Measurement of longitudinal spin asymmetries for weak boson
production in polarized proton-proton collisions at RHIC

Submitted to Phys. Rev. Lett.
arXiv: 1404.6880
STAR run 2011 + 2012 pp510 data
Luminosity = 9 + 77 pb-1
Beam polarization = 0.49 (2011), 0.56 (2012)

Figure 1: ETe distribution of W+/- candidate events, background contributions, and sum of backgrounds and W → eν MC signal.



Electron |eta|<0.5
ET Z/gamma->ee W->tau->e second EEMC Data driven QCD W->enu MC Data Data Err
15 1.73 2.64 36.00 53.08 1.06 99.00 9.95
17 0.85 3.58 24.00 29.30 1.76 55.00 7.42
19 1.41 3.58 13.00 17.72 2.51 35.00 5.92
21 1.43 3.07 10.00 9.75 3.78 36.00 6.00
23 1.55 2.83 6.00 5.13 5.98 25.00 5.00
25 1.26 2.27 4.00 4.04 9.28 21.00 4.58
27 0.96 2.17 3.00 2.19 10.06 20.00 4.47
29 1.65 1.95 4.00 1.98 16.47 24.00 4.90
31 0.44 0.99 0.00 1.39 24.95 24.00 4.90
33 1.06 1.26 2.00 0.82 31.36 42.00 6.48
35 1.57 0.14 1.00 0.31 44.05 53.00 7.28
37 1.43 0.42 3.00 0.57 58.39 65.00 8.06
39 0.30 0.49 1.00 0.38 59.02 61.00 7.81
41 1.36 0.07 1.00 0.34 35.38 29.00 5.39
43 0.74 0.07 0.00 0.08 16.47 22.00 4.69
45 0.76 0.00 0.00 0.05 7.77 8.00 2.83
47 0.31 0.00 0.00 0.16 4.01 7.00 2.65
49 0.30 0.00 0.00 0.00 1.74 2.00 1.41
51 0.15 0.00 0.00 0.15 1.27 4.00 2.00
53 0.00 0.00 0.00 0.13 0.78 3.00 1.73
55 0.07 0.00 0.00 0.08 0.50 3.00 1.73
57 0.00 0.00 0.00 0.06 0.69 0.00 0.00
59 0.08 0.00 0.00 0.00 0.07 1.00 1.00
61 0.00 0.00 0.00 0.00 0.22 2.00 1.41
63 0.00 0.00 0.00 0.00 0.21 0.00 0.00
65 0.00 0.00 0.00 0.06 0.00 0.00 0.00

Electron 0.5<|eta|<1.1
ET Z/gamma->ee W->tau->e second EEMC Data driven QCD W->enu MC Data Data Err
15 1.64 2.82 118.00 68.19 2.52 180.00 13.42
17 1.64 2.63 50.00 36.22 4.35 108.00 10.39
19 1.99 2.75 24.00 19.98 7.04 83.00 9.11
21 1.06 3.30 19.00 9.79 8.92 48.00 6.93
23 1.42 2.54 10.00 6.26 11.57 42.00 6.48
25 1.07 2.60 9.00 3.41 14.99 48.00 6.93
27 0.74 2.18 3.00 3.54 20.75 39.00 6.24
29 0.61 1.27 5.00 1.24 24.99 35.00 5.92
31 1.04 1.41 2.00 1.16 27.36 44.00 6.63
33 0.29 0.64 4.00 0.80 34.93 52.00 7.21
35 0.60 0.70 1.00 0.44 42.09 45.00 6.71
37 0.46 0.35 0.00 0.37 44.31 48.00 6.93
39 0.81 0.21 3.00 0.68 42.94 38.00 6.16
41 0.74 0.00 2.00 0.55 27.15 37.00 6.08
43 0.47 0.00 2.00 0.56 12.18 22.00 4.69
45 0.37 0.00 0.00 0.19 5.48 13.00 3.61
47 0.67 0.00 0.00 0.07 2.40 2.00 1.41
49 0.37 0.00 0.00 0.00 1.53 7.00 2.65
51 0.07 0.00 0.00 0.00 0.77 2.00 1.41
53 0.00 0.00 0.00 0.01 0.72 0.00 0.00
55 0.00 0.00 0.00 0.08 0.14 1.00 1.00
57 0.00 0.00 0.00 0.00 0.21 1.00 1.00
59 0.07 0.00 0.00 0.13 0.00 0.00 0.00
61 0.00 0.00 0.00 0.00 0.15 0.00 0.00
63 0.00 0.00 0.00 0.00 0.07 0.00 0.00
65 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Positron |eta|<0.5
ET Z/gamma->ee W->tau->e second EEMC Data driven QCD W->enu MC Data Data Err
15 1.45 13.80 44.00 105.73 14.83 180.00 13.42
17 1.14 17.54 25.00 58.95 22.57 125.00 11.18
19 0.52 14.19 20.00 35.40 35.63 98.00 9.90
21 1.06 12.82 5.00 19.36 54.11 108.00 10.39
23 1.13 14.43 9.00 10.32 71.59 103.00 10.15
25 0.89 12.90 5.00 7.82 94.12 136.00 11.66
27 1.14 9.82 4.00 4.34 119.84 149.00 12.21
29 0.88 7.32 3.00 3.87 143.70 164.00 12.81
31 0.97 4.59 2.00 2.79 167.51 174.00 13.19
33 0.30 3.62 2.00 1.60 197.24 184.00 13.56
35 1.23 1.56 4.00 0.63 218.45 210.00 14.49
37 1.04 2.00 1.00 1.13 234.27 232.00 15.23
39 2.01 0.70 1.00 0.77 209.74 167.00 12.92
41 0.60 0.29 3.00 0.63 125.71 129.00 11.36
43 1.20 0.07 0.00 0.16 60.31 75.00 8.66
45 0.97 0.07 0.00 0.09 28.24 39.00 6.24
47 0.22 0.00 0.00 0.33 15.33 17.00 4.12
49 0.23 0.00 0.00 0.00 8.96 7.00 2.65
51 0.07 0.00 1.00 0.28 5.62 12.00 3.46
53 0.30 0.00 1.00 0.28 2.75 3.00 1.73
55 0.16 0.00 0.00 0.18 2.48 1.00 1.00
57 0.00 0.00 0.00 0.14 1.63 1.00 1.00
59 0.15 0.00 0.00 0.00 1.28 0.00 0.00
61 0.00 0.00 0.00 0.00 0.84 0.00 0.00
63 0.00 0.00 0.00 0.00 0.49 1.00 1.00
65 0.00 0.00 0.00 0.14 0.49 0.00 0.00

Positron 0.5<|eta|<1.1
ET Z/gamma->ee W->tau->e second EEMC Data driven QCD W->enu MC Data Data Err
15 2.13 9.92 134.00 105.01 26.87 290.00 17.03
17 1.64 10.94 66.00 52.59 37.89 157.00 12.53
19 0.74 11.80 31.00 29.19 47.35 134.00 11.58
21 1.44 9.71 31.00 15.04 58.53 132.00 11.49
23 0.67 8.26 19.00 9.02 64.47 96.00 9.80
25 0.46 6.40 8.00 5.77 65.80 114.00 10.68
27 0.89 6.31 8.00 4.75 76.72 97.00 9.85
29 1.11 5.09 5.00 1.60 80.08 93.00 9.64
31 0.74 3.56 5.00 1.30 86.88 122.00 11.05
33 0.90 3.39 3.00 1.31 97.46 140.00 11.83
35 0.96 1.62 2.00 0.79 121.51 138.00 11.75
37 0.52 0.64 1.00 0.23 143.92 143.00 11.96
39 0.74 0.50 2.00 0.42 137.31 125.00 11.18
41 0.61 0.07 2.00 0.58 80.73 71.00 8.43
43 1.06 0.15 1.00 0.39 35.09 51.00 7.14
45 1.05 0.07 2.00 0.25 16.89 29.00 5.39
47 0.37 0.07 0.00 0.08 9.30 12.00 3.46
49 0.15 0.00 0.00 0.00 5.58 10.00 3.16
51 0.22 0.00 1.00 0.00 3.40 3.00 1.73
53 0.00 0.00 0.00 0.06 2.13 1.00 1.00
55 0.07 0.00 0.00 0.09 1.92 2.00 1.41
57 0.00 0.00 0.00 0.00 0.64 3.00 1.73
59 0.00 0.00 0.00 0.01 0.71 1.00 1.00
61 0.00 0.00 0.00 0.00 0.21 1.00 1.00
63 0.00 0.00 0.00 0.00 0.14 1.00 1.00
65 0.00 0.00 0.00 0.00 0.29 0.00 0.00

Figure 2: (a) Signed PT-balance distribution for e± candidates reconstructed in the EEMC and (b) distribution of the product of the TPC reconstructed charge sign and ET/pT.



(a) Signed pT-balance
Signed pT-balance Data Z->ee W->tau->e QCD W->enu MC
-30 0.00 ± 0.00 0.00 0.00 0.00 0.00
-26 0.00 ± 0.00 0.00 0.00 1.41 1.41
-22 0.00 ± 0.00 0.29 0.00 1.71 1.71
-18 0.00 ± 0.00 0.22 0.00 0.22 0.22
-14 4.00 ± 2.00 0.68 0.00 4.92 4.92
-10 4.00 ± 2.00 0.98 0.00 2.39 2.39
-6 6.00 ± 2.45 1.94 0.00 1.94 1.94
-2 6.00 ± 2.45 1.91 0.00 10.39 10.46
2 11.00 ± 3.32 2.00 0.00 13.30 13.45
6 7.00 ± 2.65 1.19 0.07 4.08 4.22
10 7.00 ± 2.65 0.91 0.15 5.30 5.58
14 8.00 ± 2.83 0.00 0.07 4.31 4.67
18 8.00 ± 2.83 0.07 0.00 5.73 6.22
22 10.00 ± 3.16 0.00 0.21 3.04 5.74
26 27.00 ± 5.20 0.83 1.14 1.96 20.02
30 35.00 ± 5.92 0.44 0.71 1.15 21.80
34 35.00 ± 5.92 0.00 0.56 0.56 23.28
38 20.00 ± 4.47 0.07 0.07 0.14 23.59
42 6.00 ± 2.45 0.00 0.00 0.00 15.58
46 1.00 ± 1.00 0.16 0.00 0.16 2.81
50 0.00 ± 0.00 0.07 0.00 0.07 0.58
54 0.00 ± 0.00 0.00 0.00 0.00 0.14
58 0.00 ± 0.00 0.00 0.00 0.00 0.07

(b) Charge Separation
Q*ET/pT Data e- e+
-2.9 0.00 ± 0.00 1.09 0.01
-2.7 1.00 ± 1.00 1.34 0.01
-2.5 1.00 ± 1.00 1.60 0.02
-2.3 2.00 ± 1.41 1.90 0.03
-2.1 0.00 ± 0.00 2.29 0.06
-1.9 4.00 ± 2.00 2.96 0.09
-1.7 4.00 ± 2.00 4.24 0.14
-1.5 9.00 ± 3.00 6.39 0.21
-1.3 10.00 ± 3.16 9.12 0.31
-1.1 9.00 ± 3.00 11.34 0.44
-0.9 14.00 ± 3.74 11.81 0.60
-0.7 11.00 ± 3.32 10.19 0.79
-0.5 9.00 ± 3.00 7.42 1.01
-0.3 5.00 ± 2.24 4.78 1.30
-0.1 7.00 ± 2.65 2.99 1.73
0.1 9.00 ± 3.00 2.01 2.57
0.3 5.00 ± 2.24 1.49 4.24
0.5 8.00 ± 2.83 1.18 6.97
0.7 9.00 ± 3.00 0.93 10.16
0.9 16.00 ± 4.00 0.73 12.32
1.1 13.00 ± 3.61 0.56 12.11
1.3 9.00 ± 3.00 0.42 9.64
1.5 10.00 ± 3.16 0.30 6.39
1.7 3.00 ± 1.73 0.21 3.76
1.9 2.00 ± 1.41 0.15 2.21
2.1 1.00 ± 1.00 0.10 1.44
2.3 0.00 ± 0.00 0.07 1.05
2.5 1.00 ± 1.00 0.04 0.79
2.7 1.00 ± 1.00 0.03 0.60
2.9 0.00 ± 0.00 0.02 0.44

Figure 3: Distribution of the invariant mass of Z/γ* → e+ e- candidate events,with MC for comparison.



Z invariant mass
Mass(GeV) Data MC
25 0.00 ± 0.00 0.00
27 0.00 ± 0.00 0.00
29 2.00 ± 1.41 0.48
31 1.00 ± 1.00 1.47
33 2.00 ± 1.41 2.12
35 1.00 ± 1.00 2.34
37 3.00 ± 1.73 2.03
39 1.00 ± 1.00 1.72
41 0.00 ± 0.00 2.17
43 4.00 ± 2.00 1.53
45 0.00 ± 0.00 1.30
47 3.00 ± 1.73 1.14
49 1.00 ± 1.00 1.78
51 0.00 ± 0.00 0.64
53 0.00 ± 0.00 0.80
55 0.00 ± 0.00 0.32
57 2.00 ± 1.41 1.07
59 1.00 ± 1.00 0.57
61 1.00 ± 1.00 1.39
63 4.00 ± 2.00 0.57
65 1.00 ± 1.00 0.64
67 1.00 ± 1.00 0.72
69 1.00 ± 1.00 1.12
71 1.00 ± 1.00 0.72
73 1.00 ± 1.00 1.14
75 3.00 ± 1.73 1.79
77 1.00 ± 1.00 1.31
79 4.00 ± 2.00 1.88
81 4.00 ± 2.00 2.59
83 6.00 ± 2.45 4.14
85 15.00 ± 3.87 8.60
87 9.00 ± 3.00 12.19
89 11.00 ± 3.32 20.92
91 14.00 ± 3.74 17.92
93 4.00 ± 2.00 9.65
95 7.00 ± 2.65 2.24
97 3.00 ± 1.73 1.14
99 2.00 ± 1.41 0.31
101 1.00 ± 1.00 0.32
103 1.00 ± 1.00 0.33
105 0.00 ± 0.00 0.23
107 0.00 ± 0.00 0.16
109 1.00 ± 1.00 0.49
111 0.00 ± 0.00 0.00
113 0.00 ± 0.00 0.08
115 0.00 ± 0.00 0.08
117 0.00 ± 0.00 0.00
119 0.00 ± 0.00 0.00

Figure 4: Longitudinal single-spin asymmetry AL for W production as a function of lepton pseudorapidity.



STAR W+ AL
Eta avr Eta rms asym avr value Asym low limit Asym up limit Asym avr error
-1.18 0.17 0.009 -0.223 0.249 0.241
-0.72 0.15 -0.239 -0.296 -0.181 0.057
-0.25 0.14 -0.343 -0.389 -0.298 0.045
0.25 0.14 -0.429 -0.475 -0.384 0.045
0.72 0.15 -0.472 -0.528 -0.416 0.056
1.18 0.17 -0.649 -0.863 -0.426 0.218

STAR W- AL
Eta avr Eta rms asym avr value Asym low limit Asym up limit Asym avr error
-1.22 0.16 0.195 -0.045 0.431 0.238
-0.76 0.15 0.247 0.148 0.347 0.100
-0.26 0.15 0.280 0.176 0.383 0.104
0.26 0.15 0.202 0.097 0.305 0.104
0.76 0.15 0.391 0.292 0.490 0.099
1.22 0.16 0.182 -0.069 0.425 0.247

Relative luminosity uncertainty: 0.007
Beam polarizatoin scale uncertainty: 3.4%

Theory: W+/- AL
Eta avr W+ DSSV08 RHICBOS W+ DSSV08 CHE NLO W+ LSS10 CHE NLO W- DSSV08 RHICBOS W- DSSV08 CHE NLO W- LSS10 CHE NLO
-1.75 -0.186 -0.173 -0.145 0.003 0.013 0.070
-1.25 -0.236 -0.225 -0.195 -0.011 0.000 0.082
-0.75 -0.280 -0.267 -0.239 -0.011 -0.003 0.096
-0.25 -0.327 -0.316 -0.286 0.040 0.043 0.132
0.25 -0.378 -0.369 -0.353 0.161 0.159 0.225
0.75 -0.418 -0.419 -0.412 0.286 0.281 0.350
1.25 -0.447 -0.467 -0.477 0.379 0.382 0.468
1.75 -0.507 -0.522 -0.558 0.447 0.450 0.583



Figure 5: Longitudinal double-spin asymmetry ALL for W production as a function of lepton pseudorapidity.



STAR W+ ALL
Eta avr Eta rms asym avr value Asym low limit Asym up limit Asym avr error
0.25 0.14 -0.053 -0.137 0.031 0.084
0.72 0.15 0.134 0.029 0.238 0.104
1.18 0.17 0.088 -0.341 0.514 0.428

STAR W- ALL
Eta avr Eta rms asym avr value Asym low limit Asym up limit Asym avr error
0.26 0.15 -0.207 -0.394 -0.018 0.188
0.76 0.15 0.168 -0.015 0.348 0.181
1.22 0.16 -0.169 -0.588 0.253 0.421

Beam polarizatoin scale uncertainty: 6.5%

Theory: W+/- ALL
Eta avr W+ DSSV08 CHE NLO W- DSSV08 CHE NLO
0.25 0.077 -0.018
0.75 0.073 -0.011
1.25 0.069 -0.002