RHIC AND THE HELICITY DISTRIBUTIONS OF THE QUARKS AND GLUONS E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012
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RHIC AND THE HELICITY DISTRIBUTIONS OF THE QUARKS AND GLUONS E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 1 RHIC@BNL Today Jet/C-Polarimeters 12:00 o’clock RHIC PHENIX 8:00 o’clock LINAC NSRL EBIS Booster AGS ANDY 2:00 o’clock RF Beams: √s=<500 GeV pp; 50-60% polarization 4:00 o’clock Lumi: ~10 pb-1/week STAR 6:00 o’clock STAR ERL Test Facility Tandems E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 2 RHIC polarized protons – luminosity and polarization • <P> increased from 37% to 46% at 250 GeV in Run-11 still significant effort needed to reach goal of 70% also for 100GeV Beams • Building blocks for pp design luminosity at 250 GeV demonstrated in Run-9 and Run-11 need to be put together plans to go beyond • Expect no significant increase in luminosity at 100 GeV before electron lenses E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 3 Predictive power of pQCD P1 q(x1) x1P1 Hard Scattering Process sˆ P2 x2P2 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) DIS E.C. Aschenauer ? pQCD Universal nonperturbative functions e+e- INT-Workshop, Orbital Angular Momentum in QCD, 2012 4 Underlying processes in pp Mid-rapidity pp p0/jetX dominated by gggg and gqgq Forward-rapidity pp p0/jet X dominated by gqgq s ++ - s +- Dfa Dfb ALL = ++ µ aˆ LL +s +s fa fb =3.3, s=200 GeV qq qq gq gq gg gg E.C. Aschenauer kinematics is unknown Scale: pT parton kinematics needs to be unfolded in theo. calculation INT-Workshop, Orbital Angular Momentum in QCD, 2012 5 The Gluon Polarization RHIC: many sub-processes with a dominant gluon contribution high-pT jet, pion, heavy quark, … T in NLO h e o r e t i c a l unpolarised cross sections nicely reproduced in NLO pQCD P E.C. Aschenauer r in QCD, 2012 INT-Workshop, Orbital Angular Momentum 6 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% E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 7 Current knowledge on DIS Dg and polarized pp Δg from inclusive DIS Scaling violations of g1 (Q2-dependence) give indirect access to the gluon distribution via DGLAP EIC RHIC polarized pp collisions at midrapidity directly involve gluons evolution. Rule out large DG for 0.05 < x < 0.2 DIS RHIC constrained x-range still very limited E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 8 Much more data Direct photon Phys. Rev. D 79, 012003 : √s = 62.4 GeV Increased √s allows to go to lower x low pt low x ?Scale uncertainty? Different final states select between gg and qg scattering sign of Dg Future measurements will include di-hadron at forward rapidity constrain x and to go to lower x E.C. Aschenauer η ALL : Phys. Rev. D 83, 032001 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 INT-Workshop, Orbital Angular Momentum in QCD, 2012 9 Reconstructing Jets at STAR MC Jets GEANT PYTHIA Particle Detector Data Jets e,n,g, p,p,etc q E.C. Aschenauer g The large acceptance of the STAR detector makes it well suited for jet measurements: TPC provides excellent charged-particle tracking and pT information over broad range in η Extensive EM calorimetry over full 2π in azimuth and for -1 < η < 2 Sophisticated multi-level trigger on EMC information at tower and patch scale Use midpoint cone algorithm many more have been used Dominated by qg sign of DG INT-Workshop, Orbital Angular Momentum in QCD, 2012 10 Correlation Measurements: ΔG STAR Inclusive ALL measurements at fixed pT average over a broad range of xgluon Reconstructing correlated probes (eg. di-jet, γ-jet) provides information on initial state partonic kinematics at LO x1 = x2 = 1 s 1 s (p (p T3 M= eh + pT 4 eh 3 T3 4 e - h + pT 4 e - h 3 ) 4 This allows for constraints on the shape of Δg(x) ) x1x2 s x1 h 3 + h 4 = ln x2 E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 11 STAR E.C. Aschenauer Much more data INT-Workshop, Orbital Angular Momentum in QCD, 2012 12 Inclusive Results: p0,p+,p- ALL STAR In Run 6, STAR measured p0 ALL in three different pseudorapidity ranges Mid-rapidity results excludes maximal Δg model, consistent with EEMC result qg scattering dominates at high η with large x quarks and small x gluons • In Run 5, STAR measured ALL for inclusive charged pions • ALL(π+) - ALL(π-) is sensitive to the sign of ΔG • Trigger using neutral jet patch Introduces significant trigger bias (charged pions often subleading particles in jets) E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 13 DG: Path Forward Limitations in current data: Limited x-range covered Weak sensitivity to the shape of DG(x) Improve precision of current measurements Get more data Extend xg-range Move to forward rapidities Constrain kinematics: map DG vs xg More exclusive channels: pp g + jet and pp jet + jet E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 14 Forward Calorimetry: PHENIX MPC Muon Piston Calorimeter (MPC): PbWO4 3.1 < || < 3.9 2p azimuth Gives access to lower: x10-3 Fully available from 2008 PHENIX pp p0 X : projections ||<0.35 MPC p0 500 GeV 300 pb-1 P=0.55 E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 15 STAR Expected Future Inclusive Jet Sensitivity Plan to measure inclusive jet ALL in 500 GeV collisions during 2012 and 2013 RHIC runs • Sensitive to smaller xg at higher beam energy • Smaller asymmetries expected, so control of systematics important Future running at 200 GeV expected to significantly reduce uncertainties relative to 2009 data as well E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 16 STAR Projected Di-jet Sensitivity @ 500 GeV Projected Stat. Uncertainty: 50% Pol 390 pb-1 Higher energies give access to lower xg Expect ALL to be smaller than 200 GeV Mjj [GeV] Mjj [GeV] Projections shown are purely statistical Forward jets in EEMC region sensitive to even lower xg Mjj [GeV] E.C. Aschenauer Mjj [GeV] INT-Workshop, Orbital Angular Momentum in QCD, 2012 17 Marco Heavy Flavor Very Very difficult: Need to shrink uncertainties at least by x50 (x2500 in lumi!!!) Correlations may give larger asymmetries, but will have even smaller stat. power. Both experiments have / or will have -vertex detectors Heavy Flavor • • • Production dominated by gluon gluon fusion Measured via e+e-, +-, e, eX, X Need more P4L E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 18 Relative Luminosity Biggest systematic uncertainty Need to control R to < 10-4 for low x measurements Beam-Beam Counters (BBC) ++ L++ L-- N BBC R = +- = -+ = +L L N BBC PHENIX: Δη = ±(3.1 to 3.9), Δφ = 2π STAR: Δη = ±(3.3 to 5.5) Cross checked with ZDC: <2.5 mrad (>6) Different physics signal, different kinematic region ALL of BBC relative to ZDC is ~0 Results-200 GeV i.e. for PHENIX, STAR very similar 2005: R ~ (25)10-4 ALL ~ (13)10-4 2006: R ~ (7.5)10-4 ALL ~ (8.2)10-4 2009: R ~ (14)10-4 ALL ~ (8.2)10-4 E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 19 Dq: W Production Basics Since W is maximally parity violating W’s couple only to one parton helicity large Δu and Δd result in large asymmetries. u No Fragmentation ! d Similar expression for W- to get Δ E.C. Aschenauer and Δd… INT-Workshop, Orbital Angular Momentum in QCD, 2012 20 expectations for ALe in pp collisions de Florian, Vogelsang t large strong sensitivity to E.C. Aschenauer u large t large u large limited sensitivity to INT-Workshop, Orbital Angular Momentum in QCD, 2012 21 Central region: W e from Run9 Triggered by energy in EMCal Momentum from energy in EMCal Charge from tracking in B field STAR: |e|<1 PHENIX: |e|<0.35 e+ eL=12 pb-1 L=8.6 pb-1 e+ E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 e22 Measured Cross Sections Reconstruction efficiency determined from MC Acceptance from NLO calculation with PDF uncertainty folded in Good agreement between experiment and theory over wide kinematic range arXiv:1112.2980 s Wtot( Z) × BR ( W ( Z ) ® en ( ee )) = E.C. Aschenauer NWobs( Z) - NWbkgd ( Z) L × e Wtot( Z) × AW ( Z) INT-Workshop, Orbital Angular Momentum in QCD, 2012 23 23 W Cross Section Ratio: RW STAR Ratio of W+ to W- cross sections sensitive to unpolarized sea quark flavor asymmetry Complementary to fixed-target DY and LHC collider measurements arXiv:1112.2980 PRL 80, 3715 (1998) obs bkgd tot s W+ NW+ - NW+ e W+ u(x1 )d (x2 ) + d (x1 )u(x2 ) RW = = obs × tot = bkgd s W- NW- - NW- e W- u(x1 )d(x2 ) + d(x1 )u(x2 ) E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 24 24 ALW: First proof of principle Run-09 P=0.39 L=8.6/12 pb-1 in PHENIX/STAR PHENIX: PRL106, 062001 (2011) STAR: PRL106, 062002 (2011) STAR E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 25 Future STAR W Measurements Forward GEM Tracker upgrade 6 light-weight triple-GEM η=1 disks using industrially produced GEM foils Partial Installation for 2012 η=2 FGT E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 26 26 PHENIX: Forward -Arm upgrade MuID Trigger existing: Selecting momentum > 2 GeV E.C. Aschenauer MuTRG (fully installed): Fast selection of high momentum tracks RPC 1 & 3 (installed): Provide timing and rough position information INT-Workshop, Orbital Angular Momentum in QCD, 2012 27 PHENIX Forward Arm: W trigger eff. First data collected in 2011: L~15 pb-1 P~0.52 Data being analyzed Raw yields with different triggers and cuts trigger rejection Expected W yield More challenging than We at ~0 E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 28 W l : Projections PHENIX: W PHENIX: We STAR: We S/B = 5 Lumi: 300 pb-1 & 60% polarisation E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 29 Dq from Hyperon Spin Transfer STAR PRD 80 111102 (2009) Future: Can improve statistics at ||<1 significantly Go to more forward rapidities W.Zhou, PRD81,057501,2010 2005 Data at √s=200 GeV Caveat: many theoretical models, but L is product of hyperon decays --> Impact on Dq ???? E.C. Aschenauer √s=500 GeV at 2.5<<3.5 INT-Workshop, Orbital Angular Momentum in QCD, 2012 30 ALW: Future Possibilities Can we increase p-beam energy? 325 GeV: factor 2 in sW access to lower x for Dg(x) ALW: pp @ 500 GeV ALW: He3-p @ 432 GeV Increased beam-energy and polarized He-3 beam full flavor separation phase 2 of pp2pp@STAR can separate scattering on n or p E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 31 Critical √s of W cross section s w (650GeV) ~2 s w (500GeV) Main issues: Quench performance of magnets (DX, arc dipoles and quads, IR quads) Crossing angles at IPs and luminosity estimated # of training quenches Polarization Current feed-throughs Power supplies and transformers polarised He-Beams Dump kicker (strength, pre-fires) had a aat workshop to discuss possibilities Reliability generallyreduced higher energies https://indico.bnl.gov/conferenceDisplay.py?confId=405 Report: W. MacKay BNL C-A/AP/422 no show stoppers, but need additional snakes in RHIC Conclusion: many ideas to increase luminosity of RHIC techniquely challenging, CEC magnets 10% increase to275 GeV feasible with i.e. current about 20 DX, 10 other training quenches, more cooling at some current leads Requires some hardware upgrades (power supplies) Effect on polarization still needs study Energies >275 GeV require too many training quenches hundreds of arc dipole training quenches alone for 325 GeV E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 32 What can be done in polarized pp constraining Jg E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 33 From pp to gp Get quasi-real photon from one proton Ensure dominance of g from one identified proton by selecting very small t1, while t2 of “typical hadronic size” small t1 large impact parameter b (UPC) Final state lepton pair timelike compton scattering timelike Compton scattering: detailed access to GPDs including Eq;g if have transv. target pol. Challenging to suppress all backgrounds Final state lepton pair not from g* but from J/ψ Done already in AuAu Estimates for J/ψ (hep-ph/0310223) transverse target spin asymmetry calculable with GPDs AUT (t ,t) ~ t0 - t Im(E * H) mp |H| M J2 /Y t= s information on helicity-flip distribution E for gluons golden measurement for eRHIC Work in collaboration with Jakub Wagner, Dieter Mueller, Markus Diehl E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 34 phot on-phot on ples are nuclear air and meson . T he exchange i, yielding large al st at es t o low riment al signahe first observauct ion, AuAu → ccompanied by Au ρ0 . Ult ralaborat ory for o fixed-t arget ρ0 meson exchange, as indicat ed by t he rise of t he ρ product ion cross sect ion wit h increasing energy in lept onnucleon scat t ering [6]. In addit ion t o coherent ρ0 product ion, t he exchange of virt ual phot ons may excit e t he nuclei. T hese processes are assumed t o fact orize for heavyion collisions, which is just ified by t he similar case of two-phot on int eract ions in relat ivist ic ion collisions accompanied by nuclear breakup, where it was shown t hat t he non-fact orisable diagrams are small [7]. T he process AuAu → Au Au ρ0 is shown in Fig. 1b. In lowest order, mut ual nuclear excit at ion of heavy ions occurs by t he exchange of two phot ons [8, 9]. Because of t he Coulomb What is feasible Thomas Ullrich and Tobias Toll have written an MC for exclusive VM / DVCS production in ep & eA Modified to UPC in AA a) Au → AuAuρ (c.f. s¨acker-Williams e vect or meson by one nucleus scat t ers elast inuclei are not olely of t he two uct s [5]. In t he #* 0 ! P Au b) Au Au #* ² ! ² P Au Au ² ² Au* #* #* Au* a: elastic scattering b: nucleus breaks up by emitting neutrons ZDC FIG. 1: Diagram for (a) exclusive ρ0 product ion in ult raperipheral heavy ion collisions, and (b) ρ0 product ion wit h nuclear excit at ion. T he dashed lines indicat e fact orizat ion. Also modified for UPC in pp AuAu Au+Au+r First simulations underway cross sections agrees with hep-ph/0310223 s ~ 6.2 nb STAR has good acceptance for J/psi Roman-Pots to tag exclusivity SATRE still needs to be tracked through the STAR-MC to get resolution effects included Good agreement Need to do full rate estimate E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 35 UPC in polarized pp collisions STAR Phase-I (installed): for low t-coverage Phase-II (proposed): for high t-coverage No special b* running needed any more E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 36 NYC,BNL and RHIC are beautiful Summary and the GIANTS won the Superbowl E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 37 BACKUP E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 38 How do the partons form the spin of protons Is the proton looking like this? DG SqDq q Lg SqLq f1T SqL q SqDq DG f1T q Lg “Helicity sum rule” gluon spin 1 = P, 1 | J z | P, 1 = 1S z + S z + Lz + Lz q g å q g 2 2 QCD 2 å q 2 q total u+d+s quark spin E.C. Aschenauer Where do we stand solving the “spin puzzle” ? angular momentum INT-Workshop, Orbital Angular Momentum in QCD, 2012 39 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 E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 40 What We Measure Two-spin helicity asymmetry: ALL versus 1 N++/L++ N+/L+ P1P2 N++/L++ + N+/L+ Can be large in pQCD hard scatter. Stat. Unc. ~ (P12P22 L dt )1/2 One-spin helicity asym. AL violates parity if non-vanishing, but can be large in weak processes like W prod’n. Single-spin transverse asym. N/L N/L AN 1 P1 N/L + N/L versus E.C. Aschenauer 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. Stat. Unc. ~ (P12 L dt )1/2 INT-Workshop, Orbital Angular Momentum in QCD, 2012 41 Inclusive Jet Cross Section pT [GeV/c] pT [GeV/c] • Data well described by NLO pQCD when including hadronization and underlying event corrections from PYTHIA • Hadronization and UE corrections more significant at low jet pT E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 42 42 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 ALL systematics (x 10 -3) Reconstruction + Trigger Bias [-1,+3] (pT dep) p + e p Non-longitudinal ~ 0.03 Polarization p (pT dep) Relative Luminosity 0.94 Backgrounds 1st bin ~ 0.5 Else ~ 0.1 pT systematic 6.7% Helicity asymmetry measurement GRSV curves and data with cone radius R= 0.7 and -0.7 < < 0.9 E.C. Aschenauer STAR INT-Workshop, Orbital Angular Momentum in QCD, 2012 4343 Studying Gluon Polarization at RHIC s ++ - s +- Dfa Dfb ALL = ++ µ aˆ LL +s +s fa fb Partonic fractions in jet production at 200 GeV 0 10 E.C. Aschenauer 20 30 pT(GeV) INT-Workshop, Orbital Angular Momentum in QCD, 2012 44 Correlation pT – x and √s 2-2.5 GeV/c 4-5 GeV/c 9-12 GeV/c 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 E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 45 Star: Forward Physics program add electromagnetic calorimetry at forward rapidity access low and high x TPC: TPC: BEC: BEC: -1.0 -1.0 -1.0 -1.0 < < < < < < 1.0 1.0 < < 1.0 1.0 E.C. Aschenauer 2003: FPD: 3.3 < < 4.1 2008: FMS: 2.5 < < 4.1 INT-Workshop, Orbital Angular Momentum in QCD, 2012 46 STAR Forward Pion Detectors Permit Study of Hadron Prod’n @ High Rapidity Pb-glass arrays S N High-energy p0 in this region are predominantly high-z fragments from asymmetric q-g scattering @ moderate pT <z> <xq> NLO pQCD Jaeger,Stratmann,Vogelsang,Kretzer <xg> E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 47 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 parton kTx x y z BUT Processes Universality vs non-universality: Semi-Inclusive deep inelastic scattering ✔ Drell-Yan ✔ ✔ Watch out for sign flips ! e+/e- annihilation ✔ p + p h1 + h2 + X ! ! TMD PDF is not just non-universal, arXiv:1102.4569 it is ill-defined at the operator level ! work has started to fix this problems E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 48 2009 Inclusive Jet ALL Separate into two η bins which sample different partonic kinematics Models predict a ~20% reduction in ALL from |η|<0.5 to 0.5<|η|<1 Data falls between DSSV and GRSV-STD in both ranges E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 49 49 Charged pions opposite jets ALL ALL Trigger and reconstruct a jet, then look for a charged pion on the opposite side Correlation measurement significantly increases the sensitivity of ALL(π+) Full NLO calculations for this observable: de Florian, arXiv:0904.4402 E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 50 50 W → e + ν Candidate Event • Isolated track pointing to isolated EM deposit in calorimeter • Large “missing energy” opposite electron candidate Di-jet Background Event • Several tracks pointing to EM deposit in calorimeter spread over a few towers • Vector pt sum is balanced by opposite jet, “missing energy” is small E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 51 51 W/Z Algorithm Description Match high pT track to BEMC cluster Isolation Ratios Signed-Pt Balance E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 52 52 Background Estimation Sources: EWK: W -> τ , Z -> e+e- QCD: Data-driven Good Data/MC agreement E.C. Aschenauer INT-Workshop, Orbital Angular Momentum in QCD, 2012 53 53 RHIC: AL for W bosons RHIC: can detect only decay leptons; lepton rapidity most suited observable de Florian, Vogelsang, arXiv:1003.4533 • strong correlation with x1,2 allows for flavor separation for 0.07 < x < 0.04 Δχ2 = 2% uncertainty bands of DSSV analysis E.C. Aschenauer Δχ2 = 2% uncertainty bands with RHIC data INT-Workshop, Orbital Angular Momentum in QCD, 2012 54