Physics Prospects of Super KEKB and Belle II

Physics Prospects of Super KEKB and Belle II

Kurtis NishimuraUniversity of Hawaii

(on behalf of the Belle II Collaboration)

Lake Louise Winter Institute, 2011February 24, 2011

Nishimura - Physics Prospects of Super KEKB / Belle II 2

History of Successes from B Factories• Belle and BaBar have made a wide variety of achievements

over ~10 year running period:– CKM measurements of:

• Matrix elements• Unitary triangle anglesCKM is correct to ~first order

– Direct CP violation:• B K ¼

– New hadronic states:• X,Y,Z mesons

– Rare probes of new physics:• b s °• b s

• Belle II at SuperKEKB provides a unique opportunity to constrain and search for new physics at the intensity frontier, in a complimentary way to LHC.

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`+`¡


Belle II @ SuperKEKB: Toward 50 ab-1

*Details of SuperKEKB / Belle II detector covered in previous talk (H. Nakayama)LLWI - Feb. 24, 2011

ZL

dt(a

b¡1)

L(c

m¡

2s¡

1)

• Belle II / Super KEKB* timeline:– Expect to begin operation in 2014. – Collect ~50 ab-1 by 2020-2021.

• Physics Prospects:– What can we do with 50 ab-1 of data? (…and what can we do along the way?)– How are super B factory

measurements complementary to those at LHC?

• Selected physics topics, examples of:– Modes with missing energy: B ¿ º– Direct CP violation: B K ¼– Mixing-induced CP violation: b s °– Many more available at: http://belle2.kek.jp/physics.html & arXiv:1002.5012

http://belle2.kek.jp/physics.html


• At Belle II, B’s are produced by:– One B meson (“tag” B) can be reconstructed in a common decay.

• Fully reconstructed: e.g., B D(*) ¼, B D(*) ½, …• Partially reconstructed: e.g., semileptonically

– Allows determination of “signal” B flavor, charge, momentum.• Particles associated with “tag” B can be removed from event. Allows searches for modes with missing energy.

Benefits of e+e- Environment

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(7.0 GeV)(4.0 GeV)

e+e¡ ! ¨ (4S) ! B ¹B


Missing Energy Modes: B- ¿ - º

• Better measurement of B(B ¿ º) may reveal source of the tension.

Tag-side information vital when ¸2 º’s in final state! Signal is seen as zero excess EECL.

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Example w/ semileptonic tag, 657M BB

B(B ¡ ! ¿¡ ¹º¿ ) = (1:54+0:38

¡ 0:37(stat)+0:29¡ 0:31(syst)) £ 10¡ 4

• Tension between the global CKM fit and :Current world ave.

Expectation from CKM fit

B(B ! ¿º)

PRD82:071101 (2010)

~2.8 ¾ discrepancy

Bkg only.Sig + bkg


B ¿ º at Belle II

• Also sensitive to new physics:• In type-II Two-Higgs Doublet Model (THDM), the SM

branching fraction of B- ¿ - º is modified:

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Belle II discovery region with 5 ab-1

• Assumes improvements in theory values:• 5% |Vub| error• 5% fB error5 ¾ discovery regioncurrent 95% exclusion

B(B ¡ ! ¿¡ ¹º¿ ) = BSM (B ¡ ! ¿¡ ¹º¿ )·1¡

m2B

m2H

tan2 ¯¸


B ¿ º at Belle II

• Also sensitive to new physics:• In type-II Two-Higgs Doublet Model (THDM), the SM

branching fraction of B- ¿ - º is modified:

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Belle II discovery region with 50 ab-1

• Assumes improvements in theory values:• 2.5% |Vub| error• 2.5% fB error

B(B ¡ ! ¿¡ ¹º¿ ) = BSM (B ¡ ! ¿¡ ¹º¿ )·1¡

m2B

m2H

tan2 ¯¸

5 ¾ discovery regioncurrent 95% exclusion

*Does not yet account for improvements in full-recon efficiency. Recently work suggests O(2x) improvements.


Direct CP Violation: B K ¼• Puzzle of direct CP violation in K ¼:– Difference in DCPV in charged/neutral B decays:

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B K ¼ w/ 535M BBNature 452, 332 (2008).

• If the only diagrams are:

then we expect ¢A = 0– Missing diagrams?– Hadronic interactions? These result in large theoretical uncertainty…


CPV in B K ¼ at Belle II• However, we can compare to a model independent

sum rule:

– This rule is free of the previous theoretical complications.– Can be represented as a diagonal band:

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• Current situation:

*Slope determined by branching fractions & lifetimes, fairly precisely known.

Gronau, PLB627, 82 (2005)



sum rule:


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• Current situation:Shaded region is overlap of A(K0 ¼0) and A(K0¼+).

Belle II is especially well suited to measure the all neutral final state: K0 ¼0

Gronau, PLB627, 82 (2005)

Benefits from: Charged K/¼ ID (TOP counter) ¼0 ° ° detection (ECL) KS vertexing eff. (increased SVD radius) …and of course, statistics



sum rule:


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• Current situation:Shaded region is overlap of A(K0 ¼0) and A(K0¼+).

Gronau, PLB627, 82 (2005)

Belle II is especially well suited to measure the all neutral final state: K0 ¼0

Benefits from: Charged K/¼ ID (TOP counter) ¼0 ° ° detection (ECL) KS vertexing eff. (increased SVD radius) …and of course, statistics

Projected w/ 50 ab-1


Mixing Induced CP Violation in b s °• In SM, photon polarizations in b s ° depend

on b flavor:

• Presence of significant mixing-induced CP violation would indicate the presence of right handed currents and clear hints of new physics.– This type of new physics does not require a new phase.

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b

b

: Allowed

: Suppressed by ms / mb

s°L

¹s°R


Time Dependent CPV in b s °• A recent example: – Search for TCPV in B Á K °

– Measurements are statistics limited…• Also the case for similar modes: B KS ¼0 °, B K* °

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Belle preliminary, arXiv: 1012.0481B Á K ° with 772M BB

S(B ! ÁK °) = +0:74+0:72¡ 1:05(stat)+0:10

¡ 0:24(syst)

A(B ! ÁK °) = +0:35§ 0:58(stat)+0:23¡ 0:10(syst)


Time Dependent CPV in b s °

– Statistics limited for S(b s °) in other modes

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Time Dependent CPV in b s °

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• Example improvements in the error of S as a function of integrated luminosity for:

• This sensitivity can help distinguish between models…

Nonresonant KS ¼0 °

All KS ¼0 °

Belle II projected

Resonant K*0 °

Efficiency for KS ¼+ ¼- improves with SVD radius.


Identifying NP at Belle II

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Projected with 5 ab-1

Randomly chosen parameter point

Current 99% CL on S(B Á KS)

Belle II can identify the nature of NP, in some cases indistinguishable at LHC.


Summary• Belle II at SuperKEKB will enable a new generation of

precision studies in flavor physics.– A number of unique opportunities to further constrain SM

and search for new physics.

• Significant opportunities both during data collection and with final dataset (50+ ab-1).– Only a short sampling of modes given here… for more

information, see:• http://belle2.kek.jp/physics.html • Belle II Technical Design Report - arXiv:1011.0352

Belle II and LHC experiments will be nicely complimentary.

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http://belle2.kek.jp/physics.html

http://arxiv.org/abs/1011.0352

Nishimura - Physics Prospects of Super KEKB / Belle II 18LLWI - Feb. 24, 2011


;º

;º

Missing Energy Modes: B K ºº• FCNC process:– Loops in penguin / box diagrams make B Kºº sensitive to

new physics.

– SM prediction [Buchalla, PRD 63, 014015 (2001)]:

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;º ;º

B(B+ ! K +ºº) < 1:3£ 10¡ 5

B(B0 ! K 0ºº) < 5:6£ 10¡ 5

BaBar analysis w/ 657M BBPRD 82, 112002 (2010)

Current best upper limits by BaBar:

B(B ! K º ¹º) = (3:8+1:2¡ 0:6) £ 10¡ 6

Another mode with two neutrinos: well-suited for B-factory environment.


B K(*) ºº at Belle

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Nishimura - Physics Prospects of Super KEKB / Belle II 21LLWI - Feb. 24, 2011


B D* ¿ º

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CKM Fitter

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Physics Prospects of Super KEKB and Belle II

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