Extraction of Jet Properties from Two Particle Azimuthal Correlations in Pp and AuAu Collisions at [square Root of S Subscript NN] PDF Download
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![Extraction of Jet Properties from Two Particle Azimuthal Correlations in Pp and AuAu Collisions at [square Root of S Subscript NN] PDF](https://books.google.com/books/content/images/frontcover/jRTxNwAACAAJ?fife=w150-h200)
Author: Paul Constantin
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Languages : en
Pages : 218
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Two particle azimuthal correlation functions measured in pp and AuAu collisions at [square root of s subscript NN] = 200 GeV at midrapidity with the central arms of the PHENIX detector are analyzed in order to extract the properties of hadronic jets produced in QCD vacuum and highly excited QCD media, like the jet shape parameters j[Subscript T] and k[Subscript T], the jet conditional yields (number of associated hadrons per high p[Subscript T] trigger hadron), and the jet fragmentation function. The analysis of pp data starts with the measurement of the vacuum fragmentation function from which the p[Subscript T] dependence of the mean fragmentation momentum fraction z is extracted. We obtain a constant value of z = 0.74±0.02 for p[Subscript T] above 3 GeV/c. Soft (non-perturbative) parton fragmentation becomes significant below 3 GeV/c and the slope of the fragmentation function is p[Subscript T] dependent in this region. Gaussian fits to jet induced azimuthal correlations are employed to measure the mean jet fragmentation transverse momentum j[Subscript Ty] = 359 ± 11 (stat) ± 6 (syst) MeV/c and the mean partonic transverse momentum k[Subscript Ty] = 964 ± 49 (stat) ± 16 (syst) MeV/c. The analysis of AuAu data is based on azimuthal correlation functions between charged hadrons in the 1.5-3 GeV/c and 3-5 GeV/c p[Subscript T] regions in five classes of collision centrality. The mean jet fragmentation transverse momentum j[Subscript Ty] is centrality independent and consistent with the value in pp data mentioned above. A strong broadening with the centrality of the extracted mean partonic transverse momentum k[Subscript Ty] (multiplied by z[Subscript trigg]) is observed. This is an important finding because hadronic jet quenching through energy loss is expected to be accompanied by a broadening effect. Another important finding is that the jet conditional yields in both the near (delta phi [Difference] 0) and away (delta phi [Difference] pi) regions exhibit a slightly raising trend with centrality. This was also expected to accompany the jet quenching found at higher p[Subscript T] based on simple energy conservation considerations.
![Extraction of Jet Properties from Two Particle Azimuthal Correlations in Pp and AuAu Collisions at [square Root of S Subscript NN] PDF](https://books.google.com/books/content/images/frontcover/jRTxNwAACAAJ?fife=w80-h100)
Author: Paul Constantin
Publisher:
ISBN:
Category :
Languages : en
Pages : 218
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Book Description
Two particle azimuthal correlation functions measured in pp and AuAu collisions at [square root of s subscript NN] = 200 GeV at midrapidity with the central arms of the PHENIX detector are analyzed in order to extract the properties of hadronic jets produced in QCD vacuum and highly excited QCD media, like the jet shape parameters j[Subscript T] and k[Subscript T], the jet conditional yields (number of associated hadrons per high p[Subscript T] trigger hadron), and the jet fragmentation function. The analysis of pp data starts with the measurement of the vacuum fragmentation function from which the p[Subscript T] dependence of the mean fragmentation momentum fraction z is extracted. We obtain a constant value of z = 0.74±0.02 for p[Subscript T] above 3 GeV/c. Soft (non-perturbative) parton fragmentation becomes significant below 3 GeV/c and the slope of the fragmentation function is p[Subscript T] dependent in this region. Gaussian fits to jet induced azimuthal correlations are employed to measure the mean jet fragmentation transverse momentum j[Subscript Ty] = 359 ± 11 (stat) ± 6 (syst) MeV/c and the mean partonic transverse momentum k[Subscript Ty] = 964 ± 49 (stat) ± 16 (syst) MeV/c. The analysis of AuAu data is based on azimuthal correlation functions between charged hadrons in the 1.5-3 GeV/c and 3-5 GeV/c p[Subscript T] regions in five classes of collision centrality. The mean jet fragmentation transverse momentum j[Subscript Ty] is centrality independent and consistent with the value in pp data mentioned above. A strong broadening with the centrality of the extracted mean partonic transverse momentum k[Subscript Ty] (multiplied by z[Subscript trigg]) is observed. This is an important finding because hadronic jet quenching through energy loss is expected to be accompanied by a broadening effect. Another important finding is that the jet conditional yields in both the near (delta phi [Difference] 0) and away (delta phi [Difference] pi) regions exhibit a slightly raising trend with centrality. This was also expected to accompany the jet quenching found at higher p[Subscript T] based on simple energy conservation considerations.
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Jets have been studied in high energy heavy ion collisions by measuring the angular correlation between particles at high transverse momentum. Differences in the yield and shape of the angular correlations as a function of system size give information on the medium produced in the collision. Such modifications can be used to infer the presence of a Quark-Gluon Plasma phase, wherein parton degrees of freedom are manifest over nuclear rather than nucleonic scales. In the present work, two-particle correlations were studied in \(d+Au\) and \(Au+Au\) collisions at \(\sqrt{s_{NN}}\) = 200 GeV measured by the STAR experiment at RHIC. The technique was extended to include pseudo-rapidity, permitting jets to be characterised in two-dimensions, and enabling the jet shape to be studied in greater detail. Corrections were developed for the incomplete detector acceptance and finite two-track resolution. Both unidentified and identified particle correlations were studied, using charged tracks and neutral strange particles \(\Lambda, \overline{\Lambda}\), and \(K^0_{Short}\) reconstructed from their characteristic \(V\)0 decay topology. The focus of the analysis was the correlation peak centred at zero azimuthal separation, which is significantly enhanced in central \(Au+Au\) collisions compared to lighter systems. The modified peak was found to comprise a jet-like peak broadened in the pseudo-rapidity direction, sitting atop a long range pseudo-rapidity correlation. The former is suggestive of jet modification by the medium, and the latter may indicate a medium response to jets. Correlations with identified particles indicated the modified same side peak may in part be formed from particles originating from the underlying event.
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Languages : en
Pages : 39
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In this study, the quark-gluon plasma is studied via medium-induced changes to correlations between jets and charged particles in PbPb collisions compared to pp reference data. This analysis uses data sets from PbPb and pp collisions with integrated luminosities of 166 inverse microbarns and 5.3 inverse picobarns, respectively, collected at $ \sqrt{s_{\mathrm{NN}}}=2.76 $ TeV. The angular distributions of charged particles are studied as a function of relative pseudorapidity ([Delta][eta]) and relative azimuthal angle ([Delta][Phi]) with respect to reconstructed jet directions. Charged particles are correlated with all jets with transverse momentum (pT) above 120 GeV, and with the leading and subleading jets (the highest and second-highest in pT, respectively) in a selection of back-to-back dijet events. Modifications in PbPb data relative to pp reference data are characterized as a function of PbPb collision centrality and charged particle pT. A centrality-dependent excess of low-pT particles is present for all jets studied, and is most pronounced in the most central events. This excess of low-pT particles follows a Gaussian-like distribution around the jet axis, and extends to large relative angles of [Delta][eta] ≈ 1 and [Delta][Phi] ≈ 1.
![Fragmentation Properties of Jets Produced in Pp Collisions at [square Root Sign] S PDF](https://books.google.com/books/content/images/frontcover/dItHAQAAMAAJ?fife=w80-h100)
Author: Bradley Hubbard
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Languages : en
Pages : 246
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Languages : en
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The production of jets in association with Z bosons, reconstructed via the mu+mu- and e+e- decay channels, is studied in pp and, for the first time, in PbPb collisions. Both data samples were collected by the CMS experiment at the LHC, at a center-of-mass energy of 5.02 TeV. The PbPb collisions were analyzed in the 0-30% centrality range. The back-to-back azimuthal alignment was studied in both pp and PbPb collisions for Z bosons with transverse momentum ptz> 60 GeV/c and a recoiling jet with ptj> 30 GeV/c. The pt imbalance, xjz= ptj/ptz, as well as the average number of jet partners per Z, rjz, were studied in intervals of ptz, in both pp and PbPb collisions. The rjz is found to be smaller in PbPb than in pp collisions, which suggests that in PbPb collisions a larger fraction of partons, associated with the Z bosons, lose energy and fall below the 30 GeV/c ptj threshold.
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Languages : en
Pages : 23
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The results from the STAR Collaboration on directed flow (v1), elliptic flow (v2), and the fourth harmonic (v4) in the anisotropic azimuthal distribution of particles from Au+Au collisions at (square root)s{sub NN} = 200 GeV are summarized and compared with results from other experiments and theoretical models. Results for identified particles are presented and fit with a Blast Wave model. For v2, scaling with the number of constituent quarks and parton coalescence is discussed. For v4, scaling with v22 and quark coalescence predictions for higher harmonic flow is discussed. The different anisotropic flow analysis methods are compared and nonflow effects are extracted from the data. For v2, scaling with the number of constituent quarks and parton coalescence are discussed. For v22 and quark coalescence are discussed.
Author: Doga Can Gulhan
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Languages : en
Pages : 232
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Two dijet measurements, one using 35 pb-1 pPb data at [square root]sNN- 5.02 TeV, and another with 166 [mu]b-1 PbPb and 5.3 pb-1 pp data at [square root]sNN = 2.76 TeV collected with CMS detector at the LHC, are presented. In pPb collisions, the dijet PT ratios, azimuthal angle differences and pseudorapidity distributions are measured and compared to PYTHIA and PYTHIA+HIJING simulations as well as NLO QCD predictions for the latter observable. No significant signs of final state interactions, such as a decrease in the mean dijet PT ratios or a broadening in the correlation of the dijets in azimuthal angle, with increasing forward activity, are observed. The dijet pseudorapidity distributions are also measured, and are sensitive to nuclear PDFs for x values of 0.001 - 0.5. Selections on event activity are found to yield unexpected centrality biases on dijet pseudorapidity distributions, which aided the interpretation of similar biases seen in inclusive jet measurements by ATLAS. In PbPb collisions, a detailed scan of charged particle distributions in correlation with the dijet system is carried out. The PT projection of charged particles on the dijet axis is measured at different distances of [delta] = [mathematical formula ...] 2 with respect to the leading and subleading jet axes. In this way, the spectra and angular distribution of the additional particles, which recover the overall event balance in dijet events with enhanced PT asymmetry in PbPb compared to pp collisions, are obtained up to [delta] = 1.8 in steps of 0.2. A significant excess of low PT particles associated with a subleading jet at large [delta] values is observed, and this excess is shown to get larger for dijet events with PT asymmetry. The scan is carried out for variety of anti-kT R parameters, which provides a way of varying jet width and fragmentation. Medium response to jet quenching at wide angles for jets with different fragmentation is studied. Only an insignificant increase of the magnitude of low PT particle excess at large angles, but a significant increase in the modification of the balance distribution close to the jet axes is observed by increasing R.
![High P[sub Partial] Inclusive Charged Hadron Distributions in Au+Au Collisions at Square Root(s[sub NN] PDF](https://books.google.com/books/content/images/frontcover/f72dDAEACAAJ?fife=w80-h100)
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This thesis reports the measurement of the inclusive charged particle (h[sup+]+ h[sup -]) p[perpendicular] spectra for 1.7
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Languages : en
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A measurement of the decorrelation of azimuthal angles between the two jets with the largest transverse momenta is presented for seven regions of leading jet transverse momentum up to 2.2 TeV. The analysis is based on the proton-proton collision data collected with the CMS experiment at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 19.7 fb$^{-1}$. The dijet azimuthal decorrelation is caused by the radiation of additional jets and probes the dynamics of multijet production. The results are compared to fixed-order predictions of perturbative quantum chromodynamics (QCD), and to simulations using Monte Carlo event generators that include parton showers, hadronization, and multiparton interactions. Event generators with only two outgoing high transverse momentum partons fail to describe the measurement, even when supplemented with next-to-leading-order QCD corrections and parton showers. Much better agreement is achieved when at least three outgoing partons are complemented through either next-to-leading-order predictions or parton showers. This observation emphasizes the need to improve predictions for multijet production.
Author: Essam Othman Elhalhuli
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Languages : en
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This work has studied the particle composition of jets by determining the ratios p±/p± and K±/p± in Au + Au and d + Au collisions at vsNN = 200 GeV measured by the STAR experiment at RHIC. Jets were found by measuring the angular azimuthal correlation between particles at high transverse momentum. Jets were then identified by their back-to-back correlation. A technique was developed to identify charged particles using their specific ionisation measured in the STAR Time Projection Chamber (TPC). This thesis contains one of the first implementations of using direct photons to tag jets in heavy ion collisions. An attempt was made to extract a trigger sample rich in direct photons from neutral triggers. The hadron ratios were calculated from the jet yields as a function of transverse momentum in each collision system. Although the away side yield is suppressed in central Au + Au, there is no evidence that the relative particle yields are changed. The hadron ratios for the three systems were found to be consistent with simulated p + p events generated using the Pythia Monte Carlo event generator. This reinforces the conclusion that the fragmentation process is unchanged by interactions with the medium.
