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Paper proposal: run15 DLL and DTT of Lambda Hyperon

Updated on Mon, 2023-12-04 06:17. Originally created by yiyu on 2022-09-18 03:43.

Title: Longitudinal and transverse spin transfer to $\Lambda$ and $\bar{\Lambda}$ hyperons in polarized p+p collisions at $\sqrt{s}=200$ $\mathrm{GeV}$

PAs: Yike Xu, Yi Yu, Qinghua Xu and Jinlong Zhang
Intended journal: Phys. Rev. D

Abstract:

 
The longitudinal and transverse spin transfers to $\Lambda$ ($\overline{\Lambda}$) hyperons in polarized proton-proton collisions are expected to be sensitive to the helicity and transversity distributions, respectively, of (anti-)strange quarks in the proton, and to the corresponding polarized fragmentation functions. We report improved measurements of the longitudinal spin transfer coefficient to $\Lambda$ and $\overline{\Lambda}$, $\DLL$, and the transverse spin transfer coefficient to $\Lambda$ and $\overline{\Lambda}$, $\DTT$, in  polarized proton-proton collisions at $\sqrt{s}$= 200 GeV by the STAR experiment at RHIC. The data set includes longitudinally polarized proton-proton collisions with an integrated luminosity of 52 pb$^{-1}$, and transversely polarized proton-proton collisions with a similar integrated luminosity. Both data sets have about twice the figure-of-merit of previous results and cover a kinematic range of hyperon $|\eta|$ $<$ 1.2 and transverse momentum $\pth$ up to 8 $\GeV/c$. We also report the first measurements of the hyperon spin transfer coefficients $\DLL$ and $\DTT$ versus the fractional momentum $z$ of the hyperon within a jet, which can provide more direct constraints on the polarized fragmentation functions.

Conclusions:

1) Improved measurements on longitudinal spin transfer D_LL for Lambda and anti-Lambda hyperons versus hyperon pT in p+p collisions at 200 GeV from STAR 2015 dataset, with twice the statistics of the previously published run9 results. The new results are consistent with previous measurements. D_LL may provide information for the strange quark helicity distributions and the polarized fragmentation functions.
2) The first measurement of D_LL  versus hyperon’s fractional momentum z within a jet in p+p collisions at 200 GeV, which directly probes the longitudinally polarized fragmentation function.  The results are in agreement with model calculations. 
3) Improved measurements on transverse spin transfer D_TT for Lambda and anti-Lambda hyperons versus hyperon pT in p+p collisions at 200 GeV from STAR 2015 dataset, with twice the statistics of the previously published run12 results. The new results are consistent with previous measurements. D_TT is  sensitive to strange quark transversity distributions and the polarized fragmentation functions.
4) The first measurement of D_TT  versus hyperon’s fractional momentum z within a jet in p+p collisions at 200 GeV, which provides direct probe to the transversely polarized fragmentation function.

Analysis Notes:
drupal.star.bnl.gov/STAR/starnotes/private/PSN0809

Analysis Codes: offline/paper/psn0809


Paper draft:
2023-08-09 last version before institutional review
2023-09-08 Updates based on comments from institutional review 
2023-09-13 Updates based on comments from GPC
2023-09-18 Minor update based suggestion from Frank before announcing to RHIC
2023-11-30 Phys. Rev. D accepted version
 
Presentations:
PWGC Preview
for $D_{LL}$:
$D_{LL}$ vs $p_T$ preliminary request page: preliminary request
$D_{LL}$ vs $z$ preliminary request page: preliminary request

for $D_{TT}$:
$D_{TT}$ vs $p_T$ preliminary request page: preliminary request
$D_{TT}$ vs $z$ preliminary request page: preliminary request

Reply to institutional review
2023-09-04
Reply to Creghton group
Reply to AGH UST
Reply to Valparaiso University
2023-09-07
Reply to NCKU

2023-09-13
Reply to Creghton group
Reply to AGH UST
Reply to Valparaiso University
Reply to NCKU


Figures:

Figure 1: Invariant mass spectra of $\Lambda$ (closed circles) and $\overline{\Lambda}$ (open circles) candidates with $1< \pt < 8$ GeV$/c$  from (a) longitudinally and (b) transversely polarized proton-proton collisions at $\sqrt{s} = 200$ GeV.

Figure 2: The correlation of jet momentum fraction $z$ carried by $\Lambda$ (upper panels) and $\overline{\Lambda}$ (lower panels) at particle level and detector level, for jet triggers JP1 (left) and JP2 (right). The red points give the mean values of ``detector $z$" and ``particle $z$" in each bin while the error bars represent the standard derivations. The dashed lines at $y=x$ are for guidance.


Figure 3: (a) Longitudinal spin transfer coefficient $\DLL$ of $\Lambda$ and $\overline{\Lambda}$ as a function of cos\theta for hyperons with $3 < \pth < 4$ $\GeV/c$. (b) Transverse spin transfer coefficient $\DTT$ of $\Lambda$ and $\overline{\Lambda}$ as a function of cos\theta for hyperons with momentum fraction $0.5 < z < 0.7$.

Figure 4: Longitudinal spin transfer coefficient $\DLL$ of $\Lambda$ and $\overline{\Lambda}$ as a function of hyperon $p_T$ in proton-proton collisions at $\sqrt{s}=200$ $\GeV$. The top and bottom panels show the results for positive and negative hyperon $\eta$ regions, respectively. The vertical bars and boxes indicate the statistical and systematic uncertainties, respectively. The $\overline{\Lambda}$ results have been slightly offset horizontally for clarity.


Figure 5: (a) Comparison of longitudinal spin transfer coefficient $D_{LL}$ as a function of the hyperon $\pt$ for positive $\eta$ with previously published results. (b) Upper sub-panel: combined results of $D_{LL}$ for positive $\eta$ from current and previous measurements, in comparison with theoretical prediction; Lower sub-panel: the $\Lambda + \overline{\Lambda}$ combined results, in comparison with theoretical predictions.

(c) Combined results of $D_{LL}$ for negative $\eta$ from current and previous measurements. The previously published results in panel (a) and the results of $\overline{\Lambda}$ in all panels are slightly shifted for clarity. 



Figure 6: Longitudinal spin transfer coefficient $\DLL$ as a function of momentum fraction $z$ in a jet in proton-proton collisions at $\sqrt{s}=200$ $\GeV$ compared with theoretical calculations. Panels (a) and (b) show the results for positive and negative jet eta, respectively. The average jet $\pt$ at the particle level in each $z$ bin is shown in panel (c). 

Here the differences of $z$ value for $\Lambda$ and $\overline\Lambda$ along the horizontal axis reflect their average $z$ in that bin after the correction to particle level, not an artificial offset.



Figure 7: Transverse spin transfer coefficient $\DTT$ as a function of hyperon $p_T$ in proton-proton collisions at $\sqrt{s}=200$ $\GeV$ at STAR. The top and bottom panels show the results for positive and negative hyperon eta, respectively. The $\overline{\Lambda}$ results have been slightly offset horizontally for clarity.

Figure 8: (a) Comparison of transverse spin transfer coefficient $D_{TT}$ versus hyperon $\pt$ for positive $\eta$ with previously published results. (b) Combined results of $D_{TT}$ for positive $\eta$ from current and previous measurements, in comparison with theoretical predictions. (c) Combined results of $D_{TT}$ for negative $\eta$ from current and previous measurements.The previously published results and the results of $\overline{\Lambda}$ in this measurement are slightly shifted horizontally for clarity.

Figure 9: Transverse spin transfer coefficient $\DTT$ as a function of momentum fraction $z$ in a jet at $\sqrt{s}=200$ $\GeV$. The panels (a) and (b) show the results for positive and negative jet eta, respectively.The average jet pt at particle level in each $z$ bin is shown in panel (c). Here the differences of $z$ value for $\Lambda$ and $\overline\Lambda$ along the horizontal axis reflect their average $z$ in that bin after the correction to particle level, not an artificial offset.

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