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Polarization at HERA Fabio Metlica ( Penn State University) ZEUS Students Seminar 06/06/03

Polarization at HERA Fabio Metlica ( Penn State University) ZEUS Students Seminar 06/06/03. Polarization at HERA. Physics with Polarized Lepton Beams The HERA Upgrade => HERA II Polarization at HERA HERA Polarimeters: TPOL and LPOL Summary.

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Polarization at HERA Fabio Metlica ( Penn State University) ZEUS Students Seminar 06/06/03

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  1. Polarization at HERA • Fabio Metlica • (Penn State University) • ZEUS Students Seminar • 06/06/03 Polarization at HERA , F. Metlica

  2. Polarization at HERA • Physics with Polarized Lepton Beams • The HERA Upgrade => HERA II • Polarization at HERA • HERA Polarimeters: TPOL and LPOL • Summary Polarization at HERA , F. Metlica

  3. HERA II: Physics with Polarized Lepton Beams The study of polarized lepton (e+/e-) proton deep inelastic scattering at high will be one of the main physics topics at HERAII. Accurate polarization (P0.7) measurement together with high luminosity opens a new field for HERA physics at high . Possibility to study the chiral structure of the SM: -Charged currents: only LH particles interact -Neutral currents: LH, RH particles interact with Z unequally • Electroweak physics: study EW interactions using the 4 possible combinations: e-, e+ with P<0 and P>0. (Future Physics at HERA workshop). -Polarized NC,CC cross section measurements; -Light quark couplings to the Z-boson; -Precise measurements of EW parameters. • QCD: G2 structure function • Search for new physics: physics beyond SM -Right handed charged currents -Leptoquarks Polarization at HERA , F. Metlica

  4. Polarized NC, CC Cross Sections Investigate EW physics: NC and CC cross section measurements at high with P>0, P<0. Cross sections for NC and CC }X(p`) }X(p`) Polarization at HERA , F. Metlica

  5. Light Quark Couplings to the Z Boson • Polarization effect is large on cross sections for . • Different behavior at high due to Z exchange. • Split up to factor 2, at . • Exploit difference to extract the light quark(u,d) couplings to the Z-boson. Neutral Current x=0.2 Polarization at HERA , F. Metlica

  6. Light Quark Couplings to the Z Boson • Measurement of polarized NC,CC disentangle the light quark(u,d) couplings to Z. Done by using all four charge/polarization combinations. • Unpolarized DIS with e-/e+ beams axialcouplings. • Polarized DIS with the 4 charge/ polarization combinations vector couplings. 1 Contours for NC Couplings for Different Polarizations u coupling fixed d coupling fixed Polarization at HERA , F. Metlica

  7. Light Quark Couplings to the Z Boson • With of data equally divided between e+/e- and P=±0.7: • Based on full MC simulation; detector improvements would improve precision. • Complementary to LEP measurements with heavy quarks and similar to LEP precision for heavy quarks. u,d couplings to Z-boson Polarization at HERA , F. Metlica

  8. Measurements of EW Parameters: • Free parameters in SM • Measure constrain  • data from NC/CC cross sections with • beam polarization  • Test of EW universality. • LH gives highest precision: cross section largest. • High Pol. is worth a factor 4 in Lumi for NC. Polarization at HERA , F. Metlica

  9. Measure G2 Structure Function • structure function arising from Z interference. • G2 can be measured from the neutral current parity violating asymmetry  = degree of polarization (P)= axial charge of electron • Simulation for P=50% with for each polarization setting: G2 can be well measured at high x (M. Klein DIS2001 Bologna). x1 Polarization at HERA , F. Metlica

  10. Search for Right Handed CC • Standard model: only LH CC exists • Cross section vanishes for purely • RH electron (for P=+1): LHCC RHCC For e+ reverse sign Polarization at HERA , F. Metlica

  11. Search for Right Handed CC • Set a limit on the mass of the hypothetical boson (model dependent) • (~250 data). • Direct search. • Need high polarization 50%, and • precise polarization measurement. e-p SM MC e+p SM MC Polarization at HERA , F. Metlica

  12. New Physics: Beyond SM • Polarization is a useful tool for searching new physics signals. • SM backgrounds can be reduced (turned off) by varying the degree of polarization. If new physics have different couplings, the S/B will be increased. • Helps determine properties of newly discovered particles. • Study chirality of new particles e.g. leptoquarks. Polarization at HERA , F. Metlica

  13. HERA II • HERA UPGRADE: increase luminosity and provide longitudinal lepton beampolarization to the colliding experiments. Long shutdown 2000-2001, to modify IP and install spin rotators. LUMINOSITY UPGRADE • Strong focusing at IP:major changes of machine lattice near IP. Sets of superconducting quadrupoles installed close to the H1/ZEUS IP, inside the detectors. • Design luminosity HERA I (achieved): • Delivered by HERA I: (during 1992-2000) • Design luminosity HERA II : • To be delivered by HERA II by end 2006: (original plan, now?) Likely startup value for lumi: IP AREA Polarization at HERA , F. Metlica

  14. POL2000 Group: Polarization Upgrade • ZEUS: TPOL position sensitive detector(silicon microstrip + fiber detector)IC-London and Tokyo Metropolitan University • H1: LPOL cavity and fast DAQ for TPOL • HERMES: LPOL operation • HERA: polarized lepton beam studies and operation Polarization at HERA , F. Metlica

  15. HERA II: Polarization • In HERA leptons become transversely polarized through the emission of synchrotron radiation (spin flips): Sokolov-Ternov effect. • The transverse polarization is converted into longitudinal polarization near the interaction points by Spin Rotators (HERA I: HERMES; HERA II also H1/ZEUS) . • The lepton beam transverse polarization is measured by the TPOL polarimeter, and the longitudinal polarization is measured at the LPOL polarimeter, independently. Polarization at HERA , F. Metlica

  16. Polarization • Polarizationis defined as: • Polarization has to be known at the same level of precision as Total Luminosity, because it enters linearly in the cross section for many processes e.g.: • Polarization precision goal for HERA II: 0.01 ( 0.02-0.04 for HERA I), needed for polarization physics. • The absolute value of the degree of lepton polarization is the same along the whole ring. The actual location of the polarization measurement is not confined to the experiment IP. • Precise measurement from the TPOL/LPOL polarimeters together with machine lattice simulations, will provide confidence of having an accurate P measurement at IP. Polarization at HERA , F. Metlica

  17. Polarization • Polarization builds up and settles asymptotically to an equilibrium value. HERA I • Theoretical max polarization 92%, but reduced by counteracting depolarizing effects (dependence on ring parameters), • each spin rotator pair reduces polariz ~3%. • HERA I: 55%-65% polarization • HERA II : startup 50% polarization (aim for more 60%). Spin rotators and different lattice setups reduces polarization. HERA I Polarization at HERA , F. Metlica

  18. Polarization Measurement • The polarimeters make use of the spin-dependent cross section for Compton scattering of polarized photons on polarized leptons(e+/-) : • Alternatively L/R (~100Hz) circularly polarized laser light is scatteredoff leptons . The produced Compton photons are backscattered (in lab frame) into a narrow cone centered around the initial lepton direction and are detected by the polarimeter (LPOL or TPOL). • The Compton beam size at the TPOL is: Polarization at HERA , F. Metlica

  19. Polarization Measurement The polarization at HERA is determined by measuring asymmetries. LPOL TPOL Polarization at HERA , F. Metlica

  20. Polarization Measurement • The polarization of lepton colliding and non-colliding bunches differs (measured by LPOL at HERA I). Depends on the machine polarization tuning and varies in time (beam-beam effects). • Need accurate per bunch per minute polarization measurement  LPOL and TPOL upgrade for HERA2. HERA I LPOL Polarization at HERA , F. Metlica

  21. Polarization: TPOL TPOL upgrade completed • Fast DAQ to measure the polarization of individual bunches per minute. • Radhard silicon position sensitive detector to allow in-situ eta-y calibration. • TPOL ready for polarization measurement. Laser room 9th floor HERA B TPOL Setup (similar setup for LPOL) HERA Tunnel HERA B TPOL Lepton direction Polarization at HERA , F. Metlica

  22. TPOL-Spatial Asymmetry • Spatial asymmetry: • The typical total average vertical shift is about 0.15 mm. • In practice is obtained by measuring the up-down calorimeter energy asymmetry of the Compton photons: • determined by the calibration MC + test beam data. • transformation is of primary importance (main source of systematic error). test beam data Polarization at HERA , F. Metlica

  23. TPOL: HERA I • TPOL: Tungsten scintillator sampling calorimeter, 10W CW laser alternating LCP, RCP at 90Hz . • Operated in Single -photon mode: 1 photon per 200 bunch crossings; Compton energy spectrum of TPOL (HERA1) Compton spatial distribution at TPOL (HERA1) Polarization at HERA , F. Metlica

  24. Upgraded TPOL • TPOL calo measures: total energy . ,vertical position Yof the Compton  by the transformation. • Silicon detector: improve position resolution from ~1 mm (calo) to better than 50 m (silicon); intrinsic silicon resol. is 24m. • Transformation: determine accurately in-situ in real time, do not have to rely on test beam data. • Silicon position sensitive detector: prototype (1cm*1cm), final setup (6.3cm*6.3cm) (IC-London). • A single scintillating fiber detector for position calibration (5m) and monitoring of the Si-detector (Tokyo Metro. Uni). TPOL calo: Tungsten scintillator sampling calorimeter. Laser: 10W CW laser alternating LCP,RCP 90Hz . Polarization at HERA , F. Metlica

  25. Prototype Silicon Detector for TPOL • Prototype silicon detector:1cm*1cm, APV25 readout chip. • Tested with DESY T22 test beam (6 GeV electrons). Landau distr. • Results in ZEUS Note: ZEUS-01-019 • Strips S/N  20, Efficiency  97% • Position resolution < 50 m (beam telescope). • Good Eta-Y measurement Polarization at HERA , F. Metlica

  26. Silicon Detector for TPOL • CERN test beam: 6-50 GeV • Si detector(6.3cm*6.3cm),readout by 6 APV25, 80m pitch • Spare TPOL calo. (tungsten-scintillator sampling) • Scintillating fiber Detector: (7cm,1mm) • precision stage motor (reso. ~1 m). CERN test beam results and upgraded TPOL setup in ZEUS Note: ZEUS-02-019 Polarization at HERA , F. Metlica

  27. CERN Test Beam Results Good eta-y Non-Linearity:<1% Fiber calib. Precis:~50m Resolution:~ 25%/sqrt(E) Polarization at HERA , F. Metlica

  28. TPOL: HERAII Data Silicon event Silicon Raw data signal Polarization at HERA , F. Metlica

  29. Silicon Detector for TPOL Silicon 80m Pitch Adaptor 44m->80m Silicon APV25 44m Polarization at HERA , F. Metlica

  30. TPOL in HERA Tunnel Open TPOL( Calo+Silicon+Fiber) TPOL BOX Polarization at HERA , F. Metlica

  31. LPOL No major change: Original LPOL operational • Two calorimeters (Crystal and Sampling ) which may be used alternatively (movable support tables). Change to sampling: better energy linearity. • Pulsed laser: operates in Multi-photon mode: approx. 600 to1000 Compton photons produced per laser pulse (~100 Hz) shot on a lepton bunch. • Measure shifts of energy spectra for the two light polarizations. • Large difference in the spectra close to the Compton edge. • LPOL ready for polarization measurements. RCP LCP Polarization at HERA , F. Metlica

  32. LPOL Cavity Upgrade in Progress LPOL upgrade: New more powerful laser system ( Fabry-Perot cavity + new laser) to operate in single photon mode (~1-2 photons per bunch crossing). Large laser photon flux: increase probability of Compton scattering. • 1) direct calibration with Compton edge (define energy scale of calo) • 2) improve statistical error by having a high average laser power ~10kW (not commercially available). LPOL Cavity IP HERMES Lepton direction LPOL IP CW laser Original LPOL IP Circular polarized laser light Linear polarized laser light Polarization at HERA , F. Metlica

  33. LPOL Cavity (Orsay) • The cavity has been successfully installed during shutdown in HERA tunnel (near HERMES). • Cavity is locked and stable (gain factor ), should be ready by end of shutdown. • Startup plan: start with original LPOL setup, then move to laser cavity setup. Polarization at HERA , F. Metlica

  34. LPOL Cavity Installation in HERA Tunnel, 2003 Polarization at HERA , F. Metlica

  35. HERA Polarization Tuning 2003 • High polarization, P~50%, with all 3 • spin rotators on and colliding beams. • Both LPOL and TPOL working, and in reasonable agreement. TPOL minor technical problems: low TPOL luminosity. Polarization at HERA , F. Metlica

  36. Polarimeter Online Java Display Displays various polarization info Polarization at HERA , F. Metlica

  37. Polarization Data for ZEUS • Allpolarimeter info is stored into the ORACLE database. Accessible to all HERA experiments. • Software developed (Arafat Gabareen) to read polarization data from ORACLE and integrate it with the rest of the ZEUS data. • Polarization data integration: during ZEUS event reconstruction, typically a few days or a week after the data is taken. • Two ADAMO tables: 1)TPOL and LPOL values P,P for all 220 bunches. 2)TPOL and LPOL values P,P average for colliding and non-colliding bunches. Polarization at HERA , F. Metlica

  38. Extra Info • e+e- 4-6 weeks. Orbits differ, magnets need to be moved by ~6mm. • Longitudinal Polarization flip: ~1-2 days. HERA1 (LPOL) done once a month during access day (mechanical movement of magnets) plus time for beam polarization tuning. • Longitudinal Polarization direction (P<0 or P>0): each experiment can choose independently. • Polarimeters: no background problem seen. No lattice modification carried out at polarimeter locations, backgrounds similar to HERA1. • Lepton transverse polarization did not affect the measurements at HERAI (H1/ZEUS). suppressed to order compared to . (Does Transverse Electron Polarization Affect Measurements at HERA? M. Kraemer et. al.) Polarization at HERA , F. Metlica

  39. Summary • HERA has been upgradedHERAII: - luminosity increase - lepton beam polarization P50% with P/P ~1% (upgraded polarimeters). • New field of HERA physics is opened with polarized lepton beams. • Two polarimeters LPOL(cavity upgrade to be completed) and TPOL to provide accurate polarization measurements to the HERAII experiments. • Polarimeters will operate independently and cross check one another; together with HERAII machine lattice simulations will provide confidence in the IP polarization value. • TPOL/LPOL working, measured 50% polarization before start of shutdown. • Discussion between experiments and DESY to organize running and maintenance of the polarimeters. Polarization at HERA , F. Metlica

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