Measurement Of Longitudinal Single Spin …Measurement Of Longitudinal Single-Spin Asymmtry, A L For...

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Measurement Of Longitudinal Single-Spin Asymmtry, A L For W Boson Production In Polarized P+P Collisions At RHIC Devika Gunarathne [Temple University, STAR collaboration] ――――INTRODUCTION RESULTS EXPERIMENT ANALYSIS ~ 30% ΔΣ = ( Δu + Δd + Δs + Δ u + Δ d + Δ s ) dx Quark / antiquark Contribution spin sum rule SPIN STRUCTURE OF THE PROTON < S p >= 1 2 = 1 2 ΔΣ + ΔG + L polarized beam proton proton polarized beam unpolarized beam proton probing d quark proton collision zone polarized beam unpolarized beam proton W - e- probing d quark proton collision zone polarized beam unpolarized beam proton W - e- e- probing u quark probing d quark proton collision zone polarized beam unpolarized beam proton W - e- e- e- probing u quark probing quark sum (u+d) proton collision zone polarized beam unpolarized beam proton W - W Boson Production in polarized p+p collisions Maximum parity violation No fragmentation involve. Easy detection DSSV global analysis of helicity PDF Direct access to Δq / Δq Endcap Electro-Magnetic Calorimeter (EEMC) Barrel Electro-Magnetic Calorimeter (BEMC) Time Projection Chamber (TPC) Beam - Beam Counter (BBC) Forward Gem Tracker (FGT) Magnet STAR Detector TPC : -1.3 < η < +1.3 , Tracking and Particle ID BEMC : -1.0 < η < +1.0 EEMC : +1.1 < η < +2.0 Barrel and Endcap 2π calorimetry BBC / ZDC : Relative Luminosity Calorimeter response from a simulated QCD type di-jet background event W candidate tracks as a function of transverse Energy Reconstruction of W bosons from decay electron and positrons Calorimeter response from a simulated W event Isolated high energetic TPC tracks pointing to calorimeter tower. Energy from the maximum 2x2 cluster. Undetected neutrino leads to large opposite missing energy , large imbalance in the transverse momentum. Transverse plane views ptBalance 4pi - nearCone electron nearCone ΔR =0.7 E T ΔR < 0.7 E e T / E T ΔR < 0.7 > 88% 4X4 TPC track extrapolated to Barrel colorimeter tower grid E e T Cuts designed to take the advantage of topological difference between W and QCD type BG event ! p T balance = ! p T e + ! p T jets ΔR>0.7 E e T / E T 4X4 > 95% TPC Charge sign separation Background Estimation QCD BG using data driven procedure Electroweak BG (W->tau, Z- >e + /e - ) using MC simulation W - W + STAR Run 2013 W AL Projections STAR Run 2012 W AL Published Results 6r 2 0 6d(x,Q 2 ) dx 1 0.05 DSSV+ DSSV++ w/ proj. W data DSSV++ w/ STAR W data Q 2 = 10 GeV 2 DSSV 6r 2 =2% 0 5 10 15 -0.08 -0.06 -0.04 -0.02 0 0.02 A L = 1 P 1 N ++ + N +N −− N + N ++ + N ++ N −− + N + A L = σ + σ σ + + σ single spin asymmetry = TPC BEMC EEMC FGT Y Z η=-1.1 η=-0.5 η=0 η=+0.5 η=+1.1 1 2 3 4 DSSV++ Global Analysis includes published STAR W AL Results NNPDF analysis of anti U quark polarization. 6r 2 0 6u(x,Q 2 ) dx 1 0.05 DSSV+ DSSV++ w/ proj. W data DSSV++ w/ STAR W data DSSV 6r 2 =2% 0 5 10 15 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 Impact of Recent STAR W AL Results on Recent Global Analyses and Predictions for future STAR Results CONCLUSION Large uncertainty for sea quark polarization Large anti u quark polarization than theoretical prediction Large data set in run 2013 expect to reduce uncertainty further The production of W bosons in polarized P+P collisions provides an excellent way to study the spin and flavor asymmetries of the proton quark and antiquark distributions. STAR has measured the parity violating single spin asymmetry A L for pseudo- rapidity between -1.4 and +1.4 from STAR 2012 and 2011 data providing the first detailed look at the asymmetries η dependance. STAR 2012 W A L results provide significant constraints on anti u and anti d quark polarizations. Large data set of STAR 2013 is being analyzed currently in mid rapidity region (pseudo-rapidity between -1.0 and +1.0) and expects results reduce uncertainty further. High precision results from STAR 2013 data will improve he constraints on the anti u and anti d quark polarizations. ———— - Candidate track and BEMC cluster reconstructed. BLUE - E e T > 14 GeV and E e T / E 4x4 T > 0.95 Green - E e T / E ΔR<0.7 T > 0.88 Red - sign PT balance cut > 14 GeV W + W -
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Transcript of Measurement Of Longitudinal Single Spin …Measurement Of Longitudinal Single-Spin Asymmtry, A L For...

  • Measurement Of Longitudinal Single-Spin Asymmtry, AL For W Boson Production In Polarized P+P Collisions At RHIC

    Devika Gunarathne [Temple University, STAR collaboration]

    ――――↽

    INTRODUCTION RESULTS

    EXPERIMENT

    ANALYSIS

    ~ 30%ΔΣ = (Δu+Δd +Δs+Δu +Δd +Δs )∫ dx

    Quark / antiquark Contribution

    spin sum rule

    SPIN STRUCTURE OF THE PROTON

    < Sp >=12=12ΔΣ+ΔG + L

    polarizedbeam

    proton proton

    polarizedbeam

    unpolarizedbeam

    proton

    probingd quark

    protoncollision zone

    polarizedbeam

    unpolarizedbeam

    proton

    W-

    e-probingd quark

    protoncollision zone

    polarizedbeam

    unpolarizedbeam

    proton

    W-

    e- e-probingu quark

    probingd quark

    protoncollision zone

    polarizedbeam

    unpolarizedbeam

    proton

    W-

    e-

    e-

    e-probingu quark

    probingquark sum (u+d)

    protoncollision zone

    polarizedbeam

    unpolarizedbeam

    proton

    W-

    W Boson Production in polarized p+p collisions

    •Maximum parity violation•No fragmentation involve.

    •Easy detection

    DSSV global analysis of helicity PDF

    •Direct access to Δq / Δq

    Endcap Electro-Magnetic Calorimeter (EEMC)

    Barrel Electro-Magnetic Calorimeter (BEMC)

    Time Projection Chamber (TPC)

    Beam - Beam Counter (BBC)

    Forward Gem Tracker (FGT)

    Magnet

    STAR Detector

    TPC : -1.3 < η < +1.3 , Tracking and Particle ID

    BEMC : -1.0 < η < +1.0 EEMC : +1.1 < η < +2.0

    Barrel and Endcap 2π calorimetry

    BBC / ZDC : Relative Luminosity

    Calorimeter response from a simulated QCD type di-jet background event

    W candidate tracks as a function of transverse EnergyReconstruction of W bosons from decay electron and positrons

    Calorimeter response from a simulated W event

    • Isolated high energetic TPC tracks pointing to calorimeter tower. Energy from the maximum 2x2 cluster.

    •Undetected neutrino leads to large opposite missing energy , large imbalance in the transverse momentum.

    Transverse plane views

    ptBalance4pi -

    nearCone

    electr

    on

    nearCone ΔR =0.7

    ETΔR < 0.7

    EeT / ETΔR < 0.7 > 88%

    4X4

    TPC track extrapolated to Barrel colorimeter tower grid

    EeT

    •Cuts designed to take the advantage of topological difference between W and QCD type BG event

    !pTbalance =

    !pTe +

    !pTjets

    ΔR>0.7∑

    EeT / ET4X4 > 95%

    TPC Charge sign separation

    Background Estimation

    •QCD BG using data driven procedure

    •Electroweak BG (W->tau, Z->e+/e-) using MC simulation

    W-W+

    STAR Run 2013 W AL Projections

    STAR Run 2012 W AL Published Results

    2

    d(x,Q2) dx1

    0.05

    DSSV+

    DSSV++w/ proj. W data

    DSSV++w/ STAR W data

    Q2 = 10 GeV2

    DSSV2=2%

    0

    5

    10

    15

    -0.08 -0.06 -0.04 -0.02 0 0.02

    AL =1P1N++ + N+− − N−− − N−+N++ + N+− + N−− + N−+

    AL =σ + −σ −

    σ + +σ −

    single spin asymmetry

    =

    TPC

    BEMC

    EEMC

    FGT

    Y

    Z

    η=-1.1

    η=-0.5

    η=0

    η=+0.5

    η=+1.112 3

    4

    DSSV++ Global Analysis includes published STAR W AL Results NNPDF analysis of anti U quark polarization.

    2

    u(x,Q2) dx1

    0.05

    DSSV+

    DSSV++w/ proj.W data

    DSSV++w/ STAR W data

    DSSV2=2%

    0

    5

    10

    15

    -0.06 -0.04 -0.02 0 0.02 0.04 0.06

    Impact of Recent STAR W AL Results on Recent Global Analyses and Predictions for future STAR Results

    CONCLUSION

    •Large uncertainty for sea quark polarization

    •Large anti u quark polarization than theoretical prediction

    •Large data set in run 2013 expect to reduce uncertainty further

    • The production of W bosons in polarized P+P collisions provides an excellent way to study the spin and flavor asymmetries of the proton quark and antiquark distributions.

    • STAR has measured the parity violating single spin asymmetry AL for pseudo-rapidity between -1.4 and +1.4 from STAR 2012 and 2011 data providing the first detailed look at the asymmetries η dependance.

    • STAR 2012 W AL results provide significant constraints on anti u and anti d quark polarizations.

    • Large data set of STAR 2013 is being analyzed currently in mid rapidity region (pseudo-rapidity between -1.0 and +1.0) and expects results reduce uncertainty further.

    • High precision results from STAR 2013 data will improve he constraints on the anti u and anti d quark polarizations.

    ———— - Candidate track and BEMC cluster

    reconstructed.

    BLUE - EeT > 14 GeV and EeT / E4x4T > 0.95

    Green - EeT / EΔR 0.88

    Red - sign PT balance cut > 14 GeV W+

    W-