Measurement of Transverse Spin Transfer of Λ and Λ in … · 2017. 5. 14. · SPIN2016, UIUC,...

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SPIN2016, UIUC, Jincheng Mei Measurement of Transverse Spin Transfer of Λ and Λ in Transversely Polarized Proton+Proton Collisions at RHIC-STAR Jincheng Mei Shandong University & Brookhaven National Laboratory 1

Transcript of Measurement of Transverse Spin Transfer of Λ and Λ in … · 2017. 5. 14. · SPIN2016, UIUC,...

Page 1: Measurement of Transverse Spin Transfer of Λ and Λ in … · 2017. 5. 14. · SPIN2016, UIUC, Jincheng Mei Motivation The transverse spin transfer of ( ) can provide insights into

SPIN2016, UIUC, Jincheng Mei

Measurement of Transverse Spin Transfer of Λ and Λin Transversely Polarized Proton+Proton Collisions

at RHIC-STAR

Jincheng Mei Shandong University & Brookhaven National Laboratory

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Outline

✦ Motivation

✦ ( ) Reconstruction

✦ Measurement Method

✦ DTT measurement results

✦ Summary

⇤ ⇤̄

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SPIN2016, UIUC, Jincheng Mei

Motivation✦ The transverse spin transfer of ( ) can provide insights into transversely polarized

fragmentation function and transversity distribution.

✦ Transversity is one of the important pdfs to describe the transverse spin structure of nucleon.

✦ ( ) polarization can be extracted from the angular distribution of its decay product in its rest frame.

transversity distribution

transverse spin transfer

transversely polarized fragmentation function

pQCD calculation

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Sp

π- ! rest frame

θ*

θ* : the angle between decay particle (proton) momentum in !’s rest frame and the direction of ! polarization

⇤ ⇤̄

⇤ ⇤̄

α: decay parameter 0.642 for and -0.642 forP!: polarization of ( )⇤ ⇤̄

⇤ ⇤̄

Xu, Qing-hua et al.Phys.Rev. D73 (2006) 077503

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SPIN2016, UIUC, Jincheng Mei

✦ DTT : the spin transfer along the polarization of outgoing quark considering the rotation in scattering plane. In this analysis, reconstructed jet axis is used as substitute of the outgoing quark momentum direction

✦ Previous measurement of transverse spin transfer. -Only DNN spin transfer w.r.t. production plane (Fermilab E704 Collaboration,1997). DNN : spin transfer along normal direction of Λ production plane.

Definition of Transverse Spin Transfer

DTT

J.Collins et al, NPB420 (1994)565

Significant spin transfer was found at large xF.

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SPIN2016, UIUC, Jincheng Mei

RHIC - Relativistic Heavy Ion Collider

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✦ The Relativistic Heavy Ion Collider(RHIC) is the first and only polarized proton collider in the world.

✦ Data sample: transversely polarized P+P collision at  200GeV at STAR taken in 2012.✦ RHIC Beam polarization: blue beam: 64%, yellow beam: 58% (2012_PP200GeV)

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SPIN2016, UIUC, Jincheng Mei

STAR Detectors

✦ TPC : Time Projection Chamber " ~ (-1.2, 1.2) Track reconstruction of charged particles and charged particle identification.

✦ BEMC: Barrel Electromagnetic Calorimeter " ~ (-1.0, 1.0) For triggering.

STAR experiment detectors

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mass[GeV]1.08 1.09 1.1 1.11 1.12 1.13 1.14 1.15 1.160

20

40

60

80

100

120

140

310×h_im_L_J1_pT0

Fitted mean: 1.1154

Cand.: 489832Λ

Bkg Frac.: 0.079 Signal m : 1.111 ~ 1.119

h_im_L_J1_pT0

mass[GeV]1.08 1.09 1.1 1.11 1.12 1.13 1.14 1.15 1.160

10000

20000

30000

40000

50000

60000

70000

h_im_L_J1_pT1

Fitted mean: 1.1156

Cand.: 322603Λ

Bkg Frac.: 0.085 Signal m : 1.111 ~ 1.121

h_im_L_J1_pT1

mass[GeV]1.08 1.09 1.1 1.11 1.12 1.13 1.14 1.15 1.160

5000

10000

15000

20000

25000

30000

h_im_L_J1_pT2

Fitted mean: 1.1158

Cand.: 182517Λ

Bkg Frac.: 0.073 Signal m : 1.109 ~ 1.123

h_im_L_J1_pT2

mass[GeV]1.08 1.09 1.1 1.11 1.12 1.13 1.14 1.15 1.160

2000

4000

6000

8000

10000

12000

h_im_L_J1_pT3

Fitted mean: 1.1159

Cand.: 78022Λ

Bkg Frac.: 0.066 Signal m : 1.108 ~ 1.124

h_im_L_J1_pT3

mass[GeV]1.08 1.09 1.1 1.11 1.12 1.13 1.14 1.15 1.160

500

1000

1500

2000

2500

3000

3500

4000

h_im_L_J1_pT4

Fitted mean: 1.1162

Cand.: 32480Λ

Bkg Frac.: 0.071 Signal m : 1.106 ~ 1.126

h_im_L_J1_pT4

mass[GeV]1.08 1.09 1.1 1.11 1.12 1.13 1.14 1.15 1.160

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

h_im_L_J1_pT5

Fitted mean: 1.1166

Cand.: 20272Λ

Bkg Frac.: 0.084 Signal m : 1.104 ~ 1.128

h_im_L_J1_pT5

mass[GeV]1.08 1.09 1.1 1.11 1.12 1.13 1.14 1.15 1.160

20

40

60

80

100

120

140

310×h_im_L_J1_pT0

Fitted mean: 1.1154

Cand.: 489832Λ

Bkg Frac.: 0.079 Signal m : 1.111 ~ 1.119

h_im_L_J1_pT0

mass[GeV]1.08 1.09 1.1 1.11 1.12 1.13 1.14 1.15 1.160

10000

20000

30000

40000

50000

60000

70000

h_im_L_J1_pT1

Fitted mean: 1.1156

Cand.: 322603Λ

Bkg Frac.: 0.085 Signal m : 1.111 ~ 1.121

h_im_L_J1_pT1

mass[GeV]1.08 1.09 1.1 1.11 1.12 1.13 1.14 1.15 1.160

5000

10000

15000

20000

25000

30000

h_im_L_J1_pT2

Fitted mean: 1.1158

Cand.: 182517Λ

Bkg Frac.: 0.073 Signal m : 1.109 ~ 1.123

h_im_L_J1_pT2

mass[GeV]1.08 1.09 1.1 1.11 1.12 1.13 1.14 1.15 1.160

2000

4000

6000

8000

10000

12000

h_im_L_J1_pT3

Fitted mean: 1.1159

Cand.: 78022Λ

Bkg Frac.: 0.066 Signal m : 1.108 ~ 1.124

h_im_L_J1_pT3

mass[GeV]1.08 1.09 1.1 1.11 1.12 1.13 1.14 1.15 1.160

500

1000

1500

2000

2500

3000

3500

4000

h_im_L_J1_pT4

Fitted mean: 1.1162

Cand.: 32480Λ

Bkg Frac.: 0.071 Signal m : 1.106 ~ 1.126

h_im_L_J1_pT4

mass[GeV]1.08 1.09 1.1 1.11 1.12 1.13 1.14 1.15 1.160

200

400

600

800

1000

1200

1400

1600

1800

2000

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h_im_L_J1_pT5

Fitted mean: 1.1166

Cand.: 20272Λ

Bkg Frac.: 0.084 Signal m : 1.104 ~ 1.128

h_im_L_J1_pT5✦ Applied topological cuts to reconstruct and via their decay channels: and

and Reconstruction⇤̄ ! p̄⇡+⇤ ! p⇡�⇤ ⇤̄

⇤ ⇤̄

Raw yields of and after selection

PT [GeV/c]1~2 489832 5442122~3 322603 381872

3~4 182517 2014134~5 78022 743125~6 32480 262796~8 20272 13773

Total 1125726 1241861

Λ :PT 1~2 GeV/c Λ :PT 4~5 GeV/c

Background fraction is estimated by side bands.The obtained Draw and their statistical uncertainties were corrected for the residual background:

DTT =Draw

TT � rDbkgTT

1� r

�DTT =

r(�Draw

TT )2 +⇣r�Dbkg

TT

⌘2

1� r

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⇤ ⇤̄

⇤ ⇤̄

r : residual background fraction

Draw

Dbkg

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Jet Correlation✦ Use anti-Kt algorithm to reconstruct jet then make correlation to a ( )by calculating #R.✦ Request ηjet ~ (-0.7, 0.9), PT > 5.0 GeV/c, neutral fraction of Jet < 0.95.

If #R < 0.6 (near side), we use the jet momentum direction as outgoing quark direction to obtain quark’s polarization direction.

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⇤ ⇤̄

Λ :PT 2~3 GeV/c Λ :PT 4~5 GeV/c

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SPIN2016, UIUC, Jincheng Mei

Measurement Method

✦ Based on the relationship between polarization of ( ) and the angular distribution of its decay product in its rest frame. In this analysis, DTT is extracted from the asymmetry of ! counts with opposite beam polarization in a small cosθ* bin:Acceptance of reverse beam polarization is expected to be the same in each cosθ* bin, and thus cancelled.

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Pbeam : polarization of beam<cosθ*> : mean in each cosθ* bin : ( ) counts with positive beam polarization : ( ) counts with negative beam polarization R: relative luminosity

N"

N#⇤ ⇤̄⇤ ⇤̄

⇤ ⇤̄

DTT =

1

↵Pbeam < cos ✓⇤ >

N" � RN#

N"+ RN#

Page 10: Measurement of Transverse Spin Transfer of Λ and Λ in … · 2017. 5. 14. · SPIN2016, UIUC, Jincheng Mei Motivation The transverse spin transfer of ( ) can provide insights into

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Extraction of Spin Transfer DTT

✦ Separate the whole range of cosθ* into 20 bins.✦ Obtain a DTT in each bin. ✦ Fit the 20 DTT with a constant.✦ Fitted result as the DTT in the pT bin.

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✦ DTT extraction in each cosθ*

*θcos1− 0.5− 0 0.5 1

TTD

0.4−

0.2−

0

0.2

0.4

0.6 / ndf 2χ 21.91 / 19

p0 0.008131±0.008204 −

/ ndf 2χ 21.91 / 19

p0 0.008131±0.008204 −

>0|ALL )η:1~2GeV|phy. T

( L |PTTDDTT for Λ :PT 1~2 GeV/c

statistical uncertainty only

✦ The method passed the null check with

DTT =

1

↵Pbeam < cos ✓⇤ >

N" � RN#

N"+ RN#

Λ : pT 1~2 GeV/c, $ > 0positive beam polarization

N"

Λ : pT 1~2 GeV/c, $ > 0negative beam polarization

N#

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✦ 1.2% scale uncertainty from RHIC beam polarization measurement. ✦ 2% from decay parameter (0.642 ± 0.013). ✦ 0.012 from relative luminosity measurement.✦ Trigger bias estimated from MC simulation.✦ Residual background fraction estimation.✦ Pileup effect.

Systematic Uncertainty

Systematic Uncertainty Summary$ > 0 Trigger Bias Residual Background

fractionPileup effect Total Systematic

Uncertainty

pT[GeV/c]

1-2 1.98E-04 2.07E-03 1.05E-05 8.44E-06 8.22E-04 9.57E-04 1.20E-02 1.22E-02

2-3 3.47E-03 1.11E-04 9.45E-06 0.00E+00 1.13E-03 7.07E-04 1.25E-02 1.20E-02

3-4 6.62E-03 1.95E-03 1.49E-05 2.41E-05 1.08E-03 3.09E-04 1.38E-02 1.22E-02

4-5 1.87E-03 7.58E-03 1.12E-05 1.42E-04 2.99E-03 5.78E-04 1.25E-02 1.42E-02

5-6 2.07E-03 8.01E-03 9.61E-04 1.25E-04 3.11E-03 1.05E-03 1.26E-02 1.45E-02

6-8 4.39E-03 2.28E-02 3.08E-03 1.91E-03 3.42E-03 1.89E-03 1.36E-02 2.59E-02

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⇤ ⇤̄ ⇤ ⇤̄ ⇤ ⇤̄ ⇤ ⇤̄

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DTT Results from STAR measurement

$ < 0$ > 0

✦ Most precise measurement on ( ) polarization in P+P collision at RHIC, which reach pT ~8 GeV/c with statistical uncertainty of 0.04 .

✦ The dominant source of systematic uncertainty is from relative luminosity.✦ DTT of and are consistent with each other and consistent with zero within uncertainty.

✦ Results of transverse spin transfer DTT of and in P+P collision at 200GeV.

STAR Preliminary STAR Preliminary

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⇤ ⇤̄

⇤ ⇤̄

⇤ ⇤̄

feed-down contribution included feed-down contribution included

Page 13: Measurement of Transverse Spin Transfer of Λ and Λ in … · 2017. 5. 14. · SPIN2016, UIUC, Jincheng Mei Motivation The transverse spin transfer of ( ) can provide insights into

SPIN2016, UIUC, Jincheng Mei

✦ First measurement on transverse spin transfer of ( ) in P+P collision, which can provide insights into transversely polarized fragmentation function and nucleon transversity distribution.

✦ The ( ) sample is the largest so far in P+P collision at RHIC and the precision of DTT is ~0.04 at ( ), which reach pT ~8 GeV/c.

✦ DTT of and are consistent with each other and consistent with zero within uncertainty.

Summary

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⇤ ⇤̄

⇤ ⇤̄

⇤ ⇤̄⇤ ⇤̄

Page 14: Measurement of Transverse Spin Transfer of Λ and Λ in … · 2017. 5. 14. · SPIN2016, UIUC, Jincheng Mei Motivation The transverse spin transfer of ( ) can provide insights into

Thanks for Your Attention!

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Backup

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SPIN2016, UIUC, Jincheng Mei

DTT comparison two axises

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/[GeV]T

p1 2 3 4 5 6 7 8

TTD

0.3−

0.2−

0.1−

0

0.1

0.2

> 0η , physical Λ for TTD

Jet Axis

) AxisΛ(Λ

> 0η , physical Λ for TTD

/[GeV]T

p1 2 3 4 5 6 7 8

TTD

0.3−

0.2−

0.1−

0

0.1

0.2

> 0η , physical Λ for TTD

Jet Axis

) AxisΛ(Λ

> 0η , physical Λ for TTD

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Theory Predict

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Transverse polarization for transverse momentum pT ≧ 8 GeV/c in PP collisions at 200 GeV with one transversely polarized beam versus pseudorapidity " of the Positive " is taken along the polarized beam direction.

⇤̄

⇤̄Xu, Qing-hua et al.Phys.Rev. D73 (2006) 077503