Sea Quark Polarization Measurement via W → μ at PHENIX Chong KIM Korea University/RIKEN 3rd PHENIX collaboration meeting Nov. 27th, 2014 for the PHENIX collaboration

3rd PHENIX collaboration meeting, Wako Outline Introduction Accessing proton spin structure RHIC and PHENIX Recent longitudinal spin runs W → μ Analysis W physics at RHIC W → μ analysis at PHENIX Muon Arms Physics impact and outlook Summary

Introduction Accessing proton spin structure 3rd PHENIX collaboration meeting, Wako Introduction Accessing proton spin structure D. de Florian et al, PRD 80. 034030 (2009) Decomposition of proton spin < S z > = 1 2 = 1 2 ∆Σ+∆G+ L z ΔΣ = (Δu+Δ u ) + (Δd+Δ d ) + (Δs+Δ s ) (Δq+Δ q ): well constrained by inclusive/semi inclusive DIS on proton/deuteron targets Δ q : only known with large uncertainties, which mainly originated from fragmentation process q ? Do they contribute significantly to proton spin? Do u and d carry similar polarization?

Introduction RHIC @ Brookhaven Lab. 3rd PHENIX collaboration meeting, Wako Introduction RHIC @ Brookhaven Lab. ＋ － … max. √s = 510 GeV (62.4, 200, and 500/510) avg. P ~ 52 % (in longitudinal direction)

3rd PHENIX collaboration meeting, Wako Introduction PHENIX

3rd PHENIX collaboration meeting, Wako Introduction PHENIX Central Arms (mid rapidity) |η| < 0.35, Δφ = π/2 Tracking: VTX, DC, PC PID/Timing: RICH, ToF EMCal: PbSc, PbGl Muon Arms (forward rapidity) 1.2 < |η| < 2.2 (S) / 2.4 (N), Δφ = 2π Tracking: FVTX, MuTr Timing: MuID, RPC1/RPC3 MPC (forward EMCal) 3.0 < |η| < 3.8

Introduction Recent longitudinal spin runs 3rd PHENIX collaboration meeting, Wako Introduction Recent longitudinal spin runs Year √s L (pb-1) <P> FoM (LP2) 2011 500 25.1 0.48 5.78 2012 510 53.1 0.52 14.36 2013 277.1 74.93 * Int. L: Muon Arms (pileup corrected) Relevant longitudinal spin runs for W physics Run 11 – Run 13 Work on progress for publish

W → μ Analysis W physics at RHIC 3rd PHENIX collaboration meeting, Wako W → μ Analysis W physics at RHIC ALW+ = Δ𝑢 𝑥 1 𝑑 𝑥 2 − Δ 𝑑 𝑥 1 𝑢( 𝑥 2 ) 𝑢 𝑥 1 𝑑 𝑥 2 + 𝑑 𝑥 1 𝑢( 𝑥 2 ) ~ Δ𝑢 𝑥 1 𝑢 𝑥 1 ( 𝑥 1 ≫ 𝑥 2 ) or ~ − Δ 𝑑 𝑥 1 𝑑 𝑥 1 ( 𝑥 2 ≫ 𝑥 1 ) * Swap u and d for W－case ALW = 1 𝑃 × 𝑁 + 𝑊 − 𝑁 − 𝑊 𝑁 + 𝑊 + 𝑁 − 𝑊 ALW : Single longitudinal spin asymmetry of W P : Beam polarization 𝑁 +(−) (W) : # of events contains leptons decayed from W with corresponding helicity (positive/negative) in experiment, * un-polarized: averaging over the spin states of the beam Δ q measurement via W bosons Probe: leptons (e±, μ±) directly decayed from W bosons Observable: Single longitudinal spin asymmetry (AL) Advantages: Fixed flavor combination: full flavor separated measurements No dependence on the fragmentation functions

W → μ Analysis At PHENIX Muon Arms 3rd PHENIX collaboration meeting, Wako W → μ Analysis At PHENIX Muon Arms Probe: reconstructed μ tracks - of course NOT all of them came from Ws Signal: W± → μ± Backgrounds: Hadronic Punch-through/in-flight decayed hadrons Mainly Ks and πs Dominant BG source Muonic Drell-Yan, Openbottom, Opencharm, Quarkonia, W/Z → Hadrons/τ, etc… Irreducible But we have a good understanding by MC study To shift grain from chaff, Uses various kinematic variables: DG0, DDG0, DCA_r, χ2, Rpc1/3DCA, fvtx_dr/dφ/dθ

W → μ Analysis Kinematic variables 3rd PHENIX collaboration meeting, Wako W → μ Analysis Kinematic variables 1 2 3 4 RPC1 MuTr MuID RPC3 Track z DDG0 DG0 Rpc3DCA Rpc1DCA FVTX FVTX match 13.0 (13.4) λI / cosθ for S (N) 7.1 λI / cosθ Side view x y MuTR St 1 DCAr Beam view DCAr : radial distance btw vertex and intpol. track FVTX_dr/dφ/dθ: match btw FVTX/MuTr tracks Rpc1DCA: distance btw Rpc1 hit and intpol. track Χ2 : reconstructed track’s Χ2 (MuTr) DDG0: angle difference btw MuID 1st hit ad extpol. track DG0: distance btw MuID 1st hit and extpol. track lastGap: last hit position of MuID Rpc3DCA: distance btw Rpc3 hit and extpol. track

W → μ Analysis Data composition (after preselection) 3rd PHENIX collaboration meeting, Wako W → μ Analysis Data composition (after preselection) 1st μ candidates selection by using kinematic variables 16 < pT < 60, DG0 < 20, DDG0 < 9, χ2 < 20, and last MuID hit in 5th gap But backgrounds are still overwhelming (> 99.9 %) even after 1st selection Signal W± → μ±, ( < 0.1 % after preselection) Muonic BGs Irreducible Model it with MC study Hadronic BGs Punch-through/in-flight decayed hadrons Dominant backgrounds * NOT represent actual composition

W → μ Analysis W likelihood (Wness) 3rd PHENIX collaboration meeting, Wako W → μ Analysis W likelihood (Wness) Likelihood One can set a likelihood to certain desired distribution, if distribution of both desired (Signal) and NOT desired (BG) is known Wness (likelihood to W) All of our kinematic variables are distinctive to W and BGs, in various degrees Then ratio between each of these probability (likelihood) can be defined: 𝜆 𝑠𝑖𝑔 𝜆 𝑠𝑖𝑔 + 𝜆 𝐵𝐺 = Wness We assign this ‘Wness’ to each event. By its definition as Wness → 1, it is more likely to be W λ sig λ(DG0) λ(DDG0) λ(DCAr) λ(χ2) RpcDCAs FVTX match Signal distributions from W MC (PYTHIA + PISA) = BG distributions from data after 1st selection (> 99.9 % BG) λ BG DCA_r

W → μ Analysis W likelihood (Wness) 3rd PHENIX collaboration meeting, Wako W → μ Analysis W likelihood (Wness) 2nd μ candidate selection by using Wness One can select events with certain Wness cut (ex. Wness > 0.1) As Wness cut increases relative purity of data also increases, but it means we’ll have lesser statistics wo/ Wness cut Wness > 0.1 Wness > 0.9 But, unfortunately… BGs are still dominant even for the final sample (tightest Wness cut (ex. Wness > 0.92) applied) Therefore alternative method is needed to measure S/BG ratio among final sample

W → μ Analysis S/BG estimation via unbinned max. likelihood fit 3rd PHENIX collaboration meeting, Wako W → μ Analysis S/BG estimation via unbinned max. likelihood fit S/BG estimation We cannot directly estimate S/BG But we know (or we can model) each of process’ distribution among final sample: likelihood based fit is possible Fit variables: η (pseudorapidity) dw23 = pT × sinθ ×dφ23 x y MuTr St 2 St 3 z θ dφ23 η total η signal = dw23 signal dw23 total η μ BG dw23 μ BG η Had BG dw23 Had BG From MC (PYTHIA + PISA) From data (BG dominant region)

W → μ Analysis S/BG estimation via unbinned max. likelihood fit 3rd PHENIX collaboration meeting, Wako W → μ Analysis S/BG estimation via unbinned max. likelihood fit Run 13 - South μ+ Result of 2D likelihood fit projection to each variable Measured S/BG ratio Run13 preliminary For each Arm and Charge

W → μ Analysis Run 13 preliminary 3rd PHENIX collaboration meeting, Wako W → μ Analysis Run 13 preliminary

W → μ Analysis Physics impact and Outlook 3rd PHENIX collaboration meeting, Wako W → μ Analysis Physics impact and Outlook Impact on DSSV global fit Δ u (left), Δ d (right) χ2 profiles for truncated integral (top), x dependent uncertainty (bottom) Top: for u , a shift away expected from current best mean w/ STAR Run12. Also it suggests Δ u > Δ d Bottom: Clear improvement is expected in determination of light sea quarks DSSV+ : pSIDIS data (1 < Q2 < 50 (GeV)) included DSSV++ (dashed) : STAR Run12 preliminary included DSSV++ (solid) : RHIC W AL projections (Run9 - 13) included

3rd PHENIX collaboration meeting, Wako Summary W physics at RHIC Aims better constraint in light sea quark polarization Fragmentation free leptons from W bosons Expectations on global analysis shows clear improvements W → μ analysis at PHENIX Muon Arms W likelihood based S/BG estimation Preliminary status in all recent 3 years Further refinements are ongoing Hadronic dw23 extrapolation study Wness optimization Refine of dimuon scaling factor Work on progress towards finalization/publish Aims publish in early 2015

Backup Forward muon trigger upgrade 3rd PHENIX collaboration meeting, Wako Backup Forward muon trigger upgrade MuTRG ADTX MRG Level 1 Trigger Board MuTr FEE Resistive Plate Chamber (RPC) (φ segmented) B 2 planes 5% 95% Interaction Region Rack Room Optical 1.2Gbps Amp/Discri. Transmit Data Merge RPC Trigger events with straight track (e.g. Dstrip <= 1) RPC / MuTRG data are also recorded on disk

Backup Signal/BG processes and Fit variable 3rd PHENIX collaboration meeting, Wako Backup Signal/BG processes and Fit variable S/BG estimation Signal/BG processes Fit variables Signal W/Z Get distribution from MC (PYTHIA + PISA) Muonic BG Various processes (quarkonia, opencharm, etc…) Scale it with factors obtained from independent study Hadronic BG Muons decayed from hadrons Get distribution from BG dominant (low Wness) region in data Getting distribution itself requires thorough study η Pseudorapidity Distribution is stable Vs. Wness dw23 pT × sinθ × dφ23 Especially effective against Hadronic BG Distribution changes seriously Vs. Wness

Backup Dimuon scaling factors 3rd PHENIX collaboration meeting, Wako Backup Dimuon scaling factors

Backup W ± → e ± @ Central Arm 3rd PHENIX collaboration meeting, Wako Backup W ± → e ± @ Central Arm

Backup STAR Run 12, RHIC Run 9 – Run 13 projection 3rd PHENIX collaboration meeting, Wako Backup STAR Run 12, RHIC Run 9 – Run 13 projection PRL 113, 072301 (2014)

Backup Central Arms Vs. Muon Arms 3rd PHENIX collaboration meeting, Wako Backup Central Arms Vs. Muon Arms e ± @ Central Arm μ ± @ Muon Arm Triggered by Energy Momentum E deposit in EMCal Tracking in B field Charge Vs. pT pT