1 / 27

Measurements of ΔG at PHENIX: Probing Gluon Spin Contribution to the Proton

This presentation focuses on the measurements of ΔG, the gluon spin contribution to the proton, at PHENIX. It covers topics such as relating ALL and ΔG, summary of ALL measurements at PHENIX, and probing ΔG at low-x. The talk also discusses the factorization of cross-sections and the extraction of ΔG from ALL measurements.

chidalgo
Télécharger la présentation

Measurements of ΔG at PHENIX: Probing Gluon Spin Contribution to the Proton

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. ΔG Measurements at PHENIX Scott Wolin University of Illinois at Urbana-Champaign RHIC & AGS Users’ Meeting 2013 2013 RHIC & AGS Annual Users' Meeting

  2. Outline • ΔG, gluon spin contribution to the proton • Relating ALL and ΔG • Summary of ALL measurements at PHENIX • Probing ΔG at low-x 2013 RHIC & AGS Annual Users' Meeting

  3. Proton Spin q+g orbital angular momentum • ΔG = gluon spin contribution Now • ΔΣ = quark spin contribution Next talk(Mikhail Stepanov) Sum the polarizations of gluons from all possible Bjorken-x 2013 RHIC & AGS Annual Users' Meeting

  4. ALL as the Observable • ALL = double longitudinal helicity asymmetry Each proton is polarized parallel(+) or antiparallel(-) to its momentum σ = cross section for same sign (++) or opposite sign (+-) protons to produce an observed final state. 2013 RHIC & AGS Annual Users' Meeting

  5. Factorize cross section fa,b=quark and gluon distribution functions Dhf=frag. function for partonic cross section from _____________pQCD 2013 RHIC & AGS Annual Users' Meeting

  6. Factorize Δ(cross section) Δ Δfa,b=polarized quark and gluon distribution functions Dhf=frag. function for Δ Δ partonic cross section from _________ ____pQCD 2013 RHIC & AGS Annual Users' Meeting

  7. ΔG from ALL • A final state that can be produced from qg or gg scattering will contain Δg in its factorization • Factorization allows a global analysis to input measured ALL to extract Δg(x). • Check that factorization is applicable at RHIC energies. 2013 RHIC & AGS Annual Users' Meeting

  8. Cross Section Comparison 200 GeV, π0, mid-rapidity 500 GeV, π0, mid-rapidity • ff Applicable over broad pT range within factorization scale uncertainty. 2013 RHIC & AGS Annual Users' Meeting

  9. Measuring ALL in PHENIX Final State particle yield from ++and +-crossings Relative Luminosity Beam Polarizations 2013 RHIC & AGS Annual Users' Meeting

  10. Longitudinal Data On Disk 2013 RHIC & AGS Annual Users' Meeting

  11. ALLπ0 Mid-rapidity Invariant mass spectrum Partonic Process Fraction Bjorken-x sensitivity 2013 RHIC & AGS Annual Users' Meeting

  12. ALLπ0 Mid-rapidity RelLumi Systematic Uncert. 2013 RHIC & AGS Annual Users' Meeting

  13. ALLπ+/- Mid-rapidity • Sensitivity to sign of ΔG • Δu>0 and Δd<0 • Duπ+ > Duπ- and Ddπ-> Ddπ+ 2013 RHIC & AGS Annual Users' Meeting

  14. ALLη Mid-rapidity • Couple ΔG with different flavor composition(FF) • In principle, a good check for consistency with ALLπ0 2013 RHIC & AGS Annual Users' Meeting

  15. ALLe Mid-rapidity arXiv:1209.3278 [hep-ex] 11/7/2019 11/7/2019 11/7/2019 2013 RHIC & AGS Annual Users' Meeting

  16. ALLe Comparison Extraction of best fit value of|ΔG/G| from data Broad curve with Δχ2=1 at|ΔG/G|~0.2. Predictions for various values of |ΔG/G| compared with measurement • With higher statistics this is a clean channel since electrons avoid the fragmentation function uncertainty altogether. • Even though not too sensitive to sign of ΔG, other channels suggest ΔG>0 2013 RHIC & AGS Annual Users' Meeting

  17. ALLπ0π0 Mid-rapidity 2013 RHIC & AGS Annual Users' Meeting

  18. DSSV++ ΔG From RHIC Data With addition of RHIC Run 9 data, DSSV++ now favors a positive gluon spin for 0.05<x<0.2 Node is disfavored. • Large uncertainty at low x may hide large contribution to ΔG • Need forward rapidity to access low x • But ALL expected to be small there • Minimizing systematic top priority 2013 RHIC & AGS Annual Users' Meeting

  19. Bjorken-x sensitivity at Forward Rapidity (MPC) xg~0.001 for π0- π0 xg~0.01 for single π0 2013 RHIC & AGS Annual Users' Meeting

  20. MPC Cluster ALL at √s=200 GeV Cluster Decomposition Until 2012, could not trigger on di-hadrons, limiting sensitivity at even lower-x 2013 RHIC & AGS Annual Users' Meeting

  21. MPC Electronics Upgrade • Fully digital trigger calculation (sharper turnon curve, high purity, etc.) • Can trigger on single hadrons • New ability (run12+13): trigger on di-hadrons so gain selectivity to x~10-3 • This range of x is unexplored in polarized pp! • Have a measurement already to extend sensitivity to x~0.01 • Would (will) be very exciting to make the first big dent here… Trigger Sum Separate Trigger Sum 2013 RHIC & AGS Annual Users' Meeting

  22. max signal expected from DSSV Challenging Measurement at Low-x Relative Luminosity Syst Error History • RL syst. uncert. O(10-3) • Run9 Stat uncert. O(10-3) • BUT • Forward asymmetry O(10-4) (expected) • On disk already: FOM 50x greater than run9, so new stat error will be O(10-4) • RL syst. uncert. hopefully also gets to O(10-4) 2013 RHIC & AGS Annual Users' Meeting

  23. ALLclusterProjections • On disk about 180 pb-1 available for a di-cluster(hadron) measurement. • Statistical errors are projected to drop from O(10-3) to O(10-4) • DSSV++ is increased from DSSV best fit, so ALL ~ O(10-4) very possible • We likely will not be prevented from seeing this due to lack of statistics • BUT the relative luminosity uncertainty will be the deciding factor if O(10-4) asymmetries can be observed. 2013 RHIC & AGS Annual Users' Meeting

  24. Relative Luminosity • R = ratio of lumi for same vs opposite sign helicity crossings crossings • Relative Luminosity is measured using coincidence counts in the BBC and the ZDC 11/7/2019 2013 RHIC & AGS Annual Users' Meeting

  25. ZDC vs BBC Comparison • BBC and ZDC sample different physics and have different cross sections. • If both track the true luminosity then ZDC/BBC=constant • Modulo the presence of a ZDC-BBC asymmetry • In practice a systematic variation is observed • Cannot be explained away as a true asymmetry • At √s=500 GeV, a ~10% variation is observed, at √s=200 GeV, a ~5% variation is seen • Conclusion: the zdc and bbc luminosities do not agree with each other at the 5-10% level ZDC rate/BBC rate χ2/DOF ~ 200 Crossing Number 2013 RHIC & AGS Annual Users' Meeting

  26. Estimate Systematic Uncertainty • Wrong luminosity means wrong relative luminosity • Uncertainties as of now are too large • Many effects could cause a non-physics based ALL to appear • Currently this happens to the tune of O(10-3) • Some new ideas are being studied (including using the FVTX) • May be possible to understand these fluctuations in luminosity monitoring and apply a correction • PHENIX is working to solve this problem • Additional studies being completed, please stay tuned! 2013 RHIC & AGS Annual Users' Meeting

  27. Summary • Single electron paper recently published (arXiv:1209.3278 [hep-ex]) • Mid-rapidity neutral pion publication in progress • Charged hadron publication ramping up • Cautious optimism on the issue of relative luminosity uncertainty. • Keep an eye out for updates over the coming weeks/months. 2013 RHIC & AGS Annual Users' Meeting

More Related