beijing, feb 3 rd, 2007 30% e+ poalarization 1 physics with an initial positron polarisation of...

Beijing, Feb 3rd, 2007 30% e+ Poalarization 1

Physics with an initial positron polarisation of ≈30%

Sabine Riemann (DESY)

Beijing, Feb 3rd. 2007 S. Riemann, 30% e+ Polarization 2

Outline

Low positron polarization

Physics Case ?

Utilization of Pe+ ≈ 30%

fast or slow helicity reversal requirements

Summary and outlook


Physics case

• Refer to previous talks given by Gudi and others:• e+ polarization

improves accuracy of SM measurements

increases sensitivity to physics beyond SM

decisively to find out what the underlying physics is

With e+ polarization • processes can be enhanced or suppressed; • clean initial states with known helicities


Advantage: e+ Polarization

• No doubts: 60% e+ polarization are needed

What about ~30% for the beginning?


Utilization of P=~30%

• Better physics?

see next slides

remember:

first LC studies were done also with a

(60%, 40%) option !!

• 30% test of facilities during the first years

of operation


Baseline Machine• Physics between 200 GeV and 500 GeV• Luminosity: Running year zero for commissioning

Year 1-4: Lint = 500 fb-1:

1. year 10% Lint ≈ 50 fb-1

2. year 30% Lint ≈ 150 fb-1

3. Year 60% Lint ≈ 300 fb-1

4. year 100% Lint ≈ 500 fb-1

expected statistics: few 104 eeHZ at 350 GeV (mH≈120 GeV) 105 ee tt at 350 GeV 5·105 (1·105) ee qq () at 500 GeV 106 ee WW at 500 GeV statistical cross section uncertainties at per-mille level !!

e+ polarization will help (beginning of LC studies: Lint ~ 50 fb-1)


Peff

• Increase of effective polarization:

ee

eeeff PP

PPP

1

Pe-/ Pe+0.6 0.3

0.8 0.95 0.88

0.9 0.97 0.94

For comparison: old LCstudies:

(60%,40%) Peff =0.8


Peff

• Decrease of error on Peff (error propagation)

eeee

eeee

eff

eff

PPPP

PPPPx

P

P

1

11 222222

e

e

e

e

P

P

P

Px

30%: Improvement by factor 2 (1.5)


Enhancement /suppression of initial state polarization

Example: suppression factors for WW production • Complicated mixture of , Z exchange

• Large LR asymmetry depending on production angle

Pe- Pe+ 0 -0.6 -0.3

0.8 0.2 0.10 0.15

0.9 0.1 0.06 0.08


Transverse polarization

• does NOT work with e- polarization only• sensitivity to new physics (CP violation,

graviton)

QPPallongitudind

d

sin2cos

RizzoMH=1.5 TeV, E=500 GeV, L=500 fb-1


(90%, 0%) (80%, 30%) ?• same size of

– Suppression of undesired hel. states for some processes

– effective polarization (~0.9)

BUT: Peff (90%; 0%) = 2…1.4 ·Peff (80%; 30%) (uncor…correlated)

Is (90%,30%) an alternative to (80%, 60%) ?• No - due to less significant physics goals


Physics goal


e+ helicity reversal

e- trains - + - + - + - + - + - +e+ trains + + + + + + - - - - - -

50% spent to ‘wrong’ helicity pairing • gain due to xs enhancement for J=1 processes by e+ pol is lost• improvement of Peff remains – if systematic errors are small

enough• asymmetries can be measured, systematic effects are largely

cancelled out

If the e+ helicity will be switched quite frequently this scheme corresponds to a ‘slow’ Blondel scheme with

luminosity ratio 1/1/1/1 for ++ / +- / -+ / --

Can use annihilation data for polarization measurement (see POWER report and work done by K. Moenig)


Helicity reversal: Blondel Scheme

Perform 4 independent measurements (s-channel vector exch.)

Can determine Pe+ and Pe- simultaneously (ALR≠0)

need polarimeters at IP for measuring polarization differences Pe-, Pe+ between + and – states P

eeLReeu

eeLReeu

eeLReeu

eeLReeu

PPAPP

PPAPP

PPAPP

PPAPP

1

1

1

1

21

eP


Helicity reversal: Blondel Scheme• this technique measures directly lumi-wted polarizations • any depolarization effect properly taken into account (?)• Polarization differences have to be measured with high

accuracy

• Estimated accuracy needed for the first 4 years:

dP/P ≤0.3% (0.5%)

• Long-term intensity stability correction and additional syst. error

22

2

21LR

LRLR

RL

RLLR

AP

P

NP

PAA

NN

NNA


Helicity reversal Frequency of e+ reversal:• + and – helicity with equal ratio No reversal during the first year(s) is

not an option at all!• often enough to avoid unknown systematic (time dependent)

uncertainties • Tolerances: Intensity asymmetry: desired 0.1% (?) at the beginning 1% is more realistic polarization asymmetry: <1% desired (at least for the ~60% e+ pol): train-by-train • Low reversal frequencies (days):

each measurement is done separately large luminosity/intensity corrections

Need accurate measured lumi and intensities etc.

Further studies are needed …


Remarks

• Need to understand relative detector efficiency for ‘+ -’ and ‘- +’ modes at level of few 10-3, later 10-4

• Need to measure polarization difference, Pe+(-) - Pe+(+) at level of <10-2 later 10-3

• To reach the high accuracy will be difficult unless can measure these modes simultaneously, ie. can switch positron polarization randomly train-to-train

Note: even if positrons are nominally unpolarized, need to verify this! Positron polarimeter at the IP is needed anyway

.


Layout of positron damping ring system showing the parallel spin rotation beam lines for randomly selecting positron polarization direction. A pair of kicker magnets is turned on between pulse-trains to deflect the beam to the spin rotation solenoids with negative B-field.

space for spin rotators must be foreseen

K. Moffeit et al.,SLAC-TN-05-045


Summary & Conclusion• 30% is benefit for physics• we could have a polarized machine from the beginning!

• Allows test of operation with both beams polarized should be used for physics – otherwise it has to be destroyed (see also slides from L. Malysheva / I. Bailey)

• Utilization of low e+ polarization needs - Positron polarization measurement - Spin rotation • frequency? Desired: train-by-train • proposed scheme exists: spin rotators before (LTR) and after the DR (RTL) are needed (see SLAC-TN-05-045, EUROTeV-Report-2005-024-1) • other solutions for helicity reversal? • no reversal is worse than no polarization! • Further design & simulation work has to be done and should include the

~30% option (depolarisation, polarimeter, spin-flip-frquency etc.)

beijing, feb 3 rd, 2007 30% e+ poalarization 1 physics with an initial positron polarisation of...

Documents

e trains

polarization measurement

s s s

polarization differences

gev mh120 gev

tter physics

e polarizationno doubts

commissioning year