physics prospects of super kekb and belle ii
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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.
LLWI - Feb. 24, 2011
`+`¡
Nishimura - Physics Prospects of Super KEKB / Belle II 3
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
Nishimura - Physics Prospects of Super KEKB / Belle II 4
• 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
LLWI - Feb. 24, 2011
(7.0 GeV)(4.0 GeV)
e+e¡ ! ¨ (4S) ! B ¹B
Nishimura - Physics Prospects of Super KEKB / Belle II 5
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.
LLWI - Feb. 24, 2011
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
Nishimura - Physics Prospects of Super KEKB / Belle II 6
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:
LLWI - Feb. 24, 2011
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 ¯¸
Nishimura - Physics Prospects of Super KEKB / Belle II 7
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:
LLWI - Feb. 24, 2011
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.
Nishimura - Physics Prospects of Super KEKB / Belle II 8
Direct CP Violation: B K ¼• Puzzle of direct CP violation in K ¼:– Difference in DCPV in charged/neutral B decays:
LLWI - Feb. 24, 2011
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…
Nishimura - Physics Prospects of Super KEKB / Belle II 9
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:
LLWI - Feb. 24, 2011
• Current situation:
*Slope determined by branching fractions & lifetimes, fairly precisely known.
Gronau, PLB627, 82 (2005)
Nishimura - Physics Prospects of Super KEKB / Belle II 10
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:
LLWI - Feb. 24, 2011
• 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
Nishimura - Physics Prospects of Super KEKB / Belle II 11
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:
LLWI - Feb. 24, 2011
• 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
Nishimura - Physics Prospects of Super KEKB / Belle II 12
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.
LLWI - Feb. 24, 2011
b
b
: Allowed
: Suppressed by ms / mb
s°L
¹s°R
Nishimura - Physics Prospects of Super KEKB / Belle II 13
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* °
LLWI - Feb. 24, 2011
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)
Nishimura - Physics Prospects of Super KEKB / Belle II 14
Time Dependent CPV in b s °
– Statistics limited for S(b s °) in other modes
LLWI - Feb. 24, 2011
Nishimura - Physics Prospects of Super KEKB / Belle II 15
Time Dependent CPV in b s °
LLWI - Feb. 24, 2011
• 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.
Nishimura - Physics Prospects of Super KEKB / Belle II 16
Identifying NP at Belle II
LLWI - Feb. 24, 2011
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.
Nishimura - Physics Prospects of Super KEKB / Belle II 17
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.
LLWI - Feb. 24, 2011
Nishimura - Physics Prospects of Super KEKB / Belle II 18LLWI - Feb. 24, 2011
Nishimura - Physics Prospects of Super KEKB / Belle II 19
;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)]:
LLWI - Feb. 24, 2011
;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.
Nishimura - Physics Prospects of Super KEKB / Belle II 20
B K(*) ºº at Belle
LLWI - Feb. 24, 2011
Nishimura - Physics Prospects of Super KEKB / Belle II 21LLWI - Feb. 24, 2011
Nishimura - Physics Prospects of Super KEKB / Belle II 22
B D* ¿ º
LLWI - Feb. 24, 2011
Nishimura - Physics Prospects of Super KEKB / Belle II 23
CKM Fitter
LLWI - Feb. 24, 2011
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