Introductory discussion on a Charm-tau factory in Frascati

G.SimiRiunione INFN 17.12.2012

“SuperB & nuovi Progetti Bandiera”

17/12/2012 2

Scope and Overview

● Discussion about the project is actively going on therefore I can give only– Partial information

– Personal interpretation

● Report on– Some aspects of the scaled down accelerator

– Physics case

– Detector design issues

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General Considerations

● Charm threshold running was part of the original B-factory program with dedicated running at 3.5GeV – 4.2GeV

● => Cabibbo lab consortium working on the feasibility study of a charm-tau factory– The financial resources required should basically match

the available funds up to some negotiations with external partners

– The physics case should be interesting and challenging to promote an international scientific collaboration

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General Considerations

● Costing is being studied and reviewed by an ad-hoc INFN commission

● Physics is being discussed by another ad-hoc INFN commission– I will not go into the details of the cost– “The financial resources required should basically

match the available funds up to some negotiations with external partners”

● Commissions will advise the INFN president

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Physics motivation

● Precision measurements in the flavor sector as a tool to investigate physics beyond standard model

● Complementary to high energy running at LHC● Investigation LFV in tau sector with 10 -9

sensitivity● Time dependent CP violation in the charm

sector

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Accelerator

● Use same concept as Y4S running to achieve high luminosity● Use same footprint (L~1.3Km, R~200m)● Energy 3.1GeV - 4.4GeV tunable● Luminosity 1035 cm-2 s-1

– σ_tautau max = 3.6nb → Ntautau

=1010 in 1 year (3 107 s)

– L µ E I ξy/βy● Lower E → ~ 1/3 reduciton, lower I due to collective effects and Touschek →

1/3 reduction ==> luminosity reduced from 1036 → 1035

● 80% polarization of both the beams– Helps reduce the background in tau decays

– Allows precision EW measurements

– With lower energy can polarize both beams

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Accelerator

● Backgrounds: important point– Touschek background increase with 1/E3 →

implications for the detector need to be studied & simulated

● Basic set of parameters have been computed, need to be validated with simulation of lattice– Energy asymmetry can be maintained

– Beam power ~ 0.5MW reduced by O(10)– Time (months) needed to validate the design

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Physics accessible

● Charm– TDCPV– Semi-leptonic decays– Rare

– Precision

– Baryons

● Tau– LFV– CP

– Precision

● EW precision● Spectroscopy● Nature of XYZ states● Dark forces

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Physics relevant

● Community is actively validating the details of the physics results that can be obtained relative to the physics that can be done at other experiments– BES III – LHCb

– BELLE II

● Discussion present here is not validated and incomplete

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Cross sectionsTau tau

DD D*D*ττDsDs

3770

40404160

4415Hadrons

s/smm

σ_ττ = 3.5nb(max)Entangled DD state

DD* sensitive to x,y instead of x2,y2

Psi2SBR(tt)=3 10-3

s(ττ)~2nb+2.5nb

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Number of events

● Integrated luminosity– 7.5 ab-1 , 1.5ab-1/year

● ττ= 2.3 1010

● DD @ 3770~ 3.6*1.5 109/year ● DD* @ 4040~ 3.2*1.5 109/year

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Charm

● Being discussed ● Belle II● LHCb

– Cannot do channels with neitrals and missing energy (neutrinos) and semileptonic

– Bigger hadronic uncertainties than in B

● CPV– Direct

– q/p , x y in mixing: can only be done

– Sensitivity similar to other experiments

– Run at 4040 gives better results at c-tau factory

● Physics committee will report soon, assume start in 2020 1.5ab/year

Background reduction in τ →µ γas for Novosibisk Super CTAU (see Bondar)

Detector Symmetry

Hermeticity

Magnetic field

SVT

DCH

PID

EMC

IFR

Electronics

Trigger

DAQ

Working hypothesis

Start from SuperB Detector

Disclaimer:

Mainly questions, no anwers

Not in-depth thought

Many things are obvious

Some documents:

Cleo-C - CLNS 01/1742

http://www.lns.cornell.edu/public/CLNS/2001/CLNS01-1742/cleocyb.pdf

BES-III:

http://arxiv.org/abs/0809.1869v1

Detector Changes from SuperB

12/12/12F.Forti - Detector 15

What changes in the events

Smaller backgrounds,

Softer particle spectrum

What needs to be changed in the detector

Smaller magnetic field

Need to be lighter to retain momentum resolution

SVT may not be beneficial if symmetric machine

Even if asymmetric SVT design needs to be reoptimized

Need PID at smaller p. Also would like to have pi/mu separation at small momentum for τµγ analysis

Symmetric or asymmetric machine ?

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Item Symmetric Asymmetric

TD CPV in charm NO YES

Vertexing for background regjection NO YES

Hermeticity Signal efficiency, invisibles veto

Better Like Babar

Backgrounds ? ?

Machine cost Cheaper Expensive

Vertex detector Probably no

Yes

The choice of asymmetric or symmetric machine is one with major implications.

Backgrounds could be significantly lower for a symmetric machine if final focus is shared and/or further away from IP

To be understood quantitatively

Boost vs polarization

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If asymmetric machine, boost optimization needs to be studied

There is a compromise between boost and polarization

Time difference resolution

cτ (D0) = 122um βγcτ order of 60 um or less.

What is the required vertex resolution ?

M.Biagini

SVT

12/12/12F.Forti - Detector 18

If symmetric machine probably no vertex detector is required

CLEO-C decided to remove the vertex detector

BES-III has none talk by Gradl tomorrow to discuss tracking issues

If asymmetric machine

Z Vertex resolution

Back of the envelope calculation: for 500 MeV pion, with 0.5%X0 in B.P.+L0 @ 1.5cm, single particle z resolution is about 30um

It should be possible to obtain a good resolution for TDCPV in charm

Need as light as possible SVT

Impact on momentum resolution

SVT will need to measure loopers and low momentum particles

Probably dE/dx useful for PID at small momentum

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Cross sections