Overview of the CMD-3 recent results at e+e- collider VEPP-2000 Fedotovich G.V. On behalf of CMD-3 collaboration Budker Institute of Nuclear Physics Novosibirsk State University MESON 2016, 2 – 7 June, Krakow 1
Outline ▪ Motivation ▪ Collider and detector ▪ Experiment ▪ Recent results: ❑ Processes with pions ❑ Processes with kaons ❑ Processes with pions & kaons ❑ Other processes ▪ Summary and perspectives 2
Motivation Muon anomaly, a m = (g-2) m /2 QED HADRONIC LbL WEAK * 2 ( e e hadrons ) ∞ K ( s ) + − α σ → γ → had a ds R ( s ) R ( s ) = ⋅ ⋅ ∫ = 2 µ 3 s ( e e ) ⋅ π + − + − σ → µ µ 2 4 m π M. Davier et al.,EPJC71(2011)1515 EXP SM a a 3 . 6 − = σ µ µ Experimental input is needed! Major contribution to (g-2)/2 coming from VEPP-2000 energy range gives 92% and determine it’s uncertainty 3
VEPP-2000 collider (2011-2013) ILU CMD-3 3 MeV Linac B - 3M VEPP-2000 BEP 250 MeV synchro- e + ,e − betatron booster SND e − → e + converter Maximum c.m. energy is 2 GeV, project luminosity is L = 10 32 1/cm 2 s at √ s = 2 GeV Unique optics with used “round beams”, allows to reach higher luminosity Experiments with two detectors, CMD-3 and SND, started by the end of 2010 4
CMD-3 detector DC – 1218 hexagonal cells with sensitive wires, W-Re alloy, 15 µ in diameter, spatial resolution ∼ 100 µ . Z-chamber – start FLT, precise determine z-coordinate ~ 500 µ (detector acceptance) LXe calorimeter thickness 5,1X 0 , 196 towers & 1286 strips. Spatial resolution 1 – 2 mm, measurement of conversion point for g ’s measurement of shower profile TOF – 16 counters, time resolution ~ 1ns particle id (mainly p, n) Calorimeter with CsI crystals ( ∼ 3,5 t), 8 octants, number of crystals - 1152, 8 X 0 . MR system – 8 octants (cosmic veto, ~ 1ns ) Project magnetic field - 1,5 T (current value 1.3 T while) 5
Collected luminosity Beam-beam limit CMD-3 data, average per run Luminosity, 1/cm 2 s Energy Limited e + ramping production Beam energy, MeV c.m. energy 2E, MeV Today the peak luminosity is limited by a deficit of positrons (650 MeV) Collected L ~ 60 pb -1 per detector and limited energy of the booster 8.3 pb -1 ω -region (higher 825 MeV). 9.4 pb -1 region below 1 GeV ( except ω ) After upgrade (completed) we expect 8.4 pb -1 ϕ -region increasing of luminosity by a factor of 34.5 pb -1 region higher than ϕ 10 at maximum beam energy. 6
e + e - → π + π - statistics and systematics Expected statistical error for 2013 data Main sources of systematics: ➢ e/ µ / π separation – 0.2% multiple ways to get detector response from data itself. ➢ Fiducial volume – 0.1% independent systems, which can be used to determine fiducial volume with cross check. ➢ Beam energy – 0.1% constant monitoring with Compton backscattering ➢ Radiative corrections – 0.1% proof from data. ➢ Many systematic studies will be rely on high statistics. 7
Energy measurement Starting from 2012, energy is monitored continuously using compton backscattering techneques Radiation coming from A and C points under angle ϕ = 0 is interference E.V. Abakumova et al.,Nucl.Instrum.Meth. A744 (2014) 35-40 8
Luminosity determination (e+e- & γγ ) π , µ e c e i m s µ o Cosmic c π e π , µ e π , µ & cosmic Cosmic and µ , π clusters begin to overlap with energy 9
Luminosity determination Fit: (0.1 ± 0.2)% Fit: (0.1 ± 0.3)% Preliminary Scan up & down, Scan up, 2012 2011 Fit: (0.5 ± 0.3)% Fit: (-0.2 ± 0.2)% ϕ→ω scan, 2013 Low energy scan, 2013 10
e + e - → π + π - 2013 data 2013 data (9.4 pb -1 ) PRELIMINARY 2013 data y r a n i m by momentum i l e r P Work in Fit: (-0.4 ± 0.5)% Work in Only statistical errors are shown progress progress by energy by energy Work in deposition deposition by energy progress by momentum deposition 11
Study of the process e + e - → K + K - The process e+e- → K + K - has been study at energies around ϕ meson mass. Events selection is based on information about average energy losses dE/dx in DC and the average momentum of pair tracks ▪ In E cm = 1004 – 1060 MeV: ▪ 25 energy points 12 ▪ Luminosity integral 5.9 pb -1
Study of the process e + e - → K + K - Preliminary Δσ nr = 10 × [ σ (fit) - σ ( ϕ )], nb Interference between ϕ with mainly ω & ρ resonances The measured cross section of the process e+e- → K + K - together with the results from CMD-2 and BaBar is shown near φ -meson 13 mass energy. The systematic error is of about 2.5%
e + e - → K L K S This process is studied using decay K s →π + π - Δσ nr = 10 × [ σ (fit) - σ ( ϕ )], nb In E cm = 1004 – 1060 MeV: 25 energy points. Collected luminosity ~5.9 pb -1 Systematic error is 2 – 3 % 14 Presented to publish in Phys. Lett. B
The difference of charged and neutral cross-sections normalized to phase space difference as well as Coulomb interaction of charged kaons in final state. σ (K + K - ) ∼ |A I=0 ( ω , φ ) + A I=1 ( ρ ) | 2 σ (K S K L ) ∼ |A I=0 ( ω , φ ) - A I=1 ( ρ ) | 2 15
e + e - → K L K S This process is studied using decay K s →π + π - CMD-3 (Preliminary) CMD-2 SND BaBar DM1 Preliminary Good agreement with all previous results In E cm = 1100 – 2000 MeV: 54 energy points Luminosity integral 32.1 pb -1 1889 events with fully reconstructed K S → π + π− 16
Cross section of the e + e - → π + π - π ° ➢ Black points - CMD-3 data (run 2011 & 2012) ➢ Green points – BaBar data ➢ Red points – SND data Analysis is based on integrated luminosity ∼ 30 pb-1 Cross section was measured at 46 energy points Preliminary Preliminary Current systematic error ∼ 7 % Red fit – sum of amplitudes: ω , ϕ , ω ’, ω ’’ 17
Dynamics of e + e - → 2 π + 2 π - & cross section a 1 (1260) a 1 (1260) a 1 (1260 ) ρ (770) ρ (770) a 2 (1320) a 1 (1260) ρ (770) A ρ 0 is always present, a 1 (1260) π and a 2 (1320) π are significant 18
e + e - → 5 π Study 2( π + π - ) π 0 final state in intermediate ηππ and ωππ production e + e - → ωπ + π − → 2( π + π − ) π 0 e + e - → ηπ + π − → 2( π + π − ) ) π 0 Preliminary Preliminary Preliminary Preliminary 19
e + e - → ηπ + π - ( η→γγ ) m( γγ ) Preliminary Preliminary m( ππ ) Cross sections are in agreement for both decay mode η→π + π − π 0 and γγ ηρ intermediate state dominates. 20
e + e - → 6 π Phys.Lett. B723(2013)82 CMD-3 (Preliminary) BaBar Preliminary Phys.Lett. B 723(2013)82 n \bar n p \bar p threshold Systematic error is about 6%, main source is model In E cm = 1450 – 2000 MeV: 38 energy points, dependence. Luminosity integral 23.8 pb -1 , Preliminary studies of dynamics: Hint of energy 10700 fully reconstructed events dependent dynamics in 1.7-1.9 GeV energy range; DATA@E = 1720 МэВ DATA@E = 2000 МэВ M( π + π - π 0 ) M( π + π - π 0 ) ω (782)3 π → (61 ± 6)% ω (782)3 π → (49 ± 11)% ρ (770)4 π → (27 ± 7)% ρ (770)f 0 (1370) → (46 ± 13)% ω (782) η → ( 12 ± 4)% a 0 (980) ρ → ( 5 ± 2)% 21
e + e - → K + K - π ° φ (1020) Preliminary Preliminary K * (892) The plot K π vs K+K- clearly shows the ϕπ ° and K*(892)K mechanism ➢ Analysis is based on the integrated luminosity34 pb -1 ➢ Two intermediate states are clearly seen: ➢ It is consistent with BaBar but more precise ϕπ ° and K*(892)K mechanism ➢ Number of selected signal events was found to ➢ Detection efficiency according to SIM was be 940 ± 57. around 12% ÷ 18% with energy ➢ The main physical background comes from the ➢ The current systematic uncertaincy we processes: e+e- � K + K - π 0 π 0 , π + π − π 0 22 estimated as 10%
e + e - → K + K - π + π - M inv (K + K - ) π / Κ M inv ( ππ ) CMD3-red&blue M inv (K π ) BaBar- green ΔΕ = Ε π + Ε π + Ε π + Ε π - 2E beam Ρ tot = | P 1+ P 2+ P 3+ P 4| ➢ CMD-3 studies uses 22 pb -1 between 1.5 and 2 GeV, more than 20000 events with 3 and 4 tracks were selected for analysis; ➢ Ionisation losses in DC dE/dx provide good K/ π separation; ➢ Analysis of π + π - , K ± π ∓ , K + K - inv. Masses clear shows signals from ρ 0 , K *0 (892) and ϕ (1020); ➢ Many different mechanisms seen: K 1 (1270)K → K ρ K, K * (892)K π , K 1 (1400)K → K * (892) π K, ϕπ + π - . Recently published in Phys.Lett. B756 (2016)153-160 23
e + e - → Φη → K + K - η red – experiment blue – sim + bkg ➢ A data sample of 22 pb -1 collected in 2011-2012 is used to study e + e - → K + K - η ➢ XS was measured at 23 energy points between 1.57 - 2.0 GeV Preliminary Preliminary ➢ Analysis: the dominant ϕη signal, studies of nonresonant K + K - η needed ➢ Background with numerous physical components is seen ➢ The data sample includes 1268 ± 43 XS e + e - → Φ (1020) η signal events 24
e + e - → K + K - ω ➢ A data sample of 12 pb -1 collected in 2011-2012 is used to study e + e - → K + K - ω ; ➢ Selected number of signal events 899 ± 37 ➢ XS was measured at 16 energy points between 1.84 - 2.0 GeV ➢ Analysis empasizes the dominant K + K - ω signal, studies of nonresonant K + K - ω needed y r a n i m i l e r P 25
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