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Paper Proposal -----------------------------------------> Jets A_{LL} 2013

Updated on Thu, 2022-06-02 07:26. Originally created by aquinter on 2018-01-31 11:21.

Title: Longitudinal double-spin asymmetry for inclusive jet and dijet production in polarized proton collisions at $\sqrt{s}=510$ GeV

PA: Daniel Olvitt, Amilkar Quintero and Bernd Surrow

Journal:  Phys. Rev. D 105 092011

Abstract: 

We report measurements of the longitudinal double-spin asymmetry, $A_{LL}$, for inclusive jet and dijet production in polarized proton-proton collisions at midrapidity and center-of-mass energy $\sqrt{s}$ = 510 GeV, using the high luminosity data sample collected by the STAR experiment in 2013. These measurements complement and improve the precision of previous STAR measurements at the same center-of-mass energy that probe the polarized gluon distribution function at partonic momentum fraction 0.015 $\lesssim x \lesssim$ 0.25. The dijet asymmetries are separated into four jet-pair topologies which provide further constraints on the $x$ dependence of the polarized gluon distribution function. These measurements are in agreement with previous STAR measurements and with predictions from current next-to-leading order global analyses; providing more precise data at low dijet invariant mass that will better constraint the shape of the polarized gluon distribution function of the proton.

 
Paper Draft:

Analysis Note:

Supplemental Materials:

Presentations:

Figures: (pdf figures below) 

Figure 1: Comparison between data (points) and embedded simulation (histogram) of the inclusive jet yield versus $p_T$ at detector level. The central panel shows the ratio of the relative differences between all data runs used in the analysis and the simulation, and the lower panel shows the ratio for data separated into high and low luminosity runs. Statistical uncertainties are smaller than most of the points.

Figure 2: Comparison between data (markers) and embedded simulation (histograms) of the dijet yield versus the invariant mass, at the detector level, for the different topology regions studied. The lower panel shows the ratio of the relative differences between data and the simulation.

Figure 3:Inclusive jet $A_{LL}$ versus $x_{T}$, compared to previous STAR results at $\sqrt{s}$ = 200 GeV \cite{JetsALL:2009,JetsALL:2015} and 510 GeV \cite{JetsALL:2012}, and evaluations from DSSV 2014 \cite{DSSV:2014} and NNPDFpol1.1 (with its uncertainty) \cite{NNPDF:2014} global analyses. The vertical lines are statistical uncertainties. The boxes show the size of the estimated systematic uncertainties. Scale uncertainties from polarization (not shown) are $\pm$6.5\%, $\pm$6.6\%, $\pm$6.4\% and $\pm$6.1\% from 2009 to 2015 respectively.

 
Figure 4: Sampled $x_1$ (solid) and $x_2$ (dashed) gluon distributions weighted by the partonic asymmetry for dijet events with detector level $M_{inv}$ in the range 12 $< M_{inv} <$ 14 GeV/$c^{2}$, obtained using the embedded simulation, for the topology A (the most asymmetric collision). A representation of the topological configuration relative to the beam line is shown.
 

 
 
Figure 5: Dijet $A_{LL}$ versus $M_{inv}$ for the A, B, C and D (top to bottom) topological configurations (explained in the text) compared to previous STAR results from 2012 data \cite{JetsALL:2012} and predictions from DSSV 2014 \cite{DSSV:2014} and NNPDFpol1.1 (with its uncertainty) \cite{NNPDF:2014} global analyses. The vertical lines are statistical uncertainties. The boxes show the size of the estimated systematic uncertainties. Topological configurations are shown for each jet orientation relative to the beam line. Scale uncertainties from polarization (not shown) are $\pm$6.6\% and $\pm$6.4\% for 2012 and 2013 respectively.

 

Summary:
In summary, we report a high precision measurement of the inclusive jet and dijet longitudinal double-spin asymmetry $A_{LL}$ in polarized proton collisions at $\sqrt{s}$ = 510 GeV and $|\eta| <$ 0.9, using the large data set collected by STAR in 2013. The results are consistent with previous STAR measurements and expectations from the latest global analyses, which included published RHIC data \cite{JetsALL:2009, DSSV:2014, NNPDF:2014}. The inclusive jet results will provide valuable new constraints on the magnitude of the gluon polarization, whereas the dijet results will have an impact on its functional form, in particular by using the topological configuration A that provides more precise data at low dijet invariant mass. These results provide sensitivity down to $x \sim$ 0.015, extending the kinematic coverage in future global analyses.


 

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