Lepton beam polarisation for the HERA experiments ZEUS and H1

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1 Lepton beam polarisation for the HERA experiments ZEUS and H1 Polarisation at collider machines The HERA storage ring The HERA polarimeters The collider experiments ZEUS and H1 The HERA II upgrade Data taking in 2003 Stefan Schmitt, University of Zürich 1 MPI München, Dec 9, 2003

2 Polarisation at collider machines Polarized beams are produced in several colliders world-wide, e.g. RHIC (pp collisions) SLAC (e + e, one beam polarized) LEP (e + e, polarisation for beam diagnostics only) HERA (ep, e beam polarized) Techniques to obtain polarized beams p beam and linear colliders: start with polarized source p storage ring: avoid depolarizing resonances during acceleration e storage ring: Sokolov-Ternov effect slow built-up of polarisation at full energy Physics analyses: polarized p study origin of proton spin longitudinally polarized e electroweak physics Stefan Schmitt, University of Zürich 2 MPI München, Dec 9, 2003

3 The Sokolov-Ternov effect Particle motion in storage ring: perpendicular to B-field of bending dipoles Spins are aligned parallel or antiparalell to the magnetic field Magnetic field particle with spin Synchotron radiation may cause spin flip Probability for spin flip p( ) differs from p( ) synchotron radiation Magnetic field spin flip Stefan Schmitt, University of Zürich 3 MPI München, Dec 9, 2003

4 The Sokolov-Ternov effect (cont d) Equilibrium: N( ) p( ) = N( ) p( ) replacements N( ) p( ) N( ) p( ) P = N( ) N( ) N( )+N( ) Theory: P = P max (1 exp( t τ )) P max = τ 100s (R/m)3 (E/GeV) 5 Real machine: depolarizing effects: non-uniform magnetic fields quadrupoles, etc smaller P max, smaller τ Slow built-up of transverse polarisation τ(lep) = O(10h) τ(hera) = O(30min) Stefan Schmitt, University of Zürich 4 MPI München, Dec 9, 2003

5 Example: polarisation built-up at HERA Current-p [ma] HERA on Saturday November p:20.7[ma] 423.8[h] 920[GeV] e+:22.2[ma] 14.4[h] 27.6[GeV] Current-e [ma], Lifetime-e [h] 60 Tau(e) Protons 50 Leptons Polarisation [%] setting e lumi optics HERA-e Polarisation on Saturday November Time [h] Maximum polarisation 45% Rise-time 30 min Transverse Longitudinal Polarisation tuning: optimize orbits and other machine parameters Constant monitoring by two independent polarimeters Time [h] Stefan Schmitt, University of Zürich 5 MPI München, Dec 9, 2003

6 The HERA storage ring HERA: ep collider E(e) = 27.6 GeV E(p) = 920 GeV E CM = 320 GeV e beam polarized Collider ZEUS, H1 experiments Fixed target exp. HERMES, HERA-b Stefan Schmitt, University of Zürich 6 MPI München, Dec 9, 2003

7 HERA I operation H1 Integrated Luminosity / pb HERA-I ( ) e-p at 319 GeV e+p at 319 GeV e+p at 300 GeV Days of running Integrated luminosity 120 pb 1 per collider experiment (ZEUS, H1), mostly in e + p collisions Transverse e beam polarisation about 60% Transverse e polarisation: Not relevant for physics analyses Longitidinal e polarisation for HERMES since 1994/95 (spin rotators) Left-handed or right-handed electrons e L, e R for HERMES, not for H1, ZEUS Stefan Schmitt, University of Zürich 7 MPI München, Dec 9, 2003

8 Spin rotators transverse polarisation longitudinal polarisation direction of motion transv. pol.: spin aligned to B-field of bending dipoles long. pol.: well defined helicity e L or e R Six dipole magnets Complex spin rotation and beam movement in 3D Beam direction after passing rotator is unchanged Stefan Schmitt, University of Zürich 8 MPI München, Dec 9, 2003

9 The HERA upgrade ( ) HERA I Iron return yoke HERA II Iron return yoke anti solenoid solenoid SR focussing magnets solenoid SR Add strong focussing magnets inside H1 and ZEUS + Increase specific luminosity Synchrotron radiation sources close to interaction region, small aperture, beam steering difficult Remove compensating coils and add spin rotators + Longitudinal polarisation for H1 and ZEUS Complex spin and beam orbit, delicate to tune Stefan Schmitt, University of Zürich 9 MPI München, Dec 9, 2003

10 The HERA lepton ring HERA lepton ring Spin rotator HERMES Spin rotator two independent polarimeters Longitudinal polarimeter TPOL measures transverse H1 Spin rotator logitudinal polarisation between the spin rotators in the straight sections for H1, HERMES, ZEUS Spin rotator ZEUS polarisation far from spin rotators P = P y LPOL measures Spin rotator Spin rotator longitudinal Transverse polarimeter transverse polarisation in the arcs and the straight section at HERA west polarisation between HERMES spin rotators P = P z HERA-B Stefan Schmitt, University of Zürich 10 MPI München, Dec 9, 2003

11 The HERA polarimeters 2.41 ev LASER beam Compton scattering of high-energy electrons and LASER photons 27.5 GeV electron beam Electron and scattered photon beams are seperated by bending magnets Detect scattered photons in a small calorimeter Cross-section is sensitive to beam polarisation σ = σ 0 (E) + P x σ x (E, ϕ) + P y σ y (E, ϕ) + P z σ z (E) e φ, Ε 3 14 GeV scattered Compton photon 14 GeV electron beam LASER beam analysis 10W cw laser interaction point dipole Compton beam converter electron beam upper half lower half slow DAQ 1kHz silicon detector PM PM fast DAQ 100 khz Stefan Schmitt, University of Zürich 11 MPI München, Dec 9, 2003

12 The HERA LPOL setup laser room entrance window Nd:YAG laser & optical system beam shutter complicated LASER transport system cable shaft 3.3 m mirror M 1 pump screen stand 10.6 m mirror M 3 screen 8.4 m mirror M 2 HERA electron beam LASER beam crosses HERA lepton beam analyze scattered Compton photons using a small calorimeter 5.6 m 47.2 m HERA exit window laser electron interaction point lens doublet HERA entrance window 6.3 m mirror M m screen mirrors M 5/6 Compton photons calorimeter electrons polarization analyzer HERA tunnel, section East Right LPOL: measure energy asymmetry between left/right circular LASER light pulsed laser <E> TPOL: measure spatial asymmetry between left/right circular LASER light cw laser spatial coord. Stefan Schmitt, University of Zürich 12 MPI München, Dec 9, 2003

13 LPOL cavity upgrade 20 mrad -8 Vacuum (10 Torr) photons beam analysis beam intensity amplified by 7000 photo diode electrons feedback, locking λ/4 Glan prism λ/2 LASER NdYag 0.7W LASER with 0.7 W intensity is amplified in a Fabry-Perot cavity Increase probability of Compton scattering (1 per bunch-crossing) High precision polarimetry Similar cavity is operational at CEBAF HERA cavity commisioning ongoing Stefan Schmitt, University of Zürich 13 MPI München, Dec 9, 2003

14 The collider experiments ZEUS and H1 0 1m 2m Software :SDRC-IDEAS level VI.i Performed by : Carsten Hartmann Status : October 1993 Typical HEP detectors: tracking, solenoid, calorimeter, muon chambers Detectors are asymmetric (E e = 27.5 GeV and E p = 920 GeV) Stefan Schmitt, University of Zürich 14 MPI München, Dec 9, 2003

15 Deep inelastic scattering cements Neutral current e p Z/γ e q ( q) dσ/dq 2 (pb/gev 2 ) PSfrag replacements HERA H1 e Charged current + p NC y < 0.9 H1 e + p CC H1 e - p CC ZEUS e + p CC ZEUS e - p CC SM e + p CC (CTEQ6D) SM e - p CC (CTEQ6D) H1 e - p NC ZEUS (prel.) e + p NC ZEUS e - p NC SM e + p NC (CTEQ6D) SM e - p NC (CTEQ6D) Q 2 (GeV 2 ) Kinematic variables momentum transfer Q 2 = (e e ) 2 center-of-mass energy of eq system: E eq = ŝ, ŝ = sx e p W ± ν q ( q) At high Q 2 : observe unification of electroweak forces With longitudinally polarized electrons: study helicity dependence Stefan Schmitt, University of Zürich 15 MPI München, Dec 9, 2003

16 Polarized Neutral current cross-section Neutral current cross-section: σ ± NC [ 1 1 Q 4 x Y+ F2 0 (x, Q 2 ) Y xf 0 3 (x, Q 2 ) +P ( Y + F P 2 (x, Q 2 ) Y xf P 3 (x, Q 2 ) )] σ NC no polarization L polarization R polarization e + e - Structure functions: F 0 2 and xf Polarized structure functions: F P 2 and xf P x=0.4 e + p and e p data: measure F 2, xf 3 +P and P : measure F P 2, xf P Q 2 /GeV 2 Stefan Schmitt, University of Zürich 16 MPI München, Dec 9, 2003

17 Structure functions: HERA I and HERA II HERA I: 100 pb 1 in e + p data 16 pb 1 in e p data per experiment (P = 0) measurement of xf 3 em F 2 -log10 (x) 5 4 HERA F 2 x=6.32e-5 x= x= x= x= x= x= x= x= x= x= ZEUS NLO QCD fit H1 PDF 2000 fit H H1 (prel.) 99/00 ZEUS 96/97 BCDMS E665 NMC x= x=0.008 x=0.013 x= x=0.032 x=0.05 x=0.08 HERA II: plan to have pb 1 for each combination of e ± p and ±P measurement of F2 P and F3 P x= x=0.18 x=0.25 x=0.4 x= Q 2 (GeV 2 ) Stefan Schmitt, University of Zürich 17 MPI München, Dec 9, 2003

18 Measurement of the electroweak couplings F 0,P 2 (x, Q 2 ) = q A q = f A 0,P q x(q + q) ( v q, a q, 1 Q 2 +M 2 Z 0 ) Simultaneous fit of v u, a u, v d, a d Study for: pb 1 of e ± p with P = ±0.7 u-type v d-type v g Vc LEP (charm) shifted, same scale SM % CL g Ac Preliminary Neutrino CCFR 1000pb pb a u-type -0.3 HERA measures light quarks Complementary to LEP measurements for heavy quarks -0.4 g Vb Preliminary SM % CL LEP (bottom) shifted, same scale g Ab a d-type Stefan Schmitt, University of Zürich 18 MPI München, Dec 9, 2003

19 Charged current cross-section cements e ± p momentum transfer CC cross-section is a linear function of P : Q 2 = q 2 ν σcc e = 1 P 2 σl CC+ 1+P 2 σr CC Right-handed cross-section is zero in the SM W ± Look for new physics at P close to 1 (e.g. W R ) Need to know P with accuracy 1% SM differential cross-section σ L CC G 2 F m 2 W Q 2 +m 2 W 2 measure W -mass Highest cross-section for P close to 1 q σ(e p νx) as a function of P Q 2 > 1000 GeV 2 Stefan Schmitt, University of Zürich 19 MPI München, Dec 9, 2003

20 W mass measurement HERA I: Result from DIS2002 (e p) m W = 79.9 ± 2.2(stat) ±0.9(syst) ± 2.1(pdf) GeV HERA II: High degree of polarisation increase σ(cc), keep σ(bgr) constant Accuracy for 1000 pb 1 m W = 50 MeV (constrained fit, use m top, etc) Stefan Schmitt, University of Zürich 20 MPI München, Dec 9, 2003

21 Conclusions: HERA II data taking has started INTEGRATED LUMINOSITY ( ) HERA operation restarted this autumn Background conditions improved for H1 and ZEUS HERA currents slowly increasing towards design values Polarized e beam for H1 and ZEUS Fri Nov 28 12: HERA-e Polarisation Sun Nov 30 12: Polarisation [%] Transverse Longitudinal 60 electroweak physics, searches Time [h] Stefan Schmitt, University of Zürich 21 MPI München, Dec 9, 2003