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Outline: 1.Introduction (pol. DIS) 2.Goals of the spin program 3.STAR detector at RHIC 4.Local polarimetry 5.Results (longitudinal pol.) 6.Summary and.

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Presentation on theme: "Outline: 1.Introduction (pol. DIS) 2.Goals of the spin program 3.STAR detector at RHIC 4.Local polarimetry 5.Results (longitudinal pol.) 6.Summary and."— Presentation transcript:

1 Outline: 1.Introduction (pol. DIS) 2.Goals of the spin program 3.STAR detector at RHIC 4.Local polarimetry 5.Results (longitudinal pol.) 6.Summary and outlook Joanna Kiryluk (MIT) 17 May 2006, Subatomic Physics Group seminar, LANL Spin Physics with STAR at RHIC

2 2 (Spin) Structure of the Nucleon Inclusive (polarized) Deep Inelastic Scattering negligible < 10-4 small  Cross section for  * square mass (scale) fraction of  * energy fraction of the proton momentum carried by the struck ‘quark’ final hadronic state mass square DIS: W 2 >M 2 and v>> M 2 F 1 and F 2 - unpolarized structure functions g 1 and g 2 - polarized structure functions  Experimentally measured: to determine spin structure function g 1 Kinematic variables:  observed ij (Lepton and nucleon - longitudinal polarization)

3 3  Measurements of g 1 (x) to determine its first moment to test spin sum rules:  Description of a nucleon structure in the naïve Quark Parton Model q(x) -spin independent and  q(x) -spin dependent parton distribution functions - Bjorken (1966) derived from current algebra and isospin symmetry; rigorous prediction of QCD Limited x-range of the measurements extrapolations needed Ellis-Jaffe (1974) derived by neglecting strange-parton contribution

4 EMC: J.Ashman et al, Nucl. Phys. B328, 1 (1989) Ellis-Jaffe prediction (1974)  ±  s= 0 assumed  … and thus the rest of J z arises from orbital motion of its constituents. EMC results (1989)  ±  ±   s = -  ±  ±  ‘Spin crisis’ : the quarks spins carry only a small fraction of the proton spin Orbital momentum? Gluons?  First measurements of  1 of the proton  S pin structure of the proton - total contribution of quarks to the spin of the proton E80,E130 EMC Disagreement between prediction and EMC measurement

5 5 ~ 10 years later: SMC, E143,... - pQCD analysis of the spin structure function: scale Q 2 dependence (caused by quarks interacting with each other by exchange of gluons) Polarized Deep Inelastic Scattering Call for alternative methods: Most promising: polarized proton-proton interactions prompt  jets scale Q 2 dependence Eb = 190 GeV Eb = 29 GeV g 1 ~ LO NLO  The singlet and non-singlet quark helicity distributions are well known,  The gluon helicity is poorly constrained, but its value is probably not huge Eb = 190 GeV Eb = 29 GeV statistical errors only NLO pQCD SMC - PRD (1998). singlet quark pol. x  gluon polarization x  g

6 6 Brookhaven National Laboratory, Upton NY, USA 542 collaborators from 51 institutions and 12 countries The STAR Collaboration PHENIX BRAHMS &PP2PPPHOBOS STAR 1.2 km RHIC STAR = Solenoid Tracker at RHIC RHIC = Relativistic Heavy Ion Collider Polarized proton-proton collisions with STAR

7 7 are to determine: gluon polarization (anti-)quark polarization (u,d) anti-strange quark polarization (model dependent, Xu et. al. hep-ph/ ) In addition: spin program with transversly polarized beams (not covered here) The goals of STAR spin program at RHIC (longitudinal polarization) Rhic-Spin program review article: G.Bunce et.al., hep-ph/

8 8 Known NLO corrections (all cases) Determination of gluon polarization - a major emphasis at STAR-Spin program at RHIC Inclusive production High production rate Classic ‘tool’ to access gluon distribution function - but rare probes How are we going to access information about pol. gluon distribution function?

9 9 perturbative series measure unknown pdf calculate  - very small (difficult to measure) We measure asymmetries instead, where most of systematic effects cancel out Required knowledge of unpolarized pdf’s in the measured kinematic region Cross section for inclusive (single) particle production Asymmetries Inclusive particle/jet production in pp interactions (1) for jets - no fragmentation functions are needed (systematics!)

10 10 Inclusive particle/jet production in pp interactions (2) Convolutions “pdf  pdf  cross section” relatively complicated and inversion is not straightforward At the moment emphasis is on NLO predictions of A LL in terms of “model”  g, to study the sensitivity of the observable Future: CTEQ-style global analysis of variety of A LL data (should include NLO) Alternative approach: “correlations” (  +jet, di-jets,  +  ) that probe kinematics in more detail Sensitivity to the gluon polarization Similar Jager et.al, PRD70(2004)  =0 V. Guzey et al., Phys.Lett.B603 (2004) W.Vogelsang RBRC/BNL, RHIC-AGS User’s Mtg talk  g=g input GRSV-std  g=0 input  g=-g input

11 scale ~ p T 2 of  Gluon polarization from Prompt Photon Production (1) The cross section asymmetry A LL for ( description at Leading Order): Direct measurement of gluon polarization Quark-Gluon Compton scattering dominates (~75%) direct  production calculable in pQCD, =A 1 p known from pol. DIS LO pQCD DIS results x A1pA1p Parton kinematics reconstruction from p T, ,   and  jet measurements: direct  production A1pA1p

12 12 Gluon polarization from Prompt Photon Production (2)  G/G  Two beam energies - large range of x g - needed to minimize extrapolation errors Simulated A LL We expect it will be determined to a precision of 0.5 Reconstructed x g (Leading Order) hep-ex/ The best determination of  G will result from a global analysis of the data from: RHIC (other channels, e.g. inclusive jet production), pDIS (HERMES, COMPASS), and possibly eRHIC through g 1 (x,Q 2 ) measurements over a wide range Compass DIS06 Deep Inelastic Scattering experiments STAR x G range from future  -jet channel

13 13 Flavor Decomposition of the proton’s spin Are the light-quark polarizations in the proton sea is large and asymmetric? Unpolarized experiments, like e.g. NMC, E866/NuSea, have shown a strong breaking of SU(2) symmetry in the antiquark sea, with: (strong x-dependence) Where?  Semi-inclusive polarized DIS - sensitivity reduced by fragmentation functions and e q 2 weighting x Q 2 =2.5GeV 2 B. Dressler et al. Predictions 13

14 14 Polarized Quark Densities (HERMES data) Good agreement with NLO-QCD  First complete separation of pol. PDFs without assumption on sea polarization  u(x) > 0 and  d(x) < 0   u(x),  d(x) ~ 0 < 0  No indication for  s(x) < 0 in measured range 0.02 < x < 0.6 Earlier HERMES conclusions of unpolarised strange sea confirmed (factor 2 smaller error bars) E. Auschenauer (HERMES), Workshop on Hardron Structure at J-PARC, November-December

15 15   - angle between lepton and proton momenta in W rest frame y W - rapidity of W boson Cross section for W production at Leading Order at Q 2 =M 2 W and p T W neglected y W (not observable) can be reconstructed from lepton p T and rapidity Additional cuts required! W+ z + z y W <0y W >0 Flavor Decomposition of the proton’s spin from W boson production at RHIC where i,j=u,d (approx) W produced through weak interaction Helicity of the quark and antiquark (u and d flavors dominate) are fixed. Ideal tool to study spin flavor structure of the proton! sign=p L,e, /| p L,e | in ~ 70% cases 15

16 16 y W - rapidity of the W boson Forward e detection gives direct probe of quark (anti-quark) polarization: Single spin asymmetry with W production W+ W- Electron(positron) detected in ElectroMagnetic Calorimeter: Barrel+Endcap -1 <  e < 2 Barrel only -1 <  e < x Pythia generator ll x ll Q 2 =M 2 W Assumption: no cuts on lepton

17 x Polarized pdf GRSV2000 M.Gluck et al, PRD , Standard Scenario: flavor symmetric light sea (antiquark) distributions Valence Scenario: completely SU(3)f broken scenario with flavor asymmetric light sea densities: STAR will distinguish between the two scenarios Unpolarized pdf GRV98 M.Gluck et al., Eur.Phys.JC5 461 NLO calculations: P.Nadolsky, C.Yuan hep-ph/

18 18 Rich program with high energy polarized pp collider Many measurements proposed by theorists over a decade ago Experimental difficulties: How to get and accelerate polarized proton beams

19 19 Difficulties in the acceleration of polarized protons (1) Assumption: protons are being accelerated in a planar circular accelerator: thus the equilibrium orbit lies in the XY-plane The spin precession and the motion of the proton: mean spin vector in the canonical rest frame reached from the frame, where the particle of spin s has velocity by the boost Since G > 0 both and rotate about with angular frequencies  c (relativistic cyclotron freq.) and  s for equilibrium orbit (R=const): |  c |=v/R, i.e.  c increases as the particle accelerates Source: W.MacKay (BNL)

20 20 Difficulties in the acceleration of polarized protons (2) In a perfect machine with uniform field : -all particles moving along the equilibrium orbit of radius R and mean spin precesses about the z- axis In a real hadron machine there are 2 effects which disturb ideal situation and lead to appearance of so called depolarizing resonance conditions ( number of spin rotations per turn = number of spin kicks per turn ) the quadrupole fields that focus the beam have a component of in the horizontal plane and B z =B z (r) there are imperfections in the fields due to misaligment of magnets and field errors (equilibrium orbit is not the idealized circle) Imperfection resonance condition: G  = spin = n  E (spacing between resonances) ~ 523 MeV Resonance condition depends on the energy of the particle and the number of resonances of varying strenght will grow with increasing energy. The i ntrinsic resonance condition due to vertical focusing fields: G  = spin = Pn ± y P: superperiodicity (AGS: 12) y : betatron tune (AGS: 8.75) n = integer Source: W.MacKay (BNL) In reality s will pick up a net non-zero precession around horizontal axes along and perp. to the beam

21 21     The unwanted precession which happens to the spin in one half of the ring is unwound the other half Result: Stable spin direction - vertical (z-direction) Spin is up in one half of the ring and down in the other half Siberian snake built and first tested at Indiana (Krish et al, 1989) At RHIC: two snakes in each ring - spin rotation around y-axis and x-axis Difficulties in the acceleration of polarized protons (3) Solution: Siberian Snakes Siberian snake - proposed by Derbenev and Kondratenko in magnet system that rotates particle’s spin s through 180 o around a horizontal axis each revolution to cancel out depolarizing effects A A A

22 22 pp Run ongoing analysis 2006 run started in March > 2006 LongTermGoals CM Energy200 GeV500 GeV Beam polarization/direction at STAR 0.15 T0.30 T/L0.40L0.45 L/T0.7 T/L L max [ s -1 cm -2 ] L int [pb -1 ] (STAR,delivered) / / GeV YBYB Helicity + Helicity - Polarization pattern at STAR(2004)  RHIC ( Relativistic Heavy Ion Collider ) - polarized pp collider  stable polarization direction at RHIC - vertical  beam polarization measured by RHIC polarimeters  longitudinal polarization at STAR and Phenix  STAR local polarimeter - to (continuously) monitor beam polarization direction

23 23 Solenoidal Magnet B = 0.5 T Tracking Detectors Time Projection Chamber |  |<1.6 Forward TPC 2.5<|  |<4.0 Silicon Vertex Tracker |  |<1 Trigger Detectors Beam-Beam Counters 3.4<|  |<5 Zero-Degree Calorimeter |  |~6 + E-M Calorimeters - installation in stages to be completed before 2006 Barrel EMC |  |<1 Endcap EMC 1.0<  <2.0 Forward Pion Detector 3.3<|  <4.1 STAR continues to add EM calorimetry to detect high-energy , e ,  0 ( wide  region ) TPC+EMC for jet reconstruction BBC + scaler board system for relative luminosity and polarization monitoring STAR detector CTB ZDC (BBC) Cutway side view of the detector where pseudorapidity  ln tan  Yellow(proton) beam Blue(proton) beam

24 24 Beam Beam Counters at STAR ~7.5m Forward Pion Detector (FPD) STAR Magnet and Time Projection Chamber BBC (East) BBC (West) Schematic side view of the STAR detector beam pipe A coincidence condition between BBC East and West (3.4 < |  | < 5) suppresses beam-gas background and used for:  triggering in pp (minimum bias, jet triggers)  (relative) luminosity measurements for A LL  local polarimetery  7.5m - scintillator annulus installed around the beam pipe, on the east and west poletips of STAR magnet at ±3.74m from IR for detection of charged particles in 2 < |  | < 5

25 25 The BBC East and West data sets sorted by beam polarization states: 1. Polarized Yellow beam (sum over Blue beam polarization states) + heads towards the East 2. Polarized Blue beam (sum over Yellow beam polarization states) + heads towards the West Beam Beam Counters - Transverse Single Spin Asymmetries for charged hadron production in forward region BBC West BBC East LeftRight Top Bottom X Top Right Left Bottom 3.4<|  |< 5.0 (small tiles only) Interaction Vertex Single spin asymmetries measured for p+p -> A + X, where A – hit(s) in the BBC Left-Right Top-Bottom N L(R) – number of counts in BBC (East or West - small annuli ) counted every bunch crossing by the scaler system

26 26  Unexpected A N of unknown origin measured with the BBC  Strong pseudorapidity dependence of A N for x F >0 and A N = 0 for x F <0  Use for local polarimetry A N BBC = p1 A N CNI +p0 A N BBC ~0.7 A N CNI ~ 1% 3.9 <  < 5.0 A N BBC = <  < 3.9 Transverse Single Spin Asymmetries BBC Preliminary Results  (CNI) (x10 -3 ) CNI Asymmetry (x10 -3 )  (BBC) (x10 -3 ) BBC Asymmetry (x10 -3 )

27 27 BBC - Local Polarimeter at STAR - Stable spin direction at RHIC is vertical - Spin Rotator brings to almost radial - D0/DX magnet causes spin precession - Longitudinal at IR - DX/D0/Spin Rotator put back to vertical Measured asymmetry i ~ A N P i Left-Right asym - sensitive to verical polarization Top-Bottom asym - sensitive to radial polarization Longitudinal polarization at STAR (P vert and P rad < 5%) - first step to A LL measurement P vert P rad Rotators OFF Rotators ON CNI polarimeter BBC DROP Rotators OFF ON CNI polarimeter non-zero non-zero BBC Left-Right ( vertical ) NON_ZERO ZERO BBC Top-Bottom ( radial ) zero zero

28 STAR Electromagnetic Calorimeter at mid-rapidity  0 (p T > 5.5 GeV/c) BEMC module Invariant Mass (GeV/c 2 ) Barrel EMC (BEMC) - a lead-scintillator sampling calorimeter, used to detect and trigger on high pT photons and jets (completed in 2005)  Coverage |  <1 and  = 2  [ TPC covarage |  <1.6 and  = 2   120 modules, total 4800 towers (  x  ) tower = 0.05 X 0.05  Depth ~ 21 X 0  Energy resolution dE/E~ 16 %/√E Shower Maximum Detector (SMD) – located at ~ 5 X 0 in BEMC, a detector with high spatial resolution (  x  ) tower = X 0.007, used for  /  0

29 29 EMC on-line event display di-jet event - via TPC p T for charged hadrons+EMC E T for e-m showers 2) Trigger used in this analysis - High Tower: E T > 2.4 GeV deposited in one tower (  x  = (0.05 x 0.05) + additional requirement of BBC coincidence. 1) Jets reconstruction - midpoint cone algorithm (Tevatron II) seed energy = 0.5 GeV, cone angle R = 0.4 in  splitting/merging fraction f=0.5 Jet reconstruction at STAR parton particle detector 4) Selections:  charged tracks  |  | 0.1 GeV/c  jets: p T jet > 5 GeV/c, 0.2< jet  (det) <0.8  beam-background: E jet (neutral)/E jet (total)< 0.8(0.9) for 2003 (2004)  |z-vertex| < 60cm 3) Data set: 0.4 pb -1 (2003 and 2004) recorded luminosity =0.3 (2003) and = 0.4 (2004) 5) Final statistics (after cuts) ~ 300k jets for A LL and ~ 40k jets for cross section (E T >3.5 GeV)

30 30 Data/Monte Carlo comparison Pythia (CDF Tune A) + GEANT3 + reconstruction  (  r) = fraction of jet p T in sub-cone  r ( common jet shape variable) HT trigger bias at low p T Bias decreases with increasing jet p T, well described by MC

31 31 Cross section for inclusive jet production ~25% ± 5% From simulations. Consistent result obtained from di-jet evts (MC) Bins of width 1-sigma (resolution)  “purity” of ~35% over range on the diagonal. Motivates application of bin-by-bin correction factors (dominated by trigger eff.) “measured” “true”

32 32 Good agreement between MB and HT data Good agreement with NLO over 7 orders of magnitude Leading systematic uncertainty –10% E-scale uncertainty  50% uncertainty on yield Other sources of systematic uncertainties (smaller, not shown): normalization, BBC trigger efficiency, background contribution Agree with NLO calculation within systematic uncertainty Preliminary results for the cross section in inclusive jet production in p+p at sqrt(s)=200 GeV vs NLO Calculation

33 33 Double Longitudinal Spin Asymmetry Measurements Require concurrent measurements: magnitude of beam polarization, P 1(2) RHIC polarimeters direction of polarization vector at interaction point relative luminosity of bunch crossings with different spin directions: STAR experiment spin dependent yields of process of interest N ij Statistical significance: BBC + scalers

34 34  Results limited by statistical precision  Total systematic uncertainty ~0.01 (STAR) + beam pol. (RHIC)  GRSV-max gluon polarization scenario disfavored jet cone=0.4 B.Jager et.al, Phys.Rev.D70(2004) Double spin asymmetry A LL (preliminary) results in inclusive jet production in p+p collisions at sqrt(s)=200GeV Sources of sys. uncertainties: background contribution, trigger bias, relative luminosity, residual (non- longitudinal) asymmetries, bunch to bunch systematic variations (random pattern analysis)+ beam pol.  A LL (P b )/A LL = 2  P b /P b ~25% Uncertainties - statistical only 25% scale uncertainty (from beam polarization) not included

35 35 High-tower trigger Jet patch trigger Statistical precision achieved for inclusive jet STAR in 2005 A LL ( jet ) Prospects for Run5 (first long pp run) and Run6(ongoing) 0.2 <  < 0.8 Potential to discriminate between several A LL predictions based on DIS parametrizations Jet patch trigger P b ~45% (~40% in Run4) L= 3/pb (0.3/pb in Run4) FoM (Run5)/FoM(Run4) = 16 Acceptance: 3/4 BEMC complete (1/2 in Run4) Two complementary jet triggers permit assessment of trigger bias due to q vs. g jet differences in shape, multiplicity, hardness in z. Run5 improvements:

36 36 Summary and Outlook First longitudinal spin results from STAR - inclusive jets Gluon polarization is not likely saturated 10 times the statistics from run-5, with better polarizations (ongoing analysis) a new run started on March 1, 2006 stay tuned for new probes and sqrt(s) = 500 GeV!

37 37 Spin Structure of the Nucleon Summary: past, present and future 1980s E80,130 - SLAC EMC - CERN 1990s consolidation SMC - CERN E142… - SLAC HERMES - DESY 2000s COMPASS - CERN HERMES - DESY RHIC-SPIN - BNL and continuing measurements 2010s planned J-PARC - KEK, eRHIC - BNL Spin Crisis Time   G  L z ??

38 38 Backup

39 39 Beam Beam Counters Instrumentation - 1 cm thick scintillator - 4 optical fibers for light collection - 1,2 or 3 tiles connected to a PMT - 15 photoelectron/MIP ~2m T B LR ~0.5m  Large hexagonal annulus: - inner (outer) diameter 38cm (193cm); - of 18 pixels, covering 2.1 < |  | < 3.3 and 0<  <2  ; - 8 PMT, no timing information  Small hexagonal annulus : - inner (outer) diameter 9.6cm (48cm); - of 18 pixels, covering 3.3<|  |< 5.0 and 0<  <2  - 16 PMT - feasible segmentation (i) two bins in h and (ii) azimuthal Top/Bottom/Left/Right, timing information tiles triplet

40 40  Monte Carlo (MC) = Pythia+Geant for STAR  BBC response simulator:  Light yield: dE/dE(MIP)x15 photoelectrons(MIP)= N photoel.  Single photoelecton resolution = 30%  PMT gain = 0.30 pC/photoelectron  ADC bin = 0.25 pC  Time resolution = 900 ps Data and MC agree Beam Beam Counters - trigger data pp minbias trigger condition = BBC East and West coincidence (3.4 < |  | < 5) Cross section:  BBC =  tot (pp) x acc(BBC) = 51 mb x 0.53 ~ 27 mb ( 87% of ) from MC In agreement with RHIC luminosity measurements (van der Meer scans) L=Rate(BBC)/  BBC e.g. at L=10 30 cm -2 s -1 the Rate(BBC) ~ 27 kHz DAQ limitations - cannot take data at this rate Solution: deadtimeless scaler boards - - very useful when ‘details’ such as ADC information not needed, but statistics is an issue

41 41 STAR Scaler Boards BBC E.W coincidence counts bunch crossing# Run Bit# Input BBC E.W (Luminosity bit) 18 BX1 19 BX2 20 BX3 21 BX4 22 BX5 23 BX6 24 BX7 …and same for BBC West Bunch crossing number Example of the BBC scaler bits BBC East PMT#i, i=1-16 The scaler board - 24 bit and 10 MHz VME memory module It has 2 24 cells, each cell 40-bit deep to keep continuous (deadtimeless) record for up to 24 hours operation at 10 MHz (10 MHz clock corresponds to bunch crossing frequency at RHIC, 107 ns) 24 input bits = 7(bunch crossing) + 17(physics inputs) 2 17 =10 5 combinations Physics input bits = data from fast detectors e.g. BBC, which consists of discriminator outputs from individual PMTs as well as logic levels produced by the STAR Level 0 trigger electronics Luminosity ~

42 42 bunch crossing# Time [Run Number] Relative Luminosity R=L ++ /L +- R = 1 and time dependent! 05/16/03 05/30/ Relative Luminosity Measurement from Beam Beam Counters  Precision of relative luminosity monitoring critical: for A LL ~1%  A LL /A LL ~5% if  R/R~10 -3  Luminosity ~ BBC coincidence rate ( large cross section of ~27mb) counted every 107ns  RHIC stores up to 120 bunches per ring - different bunches injected with different spin orientation - collision luminosity can vary with spin combination Relative luminosities uncertainties:  R stat ~ – and  R syst < beam-1 beam-2 YBYB Helicity + Helicity - Polarization pattern at STAR

43 43 BBC Event Selection for Asymmetry Measurement Right scattering 3.4 <  < <  < 4.9 Mean=2.3 RMS =1.2 Mean=2.3 RMS =1.2 Number of hits PMT number Monte Carlo simulation Data

44 44 Local polarimetry -online monitoring feadback within minutes left-right Time BBC Raw Asymmetry (x F >0) Rotators’ currents (A) Beam Polarization 3 hours RHIC CNI

45 45 Anti-Lambda at RHIC: The measurement of hyperon  polarization at RHIC can give insights into polarized fragmentation and parton distribution functions Pythia s-bar gluon DIS, set II SU(6), set II (GRSV00_std) Xu, Liang, Sichtermann, hep-ph/ STAR acceptance - D. de Florian et al, PRL81(1988)530 - C. Boros et al, PRD62(2000) B.Q. Ma et al, NPA703(2002)346 - Q.H. Xu et al, PRD65(2002) DIS, set I SU(6), set I(GRSV00_val)  Lambda-bar polarization (p+p) is sensitive (in a model dependent way) to  Lambda polarization (p+p) less sensitive to  s, because of u,d fragmentation, e.g.

46 46   reconstruction at STAR via decay channel:   p+  (Br=64%) - combining TPC tracks with opposite charges - cuts for tracks and decay vertex topology - | |~0.008 ~1.5 GeV/c Data sample (after all cuts) ~30k Lambda and ~27k anti-Lambda Lambda and anti-lambda reconstruction in p+p collisions at STAR M Λ = GeV(PDG) Invariant mass Podolanski-Armenteros plot - momentum of positive (negative) tracks parallel to the V 0 momenta - momentum of tracks perpendicular to the V 0 momentum  

47 47 Standard Method: Angular distribution of decay proton in the  rest frame  relies on knowledge of the Acceptance Function (usually from simulation). Measuring Longitudinal  polarization without Acceptanc e Function The four combinations (++, --, +-, and -+) of beam helicities at RHIC, and symmetries (parity, proton indistinguishability) in the  production process allow one to determine the longitudinal  polarization (spin transfer) from measured asymmetries in (narrow) intervals in , where  decay parameter (empirical) = 0.642(PDG) A(cos  ) acceptance in which the Acceptance Function largely cancels. N + =N ++ + N +- N - =N -- + N - + R- relative luminosity Number of Lambdas

48 48 Lambda polarization from 2003 and 2004 pp data with longitudinal polarization - Preliminary Results P  small ( |x F |~0.01, p T ~1.5GeV ) Gluon fragmentation at such low p T should be important Results limited by statistical precision Prospects for Run5 (first long pp run), Run6 (on-going) and beyond Jet-Patch trigger 160k  High-Tower trigger 80k  MinBias 36k  Run5 Run6 (10pb -1 )  D LL ~0.04 for p T > 6 GeV/c >100 pb -1 needed for  D LL ~0.01 for p T > 8 GeV/c Trigger on anti-Lambda ?  p T [GeV/c] Q. Xu, hep-ex/


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