Transcript Slide 1

Prospects for g at LHCb
Val Gibson
(University of Cambridge)
On behalf of the LHCb collaboration
Physics at the LHC
Split, October 3rd 2008
Introduction

g plays a unique role in flavour physics
— Can be measured via both tree and loop
processes

K.Trabelsi
CKM 2008
Trees
— Benchmark Standard Model reference point




g  (7027
)
,
[
2
s
]

(
29
,
113
)
29
Loops
— Sensitive to New Physics


Very impressive measurements from the
B factories
V.Sordini
CKM 2008
To fully test SM and unitarity need
— sg ~ few % precision
— measurements in B, B0 and Bs systems
3/10/08
g  (78  12) ,[2s ]  (54 ,100 )
Prospects for gamma at LHCb
2/20
LHCb

High statistics
— sbb ~ 500 mb at 14 TeV
— ℒ ~ 2 x 1032 cm-2s-1
— 1012 bb per 2 fb-1 (1 year)
— All B species (B0, Bs, Bc, Lb …)

Excellent tracking system
—
—
—
—

VELO and tracking detectors
Mass resolution, sB(D)~15 (7) MeV
B vertex resolution, sz ~ 200 mm
Proper time resolution, st ~ 40 fs
VELO
First real tracks
RICH HPDs
Excellent particle identification
— 2 RICH detectors
— p/K separation over p ~2100 GeV

Trigger
— High pT hadron trigger at L0
3/10/08
Prospects for gamma at LHCb
3/20
g with trees
B  DK Strategies
Time integrated analyses based on:
“ADS”: Atwood, Dunietz, Soni; Phys. Rev. Lett. 78 (1997) 3257;
Phys Rev. D63 (2001) 036005.
“GLW”: Gronau, London, Wyler; Phys. Lett. B253 (1991) 483;
Phys. Lett. B265 (1991)172.
“Dalitz” or “GGSZ”: Giri, Grossman, Soffer, Zupan, Phys. Rev. D68 054018 (2003)

B  DK Strategies





Measure g through interference in B  D D K decays
Provided D 0 and D 0 decay to common final state
Common parameters
CKM angle g
B  D0K
i d
Amplitude ratio, rB

r
e
B
B  D0K
Strong phase difference, dB
B
b
u
colour-allowed




s
–
K
u
c
0
D
u

0
b
u
colour-suppressed




c
0
b
D
u
s
K*0 d
d
d
colour-suppressed
colour-suppressed




3/10/08
Prospects for gamma
 at LHCb

B0 b
0
u
0
D
c
s
–
u K
rB  0.1
u
0
D
c
s
*0
K
d
rB0  rB
B g
5/20

BD(hh)K

(ADS+GLW)
LHCb-2008-011
LHCb-2008-031
Mode
Sig. Yield*
6 rates, 5 parameters
g  60o
rB = 0.10
dB = 130o (PDG)
B+DKpK (fav.)
28k 0.6
B+DKpK (sup.)
650 1.2
B+D(KKK
3k 1.2
B+D(pp)K
1k 3.6
*All signal yields
presented are for 2 fb-1
D decay parameters:
rKp = 0.0616 (PDG)
dKp = -158o
rB  0.10300..017
023
(ADS formalism requires -180o phase
shift w.r.t published result)

Constraints

11  9
d Kp  22 12
11


ICHEP 2008
Sensitivity 2 fb-1
from CLEO-c dKp (o)
PRL 100(2008) 221801
3/10/08
B/S
sg (o)
-190
-174
-158
-144
-130
12.7
10.8
13.8
12.6
10.8
Prospects for gamma at LHCb
6/20
B0

D(hh)K*0 (ADS+GLW)
6 rates, 5 parameters
g  60o
rB0 = 0.40
dB0 (scan)
Mode
LHCb-2007-050
LHCb-2008-031
Sig. Yield
B0D(KpK*0 (fav.)
3.4k [0.4,2.0]
B0D(KpK*0 (sup.)
O(500) [2.0,13.0]
B0D(KKK*0
O(500) [0,0.4]
B0D(ppK*0
O(100) [0,14.0]
D decay parameters:
rKp = 0.0616 (PDG)
dKp = -158o
68%
95%
rB0  [0.18,0.34] @ 68% c.l.
 [0.07,0.41] @ 95% c.l.
(ADS formalism requires -180o phase
shift w.r.t published result)

Constraints

11  9
d Kp  22 12
11


ICHEP 2008
Sensitivity 2 fb-1
from CLEO-c
PRL 100(2008) 221801
3/10/08
B/S
d B 0 (o ) 0
45
90
135
180
sg (o)
10.8
12.7
9.5
5.2
6.2
Prospects for gamma at LHCb
7/20
BDK3pK (ADS)



LHCb-2007-004
LHCb-2008-031
Br(DK3p) = 8.1% c.f. Br(D Kp)=3.89%
Mode
Sig. Yield B/S
4 rates
B+DK3pK 31k
0.7
Multi-body final state
B+DK3pK
— Integrate over ALL phase space
— “Coherence factor” RK3p


530
2.3
 
 B  D K  pp p K   rB2  rK23p  2rB rK 3p RK 3p cosdB  dK 3p  g 
Atwood and Soni, PRD 68 033003(2003)
rK3p = 0.0568 (PDG)

Constraints
Prelim: arXiv:0805.1722 CLEO-c
K3π (o)
Sensitivity 2 fb-1
3/10/08
RK3π
Prospects for gamma at LHCb
8/20
BDKsppK (“Dalitz”)

Kspp Dalitz plots contain a CP-violating contribution from the
B and B interference which is sensitive to g.
B
B
LHCb 2 fb-1

Two analysis methods:
— Unbinned fit based on amplitude model
— Model independent binned fit using results from (3770) on D decays
Giri et. al., PRD 68 (2003) 054018;
Bondar and Poluektov, EPJ C47 (2006) 347; hep-ph/0703267;arXiv:0801.0840
3/10/08
Prospects for gamma at LHCb
9/20
BDKsppK (“Dalitz”)



LHCb-2008-028
Signal yield ~ 5k (total) per year
BDKspp p background suppressed with max. momentum cut
(good for RICH pid)
Dominant physics background
BDKspp X plus random “K”
~16% prob. of picking up “K” from
2 fb-1
Loose K pid
underlying event or other B.
Background type
B/S
BDKsppp
< 0.095 (90% c.l.)
BD*X+K
< 0.05
(90% c.l.)
DK-signal
< 0.09
(90% c.l.)
DK-random
0.350.03
3/10/08
Prospects for gamma at LHCb
10/20
BDK
ppK (“Dalitz”)
s

LHCb-2007-048
LHCb-2007-141
Amplitude Fit: Generate and fit events assuming isobar model.
— Models of BaBar [PRL 95 (2005) 121802] and Belle [hep-ex/0411049] give
consistent results.
— Total error will include model uncertainty, currently ~ 7o [BaBar PRD 78 (2008)
034023]

Binned Fit: Removes model dependence by relating bins of Dalitz plot to
experimental observables
— Slight degradation in statistical precision
— Residual error on g from CLEO-c statistics ~1-2o [Asner, ICHEP 08]
Sensitivity 2 fb-1
sg (o)
srB
sdB (o)
Amp. Fit
9.8
0.018
9.3
Binned Fit
12.8
0.020
12.6
Amplitude fit, model error 7o
Binned fit, CLEO-c error 2o
Fit assumes pure combinatorial
background same level as DK-random
3/10/08
Prospects for gamma at LHCb
11/20
g with trees
Time Dependent B  Dh Strategies
Bs DsK: Aleskan, Dunietz and Kayser, Z. Phys. C54 (1992) 653.
B0  Dp and Bs DsK “Uspin Approach”: Fleischer, Nuc. Phys. B671 (2003) 459.
BsDsK

LHCb-2007-017
LHCb-2007-041
Measure gfs from interference between mixing and decay amplitudes.
s
Bs




b
s
s D  Mode
c s
u  BDK
K
s
s
–
u K b
c D
s
s

Large interference effects


s
rDK
1 V
ub
~
 0 .4
 Vcb
s
Bs Dsp
Sig. yield
B/S
6.2k
0.7
140k
0.2
fs input from Bs J/f (sfs~ 0.03 mrad for 2 fb-1 see A.Satta talk)
Include Bs Dsp (20x Br) to determine Dms and tagging dilution
Simultaneous fit to Bs Dsp and Bs DsK decay time distributions (tagged and
untagged)
Bs→Ds-K+
Bs→Ds-K+
Input parameters:
g  60o, Dms = 17.5 ps-1
Sensitivity 2 fb-1
10 fb-1
sg o
4.6
10.3
sDms (ps-1) 0.007
3/10/08
Prospects for gamma at LHCb
0.003
13/20
B0



Dp
LHCb-2008-035
LHCb-2007-044
Measure gfd analogous to Bs DsK
fd input from B0 J/Ks (sfd = 0.02 mrad for 2 fb-1 see ? talk)
Problems
Vub
Mode
Sig. yield
rDp ~ 
— Interference small
— 8 fold ambiguity (D small)

Vcb
 0.02
Potential solutions
B/S
Bs DsK
6.2k
0.7
B Dp
1340k
0.22
— “Conventional approach”: compare with other channels e.g. B0 D*p
— “Uspin approach”: B0 Dp and Bs DsK
Uspin approach shows very
promising results.
 30% Uspin
breaking
2 fb-1
3/10/08
Sensitivity
2 fb-1
10 fb-1
sg o for d  60o
 943
53
sg o for d  10o
g o 
30 22
20 10
12  4
 8 15
Input : g  60o (stat.  30% Upsin breaking)
Prospects for gamma at LHCb
14/20
g with trees : Global Sensitivity
LHCb-2008-031
Perform global fit to B DK with common parameters.
Include results from B0 and Bs time dependent analyses.
Input measurements:
Parameters (input value):
BD0K
BD0K
• D0Kp, KK, pp
• D0Kppp
• D0Kspp
(LHCb-2008-011)
• g (60o)
(LHCb-2007-004)
• rB – ratio of magnitude of diagrams (0.1)
• dB – strong phase difference (130o)
(LHCb-2007-048)
B0D0K*0 analogues: rB0 (0.4), dB0 (scan)
B0D0K*0
• D0Kp, KK, pp
(LHCb-2007-050)
D0 decay parameters for Kp, Kppp:
Time dependent measurements:
B0 
•
Dp
• Bs  DsK
(LHCb-2008-035)
(LHCb-2007-041)
“Conventional” approach used for
B0  Dp (sg20o with 2 fb-1) to avoid
large correlations with Bs  DsK.
3/10/08
• rKp , rK3p
well known (PDG)
o
• dKp (158 , dK3p (144o)
Constrained by
• RK3p – coherence factor CLEO-c
dB0 (o)
0
45
90
135 180
sg for 0.5 fb-1 (o) 8.1 10.1 9.3
9.5
7.8
sg for 2 fb-1 (o)
4.1 5.1
4.8
5.1
3.9
sg for 10 fb-1 (o)
2.0 2.7
2.4
2.6
1.9
Prospects for gamma at LHCb
15/20
g with loops
New physics in B  hh and B  hhh modes
B0  pp and Bs  KK :
“Uspin Approach”, Fleischer, Phys. Lett B458 (1999) 306.
B  Kpp and B0  Kspp :
“Dalitz Approach”, Bediaga, Guerrer and Miranda, Phys Rev D76 073011 (2007).
B0 pp and Bs  KK

Measure g from interference between mixing
Mode
and tree and penguin decay diagrams
B0 Bs 
W
d s 
u
d s  b
u
u
d (s )
u
d (s )
d (s )
d s 
Demonstrates excellence of RICH pid
b

LHCb-2007-059
B0  pp
36k
0.5
Bs  KK
36k
0.15
B0  Kp
140k
< 0.06
Bs  pK
10k
1.9
KK
hypothesis
pp
hypothesis
3/10/08
Sig. yield
B/S
(untagged) (incl. bb)
mhh (GeV/c2)
Prospects for gamma at LHCb
mhh (GeV/c2)
17/20
B0 pp and Bs  KK

LHCb-2007-059
Fit CP asymmetries of B0pp and BsKK events
mix
Adir
 sin(Dm  t)
f  cos(Dm  t)  A f
A (t) 
 D 
 D 
cosh
 t   AD

sinh
 t

f
 2 
 2 
BsKK
CP
f
2 fb-1
dir
mix
dir
mix
— 4 observables: App
, App
, AKK
, AKK

Parameters
— g
— penguin to tree amplitude ratio dppeiqpp, dKKeiqKK
— Input fd and fs

Weak Uspin constraint
— dpp dKK 20%, qpp , qKK indep.
Measures g and tests Uspin symmetry
3/10/08
Prospects for gamma at LHCb
t (ps)
Sensitivity
sg (o)
2 fb-1
10 fb-1
10
5
0.18
0.09
sqpp(o)
9
5
sDQ (o)
17
8
sdpp
18/20
B 
and
B0
b
d,u
b
d
W
B+  Kpp
u
s
— Use Dalitz anistropy to measure CP
asymmetry including phase differences
Si 
Dalitz analysis of B0/ B0 Kspp
— Untagged analysis possible since
B0 interference regions do not overlap
B0 and

494k
B0  Kspp
u
d u 
d
u d 
Extract penguin contribution from B Kp p
u (d )

Ks
G.Guerrer
CKM 2008
Measure g from a Dalitz analysis of B Kp p and B0Kspp
decays
Mode
Sig. yield B/S
— K* resonance (dominant contributions)
s

p p 
0.3
90k t.b.d.
m2KK

Kpp
N i  N i

i
N N

i
CP
I
II
IV
I
III
m2pp
no-CP
III
Promising results: sg~5o with 2 fb-1
3/10/08
Prospects for gamma at LHCb
S
S
19/20
Summary
LHCb offers exciting prospects for a precision measurement of g

g with trees
—
—
—
—

Standard Model benchmark
External input from CLEO-c of upmost importance
A combined sensitivity of sg~2-3o is expected with 10 fb-1 of data
Many channels still to be investigated
DKpp0, DKsKK, DKsKp, BD(*K (*, BsDs(*K1 etc
g with loops
—
—
—
—
Sensitive to New Physics
B hh analysis can measure g (sg ~ 5o with 10 fb-1) and test Upsin symmetry
B hhh very promising first studies
Other channels to investigate: Bd KK, Bs pp, Bs Kpp0 etc
First challenge: reconstruct hadronic final states with real data….. coming soon
3/10/08
Prospects for gamma at LHCb
20/20
Backup Slides
3/10/08
Prospects for gamma at LHCb
21/20
B Tagging
3/10/08
Prospects for gamma at LHCb
22/20
g with trees : Global Sensitivity
LHCb-2008-031
Weight (in %) of each contributing analysis with 2 fb-1 for two values of dB0
dB0  0o
dB0  45o
BD0(hh)K,
BD0(K3p)K
25
38
BD0(Kspp)K
12
25
B0D0(hh)K*0
44
8
BsDsK
16
24
3
5
Analysis
B0Dp
Sensitivity of B0D0K*0 improves by a factor of two in going from dB0 =45
180o. Residual dependence remains in global fit, but diluted due to
other measurements.
3/10/08
Prospects for gamma at LHCb
23/20
B 
3/10/08
Kpp
and
B0
Ks
Prospects for gamma at LHCb
p p 
G.Guerrer
CKM 2008
24/20