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ECT* workshop Flavor structure of the nucleon sea Trento July 1 st, 2013 Ralf Seidl (RIKEN) Slide 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 7/01/2013 R.Seidl: RHIC W results2 Slide 3 Most recent global analysis : DSSV NLO analysis Inclusion of SIDIS data before COMPASS Inclusion of RHIC A LL data( from 200GeV) Using most recent NLO fragmentation functions (DSS) Large uncertainties still for sea quarks Decay data forces s to become negative at small x RHIC data results in node to g 7/01/2013 R.Seidl: RHIC W results 3 de Florian et al., PRL101, 072001 (2008) Slide 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 q(x) No Fragmentation function required Very high scale defined by W mass 7/01/2013 R.Seidl: RHIC W results 4 Bourrely, Soffer Nucl.Phys. B423 (1994) 329-348 Slide 5 Quark and antiquark helicities probed in W production Building single spin asymmetries of decay lepton Positive lepton asymmetries sensitive to u (x) and d (x) Negativ lepton asymmetries sensitive to d (x) and u (x) 7/01/2013 R.Seidl: RHIC W results 5 But unfortunately we dont have a 4 detector, Need to find the Ws inclusively via their decay leptons Slide 6 Sea quark polarization via W production Single spin asymmetry proportional to quark polarizations Large asymmetries Forward/backward separation smeared by W decay kinematics 7/01/2013 R.Seidl: RHIC W results6 e-e- e+e+ ++ ++ -- -- Slide 7 W vs lepton asymmetries 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 7/01/20137 u/u d/ d d/d u/uu/u u/uu/u u/u d/ d u/u d/ d u/uu/u d/d Slide 8 W kinematics 7/01/2013R.Seidl: RHIC W results8 Slide 9 Pythia: quark flavors and x ranges 7/01/2013 R.Seidl: RHIC W results 9 W - case: almost entirely forward d quarks and backwards u W + case: predominantly forward d quarks and backwards u Central Forward Slide 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 < Slide 11 11 Relativistic Heavy Ion Collider 2 Spin Experiments PHENIX Electron detection | | PHENIX Muon trigger upgrade (tot)=60mb, L=3x10 32 cm -2 s -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 7/01/2013 R.Seidl: RHIC W results 25 PYTHIA5.7 W dominant region current trigger (MuID) threshold Slide 26 PHENIX Muon Trigger Upgrade detectors 26 MuID trigger selecting muon momentum > 2GeV/c MuTR FEE upgrade fast selection of high-momentum-tracks RPC provide timing information and rough position information MuID MuTR RPC absorber R.Seidl: RHIC W results 7/01/2013 Slide 27 RPC Muon Trigger Upgrade R.Seidl: RHIC W results27 digitized hit signal Level-1 trigger digitized hit signal digitized hit signal B MuTr timing information rough position information sagittaLevel-1 trigger board Level-1 RPCproject MuTRGproject 7/01/2013 Slide 28 PHENIX Forward W trigger upgrade installation and commissioning 7/01/2013 R.Seidl: RHIC W results 28 Slide 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 7/01/2013 R.Seidl: RHIC W results 29 Slide 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 7/01/2013 R.Seidl: RHIC W results 30 W Simulation Data Slide 31 Multivariate analysis Define Wness likelihood using 5 kinematic variables based on signal MC and data ( = mostly BG) 7/01/2013 R.Seidl: RHIC W results 31 After preselecting W like events (>0.92) perform unbinned max likelihood fit in independent variables rapidity and effective bending angle f > 0.92 Slide 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 7/01/2013 R.Seidl: RHIC W results 32 Slide 33 Outlook 7/01/2013 R.Seidl: RHIC W results 33 RHIC Spin NSAC write-up: Aschenauer et. al: arXiv:1304.0079 Slide 34 Expected impact of full data set Substantial uncertainty improvement of the sea quark helicities DSSV framework ready to include W asymmtries (see M. Stratmanns talk) NNPDF in the process of including W asymmetries (see A. Guffantis talk) 7/01/2013 R.Seidl: RHIC W results 34 Slide 35 7/01/2013 R.Seidl: RHIC W results35 Slide 36 pp @ 500 GeV 3 He p @ 432 GeV W Outlook 3 He p collisions 36 caveat: A L study assumes 216 GeV 3 He beam but 325 GeV Z/A was too optimistic conservative: 250 GeV 2/3 = 166 GeV does not affect A L much but cross section smaller caveat: A L study assumes 216 GeV 3 He beam but 325 GeV Z/A was too optimistic conservative: 250 GeV 2/3 = 166 GeV does not affect A L much but cross section smaller Marco Stratman (BNL) 7/01/2013 R.Seidl: RHIC W results Slide 37 Forward W decays 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 7/01/2013 R.Seidl: RHIC W results 37 uu dd dd uu Pythia 6.4 Slide 38 Decay kinematics due to helicity conservation 7/01/2013 R.Seidl: RHIC W results 38 W+W+ W-W- Slide 39 Sea quark polarization via W production 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 7/01/2013 R.Seidl: RHIC W results39 e-e- e+e+ ++ ++ -- -- Slide 40 Sea quark polarization via W production 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 7/01/2013 R.Seidl: RHIC W results40 e-e- e+e+ ++ ++ -- -- Slide 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 7/01/2013 R.Seidl: RHIC W results 41 Pythia 6.4, muons in rapidities 1.2 2.4