Lepton Beam Polarisation for the HERA Experiments ZEUS and H1

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 Zuric¨ h 1 MPI Munc¨ hen, Dec 9, 2003 Polarisation at collider machines

Polarized beams are produced in Techniques to obtain polarized beams several colliders world-wide, e.g. p beam and linear colliders: start RHIC (pp collisions) • • with polarized source + SLAC (e e−, p storage ring: avoid depolarizing • one beam polarized) resonances during acceleration + LEP (e e−, e storage ring: • • polarisation for beam diagnos- Sokolov-Ternov eﬀect tics only) slow built-up of polarisation at HERA (ep, e beam polarized) full energy • Physics analyses: polarized p study origin of proton spin • → longitudinally polarized e electroweak • → physics

Stefan Schmitt, University of Zuric¨ h 2 MPI Munc¨ hen, Dec 9, 2003 The Sokolov-Ternov eﬀect

Particle motion in storage ring: • perpendicular to B-ﬁeld of bending Magnetic field dipoles particle with spin Spins are aligned parallel or an- • tiparalell to the magnetic ﬁeld

Synchotron radiation may cause • spin flip synchotron Probability for spin flip • radiation p( ) differs from p( ) ↑ → ↓ ↓ → ↑ spin flip Magnetic field

Stefan Schmitt, University of Zuric¨ h 3 MPI Munc¨ hen, Dec 9, 2003 The Sokolov-Ternov eﬀect (cont’d)

Equilibrium: N( ) p( ) = N( ) p( ) ↑ × ↑→↓ ↓ × ↓→↑ N( ) p( ) PSfrag replacements ↑ × ↑→↓ N( ) N( ) P = N(↑)+−N(↓) N( ) p( ) ↑ ↓ ↓ × ↓→↑

Theory: Real machine: depolarizing eﬀects: P = P (1 exp( t )) non-uniform magnetic ﬁelds max × − − τ P = 8 0.924 quadrupoles, etc max 5√3 ≈ 3 τ 100s (R/m) smaller Pmax, smaller τ ≈ (E/GeV)5 → Slow built-up of transverse polarisation τ(LEP) = (10h) O τ(HERA) = (30min) O

Stefan Schmitt, University of Zuric¨ h 4 MPI Munc¨ hen, Dec 9, 2003 Example: polarisation built-up at HERA

HERA on Saturday November 29 2003 p:20.7[mA] 423.8[h] 920[GeV] e+:22.2[mA] 14.4[h] 27.6[GeV] Current-p [mA] Current-e [mA], Lifetime-e [h] 120 60 Tau(e) 100 Protons 50 Leptons 80 40

60 30

40 20

20 10

0 0 0 2 4 6 8 10 12 14 16 18 20 22 24 setting e lumi optics Time [h] HERA-e Polarisation on Saturday November 29 2003 Polarisation [%] 70 70 Transverse 60 Longitudinal 60 50 50 40 40 30 30 20 20 10 10 0 0 0 2 4 6 8 10 12 14 16 18 20 22 24 Time [h] Maximum polarisation 45% • ≈ Rise-time 30 min • ≈ Polarisation tuning: optimize orbits and other machine parameters • Constant monitoring by two independent polarimeters •

Stefan Schmitt, University of Zuric¨ h 5 MPI Munc¨ hen, Dec 9, 2003 The HERA storage ring

HERA: ep collider • E(e) = 27.6 GeV • E(p) = 920 GeV • E = 320 GeV • CM e beam polarized • Collider experiments • ZEUS, H1 Fixed target exp. • HERMES, HERA-b

Stefan Schmitt, University of Zuric¨ h 6 MPI Munc¨ hen, Dec 9, 2003 HERA I operation 1993-2000

HERA-I (1993-2000) 1 -1 120 Integrated luminosity 120 pb−

pb e-p at 319 GeV • / e+p at 319 GeV per collider experiment (ZEUS, e+p at 300 GeV H1), mostly in e+p collisions Transverse e beam polarisation

Luminosity Luminosity • 80 about 60% Transverse e polarisation: Not • Integrated Integrated relevant for physics analyses H1 Longitidinal e polarisation for 40 • HERMES since 1994/95 (spin rotators) Left-handed or right-handed

electrons eL, eR for HERMES, 0 0 200 400 600 800 1000 not for H1, ZEUS Days of running

Stefan Schmitt, University of Zuric¨ h 7 MPI Munc¨ hen, Dec 9, 2003 Spin rotators

transverse longitudinal polarisation polarisation

direction of motion

transv. pol.: spin • aligned to B-ﬁeld of bending dipoles

long. pol.: well deﬁned Six dipole magnets • • helicity Complex spin rotation and beam movement in 3D • eL or eR Beam direction after passing rotator is unchanged •

Stefan Schmitt, University of Zuric¨ h 8 MPI Munc¨ hen, Dec 9, 2003 The HERA upgrade (2000 2001) − HERA I HERA II Iron return yoke Iron return yoke

SR SR focussing magnets anti solenoid solenoid solenoid 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 Zuric¨ h 9 MPI Munc¨ hen, Dec 9, 2003 The HERA lepton ring

HERA lepton HERMES ring two independent Spin rotator Spin rotator • polarimeters TPOL measures Longitudinal • polarimeter transverse Spin rotator Spin rotator polarisation far logitudinal polarisation between the spin rotators from spin H1 in the straight sections ZEUS rotators P = Py for H1, HERMES, ZEUS LPOL measures • Spin rotator Spin rotator longitudinal polarisation Transverse transverse polarisation polarimeter between in the arcs and the straight section HERMES spin at HERA west rotators P = Pz HERA-B

Stefan Schmitt, University of Zuric¨ h 10 MPI Munc¨ hen, Dec 9, 2003 The HERA polarimeters

2.41 eV LASER beam Compton scattering of 27.5 GeV high-energy electrons electron beam 3−14 GeV and LASER photons e scattered Compton Electron and scattered photon beams photon • φ, Ε are seperated by bending magnets Detect scattered photons in a small calorimeter 14 GeV • Cross-section is sensitive to beam polarisation • σ = σ0(E) + Pxσx(E, ϕ) + Pyσy(E, ϕ) + Pzσz(E)

10W cw laser slow DAQ converter 1kHz electron beam Compton beam PM upper half fast lower half DAQ interaction point PM 100 kHz dipole silicon detector LASER beam analysis electron beam

Stefan Schmitt, University of Zuric¨ h 11 MPI Munc¨ hen, Dec 9, 2003 The HERA LPOL setup

cable shaft laser room entrance window LASER beam crosses HERA lepton beam 3.3 m mirror M 1

Nd:YAG laser analyze scattered Compton photons & optical system beam pump screen shutter stand using a small calorimeter

complicated LASER 10.6 m transport system 47.2 m mirror M 3 mirror M 4 screen lens doublet 2.5 m 8.4 m screen mirror M 2 HERA entrance window mirrors M 5/6 6.3 m calorimeter Compton photons HERA electron beam laser − electron 5.6 m interaction point electrons HERA exit window

polarization analyzer HERA tunnel, section East Right

LPOL: measure TPOL: measure energy asymmetry spatial asymmetry between left/right between left/right circular LASER light circular LASER light spatial coord. pulsed laser cw laser

Stefan Schmitt, University of Zuric¨ h 12 MPI Munc¨ hen, Dec 9, 2003 LPOL cavity upgrade

20 mrad beam analysis

Vacuum (10-8 Torr) photons electrons beam intensity amplified by 7000 feedback, locking photo diode

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 Zuric¨ h 13 MPI Munc¨ hen, Dec 9, 2003 The collider experiments ZEUS and H1

2m 1m 0

Software :SDRC-IDEAS level VI.i Performed by : Carsten Hartmann Status : October 1993

Typical HEP detectors: tracking, solenoid, calorimeter, muon chambers Detectors are asymmetric

(Ee = 27.5 GeV and Ep = 920 GeV)

Stefan Schmitt, University of Zuric¨ h 14 MPI Munc¨ hen, Dec 9, 2003 Deep inelastic scattering

PSfrag replacements PSfrag replacements HERA ) 2 Neutral current H1 e+p NC 94-00 Charged current - 10 H1 e p NC ZEUS (prel.) e+p NC 99-00 (pb/GeV 2 ZEUS e-p NC 98-99 1 + /dQ SM e p NC (CTEQ6D) e e σ e ν

0 d - 0 -1 SM e p NC (CTEQ6D) 10

-2 Z/γ 10 W -3 10 p H1 e+p CC 94-00 p -4 - 10 H1 e p CC ZEUS e+p CC 99-00 -5 ZEUS e-p CC 98-99 10 + SM e p CC (CTEQ6D) - -6 SM e p CC (CTEQ6D) q (q¯) 10 q (q¯) y < 0.9 -7 10 3 4 10 10 Kinematic variables Q2 (GeV2) 2 2 momentum transfer Q = (e e0) − − center-of-mass energy of eq system: Eeq = √sˆ, sˆ = sx

At high Q2: observe uniﬁcation of electroweak forces

With longitudinally polarized electrons: study helicity dependence

Stefan Schmitt, University of Zuric¨ h 15 MPI Munc¨ hen, Dec 9, 2003 Polarized Neutral current cross-section

0.3 NC ∼ Neutral current cross-section: σ no polarization e+ 1 1 0 2 σ 4 Y+F (x, Q ) 0.25 - NC ∝ Q x 2 L polarization e 0 2 Y xF3 (x, Q ) R polarization ∓ − 0.2 +P Y F P (x, Q2) × + 2 P 2 Y xF3 (x, Q ) 0.15 ∓ − Structure functions: 0 0 0.1 F2 and xF3

Polarized structure functions: 0.05 P P x=0.4 F2 and xF3

0 2 3 4 + 10 10 10 2 2 e p and e−p data: measure F2, xF3 Q /GeV +P and P : measure F P , xF P − 2 3

Stefan Schmitt, University of Zuric¨ h 16 MPI Munc¨ hen, Dec 9, 2003 Structure functions: HERA I and HERA II

HERA F2 x=6.32E-5 HERA I: (x) x=0.000102

10 x=0.000161 ZEUS NLO QCD fit x=0.000253 + H1 PDF 2000 fit

-log x=0.0004

100 pb−1 in e p data em 2 x=0.0005

≈ F 5 x=0.000632 H1 94-00 x=0.0008 16 pb−1 in e−p data H1 (prel.) 99/00 ≈ x=0.0013 ZEUS 96/97 per experiment (P = 0) BCDMS x=0.0021 4 E665 measurement of xF3 x=0.0032 → NMC x=0.005

x=0.008 3 x=0.013

x=0.021

x=0.032 2 x=0.05

x=0.08

x=0.13 HERA II: 1 x=0.18 1 x=0.25 plan to have 4 250 pb− × x=0.4 x=0.65 for each combination of ep and P 0 2 3 4 5 P P 1 10 10 10 10 10 measurement of F2 and F3 → Q2(GeV2)

Stefan Schmitt, University of Zuric¨ h 17 MPI Munc¨ hen, Dec 9, 2003 Measurement of the electroweak couplings

0.3 0,P 2 0,P F (x, Q ) = A x(q + q¯) Neutrino 2 q u-type q v 0.25 1 LEP (charm) CCFR P -1 Aq = f vq, aq, 2 2 shifted, same scale 1000pb Q +M 0.22 Z0 0.2 Preliminary 250pb-1 0.2 SM

0.18g 0.15 Simultaneous ﬁt of vu, au, vd, ad 0.16 0.14 68.3 95.5 99.5 % CL 0.48 0.5 0.52 0.1 g Ac 1 0.4 0.45 0.5 0.55 0.6 Study for: 4 250 pb− a × u-type -0.2 of ep with P = 0.7

d-type v -0.3

HERA measures light quarks -0.4 -0.28 Preliminary -0.3 Vb -0.32g LEP (bottom) -0.34 SM 68.3 95.5 99.5 % CL shifted, same scale -0.36 -0.54 -0.53 -0.52 -0.51 -0.5 -0.49 g Ab Complementary to -0.5 -0.6 -0.55 -0.5 -0.45 -0.4 a LEP measurements for heavy quarks d-type

Stefan Schmitt, University of Zuric¨ h 18 MPI Munc¨ hen, Dec 9, 2003 Charged current cross-section

momentum transfer CC cross-section is a linear function of P : 2 2 e− 1 P L 1+P R Q = q σ = − σ + σ e − ν CC 2 CC 2 CC Right-handed cross-section is zero in the SM PSfrag replacements W Look for new physics at P close to 1 (e.g. WR) → p Need to know P with accuracy 1%

σ(e−p νX) → q as a function of P

SM diﬀerential cross-section

2 2 L 2 mW σCC GF Q2+m2 ∝ W measure“W -mass” → Q2 > 1000 GeV2 Highest cross-section for P close to 1 −

Stefan Schmitt, University of Zuric¨ h 19 MPI Munc¨ hen, Dec 9, 2003 W mass measurement

HERA I:

Result from DIS2002 (e−p)

mW = 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

∆mW = 50 MeV

(constrained ﬁt, use mtop, etc)

Stefan Schmitt, University of Zuric¨ h 20 MPI Munc¨ hen, Dec 9, 2003 Conclusions: HERA II data taking has started

INTEGRATED LUMINOSITY (03.12.03) 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 electroweak physics, searches Fri Nov 28 12:00 2003 HERA-e Polarisation → Sun Nov 30 12:00 2003 Polarisation [%] 70 70 Transverse 60 Longitudinal 60 50 50 40 40 30 30 20 20 10 10 0 0 12 14 16 18 20 22 0 2 4 6 8 10 12 14 16 18 20 22 24 2 4 6 8 10 12 Time [h]

Stefan Schmitt, University of Zuric¨ h 21 MPI Munc¨ hen, Dec 9, 2003