1ICFA Seminar-2008

SLAC, 28-31/10/2008A.Skrinsky

Super Charm/Tau Factory @ Novosibirsk(project)

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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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100 m

3 m

e+e-

General scheme

RF RF

Damping/excitation/polarizationwigglers

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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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e-e-

e+ e+

I P

1 m 1 m

Final Focus solenoids (~15 T )

13 Tesla – reached at VEPP-2000!

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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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The project of Super Carm/Tau factory with Crab Waist in Novosibirsk

Current stage:

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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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Luminosity (talk by D.Shatilov)

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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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SCT locationFF region

Technical reg. (RF and injection)

Damping wiggler sections

Hall is ready

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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

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LINACS to GENERATE e+ and ACCELERATE e+ and e- to 500 MeV.

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STORAGE RING/COOLERfor e+, e-

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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.

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OF COURSE, WE HOPE FORINTERNATIONAL COLLABORATION!