1 / 32

A Review of D G measurements: Present & Future

A Review of D G measurements: Present & Future. Snowmass 2001 Working Group: Fixed Target Experiments. Abhay Deshpande RIKEN BNL Research Center Abhay@bnl.gov. Riken BNL Research Center. Overview. Fixed target polarized DIS experiments

claire
Download Presentation

A Review of D G measurements: Present & Future

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. A Review of DG measurements:Present & Future Snowmass 2001 Working Group: Fixed Target Experiments Abhay Deshpande RIKEN BNL Research Center Abhay@bnl.gov Riken BNL Research Center

  2. Overview • Fixed target polarized DIS experiments Their need to evaluate first moments of spin structure functions Methods used to get the first moments: Old & New New: pQCD analysis at NLO  Allows to access DG Lessons…-- features and faults Other “direct methods” in DIS –Photon Gluon Fusion-to access DG: Lessons-- Features and faults • Polarized Gluon Measurements at Colliders RHIC spin program present and near future Future polarized electron proton colliders: EIC/eRHIC, Polarized HERA….THERA and their ability to get Delta G. July 3, Snowmass 2001, Delta G

  3. Polarized DIS To date fixed target experiments only Both: Probe and the Target need to be polarized Electron beams up to 50 GeV/c on fixed (solid and gaseous) targets were predominantly used at SLAC (EXXX series) and DESY (HERMES) Muon beams 100-200 GeV/c on fixed (solid) targets were used at CERN(EMC,SMC) Compared to un-polarized DIS, the kinematic range is small July 3, Snowmass 2001, Delta G

  4. How far does “polarized DIS” have to go! July 3, Snowmass 2001, Delta G

  5. Measure A1(x,Q2) Use parameterizations of F2 and R to get g1(x,Q2) To move data to a fixed Q0 -- OLD Method: assume A1 independent of Q -- New Method: use pQCD analysis at NLO which treat the Q2 evolution using DGLAP equations -- Assign appropriate uncertainties Extrapolate to unmeasured high and low x regions -- Assign appropriate uncertainties…! Evaluate first moments of spin structure functions Need to evaluate the first moments and the methods… old/new July 3, Snowmass 2001, Delta G

  6. A bit of theory… g1(x,Q2) and its evolution GLAP Evolution Pij s are Polarized splitting functions known to NLO July 3, Snowmass 2001, Delta G

  7. The Method SMC PR D58 1999 (112002) • Chose a starting scale Q2 = 1 GeV2 • Parameterize the polarized parton distributions with functional form: • Each PD is normalized such that: • become the first moment of the parton distributions • First moments of singlet and gluon distributions are free parameters while the first moment of the nonsinglet is either fixed by Bjorken sum rule or in some ambitious analyses left free too. • minimization is performed for g1 measurements from experiments and evolved value of g1 using the parton distribution functions and the DGLAP evolution equations at the measured x,Q2 of the data point. July 3, Snowmass 2001, Delta G

  8. Fit to world data 133 data points (CERN,SLAC,DESY) 10 free parameters Chi2 = 116.1 using only statistical errors Experimental systematic errors handled separately Uncertainties of theoretical origin also handled separately Results & Uncertainties… SMC PRD 1999 (112002) July 3, Snowmass 2001, Delta G

  9. Experimental Sources -- Systematic uncertainties on A1 -- Uncertainties of F2 and R parameterizations Theoretical Sources -- Functional form of initial pdf  Change that redo fits  Start at a different initial scale and repeat fits -- Factorization and renormalization scales  Change by a factor of 2 up/down repeat fits -- Value of aS 0.118 +/- 0.003 -- Other smaller effects due to quark mass thresholds, a_8… PDFs and Systematic Uncertainties July 3, Snowmass 2001, Delta G

  10. Lack of low x data… consequences SMC Results Q2 = 10 GeV2 Regge/QCD July 3, Snowmass 2001, Delta G

  11. Neutron structure function… E154/SLAC • Consequence: Unertainties in low x for Bjorken sum rule… • Acceptable? No… measure low x! July 3, Snowmass 2001, Delta G

  12. Observation: Features and Faults • Method reliable… (refer to unpolarized NLO analysis of F2), uncertainties estimates rather straightforward.. Although tedious. • Largest uncertainties come from the unmeasured low x region. • pQCD analysis needs large Q2 arms which are absent in available data • Need a collider experiment e-N with sufficiently large CM energy to cross the low x barrier at the same time have large enough values of Q2 so that pQCD methods can be reliably be used to get at a the values of Delta G. July 3, Snowmass 2001, Delta G

  13. Other methods to get at DG: Photon-Gluon Fusion Signal Background HERMES Collaboration, PRL 84 (2000) July 3, Snowmass 2001, Delta G

  14. High pT Hadron:PGF HERMES Results No estimate of theoretical Uncertainty July 3, Snowmass 2001, Delta G

  15. Experimental & Theoretical Difficulties at low Scales W. Vogelsang, SPIN2000 HERMES Collaboration Fraction of VDM and its uncertainty? Scale dependence significant? A high energy polarized collider will overcome these! July 3, Snowmass 2001, Delta G

  16. BRAHMS & PP2PP (p) PHENIX (p) STAR (p) RHIC: Polarized Proton Collider RHIC pC Polarimeters Absolute Polarimeter (H jet) Siberian Snakes Spin Rotators 2  1011 Pol. Protons / Bunch e = 20 p mm mrad Partial Siberian Snake LINAC BOOSTER Pol. Proton Source 500 mA, 300 ms AGS AGS Internal Polarimeter 200 MeV Polarimeter Rf Dipoles July 3, Snowmass 2001, Delta G

  17. RHIC Spin Physics Program Production W Production Heavy Flavors STAR +PHENIX+PHOBOS STAR + PHENIX STAR +PHENIX Direct Photon BRAHMS Jet Photon Jet Jet July 3, Snowmass 2001, Delta G

  18. New Experiments for Measurements Polarized pp Polarized DIS RHIC/BNL HERA/DESY, EIC@BNL and CERN/SPS pQCD at low x Production Single and Di-Jets DIS &Photoproduction PHENIX Heavy Flavors Polarized HERA & EIC Direct Photon Photo production of charm and high hadron pairs STAR COMPASS Jet Photon HERMES Jet Jet EIC: Electron Ion Collider 3-10 GeV e  30-250 GeV polarized protons July 3, Snowmass 2001, Delta G

  19. from Prompt Photon Production Gluon Compton (85% of ) Annihilation (15% of ) Double Spin Asymmetry July 3, Snowmass 2001, Delta G

  20. Prompt Photon Production Direct access to both in PHENIX and STAR Jet for x-gluon reconstruction Observables: Double spin asymmetries July 3, Snowmass 2001, Delta G

  21. Kinematic range RHIC vs. OthersDG from Heavy Flavors prompt photon July 3, Snowmass 2001, Delta G

  22. Pion Asymmetries for leading Pions: Year 2 Gluon A Use high in order to tag Jet Model Calculation using PYTHIA and polarized PDFs from Gehrmann, Sterling 10% of design Luminosity Gluon B Gluon C July 3, Snowmass 2001, Delta G

  23. The Electron Ion Collider (EIC) w.r.t. Other Experimental Facilities • New kinematic region to be explored • EIC = eRHIC + EPIC • Kinematic Reach for DIS: • High Luminosity! EVERY THING I SAY ABOUT EIC FROM NOW IN TERMS OF ITS PHYSICS CAPABILITIES HOLDS ALSO FOR POLARIZED HERA COLLIDER July 3, Snowmass 2001, Delta G

  24. The EIC w.r.t. Other Experimental Facilities Large luminosity and high CM Energy makes EIC unique! Variable CM energy enhances its versatility! July 3, Snowmass 2001, Delta G

  25. If the EIC is built at RHIC “eRHIC”I. Ben-Zvi et al./S. Peggs et al. • Use the existing infrastructure and resources of the RHIC at BNL RHIC: Polarized proton beams  50 GeV 250 GeV ?325 GeV • Exists an unused Experimental Hall: The one at 12 o’clock position of the present RHIC reserved for “future major detector” • Add a electron LINAC beam energy variable: 3 GeV12 GeV Electron Linac RHIC at BNL Ring-Linac Design Blue ring Yellow ring July 3, Snowmass 2001, Delta G

  26. Spin Structure Function g1 at low x A. Deshpande et al. ~5-7 days of data 3 years of data A Unique Measurement! No present/future approved experiment will measure this. July 3, Snowmass 2001, Delta G

  27. First Moment of the DG(x). A. Deshpande et al. • pQCD analysis of g1 structure function at NLO gives the first moment of the polarized gluon distribution. Present value and uncertainty is: (at Q2 = 1 GeV2) 1.0 (stat) (exp.sys.) (theory/low-x) • Major source of uncertainty from low x unmeasuredregion: Theory completely unconstrained in this region. • If EIC data is obtained and the analysis is repeated, the theoretical uncertainties improve by factors of 3-5; the statistical uncertainty improves by even bigger factors. +1.0 + 0.4 +1.4 - 0.4 - 0.2 - 0.5 Complimentary determination of DG to that from RHIC Spin July 3, Snowmass 2001, Delta G

  28. Result of Di-Jet analysis at NLOG. Radel et al./A.Deshpande et al. Statistical accuracy shown for EIC for 2 luminosities Detector smearing effects studied NLO analysis for Di-Jet Included • Easy to differentiate between different scenarios of DG: Improves DG by factor of ~3 • Combined analysis: Di-Jet + pQCD analysis of g1:DG constrained by these two together further improves the uncertainties by additonal factor of ~3 Effectively factors of 10 improvement in DG can be expected! July 3, Snowmass 2001, Delta G

  29. Polarized Parton Distribution of the Photon Photoproduction studies with single and di-jet and one and 2 high pT opposite charged hadrons. At high enough energies the photon can resolve itself into its parton content With polarized protons asymmetries related to the spin structure of the photon can be extracted! A UNIQUE measurement! Asymmetries sensitive to the gluon structure as well! Direct Photon Resolved Photon July 3, Snowmass 2001, Delta G

  30. Spin structure of polarized photon!M. Stratmann & W. Vogelsang Statistical uncertainty with 1 inv.fb. ~2wks running for EIC Single and double jet asymmetries ZEUS Acceptance cuts Will resolve the photon spin structure easily! Direct Photon Resolved Photon July 3, Snowmass 2001, Delta G

  31. Summary of DG Measurements • Polarized gluon density remains to be measured. Ample evidence for it being non-zero & positive. • Attempts to measure them have been serious but have had limited success due to various things: a) Beam facilities of the past + Detectors b) Kinematics covered by data make the interpretation difficult. • Future dedicated experiments at colliders will do better:  High energy colliders … better detector designs … will cover larger kinematic regions which have little theoretical issues • Starting with RHIC Spin leading to possible EIC at BNL or Polarized HERA at DESY the prospects of accessing DG and chances of uncovering other surprises remain very good! July 3, Snowmass 2001, Delta G

  32. Everything you ever wanted to know about future polarized & Unpolarized lepton-hadron colliders but were afraid to ask…. References for Material Related to Polarized e-p colliders EIC, Polarized HERA, THERA http://www.phenix.bnl.gov/WWW/publish/abhay/Home_of_EIC/ Will soon become… http://www.bnl.gov/eic/ July 3, Snowmass 2001, Delta G

More Related