W production results from RHIC

1. W production results from RHIC ECT* workshop “Flavor structure of the nucleon sea” Trento July 1st , 2013 Ralf Seidl (RIKEN)

2. Outline • Real W production to access sea quarks and helicities • Current sea helicities • W production and expected sensitivites • RHIC, PHENIX, STAR and recent polarized runs • Central W measurements • Cross section measurements • Asymmetries • Forward W measurements • Upgrades • Asymmetries • Outlook R.Seidl: RHIC W results

3. Most recent global analysis : DSSV de Florian et al., PRL101, 072001 (2008) • NLO analysis • Inclusion of SIDIS data before COMPASS • Inclusion of RHIC ALL data( from 200GeV) • Using most recent NLO fragmentation functions (DSS) • Large uncertainties still for sea quarks • Decay data forces Ds to become negative at small x • RHIC data results in node to Dg R.Seidl: RHIC W results

4. Real W production as access to quark helicities • Maximally parity violating V-A interaction selects only lefthanded quarks and righthanded antiquarks: Having different helicities for the incoming proton then selects spin parallel or antiparallel of the quarks Difference of the cross sections gives quark helicities Dq(x) • No Fragmentation function required • Very high scale defined by W mass Bourrely , Soffer Nucl.Phys. B423 (1994) 329-348 R.Seidl: RHIC W results

5. Quark and antiquarkhelicities probed in W production • Building single spin asymmetries of decay lepton • Positive lepton asymmetries sensitive to Du (x) and Dd (x) • Negativ lepton asymmetries sensitive to Dd (x) and Du (x) But unfortunately we don’t have a 4p detector, Need to find the Ws inclusively via their decay leptons R.Seidl: RHIC W results

6. Sea quark polarization via W production e+ m+ m- e- m- m+ • Single spin asymmetry proportional to quark polarizations • Large asymmetries • Forward/backward separation smeared by W decay kinematics R.Seidl: RHIC W results

7. W vs lepton asymmetries Dd/d Dd/d • Clear correlation for W: valence quark polarizationforward sea quark  backward • However, not for decay muon/electron: enhanced for W-, mixed for W+ • reversed effect for neutrino asymmetry • neutron target reverses that due to isospin asymmetry run He3 collisions eventully? • x is not affected by this; still forward is larger x, backward smaller x Du/u Du/u Dd/d Dd/d Du/u Du/u Dd/d Du/u Du/u Dd/d R.Seidl: RHIC W results

8. W kinematics R.Seidl: RHIC W results

9. Pythia: quark flavors and x ranges Central Forward W-mcase: almost entirely forward d quarks and backwards u W+mcase: predominantly forward  d quarks and backwards u R.Seidl: RHIC W results

10. Expected sea quark sensitivities • Inclusion of W channels into global analysis DSSV prepared • Expected impact with about 200 pb-1 in PHENIX and STAR in -2 < h <2 estimated deFlorian, Vogelsang: Phys.Rev. D81 (2010) 094020 • Reduction of uncertainties in sea quark polarizations of above x~0.1 substantial R.Seidl: RHIC W results

11. Relativistic Heavy Ion Collider • RHIC Characteristics • 2 counter-circulating rings • 3.8 km in circumference • Top Energies (each beam): • 7-100GeV / Au-Au • 31-255GeV / p-p • Mixed Species (d+Au) 2Spin Experiments • PHENIX • Electron detection |h| <0.35 (EMCal, Drift chambers, RICH, VTX) • Muon arms 1.2 < |h| < 2.4 (MuonTracker, ID, RPCs, FVTX) • STAR • Electron detection -1 < h < 1 (2) (TPC,EmCals) R.Seidl: RHIC W results

12. Absolute Polarimeter (H jet) RHIC Polarized Proton Collider RHIC pC Polarimeters Siberian Snakes Siberian Snakes local polarimetry local polarimetry Polarized Source Helical Partial Snake 200 MeV Polarimeter AGS Internal Polarimeter spin rotators around IPs at PHENIX and STAR AGS pC Polarimeter R.Seidl: RHIC W results

13. Wein central rapidities R.Seidl: RHIC W results

14. Central W analysis • General Strategy: • Find the Jacobian Peak ( ~0.5 MW) in Energy or Pt spectrum for electrons • Clean up backgrounds by E/P and isolation criteria including away side (neutrino direction) if possible R.Seidl: RHIC W results

15. Raw electron yields STAR • Raw electron Pt or energy spectra and after successively applying shower shape and isolation selection criteria R.Seidl: RHIC W results

16. Jacobian peaks and background fraction • After all cuts sizeable signals and little background remain R.Seidl: RHIC W results

17. W Cross sections • Correcting acceptance and efficiencies one can obtain the absolute W/Z cross sections: • Excellent agreement of the scale dependence from RHIC to LHC PRL 106:062001(2011) PRD 85 (2012) 092010 R.Seidl: RHIC W results

18. First W results PHENIX In 2009: First exploratory RHIC run at 500 GeV Both, PHENIX and STAR obtained first central rapidity results, PRL 106:062001(2011) PRL 106:062002(2011) Real W production can be used to access the sea quark polarization! R.Seidl: RHIC W results

19. Central W asymmetries Stevens, arXiv:1302.6639 R.Seidl: RHIC W results

20. We,min forward rapidities R.Seidl: RHIC W results

21. Forward W analysis • W momentum cannot be ignored • Jacobian peak only visible for forward moving W+ decaying at close to 90 degrees • Need to understand and suppress backgrounds lacking distinct signal signature Pythia 6.4, muons in rapidities 1.2 – 2.4 R.Seidl: RHIC W results

22. Sagitta (cm) 2mm Forward Tracking into the Endcap: STAR FGT Upgrade Slides courtesy of A.Vossen and A. Ogawa Barrel EMCc η=1 e+/- η=2 Lightweight, Triple-GEM Detector FGT TPC Endcap EMC • FGT: 6 light-weight triple-GEM disks using • industrially produced GEM foils (Tech-Etch Inc.) • Needed for charge separation: • Goal: resolution of ~100mm R.Seidl: RHIC W results

23. STAR Forward GEM Tracker Commissioning Run 12 Slides courtesy of A.Vossen and A. Ogawa y [cm] Run 12 configuration Strip Layout x [cm] x [cm] Single Track Event Display R.Seidl: RHIC W results

24. STAR FGTInstallation for Run13 Slides courtesy of A.Vossen and A. Ogawa R.Seidl: RHIC W results

25. PHENIX Muon trigger upgrade current trigger (MuID) threshold • σ(tot)=60mb, L=3x1032cm-2s-1 (500GeV) • collision rate = 18MHz • (after luminosity upgrade) • DAQ rate limit < 2kHz (for muon Arm) • Therefore, required rejection ratio • > 9000 • But, MuID-trigger rejection ratio (500GeV) • < 100 • A higher momentum trigger is needed W dominant region PYTHIA5.7 R.Seidl: RHIC W results

26. PHENIX Muon Trigger Upgrade detectors RPC MuID MuID RPC MuTR MuTR μ RPC absorber RPC provide timing information and rough position information MuID trigger selecting muon momentum > 2GeV/c MuTR FEE upgrade fast selection of high-momentum-tracks R.Seidl: RHIC W results

27. B Muon Trigger Upgrade RPC project RPC timing information rough position information MuTr Level-1 trigger ADC digitized hit signal digitized hit signal digitized hit signal ADC Level-1 trigger board MuTRG project sagitta ADC R.Seidl: RHIC W results

28. PHENIX Forward W trigger upgrade installation and commissioning R.Seidl: RHIC W results

29. Forward Muon Backgrounds • Real muons from heavy flavor and DY decays get smeared to higher transverse momenta • Low energetic hadrons (huge cross section) decay within the muon tracker, mimicking a straight track • Raw yields 3 orders above signal R.Seidl: RHIC W results

30. Reducing the background components • Apply sensitivity to multiple scattering to reduce hadronic backgrounds • Initially (2011) cut based removal of backgrounds • Improved by using likelihood based pre-selection and unbinned max likelihood fit Data W Simulation R.Seidl: RHIC W results

31. Multivariate analysis • Define Wness likelihood using 5 kinematic variables based on signal MC and data ( = mostly BG) • After preselecting W like events (>0.92) perform unbinned max likelihood fit in independent variables rapidity and effective bending angle f > 0.92 R.Seidl: RHIC W results

32. Forward W asymmetries • After extracting S/BG ratios ( in 2012 preliminary data ~0.3) extract asymmetries and correct for BG (BG asymmetries are consistent with zero ) • Inclusion of FVTX information will improve BG rejection (isolation, multiple scattering) • 2011 and 2012 Analysis will be finalized soon • 2013 data analysis is ongoing R.Seidl: RHIC W results

33. Outlook RHIC Spin NSAC write-up: Aschenauer et. al: arXiv:1304.0079 R.Seidl: RHIC W results

34. Expected impact of full data set • Substantial uncertainty improvement of the sea quark helicities • DSSV framework ready to include W asymmtries (see M. Stratmann’s talk) • NNPDF in the process of including W asymmetries (see A. Guffanti’s talk) R.Seidl: RHIC W results

35. Backup R.Seidl: RHIC W results

36. W Outlook 3He p collisions Marco Stratman (BNL) pp @ 500 GeV 3He p @ 432 GeV caveat: AL study assumes 216 GeV 3He beam but 325 GeV × Z/A was too optimistic conservative: 250 GeV × 2/3 = 166 GeV does not affect AL much but cross section smaller R.Seidl: RHIC W results

37. Forward W decays Du Dd • Forward W decays advantages: • largest sensitivity to the anti-u quark polarization • some sensitivity to the anti-d quark polarizaiton (due to decay kinematics) • With high statistics possibility to test d pol sign change • But no Jacobian peak, experimentally more difficult Dd Du Pythia 6.4 R.Seidl: RHIC W results

38. Decay kinematics due to helicity conservation W+ W- R.Seidl: RHIC W results

39. Sea quark polarization via W production e+ m+ m- e- m- m+ Parity violation of weak interaction selects:lefthanded quarks and righthanded antiquaks proton spin selects (anti)parallel quark/antiquark spins  Single spin asymmetry proportional to quark polarizations R.Seidl: RHIC W results

40. Sea quark polarization via W production e+ m+ m- e- m- m+ • Parity violation of weak interaction selects: lefthanded quarks and righthanded antiquaks proton spin selects (anti)parallel quark/antiquark spins • Single spin asymmetry proportional to quark polarizations • Large asymmetries R.Seidl: RHIC W results

41. Forward W analysis • W momentum cannot be ignored • Jacobian peak only visible for forward moving W+ decaying at close to 90 degrees • Need to understand and suppress backgrounds lacking distinct signal signature Pythia 6.4, muons in rapidities 1.2 – 2.4 R.Seidl: RHIC W results