the region whereonly flow contributes2PC: fixed p T2PC: mixed p TApril 16, 2012 QNP201212

C(Df)C(f)C(Df)-1Decomposition of Ldt = Two-Particle 8 mbCorrelation Function0.999C(φ) b1.021.01òATLAS Preliminary2PC2PC(1 2v1 ,1cos φ 2vDf0-1% 2

Summary• ATLAS has measured harmonic flow coefficients– in Pb-Pb collisions at 2.76 TeV LHC energy– in wide p T , and centrality range– using Event Plane and Two-Particle Correlations methods• Significant v 2 -v 6 are observed– with weak dependence in – with p T dependence following hydrodynamic like scaling relation• Two-particle correlation functions at ||>2 and at low p T are reproduced entirely byflow collective motion plus a v 11 term, the v 11 correlation term is well described by atwo-component fit with a collective v 1 plus momentum conservation components• This suggests that in low p T range there may be little contribution allowed from themedium response to the jets effects• For details see: arXiv:1203.3087v1 [hep-ex]April 16, 2012 QNP201214

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