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Lecture IV What do we really measure

Lecture IV What do we really measure. D G. S q L q. L g. S q D q. S q D q. L g. S q L q. d q. D G. d q. How do the partons form the spin of protons. Is the proton looking like this?. “Helicity sum rule”. gluon spin. Where do we stand solving the “spin puzzle” ?. angular

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Lecture IV What do we really measure

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  1. Lecture IVWhat do we really measure Varenna, July 2011

  2. DG SqLq Lg SqDq SqDq Lg SqLq dq DG dq How do the partons form the spin of protons Is the proton looking like this? “Helicity sum rule” gluon spin Where do we stand solving the “spin puzzle” ? angular momentum total u+d+s quark spin Varenna, July 2011

  3. Probing the Proton Structure • EM interaction • Photon • Sensitive to electric charge2 • Insensitive to color charge • Strong interaction • Gluon • Sensitive to color charge • Insensitive to flavor • Weak interaction • Weak Boson • Sensitive to weak charge ~ flavor • Insensitive to color Varenna, July 2011

  4. q q qg g g Main Underlying Processes in DIS Q2 + + + + Splitting of qq hard QCD 22 if scattered lepton in detector kinematics is known xBjand Q2 can calculate parton kinematics for DIS xBj = xparton „Soft“ & Hard VMD: Elastic, diffractive, non-diffractive minimum bias Scale: pt or mq Scale: Q2 pt can be big x of parton is not known  unfolding very much like pp Varenna, July 2011

  5. Underlying processes in pp Mid-rapidity ppp0Xdominated bygggg andgqgq Forward-rapidity ppp0Xdominated bygqgq =3.3, s=200 GeV p0 ECAL g p0 g p0 kinematics is unknown Scale: pT parton kinematics needs to be unfolded in theo. calculation Varenna, July 2011

  6. e+e- ? pQCD DIS Predictive power of pQCD q(x1) Hard Scattering Process X g(x2) • “Hard” (high-energy) probes have predictable rates given: • Partonic hard scattering rates (calculable in pQCD) • Parton distribution functions (need experimental input) • Fragmentation functions (need experimental input) Universal non-perturbative functions Varenna, July 2011

  7. Correlation pT – x and √s • low pT low x • scale uncertainty • high √s low x • forward rapidity  low x 2-2.5 GeV/c 4-5 GeV/c 9-12 GeV/c 2-2.5 GeV/c 4-5 GeV/c 9-12 GeV/c Varenna, July 2011

  8. The Gluon Polarization RHIC:many sub-processes with a dominant gluon contribution high-pTjet, pion, heavy quark, … in NLO unpolarised cross sections nicely reproduced in NLO pQCD Varenna, July 2011

  9. Does QCD work: Cross Sections s=62 GeV (PRD79, 012003) s=200 GeV (PRD76, 051106) s=500 GeV (Preliminary) PRL 97, 152302 • Data compared to NLO pQCD calculations: • s=62 GeV calculations may need inclusion of NLL (effects of threshold logarithms) • s=200 and 500 GeV: NLO agrees with data within ~30% • Input to qcd fits of gluon fragmentation functions  DSS • √s=200 GeV Jet Cross Sections agree with data in ~20% Varenna, July 2011

  10. Two-spin helicity asymmetry: Can be large in pQCD hard scatter. Stat. Unc. ~ (P12P22 L dt )1/2 One-spin helicityasym. ALviolates parity if non-vanishing, but can be large in weak processes like W prod’n. N++/L++N+/L+ 1 ALL P1P2 N++/L++ + N+/L+ versus Single-spin transverse asym. Detected particle momentum N/L N/L 1 AN P1 N/L+ N/L where  () are defined with respect to reaction plane, is suppressed by chiral symmetry in pQCD hard scatter, but can occur via non-pert. aspects of initial and final-state spin dynamics. Proton spin vector versus Stat. Unc. ~ (P12 L dt )1/2 What We Measure Varenna, July 2011

  11. Scaling violations of g1 (Q2-dependence) give indirect access to the gluon distribution via DGLAP evolution. Current knowledge on Dg Δg from inclusive DIS and polarized pp DIS EIC • RHIC polarized pp collisions at midrapidity directly involve gluons • Rule out large DG for 0.05 < x < 0.2 DIS RHIC constrained x-range still very limited Varenna, July 2011

  12. STAR Much more data Varenna, July 2011

  13. u d Dq: W Production Basics Since W is maximally parity violating W’s couple only to one partonhelicity large Δuand Δdresult inlarge asymmetries. No Fragmentation ! Similar expression for W- to get Δ and Δd… Varenna, July 2011

  14. expectations for ALe in pp collisions de Florian, Vogelsang t large u large t large u large strong sensitivity to limited sensitivity to Varenna, July 2011

  15. RHIC: AL for W bosons • RHIC: can detect only decay leptons; • lepton rapidity most suited observable • strong correlation with x1,2 de Florian, Vogelsang, arXiv:1003.4533 Δχ2 = 2% uncertainty bands of DSSV analysis • allows for flavor separation for 0.07 < x < 0.04 Δχ2 = 2% uncertainty bands with RHIC data Varenna, July 2011

  16. ALW: First proof of principle Need much more statistics (300pb-1) to compete with SIDIS doubled statistics in 2011 STAR Varenna, July 2011

  17. ALW: Future Possibilities ALW: He3-p @ 432 GeV ALW: pp @ 500 GeV phase 2 of pp2pp@STAR can separate scattering on n or p Varenna, July 2011 • Can we increase p-beam energy? • 325 GeV: factor 2 in sW • access to lower x for Dg(x) • Increased beam-energy and polarized He-3 beam  full flavor separation

  18. Quantum phase-space tomography of the nucleon 3D picture in momentum space 3D picture in coordinate space transverse momentum generalized parton distributions dependent distributions  exclusive reaction like DVCS Wigner Distribution W(x,r,kt) Join the real 3D experience !! TMDs GPDs d3r d2ktdz u-quark Polarized p Polarized p d-quark Varenna, July 2011

  19. More insights to the proton - TMDs Transversity distribution function dq(x) Single Spin Asymmetries Unpolarized distribution function q(x), G(x) beyond collinear picture Explore spin orbit correlations Sivers distribution function Boer-Mulders distribution function Correlation between and Helicity distribution function Dq(x),DG(x) peculiarities of f^1T chiral even naïve T-odd DF related to parton orbital angular momentum violates naïve universality of PDFs QCD-prediction: f^1T,DY = -f^1T,DIS Correlation between and Correlation between and Varenna, July 2011

  20. u γ* p,K u,d,s p,K,g jet d u,d,s,g u,d,s u,d,s,g Processes to study Single Spin Asymmetries e+/m+ polarized SIDIS dqf, f^1T e-/m- polarized pp scattering ?dqf, f^1T? g* polarized DY f^1T polarized W-prod. f^1T Varenna, July 2011

  21. Single Transverse Spin Asymmetries • Fermilab E-704 reported Large Asymmetries AN • Could be explained as • Transversityx Spin-dep. fragmentation (Collins effect), • Intrinsic-kT imbalance (Sivers effect) , or • Twist-3 (Qiu-Sterman, Koike) • Or combination of above Left Right Varenna, July 2011

  22. left right Transverse single-spin asymmetries FNAL s=19.4 GeV BRAHMS@RHIC s=62.4 GeV BNL AGS s=6.6 GeV ANL ZGS s=4.9 GeV p0 Big single spin asymmetries in pp !! Naive pQCD (in a collinear picture) predicts AN ~ asmq/sqrt(s) ~ 0 What is the underlying process? Sivers or Twist-3 or Collins or .. Do they survive at high √s ? Is pt dependence as expected from p-QCD? Varenna, July 2011

  23. Transverse Polarization Effects @ RHIC Left -Right midrapidity: maybe gluon Sivers???? Phys. Rev. Lett. 101 (2008) 222001 Varenna, July 2011

  24. What is seen at RHIC • No strong dependence on s from 19.4 to 200 GeV • Spread probably due to different acceptance in pseudorapidity and/or pT • xF ~ <z>Pjet/PL ~ x : shape induced by shape of Collins/Sivers • Sign also consistent with Sivers and/or Transversityx Collins need other observables to disentangle underlying processes Do we understand the theory Varenna, July 2011

  25. angle of hadron relative to initial quark spin (Sivers) Sivers Collins Azimuthal angles and asymmetries angle of hadron relative to final quark spin (Collins) SIDIS allows to study subprocesses individually at RHIC we can unfortunately not define the 2 planes Only idea is to define a reaction plane in pp like in AA Varenna, July 2011

  26. y x z Colliding beams How to disentangle Sivers and Transversity Sivers: AN for direct photons AN for jets AN for dijets AN for Ws AN for heavy flavour gluon Sivers Transversity: AN for angular modulation of p in around jet axis Interference fragmentation function proton spin partonkTx BUT • Processes Universalityvs non-universality: • Semi-Inclusive deep inelastic scattering ✔ • Drell-Yan ✔ • e+/e- annihilation ✔ • p + ph1 + h2 + X ! ! arXiv:1102.4569 ✔ Watch out for sign flips ! TMD PDF is not just non-universal, it is ill-defined at the operator level !  work has started to fix this problems Varenna, July 2011

  27. STAR: Upcoming physics topics SampledLuminosityfor STAR FY11 pp 500 Transversedataset Forward Meson Spectrometer Withprojection Goal = 20 pb-1 Final = ~ 27.4 pb-1 ~137% Nice data set to study AN – jet: Siversfct. AN for single lepton from W+/-: Sign change in Siversfct. compared to SIDIS ANfor dijets: Siversfct. via back to back imbalance of 2 jets Calorimeter High Tower Withprojection Goal = 20 pb-1 Final = ~ 22.2 pb-1 ~111% W+e++X W-e-+X Varenna, July 2011

  28. What do we know: Twist-3 vs. TMD Intermediate QT Q>>QT/pT>>LQCD Transverse momentum dependent Q>>QT>=LQCD Q>>pT Collinear/ twist-3 Q,QT>>LQCD pT~Q Efremov, Teryaev; Qiu, Sterman Siversfct. critical test for our understanding of TMD’s and TMD factorization QCD: DIS: attractive FSI Drell-Yan: repulsive ISI QT/PT LQCD Q QT/PT << << SiversDIS = -SiversDY Varenna, July 2011

  29. from sign changes to sign mismatches • latest twist: “sign mismatch” Kang, Qiu, Vogelsang, Yuan 1stkT moment of Siversfct and twist-3 analogue related at operator level Boer, Mulders, Pijlman; Ji, Qiu,, Vogelsang, Yuan both sides have been extracted from data find: similar magnitude ✓but wrong sign ✖ inconsistency in formalism? possible resolutions: (1) data constrain Siversfct only at low kT; function has a node (2) analysis of Tq,Fneglects possible final-state contributions to AN phenomenological studies with more flexible Siversfct. under way Kang, Prokudin need data for AN which are insensitive to fragmentation: photons, jets, DY • on the bright side: recent progress on evolution for Siversfct Kang, Xiao, Yuan crucial for consistent phenomenology – properly related experiments at different scales Varenna, July 2011

  30. New Global Fit Parameterization: A. Prokudin, Z.-B. Kang shape ala DSSV node if ηq>0 Data-Input: HERMES and COMPASS SIDIS & STAR p0 Anselmino et al. 2009 Impact on DY AN need to measure DY xf < 0.3 Varenna, July 2011

  31. u,d,s DRELL-YAN e+/m+ e-/m- g* or how to suppress backgrounds by a factor of 1000 and more Varenna, July 2011

  32. Collision Energy Dependence of Drell Yan Production • Comments… • partonic luminosities increase with s • net result is that DY grows with s • largest s probes lowest x •  Consider large-xF DY at s=500 GeV Prediction of AN using TMDs Siversfct based on fit to HERMES & COMPASS Kang & Qiu PRD 81 (2010) 054020 Varenna, July 2011

  33. Backgrounds to DY production • Most dominat background sources • QCD 22 • Heavy flavour • photon conversion in material • All charged particle pairs between J/ and  • Hadron suppression 103-104 needed at 500 GeV • Drell Yan signal reduced in 200 GeV forward 200 GeV 500 GeV Varenna, July 2011

  34. Heavy flavor contributions • More low mass heavy flavor in forward directions • Charm & bottom contributions increase with minv • Comparison at minv < 3 GeV/c2 needs more studies • See previous slide • Smaller energy cut Varenna, July 2011

  35. QCD jet background • Drell Yan signal • 3 – 10 GeV/c2 • Energy cut • E1,2 > 2 GeV • Forward rapidities • Effectively no background left • Statistically limited • Drell Yanfor minv < 3 GeV/c2 not physical (PYTHIA settings) Varenna, July 2011

  36. ANDY @ IP-2 • Idea: have DY feasibility test • at IP-2 • staged measurements over • 3 years • re-use as much detector • equipment as possible to • finish till summer 2014 • Measurement: • why IP-2 • transverse polarization • measure parallel to • √s = 500 GeV W-program • h > 3, M>4 GeV • 0.1<xf<0.3 • optimizes • Signal / Background & DY rate • measure dANDY ~0.015 for • ∫ L~100 pb-1 • Proposal approved June 2011 • BNL PAC Final configuration 2013 Varenna, July 2011

  37. arXiv:1103.1591 jet AN measurements are required to clarify signs of quark/gluon correlators related to Sivers functions. s=200 GeV from p+pp “new” Sivers function “old” Sivers function Run11 Goal: AN for jets Determine whether AN(jet) is non-0 is a requirement for AN(DY) sign-flip measurement Varenna, July 2011 With ~10 pb-1& P=0.50 ANDY run11 can measure AN(Jet).

  38. we have just explored the tip of the iceberg you are here Du, Dd Conclusions Dutot, Ddtot Many new avenues for further important measurements andtheoretical developments Dg Ds TMDs Lq,g Finish your PhDs and join us as postdocs to unravel the puzzle around kt in PDFs spin sum rule • Thank you for your attention Varenna, July 2011

  39. BACKUP Varenna, July 2011

  40. Measuring TMDs • Measure AN for identified hadrons in pp and pHe3 • flavor separation • test of current extractions of u and dPDFs planed upgrade of pp2pp @ STAR can tag the scattering occurred on the p or n Varenna, July 2011

  41. The long term future future of pp@RHIC AN in 3He-proton collisions Siversfcts. for u and d quarks opposite in sign and slightly larger for d quarks expectations for Drell Yan Z. Kang @ 2010 Iowa RSC meeting • u <-> disospin rotation leads to different signs for AN for protons and neutrons • asymmetries for neutrons are larger (due to electric charges) proton caveat: does not yet include possibility of nodes in Sivers function To do it well we need detector upgrades neutron expectations for AN (pions) • similar effect for π± (π0 unchanged) • this time computed within twist-3 formalism • here, effect due to favored/unfavored fragmentation 3He: helpful input for understanding of transverse spin phenomena Varenna, July 2011

  42. what do we mean by “Direct”…. proton – proton: Au – Au or d-Au (3) (5) (2) (4) (1) g De-excitation for excited states “Fragmentation” much better called internal bremsstrahlung Induced Prompt Fragmentation (6) Thermal Radiation QGP / Hadron Gas p0 EM & Weak Decay Varenna, July 2011

  43. What is in Pythia 6.4 Varenna, July 2011 • Processes included which would fall under prompt (1) • 14: qqbargg • 18: qqbargg (19: qqbargZ0 20: qqbargW+ • 29: qgqg • 114: gggg • 115: gggg (106: gg J/Psig 116: gg Z0g ) • initial and final internal bremsstrahlung (g and g) (3) • Pythia manual section 2.2 • Process 3 and 4 are for sure not in pythia • I’m still checking 5 • the decay of resonances like the p0 is of course in pythia

  44. STAR   e+   Inclusive Jet Asymmetry at s=200 GeV • STAR: Large acceptance • Jets have been primary probe • Not subject to uncertainties on fragmentation functions, but need to handle complexities of jet reconstruction Helicity asymmetry measurement GRSV curves and data with cone radius R= 0.7 and -0.7 <  < 0.9 Varenna, July 2011 44

  45. Detector Developments: PHENIX Move from a 4 arm detector to a more standard high energy detector Varenna, July 2011

  46. Detector Developments: STAR • Forward instrumentation optimized for p+A and transverse spin physics • Charged-particle tracking • e/h and g/p0 discrimination • Baryon/meson separation • Discussions on a bigger forward upgrade ongoing eSTAR Varenna, July 2011

  47. Additional info on Jets Di-jet Kinematics: Varenna, July 2011

  48. Predictions from Boer & Vogelsang for various gluon Sivers models AN p spin  p q + g p Jets with 2 hadrons detected  p q + … q p partonkT  Unravel the underlying process for AN • Coincidence Transverse Spin Measurements Should Unravel Transversity, Collins, Sivers Effects • Study transversity by exploiting chiral-odd fragment’n “analyzing powers” (Collins or interference frag. fcns.) calibrated at BELLE • Search for spin-dependent transverse motion preferences inside proton via predicted leading-twist spin-dependent deviation from back-to-back alignment of di-jet axes  study unique to RHIC spin Varenna, July 2011

  49. At qgq vertex: • ½ + 1 ½ q and g have opposite spin projections (g can’t have proj’n zero along its momentum dir’n!), samehelicities • aLL= +1 at all  *; |M|2 1/cos2( */2) • Dominates for  in incident q direction!  ^ • At qq vertex: szq flips! • At qgq vertex: exchanged q and g must have opposite spin projections! • So, incident q and g must have same sign spin proj’nsoppositehelicities • aLL= -1 at all  *; |M|2 cos2( */2) • vanishes for  in incident q direction, contributes equally with first diagram for  opposite q ^ ^ Bottom line: aLL varies from 0 to 1 as  * goes from 0 to 180° and ( *) strongly increases! Spin Correlation for QCD Compton Scattering Varenna, July 2011

  50. STAR Forward Pion Detectors Permit Study of HadronProd’n @ High Rapidity NLO pQCD Jaeger,Stratmann,Vogelsang,Kretzer <z> <xq> <xg> Pb-glass arrays S N T High-energy 0 in this region are predominantly high-z fragments from asymmetric q-g scattering @ moderate pT B Varenna, July 2011

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