ip measurements at pep-ii with babar

M. Weaver Super-B III Workshop, 15 June 2006

IP Measurements at PEP-IIIP Measurements at PEP-IIwith BaBarwith BaBar

M.Weaver, C.O’Grady, J.Thompson (SLAC), W.Kozanecki (Saclay), B.Viaud (Montreal)

Super-B III Workshop

June 15, 2006


IP CharacterizationIP Characterization

BaBar’s tracking resolution and prime venue allow measurement BaBar’s tracking resolution and prime venue allow measurement of important parameters at the IPof important parameters at the IP

Use

to measure production vertices and boost vector angles

(resolution)Production vertices (x,y,z ~ 30m)

Boost trajectories ( ~ 0.6 mrad)

e- beam

e+ beam

)(, eeee


VertexingVertexing

<X>, <Y> provide steering information<X>, <Y> provide steering information

)(, eeee

X (m)

Y (m)

100m

100m


<Z> measures relative RF phase<Z> measures relative RF phase

Z (mm)

2mm


d<X>/dz, d<Y>/dz is one measure of the collision axisd<X>/dz, d<Y>/dz is one measure of the collision axis

X’ (mrad)

Y’ (mrad)

1mrad

1mrad


X-size of luminous region determined by X-size of luminous region determined by emittances and IP-beta functionsemittances and IP-beta functions

(m)Lx

x-tune move towardshalf-integer

dynamic


Boost TrajectoryBoost Trajectory

TechniqueTechnique

ee

P

n

z

x

y

n

n

momenta poorly measured trajectories well measured

reconstruct decay plane normal n


tan = - x’Bcos – y’Bsin≈

x’(or y’)B = EH x’H – EL x’L EH - EL

Boost TrajectoryBoost Trajectory


<X’<X’BB>, <Y’>, <Y’BB> is another measure of the collision axis> is another measure of the collision axis

X’B (mrad)

Y’B (mrad)

1mrad

1mrad


Crossing AngleCrossing Angle

<X’<X’BB>-<X’>-<X’LL> => = '''22

22

2

1xLxHx

xHxL

xHxL

LEHELEHE

Run4 optimum

from x-ing angle

study<X’<X’BB>-<X’>-<X’LL> (mrad)> (mrad)<X’<X’BB>>,,<X’<X’LL>> (mrad) (mrad)


X’BX’B, , Y’B Y’B dominant contribution from electron beamdominant contribution from electron beam

(mrad)Hx'

x-tune move towardshalf-integer

dynamic


Studies on Luminosity TransientStudies on Luminosity Transient

Track time resolution (~2ns) allows Track time resolution (~2ns) allows event association to RF bucket event association to RF bucket

(476 MHz)(476 MHz)

Studied many IP parameters along Studied many IP parameters along bunch trainbunch train

z-centroid, size

x,y-centroids, x-size

x’,y’ means and spread

Events

z-centroid x-size

mini-train

mini-train

full-train

20%

63m

66m

mm


**yy Msmts I - Luminosity (Z) Msmts I - Luminosity (Z)

2

2221 exp

2

2)(

3z

z

zyx

NNz

L

)(, eeee

2,

2,

2LERzHERzz

LERyyHERyy

LERyyHERyy

LERyyHERyyy z **

**2**2

//1

2*1

effyZ-resolution (~ 30m) negligible compared to z,*y

Only acceptance/efficiency matterNeglecting complications from x-y coupling, dispersion,….


Luminosity (Z) FitsLuminosity (Z) Fits

Chisq: 108, for 100-5 d.o.f. Prob: 17%

Norm 1.02125e+00 1.47665e-03 Zc 3.68052e-02 2.66972e-03 CapSigzSqrd 2.45044e+00 1.03738e-02 BetaY 1.33328e+00 1.96984e-02 Waist -8.00839e-02 1.26765e-02

Chisq: 132, for 100-5 d.o.f. Prob: 0.7%

Norm 1.02514e+00 1.63293e-03 Zc 2.64888e-02 2.62672e-03 CapSigzSqrd 2.21443e+00 9.75603e-03 BetaY 1.18414e+00 1.71040e-02 Waist -4.35208e-02 1.11199e-02

Run 62101-62613 Run 62762-63049


**yy Msmts II - Luminous Y-Size (Z) Msmts II - Luminous Y-Size (Z)

2*

21)(2

y

z

yy

yyz

yLH

LH

L

ee

Assumes common y*

Ly (cm)Y-resolution (30m) large

compared to YL (~4m).

Courageous analysis using track miss-distance to estimate

per-event resolution.

Some systematics not resolved.


Luminous Y-Size (Z)Luminous Y-Size (Z)

Specific luminosity

Specific luminosity

*y

(cm

)L y,

z=0

(cm

) Nicely anti-correlated

withSpecific luminosity


**yy Msmts III - Boost Y-Angular Spread (Z) Msmts III - Boost Y-Angular Spread (Z)

2Y’B(z) =

(H+L)(f2H + f2L) + z2 H L

(1 + z2 / 2)H + (1 + z2 / 2)L

Depends upon vertical emittances and beta-stars

collisions withuncorrelatedtrajectories

collisions withvery correlated

trajectories

(all s are at IP)

y

z

collisions withvery correlated

trajectories

2*

2*

2

LEHE

y

yLE

y

yHE

L

L

H

H

**

**

L

L

H

H

L

L

H

H

y

y

y

y

y

y

y

y


Boost Y-Angular Spread (Z)Boost Y-Angular Spread (Z)

y*

y/y*


**yy Msmts Compared Msmts Compared

dL/dz Fit

σy(z) method

Boost method

βy*(eff) from phase

advance. Courtesy of Jerry Yocky.


**yy Msmts Compared Msmts Compared

BaBar results are significantly higher than PEP BaBar results are significantly higher than PEP measurements.measurements.

Possibilities:Possibilities:

•Analysis errors

•Optics different low current vs in-collision

•X-Y coupling

promising; under investigation


Boost Angle-Position CorrelationBoost Angle-Position Correlation

x’B = x(z-zH) fH – (z-zL) fL

H+(z-zH)2

L+(z-zL)2

Depends upon beta-stars and waist locations

Negative x-x’B

correlation here

(all s are at IP)

x (y)

z

Positive x-x’B

correlation here


Boost Angle-Position CorrelationBoost Angle-Position Correlation

Z<0

Z>0

Adds an additional measured constraint upon vertical emittances and beta-function


Vertical EmittancesVertical Emittances

y’(z) fit only

y’(z) + yy’(z) fit

Systematic shift not yet understood – coupling

also possible explanation


IP Coupling MeasurementsIP Coupling Measurements

X-Y Coupling may explain systematic effects in our X-Y Coupling may explain systematic effects in our measurements and (more importantly) degrade luminosity.measurements and (more importantly) degrade luminosity.

Can we measure coupling parameters?Can we measure coupling parameters?

Measurements to exploreMeasurements to explore X-Y Tilt of Luminous Region Ellipsoid

X’-Y’ Tilt of Boost Vector Ellipse

X-Y’ Boost Vector Position-Angle Correlation

Y-X’ Boost Vector Position-Angle Correlation


BaBar IP measurements reported onlineBaBar IP measurements reported online

Luminous RegionLuminous Region centroids { x, y, z}

sizes { x, z } every 10 minutes

tilts { dx/dz, dy/dz }

dL/dz fit { z, *y } every ~hour

Boost TrajectoryBoost Trajectory mean { x’, y’ } every 10 minutes

spread { x’HER, y’HER } every 30 minutes

}


IP Measurements at Super-BIP Measurements at Super-B

yyLL will be much smaller (20 nm) will be much smaller (20 nm)

xxLL will be smaller than PEP-II will be smaller than PEP-II yyLL

Z-resolution still ~< “effective” bunch lengths and Z-resolution still ~< “effective” bunch lengths and yy**

Boost angular spread similarBoost angular spread similar

Boost angle-position correlationBoost angle-position correlation larger intrinsic correlation (1/2)

smaller x,y coordinates x-may be possible, y-not may lose due to systematic effects (alignment)

All online measurements still possible (except All online measurements still possible (except xxLL))

Some offline analyses won’t work; replace with new ideasSome offline analyses won’t work; replace with new ideas

Statistics will come much faster!Statistics will come much faster!


SummarySummary

BaBar is trying to contribute to the understanding of the BaBar is trying to contribute to the understanding of the PEP-II colliderPEP-II collider

New ideas for measurements keep accumulatingNew ideas for measurements keep accumulating

Understanding of IP parameter analyses seems to be Understanding of IP parameter analyses seems to be converging.converging.

Hope that (this and) future experiment/accelerator Hope that (this and) future experiment/accelerator combinations can benefit from our effortscombinations can benefit from our efforts


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