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Register a new userSTARs measurement of Long-range forward-backward multiplicity correlations as the signature of dense partonic matter in the Heavy Ion collisions at $sqrt{s_{NN}}=$200 GeV.}
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Brijesh K Srivastava
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Forward-backward multiplicity correlations have been measured with the STAR detector for Au+Au, Cu+Cu and {it p+p} collisions at $sqrt{s_{NN}}$ = 200 GeV. A strong, long-range correlation is observed for central heavy ion collisions that vanishes in semi-peripheral events and {it pp} collisions. There is no apparent scaling of correlation strength with the number of participants involved in the collision. Both the Dual Parton Model and the Color Glass condensate indicate that the long range correlations are due to multiple parton interactions. This suggests that the dense partonic matter might have been created in mid-central and central Au+Au collisions at $sqrt{s_{NN}}$ = 200 GeV.
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We present data on long-range multiplicity correlations in ultra-relativistic heavy ion collisions at the top RHIC energy ($sqrt{s_{NN}}$ = 200 GeV) from the STAR experiment. The data shows a long-range multiplicity correlation extending across a gap of 1.6 units in pseudorapidity. The data is over predicted by a multiparticle production model with hadronization of independent strings, or fusion of two color strings. This can be interpreted in terms of additional dynamical reduction in the number of particle sources.
A dense form of matter is formed in relativistic heavy ion collisions. The constituent degrees of freedom in this dense matter are currently unknown. Long-range, forward-backward multiplicity correlations (LRC) are expected to arise due to multiple partonic interactions. Model independent and dependent arguments suggest that such correlations are due to multiple partonic interactions. These correlations are predicted in the context of the Dual Parton Model (DPM). The DPM describes soft partonic processes and hadronization. This model indicates that the underlying mechanism creating these long-range multiplicity correlations in the bulk matter is due to multiple partonic interactions. In this thesis, long-range multiplicity correlations have been studied in heavy ion (Au+Au and Cu+Cu) and hadron-hadron ({it pp}) collisions. The behavior has been studied as a function of pseudorapidity gap ($Deltaeta$) about $eta$ = 0, the centrality, atomic number, and incident energy dependence of the colliding particles. Strong, long-range correlations ($Deltaeta >$ 1.0) as a function of $Deltaeta$ are found for central collisions of %(full overlap) heavy ions at an energy of $sqrt{s_{NN}}$ = 200 GeV. This indicates substantial amounts of dense partonic matter are formed in central heavy ion collisions at an energy of $sqrt{s_{NN}}$ = 200 GeV.
We present the first measurements of long-range angular correlations and the transverse momentum dependence of elliptic flow $v_2$ in high-multiplicity $p$$+$Au collisions at $sqrt{s_{_{NN}}}=200$ GeV. A comparison of these results with previous measurements in high-multiplicity $d$$+$Au and $^3{rm He}$$+$Au collisions demonstrates a relation between $v_2$ and the initial collision eccentricity $varepsilon_2$, suggesting that the observed momentum-space azimuthal anisotropies in these small systems have a collective origin and reflect the initial geometry. Good agreement is observed between the measured $v_2$ and hydrodynamic calculations for all systems, and an argument disfavoring theoretical explanations based on momentum-space domain correlations is presented. The set of measurements presented here allows us to leverage the distinct intrinsic geometry of each of these systems to distinguish between different theoretical descriptions of the long-range correlations observed in small collision systems.
Dihadron angular correlations in $d$+Au collisions at $sqrt{s_{rm NN}}=200$ GeV are reported as a function of the measured zero-degree calorimeter neutral energy and the forward charged hadron multiplicity in the Au-beam direction. A finite correlated yield is observed at large relative pseudorapidity ($Deltaeta$) on the near side (i.e. relative azimuth $Deltaphisim0$). This correlated yield as a function of $Deltaeta$ appears to scale with the dominant, primarily jet-related, away-side ($Deltaphisimpi$) yield. The Fourier coefficients of the $Deltaphi$ correlation, $V_{n}=langlecos nDeltaphirangle$, have a strong $Deltaeta$ dependence. In addition, it is found that $V_{1}$ is approximately inversely proportional to the mid-rapidity event multiplicity, while $V_{2}$ is independent of it with similar magnitude in the forward ($d$-going) and backward (Au-going) directions.
The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has measured $phi$ meson production and its nuclear modification in asymmetric Cu$+$Au heavy-ion collisions at $sqrt{s_{NN}}=200$ GeV at both forward Cu-going direction ($1.2<y<2.2$) and backward Au-going direction ($-2.2<y<-1.2$), rapidities. The measurements are performed via the dimuon decay channel and reported as a function of the number of participating nucleons, rapidity, and transverse momentum. In the most central events, 0%--20% centrality, the $phi$ meson yield integrated over $1<p_T<5$ GeV/$c$ prefers a smaller value, which means a larger nuclear modification, in the Cu-going direction compared to the Au-going direction. Additionally, the nuclear-modification factor in Cu$+$Au collisions averaged over all centrality is measured to be similar to the previous PHENIX result in $d$$+$Au collisions for these rapidities.
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