Super Charm/Tau Factory @ Novosibirsk (project) · Super B Factory and Super Charm/Tau Factory...
Transcript of Super Charm/Tau Factory @ Novosibirsk (project) · Super B Factory and Super Charm/Tau Factory...
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THE NOVOSIBIRSKCHARM/TAU FACTORY VEPP-5
(project, up to 5 GeV total)•High luminosity regime
“Round Beams”up to 1⋅1034 cm–2sec–1
•Longitudinally polarized collisionsup to 1⋅1033 cm–2sec–1
•High “effective” monochromaticityfor δMevent=50 KeV ≥1⋅1032 cm–2sec–1
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Injectioncomplex
VEPP-4M
VEPP-3
Charm/Tau Factory(double ring)
R≈100m
R ≈ 50m
Synchrotron
VEPP-2000
BEP
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with “ROUND BEAMS”
The option implies several important issues:a). Equal - and small! - beta values at Interaction Region
βx = βz = β0 ;
b). Equal horizontal and vertical emittances, excited via quantum fluctuations independently up to the level, required for desired luminosity
εx = εzc). Equal betatron tunes with “zero” coupling
(“no” tunes splitting)Qx = Qz ;
d). Small positive (for e+e-) tune shifts above half-integer in Qx,z(for single Interaction per turn);
e). Low (tunable) synchrotron frequency Qs.
Highest Luminosity option
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Items a), b) and c) lead to the conservation of angular momentum in transversal motion, thus converting this motion to “one-dimensional” one, with less beam-beam resonances, which can cause beam blow-up and/or degrade its lifetime. Items d)(close to half-integer) and e)(low synchrotron frequency) proved in computer simulations to be useful in rising the maximal beam-beam tune shift ξmax, which does not damage luminosity. We hope to raise this value, at least, up to 0.1 .
The additional useful effect arises due to the simple fact, thatthe beam-beam focusing for given counting bunch density is 2 times lower for round beams than for smaller dimension of flat beam.
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The new collider VEPP-2000, based on round beams approach, for energy range from pion threshold up to 2 GeV was constructed and now is in commissioning stage. First luminosity (~1·1031cm-2s-1 in 1+1 bunch mode, 2 IP) at φ meson energy was successfully achieved. Two detectors are in final preparation for data taking.
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.81 . 1029
1 . 1030
1 . 1031
1 . 1032
1 . 1033
Center of Mass Energy, GeV
L, c
m-2
s-1 VEPP-2000 Luminosity
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100 m
3 m
e+e-
RF RF
Polarization/dampingasymmetric wigglers
Longitudinal Polarization
π/2 solenoids
- independent signs -for independent e+ and e-
helicity control!
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Monochromatization(the idea)
e- e+
Higher energy Lower energy
Lower energy Higher energy
Since 1974
cetanemit_v
dispersion_Emonok
δ
Δ=Improvement:
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Contributors to the report
S.SinyatkinA.Skrinsky
P.Vobly
D.ShatilovV.Smaluk
Yu.PupkovP.PiminovV.M.PetrovI.Okunev
S.NikitinP.LogachevE.LevichevG.Kurkin
V.DruzhhininI.Koop
A.BondarV.Kiselev
A.BogomyagkovA.Blinov
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Motivation to restart:
► Exciting results of B-factories
► Invention of the crab waist collision scheme (P.Raimondi, March 2006; demonstration: DAFNE, 2007)- hope for even higher luminosity
Super B Factory needs data of Super Charm/Tau Factory class!
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Scientific case
► D-Dbar mixing► CP violation searches in charm decays► Rare and forbidden charm decays
► Standard Model tests in τ leptons decays
► Searches for lepton flavor violation τ μγ► CP/T violation searches in τ leptons decays
Requirements: L>1035 cm-2 s-1, longitudinal polarization
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Specifications
► Variable energy Ecm= 2 – 4.5 GeV(up to charmed barions)
► L = 1÷2×1035 cm-2s-1
► At least one beam (e-) should be polarized longitudinally
► No energy asymmetry is needed (B Factories!)► No beam monochromatization is needed
► Energy calibration with medium accuracy (Compton backscattering)
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Layout
Injection facility is in operation
Tunnel for the linac and the technical straight section of the factory is ready
100m long hall is ready
181*1035Luminosity, cm-2s-1
0.13Tune shift ξy
0.8Spot length, mm
0.8βz, mm
20βx, mm
34Crossing angle, mrad
1%Coupling εy/εx
10εx, nm*rad
10σz, mm
0.27σy, mcm
14σx, mcm
1.4Beam current, A
7*1010Particles per bunch
300Number of bunches
800Rings perimeter, m
2Beam energy, GeVMain design parameters
LcΠ
Nbunches⋅N1
2
4 π⋅ σx0⋅ σy0⋅⋅
σzspotσz
⋅:=
L1
2 2⋅ π⋅
cΠ
⋅ Nbunches⋅ N12
⋅1
θcross
1
2εx
3
4⋅ βx0
1
4⋅ kyx
1
2⋅ σz⋅
⋅:=
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► Two rings with a single interaction point.
Facility key features and principles
► Crab waist collision → extreme importance of the FF design (large collision angle + very small r-emittancevery short Interaction-Spot + proper sextupoles:
all beam spread energies meet in the same spot)► Wigglers to keep the same damping and emittance in the whole energy range (optimal luminosity).► Modified FODO ring cell to obtain very low x-emittance.
► Polarized e- injector and spin gymnastics based on the Central Arc solution to get the longitudinally polarized electron beam at IP.► Deep adaptation of the existing injection complex, constructionfacilities (tunnels, halls, etc.) and elements (wigglers, etc.) for cost effectiveness.
Many features/problems similar to the European SuperB.
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Damping wigglers
0.01 m-1Excitation integral i5 at 1.5 GeV
2.76 m-1Damping integral i2 at 1.5 GeV8 mTotal length0.2 mPeriod length4.3 TField amplitude at 1.5 GeV
The damping wigglers keep the damping time Tau_x =30 ms and thehorizontal emittance (10 nm) in the energy range 1.5 – 2.5 GeV
Wiggler field amplitude vs energy
Wiggler with similar parameters produced by BINP
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Longitudinal polarization at IP
← Schematic view of the longitudinally polarized e- at IP
Degree of the LP at IP →as a function of the beam energy
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Polarized electrons sourcePolarized electron source produced by BINP for AmPS
• Beam polarization 90 %• Cathode voltage 100 kV• Photocathode type Strained InGaAsP• Laser type Ti – Sapphire• Light wavelength 700 – 850 nm• Laser power in a pulse 200 W• Pulse duration 2.1 μs• Repetition rate 1 Hz• Maximum current from a gun 150 mA• Operational current 15 – 20 mA• Photocathode lifetime 190 – 560 hours
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POSITRON SOURCE
debuncher
Damping ringTo VEPP-2000
electron gun
subharmonic target
photo-gunlinac
to VEPP-4 and Charm/Tau
300 MeVlinac
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Injection facility upgrade • Today:• 2×1010 e-/pulse → (1.5% conversion) → 3 ×108 e+/pulse• × 50 Hz = 1.5×1010 e+/sec
we need 3*10-25*1*1035=3*1010
• Upgrade: • Debuncher usage (× 2) (part of the initial project)• e- current increase (× 3)• Better focusing in positron linac (× 1.5)
1.35×1011 e+/sec
• Reserve: electron energy can be increased by 100 MeV (× 1.3)
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2.5 GeV linac► Using the same accelerating structure as for the existing injection facility► 13 accelerator modules (200 MeV, 16 m) each of 4 accelerator structures.
Totally 208 m► In a 1-m straight section between the accelerator structures there are two
quadrupoles, BPM and vacuum valve► Four accelerator structures (one module) are fed by one 5045 klystron
(SLAC)► Repetition frequency is 50 Hz
The tunnel is ready.
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Search for Lepton Flavor Violation decaysSuper-B, 75 ab-1
7×1010 τ-pairs
τ→μγ decay•Current best limit:
4.5×10-8 by Belle with 5×108 ττ•At Y(4S):
ISR background e+e-→τ+τ-γUpper Limit ∝ 1/√L
• tau-charm factory with 1010
ττ should have much better effective sensitivity.
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Polarization• Michel parameters (τ leptons, Charmed barions)
• CP-violation → new physics, charged Higgs• Two amplitudes with different weak and strong phases • Observables
– Rate asymmetry: Γ(τ+→f+)-Γ(τ-→f−)~sinδ sinφ– Triple product asymmetry (T-odd) σ⋅(p1×p2)~cosδ sinφ
• For complete description of matrix element polarization and direction of τ should be known– Threshold production – low background– Polarization may increase sensitivity by several times
• CP-violation in τ-decays
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Advantages of near threshold Charm production
• Particle multiplicity at 3.77 GeV is about two times lower than at 10.6 GeV• Two body production e+e-→DD. This allows to use double tag method:
• fully reconstruct one D • then either fully reconstruct the other D (absolute branching ratios)• or look for events with one missing particle (leptonic, semileptonic decays)
• Coherent production of D pairs allows to use quantum correlations for D-meson mixing and CP violation studies
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Super B Factory and Super Charm/Tau Factory synergy:
•The model-independent Unitarity triangle Gamma angle measuring requires information on correlated DDbar decays from Super Charm/Tau Factory.
•Limits for New Physics from SBF are in B meson sector,while from SCTF – in D meson and tau-lepton sectors.
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Summary• C-tau factory with L = 1035 cm-2 s-1 seems to be an extremely
attractive facility for HEP experiments
• Crab-waist approach allows us to obtain such luminosity with “modest” beam intensity, low emittance achieved at light sources, injection efficiency has been already obtained in B- and Phi-factories and, longitudinal polarization is already in use etc.
• We are in the beginning now and there are many things have to bedone (further optimization of the FF design, the Dynamic Apertureoptimization (!), intra-beam lifetime increase, etc.). But at the same time we (at Novosibirsk) have an advantage - ground to start the project: injection facility is under commissioning, tunnels for linac and injection lines are ready, a lot of the facility solutions are based on our existing wares and technologies.