BINP Novosibirsk Current status of luminosity measurement with
BINP, Novosibirsk Current status of luminosity measurement with CMD-3 detector at the VEPP-2000 e+e - collider G. V. Fedotovich A. E. Ryzhenenkov on behalf of the CMD-3 collaboration WG 18 -19 November LNF, Frascati, Italy
Motivation As a rule the hadronic cross sections in experiments at e+e- colliders are normalized on the integrated luminosity For luminosity determination it is necessary to use well known QED processes which have the large cross sections and a simple signature in detector e+e-, , + -. Cross check capability will be in hands to believe 1% precision (or better). Luminosity determination at least better than 0. 5% is required. Hadron contribution to (g-2) of muon is about 60 ppm: 60 0. 005 = 0. 3 ppm Indeed, in our experiments (for the main channel e+e- + -) we determine the ratio N N ee + ) which has better systematic accuracy The aim new FNAL experiment for the (g-2)/2 of muon is to improve the previous BNL result by a factor of 4! and to achieve accuracy 0. 15 ppm good test of SM. The similar accuracy plan to achieve in JPARC experiment
VEPP-2000 storage ring ILU 3 Me. V Linac CMD-3 B-3 M VEPP-2000 BEP 250 Me. V synchrobetatron e+, e booster 825 Me. V SND e e+ converter • Up to 2 Ge. V c. m. energy Status: • VEPP-2000 uses special optics Plans: ≈100 pb-1 per detector per year 2010 – start of experiments providing “round beams” give additional gain in luminosity and will provide: L 1032 cm-2 c-1, √s=2. 0 Ge. V
VEPP-2000 with round beams Integrated luminosity ~ 100 pb-1 per detector/year revolution time – 82 ns beam length – 3. 3 cm circumference – 24. 4 m L = 1032 cm-2 s-1 at 2. 0 Ge. V beam current – 200 m. A energy spread – 0. 7 Me. V beta function in IP x= z =4. 3 cm Lpeak = 1031 cm-2 s-1 at 1 Ge. V CMD-3 SND 4
3 D view CMD-3 detector DC – 1218 hexagonal cells with sensitive wires, W-Re alloy, 15 in diameter. Z-chamber – start FLT, precise determine z-coordinate ~ 500 (acceptance) LXe calorimeter thickness 5 X 0, 264 towers & 2112 strips. Spatial resolution 1 – 2 mm Calorimeter with Cs. I crystals ( 3, 5 t), 8 octants, number of crystals - 1152, 8 X 0. TOF – 196 counters, time resolution ~ 1 ns Muon range system – 8 octants (cosmic veto, time resolution ~ 1 ns ) Magnetic field is about 1. 3 T
Collected Luminosity Averaged over run Luminosity 1031 cm-2 c-1 at √s=2. 0 Ge. V Collected L ~ 60 pb-1 per detector Currently the luminosity at high energy 8. 3 pb-1 ω - region is limited by a deficit of positrons and 9. 4 pb-1 < 1 Ge. V (except ω) maximum energy of the booster (825 Me. V) 8. 4 pb-1 φ - region After upgrade it will gain at least by 34. 5 pb-1 > 1. 04 Ge. V the factor of ten
e+e- π+π- by CMD 3 Clean collinear events (mostly without background) Plans to reduce systematic error from 0. 6% -> 0. 3%: ✗ Event separation will be checked by different methods 0. 2% ✗ More proof of Radiative corrections 0. 2% -> 0. 1% ✗ Determination of fiducial volume controlled independently by LXe and ZC subsystems (0. 1%) Statistical precision of cross section measurement Collected L ~ 60 pb-1 8. 3 pb-1 ω - region 9. 4 pb-1 < 1 Ge. V (except ω) 8. 4 pb-1 φ - region 34. 5 pb-1 > 1. 04 Ge. V
Event e+e- in CMD-3 R- plane e+e-
Event selection (e+e-) Two collinear tracks in DC, π-1. 0>( θ 0 +(π- θ 1))/2 > 1. 0 E 2, Me. V E 2 vs E 1 m. i. p. e+ e- → e + e- E 1, Me. V Energy cuts: Ebeam/2 < E 0, E 1< 3*Ebeam/2 9
Event selection First step - Collinear events selection ü ü Number hits on each track in DC more than 5 (max 19) Total charge = 0 Acollinearity angle in R - plane: | | φ1 -φ0|-π | < 0. 15 rad Acollinearity angle in R – z plane: |θ 1 + θ 0 -π| < 0. 25 rad Second step - Bhabha events selection ü Number of clusters in LXe calorimeter is 2 exactly associated with traks ü Polar angle (π - 1. 0) < ( θ 1 lxe- θ 0 lxe + π )/2 < 1. 0 rad ü Energy of every cluster E 1, 2 > 0. 5 Ebeam ü Number of hitted sectors in z-chamber > 1
Event e+e- -> γγ in CMD-3 R- plane
Events selection e+e- -> γγ No tracks in DC No signals in ZC sectors Back-to-back cluster in calorimeter with: angle cuts π - 1. 0 > ( θ 0 +(π-θ 1))/2 > 1. 0 energy cuts Ebeam/2 < E 0, E 1< 3*Ebeam/2 E 2, Me. V E 2 vs E 1 e+e- -> γγ E 1, Me. V
Luminosity determination L = Ne+e-/[σBorn rad (εdc)2(εcl)2 tr] Ne+e-- number of the selected Bhabha events σBorn - Born cross section rad - radiation correction MCGPJ ( 95. 1 ± 0. 2% ) εDC - track reconstruction efficiency in DC (99. 23 ± 0. 08)% To determine track reconstruction efficiency in DC events are selected using calorimeters and ZC information only: ü Two back-to-back clusters in calorimeters with a good quality. ü Signals in ZC sectors associated with clusters should be. ü Look for tracks in DC which belong to clusters εcl - cluster reconstruction efficiency in calorimeter (99. 5± 0. 2)% ü Two back-to-back tracks in DC ü Back-to back signals in ZC sectors associated with tracks ü Look for clusters in LXe calorimeter which belong to tracks tr-charge trigger efficiency was based on neutral trigger information
Track reconstruction efficiency in DC Test events selections based on cal. information only 1 lxe-φ0 lxe -π, rad θ 1 lxe + θ 0 lxe -π, rad ||φ1 lxe-φ0 lxe-π| - φrot | < 0. 05 | θ 1 lxe + θ 0 lxe -π| < 0. 3 Ebeam/2 < E 0, E 1< 3/2*Ebeam εdc = N 2 tr_coll / Ntotal ~ 99. 6 %
back-to-back clusters in calorimeter LXe calorimeter has 33 towers in r- plane. In ideal case the horizontal axis should go through the gap between two adjacent towers. The opposite axis side should pass through the center of the tower. Indeed, Indeed the electrodes of cal. turned a bit against watch arrow. This effect is a cause of the small asymmetry between left and right peaks.
Collinear γγ events in CMD-3 no tracks in DC back-to-back clusters in calorimeter | φ1 -φ0|-π < 0. 15 |θ 1 + θ 0| -π < 0. 6
Ratio of luminosities (2011) Blue points – scan up Red points – scan down Number of points – 39 Integrated Luminosity ~ 22 pb-1 Fit: (2 1)% Only statistical errors are shown
Ratio of luminosities Only scan up Blue points – scan 2012 Number of points – 15 Integrated Luminosity ~ 12. 5 pb-1 Fit: (0. 1 0. 2)% Only statistical errors are shown
Ratio of luminosities 2013. First scan energy region from to Number of points – 10 Integrated Luminosity ~ 3 pb-1 Only statistical errors are shown Fit: (-0. 3 0. 3)% 19
Events separation based on momentum distribution Е = 250 Мэ. В Е = 160 Мэ. В E = 330 Me. V
e/ / separation using particles momentum Can measure N( )/N(ee) & compare with QED CMD-2 CMD-3 -2 1. 3 % -0. 43 0. 47 % systematic errors are under study
Systematic error for luminosity due to polar angle resolution in DC Polar angle resolution vs run number Correction to Bhabha XS It is necessary to study every run and determine polar angle resolution!!!
Systematic error for luminosity due to the slope of the DC axis with respect to beam axis e- distribution in r- plane 2 mm inserted to Sim e+ distribution in r- plane 2 mm inserted to Sim Measurement the amplitude of the wave allows to estimate the angle of the slope This slope corresponds to the angle of 5 mrad
Some systematic errors for luminosity The list of statistical and systematics errors e+e. Statist. err. 0. 3% RC 0. 2% Fiduc. vol. 0. 4 1. 5% Slope of the 0. 3 0. 5% beam axis Ø Wall of the 0. 3% vacuum chamber Ø Event 0. 2 0. 4% separation Ø Ø e r Ø Beam energy 0. 2% calibration Ø Efficiency corrections 0. 4% p Ø Total (syst. ) 1% 0. 2% 0. 5% 0. 2% a in il m 0. 8 1. 7% y r Limited by collected luminosity MCGPJ unstable z-resolution in DC –will improv. unstable direction of the beam axis while data taking – will monitoring 0. 3% do not know correctly the thickness of the wall and chemical composition 0. 5% physical background and overlapping of the e/ / / energy distributions of the energy deposition in calorimeters 0. 2% will be improve in future using Compton back scattering techniques 0. 4% will be improved in future runs 0. 9% aim to obtain syst. error 0. 5%
Summary Peak L~2 x 1031 cm-1 sec-2 has been reached, but it is limited by positrons production rate. “Unlimited” positron source is in preparation. Hope for X 10 in luminosity and statistics Luminosity was measured using two processes: e+e- → e+e-, . The currant systematic error for integrated luminosity is estimated as 1% First scan up and down from 1 Ge. V to 2 Ge. V with 25 Me. V step with ~0. 5 pb-1/point was completed in 2011. This region was scanned again with smaller step and 1 pb -1/point in 2012 The new scan with precision energy measurement is done during 2013 season (2 E < 1 Ge. V) First preliminary results for the ratio (N /Nee)/( / ee) are demonstrated: The test accuracy of QED is about (– 0. 5)% and limited by statistic while. We need accuracy 0. 2% or better (MCGPJ) Analysis of the systematic errors is going on and currently it is estimated as (1 2)% for the whole energy region.
Back slides 27
SM prediction for muon g-2 aμexp = (g-2)μ/2 = (11 659 208. 9 ± 6. 3)x 10 -10 aμth = aμQED + aμEW + aμhadr (Exp. – Theor. )~3. 3 -3. 6 δaμ QED contribution EW contribution NLO hadronic 11 658 471. 808 ± 0. 015 Kinoshita & Nio, Aoyama et al 15. 4 ± 0. 2 Czarnecki et al − 9. 8 ± 0. 1 HLMNT 11 694. 1 ± 4. 3 x 10 -10 HLMNT 11 Main channels which contribute to precision at √s<1. 8 Ge. V π+π− 505. 65 ± 3. 09 π+π− 2π0 18. 62 ± 1. 15 π+π−π0 47. 38 ± 0. 99 (mostly from omega region) 2π+2π− 13. 64 ± 0. 36 (Ba. Bar) K+K 22. 95 ± 0. 26 (Ba. Bar) Isospin relations: 5. 98 ± 0. 42 for not measured KK , KK 2π, 2π4π0, 2π3π0 12. 46 ± 0. 76 for √s<2 Ge. V) (1. 5 - 3σ of total error - crucial in case of isospin violation) Rqcd[2 -11 Ge. V] LBL Theory TOTAL 41. 19 ± 0. 82 10. 5 ± 2. 6 Prades, de Rafael & Vainshtein need more theory ± 4. 9
R(s) measurements at low s At low s R(s) has to be measured in each channel. The value and the error of the hadronic contribution to muon (g-2) are dominated by low energy R(s) (<2 Ge. V give 92%). a. QED(MZ) – half of error comes from 2 E < 4 Ge. V 29
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