High Precision Energy Calibration with Resonant Depolarization at VEPP-4M Collider S.A. Nikitin BINP, Novosibirsk 3 July 2014, Valencia, Spain

V.Blinov 1,2,3, A.Bogomyagkov 1,2, V.Cherepanov 1, V. Kiselev 1, E.Levichev 1,3, S.Mishnev 1, A.Mikaiylov 1, N.Muchnoi 1,2, I. Nikolaev 1,2, D.Nikolenko 1, K.Todyshev 1,2, D.Toporkov 1, G.Tumaikin 1, A.Shamov 1,2, E.Shubin 1, V.Zhilich 1,2 1) Budker Institute of Nuclear Physics, Novosibirsk, Russia 2) Novosibirsk State University, Novosibirsk, Russia 3) Novosibirsk State Technical University, Novosibirsk, Russia Work was supported in a part by RFBR , , , , Co-authors

Content VEPP-4 general information RD and CBS: two methods of energy measurement at VEPP-4M Obtaining and measurement of polarization in VEPP-3 booster storage ring Touschek polarimeter and its features Transverse field depolarizer tuning Mass measurement experiments at VEPP-4 Accuracy and stability Discussion and outlooks

VEPP-4 accelerator facilities 2Е=2  11 ГэВ L=2х10**30 см -2 с -1 L= 8х10**31 см -2 с -1 Mono-ring collider with 2e +  2e - bunches and electrostatic orbit separation in 3 parasitic IPs

The luminosity of VEPP-4M is rather low. But… Large energy region 2Е=2  11 ГэВ Detector KEDR equipped by LKr calorimeter with high energy and space resolution (3.5% and 1 mm at 1.8 GeV) High resolution tagging system (two-photon physics) Technology of high precision measurement of the beam energy (concentration on high precision particle mass measurement) VEPP-4M and KEDR detector

6  Accuracy ~ 5  10 -5, t meas ~ 10 min  Beam energy spread measurement (7-10%)  Energy monitoring during statistics acquisition  Limitation in beam energy E b <3.5 ГэВ (  max <6 MeV)  Accuracy ~ 10 -6, t dep ~ 1 sec  Needs polarized beam  Up to 2-3 serial measurements possible with the same beam  Polarized beam obtained in ranges E=1.5-2 GeV, GeVГэВ Energy measurement methods at VEPP-4M BINP proposal (1968), applied for mass measurement in 1975 Resonant Depolarization VEPP-4M, , MeV Na 24 (1)= keV Na 24 (2)= keV Na 24 (1+2)= keV Compton Back Scattering energy monitor

Large polarization time in VEPP-4M  large radiative relaxation time of depolarization processes related to magnetic field errors  possibility to have an enough time after injection of polarized beam for application of RD technique in vicinity of dangerous machine spin resonance  Spin resonance grid and VEPP-3 Working Point position on betatron tune plane at 1850 MeV. Working Point is maintained with feedback system during polarization process. Obtaining of polarization Polarized beam injection into VEPP-4M ring 1MGHz per 2 mA VEPP-3 Sokolov-Ternov radiative polarization time pulse solenoid VEPP-4M e–e– e+e+ Vertical component of e GeV vs rotation angle in solenoid Vertical components of e - and e + polarization at Injection point vs Beam Energy  H sol ds=5 T  m

8 Measurement of polarization in VEPP-3 booster storage ring Deuterium atomic beam with electron polarization Pe  1 Target thickness of 5x10 11 electon/cm 2 Holding field of Gauss alternating in sign Counting rate of 6 Hz at I=100 mA Moller polarimeter with internal polarized target Equilibrium radiative polarization degree in VEPP-3 energy region from  threshold up to  (2s)

9 Energy calibration using Touschek polarimeter Depolarizer Control Scanning the depolarizer frequency Synthesizer with resolution better than Hz Standing/Travelling wave mode Depolarization Jump

10 Touschek polarimeter Transverse cross-section of the vacuum chamber with the scintillation counters and depolarizer plates Arrangement of polarimeter at the VEPP-4M technical section and experimental hall Two more TEM wave-based depolarizers and two scintillation counter pairs are used separately at other azimuths

Depolarization jump magnitude vs  betatron coupling  and beam energy  Features of Touschek polarimeter Counting rate normalized on beam volume and squared current vs beam energy Distance from counter to orbit, mm Rate, kHz/mA 2 Measured and calculated count rate Theor.  E -3 Possible sources of discrepancy: -inhomogeneity of experimental conditions with changing energy; -uncertainty of effective beam angular spread definition Calculated jump vs. coupling

Depolarizer tuning Thrice-repeated partial depolarization All three measured energy values are in the 6 keV interval (3  ) due to guide field drift Spin Response Function vs VEPP-4M azimuth Efficiency of a transverse field depolarizer depends on Spin Response Function module at an azimuth of depolarizer placement as well as on a rate of frequency scanning Depolarizer is tuned to can depolarize at a main spin resonance but to be not enough in strength for that at modulation one VEPP-4M: 366 m, 1.85 GeV,  E=27 keV (1.46  ) at 50 Hz ripples We suppressed ripples to below 10 ppm level where  (1) /  (0)  8 FCC e+e-: 90 km, 45 GeV,  E=6.5 MeV (1.45  ) at 50 Hz ripples Large shift! But small relative strength:  (1) /  (0)  1000 at 10 ppm Relative strength of 50 Hz sideband resonance

Scan modes Long-drawn jump in “CPT” mode scans testifies to spin line width of ~ due to spread of beam particle trajectories in nonlinear guide field in accordance with theoretical estimate Scan with 2  depolarization frequency resolution “Club”: quick energy calibrations in regions of resonance substructure “J/Psi”: most precise calibrations in narrow resonance peaks “CPT”: precise comparison of spin frequencies of electron and positron

Mass measurements at VEPP-4: history ParticleE, MeV Accuracy,  E/E Detector Years J/  ± ·10  OLYA  (2S) ± ·10  OLYA  ±0.09± ·10  MD '' ±0.55.0·10  MD  '' ±0.54.8·10  MD J/  ±0.010± ·10  KEDR  (2S) ±0.006± ·10  KEDR  ±0.5±0.62.1·10  KEDR D0D ±0.60± ·10  KEDR D+D ±0.45± ·10  KEDR  1.3·10  KEDR Why mass measurement? Fundamental parameter Test of theoretical models Bench mark on the mass scale of elementary particles Bench mark on the energy scale of a given collider (J/ ,  (2s) masses used in BEPC-II  - lepton mass experiment) Absolute calibration of momentum measurements in detector tracking systems Other mass measurement experiments using RD  (OLYA, VEPP-2M, 1978) K ± (EMUL, VEPP-2M, 1979)  (CUSB, CESR, 1984)  ’ (ARGUS, DORIS, 1984) Z (ALEPH etc., LEP, 1991)

Measurement of J/ ,  (2S) and  (3770) masses Psi’’ 2 times improved Current status (PDG 2012) KEDR  (3770): the best systematic error KEDR  (2S): 6 times improved as compared with OLYA PDG 2012 J/   (2S) Only 5 particle masses measured with higher accuracy ParticleΔm/m, ppm n p e μ π ± J/ψ ψ′ π

Tau lepton mass measurement The measured cross section of e+e →  +  - versus center-of-mass energy and fit World average m  = MeV KEDR m  = MeV Resonance depolarization technique for absolute beam energy calibration was successfully applied in spite of vicinity of integer spin resonance (Ebeam=1763 MeV) owing to special scenario of experiment Joint energy measurements with RD and CBS in 2006 April runs Tau-mass measurement the fundamental fermion test of the SM of weak interactions test of the  -  universality

17 Accuracy questions considered I.Groups of error sources -mean energy value determination basing on measured spin frequency -energy stability in time domains between energy calibrations -determination of produced particles energy in a Center-of-Mass system basing on energy of one of colliding beams measured with RD II.Methods of accounting - correction of measurement data -declaration of uncertainty III.Sources of errors -radial orbit distortions (non-stability of currents in magnet coils, temperature variations, geomagnetic storms, solar and lunar daily geomagnetic variations…) -vertical orbit bumps at sections without bend magnets -violation of simple energy-spin tune relation (random perturbations of vertical orbit, weak longitudinal magnetic fields, vertical orbit bumps at sections with bend magnets) -azimuthal dependence of beam energy due to radiative losses -effect of beam parameters in IP (momentum spread, inaccurate colliding beam convergence, parasitic vertical dispersion, FF chromaticity, beam potential…)

Some examples of energy drift and systematic error manifestations Processing of energy data with “predication function” in J/Psi run Correlation of daily energy oscillations with mean orbit radius deviations Spring dissolution front runs to tunnel walls Measurement of spin tune shift related to decompensation of KEDR field Results: - optimal anti-solenoid (AS) current found; - betatron coupling (~1% in AS current) and - energy error (down to ~1 keV) minimization Use of water cooling of magnets and thermo-stabilization (0.1  C) eliminates large oscillations (like 2002)

Comparison of e + and e - beam energies Electrons Positrons Simultaneous energy calibration of e + and e - E p - E e =(1.32  0.14 ) keV Reason of difference: electrostatic orbit separation in 4 IPs Distinct-in-time comparison: measured beam energy in series of consecutive calibrations of e + and e - with electrostatic orbit bumps ON hours (Feb )

Discussion and outlooks Since 2012 we have performed a series of mass measurement experiments with KEDR detector using RD technique for absolute beam energy calibration of accuracy Masses of J/Psi and Psi(2S) (best accuracy); D 0 (second after CLEO); D  (best direct measurement), tau-lepton (best result) have been measured News were application of CBS for monitoring energy ( keV) between RD calibrations and energy spread (7-10%) in these experiments R-measurement with use of RD and CBS in GeV range is in progress now Touschek polarimeter in use for RD at VEPP-4M works very well at E beam 4 GeV because of considerable decrease of effect and counting rate with energy (We consider laser polarimeter as alternative for possible mass measurements in the range of  resonance family)

Experience of VEPP-4 in RD technique, especially meaning application of transverse field depolarizer, and in analysis of sources of errors can prove useful for planned experiments at FCC, in particular, because of more higher supposed requirements to accuracy of Z mass measurement as compared with LEP experiment (  M/M~2.5  ). Thank you! What about FCC?