g at LHCb A Bertolin on behalf of the LHCb collaboration Outlook short introduction a timeintegrated g measurement a timedependent g measurement the LHCb g combination ID: 285207
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Slide1
Measurement of the CKM angle
g at LHCb
A. Bertolin on behalf of the LHCb collaboration
Outlook: short introduction a time-integrated g measurement a time-dependent g measurement the LHCb g combination new channel to measure g summary and future prospects
A. Bertolin, INFN (Padova)
1Slide2
the angle
g:
is the least well known phase of the CKM matrix it can be determined: from tree-level decay not affected by BSM processes standard candle for BSM-sensitive measurements using indirect measurements: global CKM fit: using direct measurements: BaBar
(DK-, D*K-
and DK*
-
):
Belle (DK
- and D*K-): LHCb (more on this talk):
PRD 87 (2013) 052015
arXiv
: 1301.2033 [
hep-ex]
JHEP 10 (2014) 97
not included in the global CKM fit
need to fill the gap between the uncertainty of the direct and indirect measurements
The CKM angle
g (º j
3)
A. Bertolin, INFN (Padova)
2Slide3
p beams
LHCb at the LHC
3Slide4
Time integrated g measurement with B± ® D K
± and D ® K0s h+ h-
JHEP 10 (2014) 097method:
g obtained comparing the distribution of the events in the D ® K0s h+ h- Dalitz plot for reconstructed B+ and B- mesons, h = p, Kdata sample: 3.0 fb-1 (2011+2012)
total number of
evts
»
2500
D
®
K0s
(®
p+ p
- )
p+ p-
m
±
= m(K0s
h ±)A. Bertolin, INFN (Padova)4
long
long
downstream
downstream
B
+
B
-Slide5
flattish
dotted histo in the right plot: expectation with no CPVcontinuous histo: expectation
with best fit values of the CPV parametersi.e. rB d
B and g
final outcome:
consistent and competitive with other (more mature) experiments
Time integrated
g
measurement with
B
±
® D K± and D ® K0s h+
h-JHEP 10 (2014) 097
A. Bertolin, INFN (Padova)5
histo not identically at 0 because the B
+ and B– measured yields are not identicalSlide6
Time dependent
g measurement with Bs
® Ds∓ K±JHEP 11 (2014)
060method: g obtained from the study of the time-dependent decay rates of the initially produced flavor eigenstatesdata sample: 1.0 fb-1 (2011)
g
–
2
b
S
week phase difference
A. Bertolin, INFN (Padova)
6
r
DsK magnitude
strong phase differenceGs, DGs
, Dms : fixed from other measurements
only 5
parameters:
fixed from other measurements Slide7
Time dependent g measurement with Bs
® Ds∓ K±JHEP 11 (2014) 060
red: failing particle idblack: passing particle id
total number of evts » 1800A. Bertolin, INFN (Padova)7
D
S
®
K
K
p
D
S
® p
p
pDS
® K p p
Slide8
Time dependent
g measurement with Bs
® Ds∓ K±JHEP 11 (2014) 060
extract
g
from them:
-2
b
S
under minimal theoretical assumptions is a small correction consistent with 0
folded time dependent decay rate asymmetry: shows clearly the effect of CPV
A. Bertolin, INFN (Padova)8
fit the decay time distribution to extract: Cf , A
f , Afbar , Sf and
SfbarSlide9
g combinationLHCb-CONF-2014-004
several decay channels can be used to measure gsome are more sensitive to g than others (large r helps)mostly due to unfavorable BRs have O(2000) events for the most sensitive onesÞ
combine them all to squeeze the uncertainty on g
parameters of the combined fit
parameters constrained using “external” inputs:
CLEO-c, CLEO, Belle, HFAG, LHCb
(for example for
2
b
S
)
9
h
+
= K
+Slide10
g
combinationLHCb-CONF-2014-004
final outcome:
how to improve further: add more luminosity … add new channels … do both …A. Bertolin, INFN (Padova)10Slide11
First observation of
B
s
® Ds*∓ K± with Ds* ® Ds garXiv:1503.09086 [hep-ex
], submitted to JHEP
it looks easy to replace the D
s
with a D
s
* …
BUT BR(Ds* ® Ds g)
» 94 %BR(Ds* ® Ds
p0)
» 6 % (experimentally even worse than the former because of the 2 g)
1 GeV
11
total number of
evts
» 1000 with 3.0 fb-1 and the K K p decay modeSlide12
First observation of
Bs ® D
s*∓ K± with D
s* ® Ds garXiv:1503.09086 [hep-ex]
A. Bertolin, INFN (Padova)
12
so far so good … next step: add this decay mode to the LHCb
g
combination
PRL 104 (2010) 231801Slide13
A. Bertolin, INFN (Padova)
13
Summary and future prospects
competitive g results have been reached by LHCb: high statistic, manageable backgrounds using decay modes involving also neutrals ! in the present g combination mixture of 1 and 3 fb-1 data sets update all channels to 3 fb-1 add new channels:
Bs
®
D
s
*∓
(® Ds ∓ g
) h ± B ∓
® D (®h+ h- p
0, K ∓
p ± p0
) h ∓ arXiv:1504.05442 [hep
-ex]stay tuned for an updated g combination ! have also B
0s ® h+ h- (h= p, K) data, JHEP 10 (2013) 183, that should be merged in the “big picture”
last but not least, new pp collisions in LHC are coming closer and closer, will boost the
g accuracy
LHCb-CONF-2014-004Slide14
Backup slidesA. Bertolin, INFN (Padova)
14Slide15
Time integrated g measurement with B± ® D K
± and D ® K0s h+ h-
A. Bertolin, INFN (Padova)15Slide16
A. Bertolin, INFN (Padova)
16