Invariant mass spectra of $τ^{-} \rightarrow h^{-}h^{-}h^{+}ν$ decays

0.56 MB·English

by  Ian M. Nugent

NuclearPhysicsB
Proceedings
Supplement
NuclearPhysicsBProceedingsSupplement00(2013)1–2
Invariant mass spectra of τ− → h−h−h+ν decays
τ
I.M.Nugent[onbehalfoftheBABARCollaboration]
III.PhysikalischesInstitut,Physikzentrum,RWTHAachen,52056Aachen
DepartmentofPhysicsandAstronomy,UniversityofVictoria,POBox3055,STNCSC,Victoria,BC,V8W3P6Canada
3
1
0
2
Abstract
n
a Using342fb−1 ofe+e− annihilationdatacollectedwiththeBABARdetectorattheSLACPEP-IIelectron-positron
J
asymmetric energy collider operating at a center-of-mass energies near 10.58GeV, we present the preliminary
9
measurements of the invariant mass distributions of τ− → π−π−π+ν , τ− → K−π−π+ν , τ− → K−π−K+ν and
2 τ τ τ
τ− → K−K−K+ντ,whereeventswithKS0 →π+π−decaysareexcluded.
]
x Keywords: Tau,Invariant-Mass
e
-
p
e 1. Introduction 3. InvariantMassMeasurements
h
[

The analysis of the invariant mass spectra presented
1 Hadronicτdecaysprovideanopportunitytomeasure
inthisworkisacontinuationofbranchingfractionmea-
v thecouplingstrengthoftheweakcurrenttothefirstand
5 surementsfrom[4]. Therefore,theworkpresentedhere
second generations of quarks [1]. They also provide a
0 usestheeventselectionprocedurefrom[4],butincorpo-
cleanenvironmenttoprobelowenergyQCDandmea-
1 ratesresultsfromadditionalstudies.Fortheeventselec-
7 sure fundamental properties of the Standard Model of tion,asampleofτ− → h−h−h+ν decaysfrome+e− →
. ParticlePhysics. Hadronicτdecaysalsoplayacritical τ
1 τ+τ− events is selected by requiring the partner τ+ to
role as a probe to search for new physics at the LHC.
0 decay leptonically. Within this sample, each of the h±
3 With the recent data collected at the B-Factory detec-
mesonsisuniquelyidentifiedasachargedpionorkaon,
1 tors, significantimprovementsinourknowledgeofthe
and the decay categorized as τ− → π−π−π+ν , τ− →
: hadronicdecaystructurecanbemade,allowingforim- τ
v K−π−π+ν , τ− → K−π−K+ν or τ− → K−K−K+ν ,
Xi provedmodelingofτdecaysattheLHCandatthenext whereeveτntswithK0 →π+π−τhavebeenexcluded. Aτn
generationB-Factories. S
r efficiency correction, initially obtained from MC and
a corrected using data control samples, is used to cor-
rect for efficiency losses from the event selection for
2. Detector,DataSampleandMonteCarlosamples each interval in the invariant mass distribution. A de-
tailed description of the selection can be found in [4].
After events are selected the invariant mass distribu-
ThisanalysisemploysdatacollectedwiththeBABAR tions are analyzed. First, an arithmetic subtraction of
detector at the PEP-II storage ring which has a centre- thebackgroundsisappliedtotheinvariantmassdistri-
√
of-mass (CM) energy near ( s) near 10.58GeV. At butions for each channel. The τ− → h−h−h+ν back-
τ
theseenergies,thecrosssectionisσe+e−→τ+τ− =(0.919± grounds between the channels caused by particle mis-
0.003)nb[2].AdetaileddescriptionoftheBABARdetec- identification (cross-feed) are normalized to the mea-
torandMCSimulationcanbefoundin [3]and [4]. suredbranchingfractionsinBABAR[4]. Detectoreffects
/NuclearPhysicsBProceedingsSupplement00(2013)1–2 2
arethenremovedusingBayesianUnfolding[5],which 6. Acknowledgements
has been trained using the signal MC for each decay
mode. The invariant mass distributions are then nor- Wearegratefulfortheextraordinarycontributionsof
malizedtounity. our PEP-II colleagues in achieving the excellent lumi-
nosityandmachineconditionsthathavemadethiswork
possible. The success of this project also relies criti-
4. Results cally on the expertise and dedication of the computing
organizationsthatsupportBABAR. Thecollaboratingin-
The measured and unfolded invariant mass distribu- stitutions wish to thank SLAC for its support and the
tions for the τ− → π−π−π+ντ, τ− → K−π−π+ντ, τ− → kind hospitality extended to them. This work is sup-
K−π−K+ντ and τ− → K−K−K+ντ can be seen in Fig- ported by the US Department of Energy and National
ures 1 to 4. Due to the good resolution of the BABAR Science Foundation, the Natural Sciences and Engi-
detector,theunfoldingprocedurehasaminorimpacton neering Research Council (Canada), the Commissariat
theinvariantmassdistributions.Thisisincontrasttothe a` l’EnergieAtomiqueandInstitutNationaldePhysique
subtractionofthebackgroundswhichhavethemostsig- Nucle´aire et de Physique des Particules (France), the
nificant impact on these distribtuions. The main back- Bundesministerium fu¨r Bildung und Forschung and
groundscomefromthecross-feedfromtheotherτ− → DeutscheForschungsgemeinschaft(Germany),theIsti-
h−h−h+ντdecaysinwhichapionorkaonhasbeenmis- tuto Nazionale di Fisica Nucleare (Italy), the Founda-
identifiedandfromeventswithanextraπ0. Thecross- tionforFundamentalResearchonMatter(TheNether-
feed backgrounds are estimated to be (0.85±0.01) for lands),theResearchCouncilofNorway,theMinistryof
the τ− → π−π−π+ντ channel, (38.5±0.2) for the τ− → EducationandScienceoftheRussianFederation,Min-
K−π−π+ντ channel, (2.9±0.1)fortheτ− → K−π−K+ντ isteriodeCienciaeInnovacio´n(Spain),andtheScience
channeland(27.7±3.0)fortheτ− → K−K−K+ντ chan- and Technology Facilities Council (United Kingdom).
nel,wheretheuncertaintiesarefromMCstatistics. The IndividualshavereceivedsupportfromtheMarie-Curie
background fractions from events with an extra π0 in IEF program (European Union) and the A. P. Sloan
thecandidatesamplesareestimatedtobe(3.6±0.3)% Foundation(USA).
fromτ− →π−π−π+π0νinτ− →π−π−π+ντ,(2.3±0.4)% AdditionalsupportforI.M.Nugentwasprovidedby
from τ− → K−π−π+π0ν in τ− → K−π−π+ντ, (0.4 ± theAlexandervonHumboldtFoundation.
0.1)% from τ− → K−π−K+π0ν in τ− → K−π−K+ν
τ
and less than 5.0% from τ− → K−K−K+π0ν in τ− →
K−K−K+ν . Thenon-τbackgroundscompriselessthan References
τ
0.5%oftheeventsforeachchannel.
[1] N.Cabibbo,UnitarySymmetryandLeptonicDecays,Phys.Rev.
Lett. 10 (1963) 531–533. doi:10.1103/PhysRevLett.10.
531.
5. DiscussionandConclusion [2] B. F. L. Ward, S. Jadach, Z. Was, Precision calculation for
e+e− → 2f: The K K MC project, Nucl. Phys. Proc. Suppl.
In this paper, we have presented unfolded invari- 116(2003)73–77. arXiv:hep-ph/0211132,doi:10.1016/
S0920-5632(03)80147-0.
ant mass spectra using Baysian unfolding for the de-
[3] B. Aubert, et al., The BaBar detector, Nucl. Instrum. Meth.
cay modes τ− → π−π−π+ν , τ− → K−π−π+ν , τ− →
τ τ A479(2002)1–116.arXiv:hep-ex/0105044,doi:10.1016/
K−π−K+ν and τ− → K−K−K+ν . Additional studies S0168-9002(01)02012-5.
τ τ
have been conducted that confirm the BABAR branch- [4] B.Aubert,etal.,Exclusivebranchingfractionmeasurementsof
ing fraction measurement [4] using control samples to semileptonictaudecaysintothreechargedhadrons,τ−→φπ−ντ
cross-check all the main backgrounds. The τ− → a0n7d07τ.−2→981φ,Kd−oνiτ:,1P0h.y1s1.0R3e/v.PLhyetstR.e10v0Le(2t0t0.81)0001.10810118.0a1r.Xiv:
K−π−π+π0ν and τ− → K−π−K+π0ν are also used to [5] G.D’Agostini,AMultidimensionalunfoldingmethodbasedon
τ τ
validatethattheK/πmis-identificationratesareconsis- Bayes’ theorem, Nucl. Instrum. Meth. A362 (1995) 487–498.
doi:10.1016/0168-9002(95)00274-X.
tentwithintheassignedsystematicuncertainties. These
[6] P.Golonka,B.Kersevan,T.Pierzchala,E.Richter-Was,Z.Was,
invariant mass distribtuions are essential for determin- etal., TheTauolaphotosFenvironmentfortheTAUOLAand
ing the strange and non-strange spectral density func- PHOTOS packages: Release. 2., Comput.Phys.Commun. 174
tion and for the extraction of |V |. Work is ongoing (2006)818–835. arXiv:hep-ph/0312240,doi:10.1016/j.
us cpc.2005.12.018.
with T. Przedzinski, P. Roig, O. Shekhovtsova, Z. Was
to improve the modeling of these decay modes for the
LHCandforthenextgenerationB-Factoriesusingthis
data.
/NuclearPhysicsBProceedingsSupplement00(2013)1–2 3
×××××111110000033333
2222)V/c)V/c)V/c)V/c (a) BABAR 22222)V/c)V/c)V/c)V/c)V/c (b) BBAABBAARR 2222)V/c)V/c)V/c)V/c44440000000000000000 (c) BABAR
MeMeMeMe44440000000000000000 preliminary MeMeMeMeMe pprreelliimmiinnaarryy MeMeMeMe preliminary
Events/(10Events/(10Events/(10Events/(1033330000000000000000 Entries/(10Entries/(10Entries/(10Entries/(10Entries/(10 111110000000000 Events/(10Events/(10Events/(10Events/(102323232300000000000000000000000000000000
22220000000000000000
5555500000
11110000000000000000
11110000000000000000
0000 00000 0000
0000....5555 1111 1111....5555 00000.....55555 11111 11111.....55555 0000....5555 1111 1111....5555
MMMM((((ππππ----ππππ----ππππ++++)))) ((((GGGGeeeeVVVV////cccc2222)))) MMMMM(((((πππππ-----πππππ+++++))))) (((((GGGGGeeeeeVVVVV/////ccccc22222))))) MMMM((((ππππ----ππππ----)))) ((((GGGGeeeeVVVV////cccc2222))))
2)V/c 0.03 ((dd)) BABAR 2)V/c 0.04 (e) BABAR 2)V/c0.025 (f) BABAR
Me preliminary Me preliminary Me 0.02 preliminary
+)]/N)/(10 0.02 +)]/N)/(10 00..0023 -)]/N)/(100.015
p- p- p-
pp-([dN/dM( 0.01 p([dN/dM( 0.01 p([dN/dM(0.00.0051
0 0 0
0.5 1 1.5 0.5 1 1.5 0.5 1 1.5
M(p-p-p+) (GeV/c2) M(p-p+) (GeV/c2) M(p-p-) (GeV/c2)
Figure1: Thereconstructedandunfoldedinvariantmassspectrafortheτ−→π−π−π+ντchannels.Thereconstructedinvariantmassdistributions
for(a) M(π−π−π+),(b) M(π−π+)and(c) M(π−π−)arepresentedinthefirstrow. Inthesecondrow,the(d) M(π−π−π+),(e) M(π−π+)and(f)
M(π−π−)unfoldedinvariantmassspectraareshown. Forthereconstructedmassplots,thedataisrepresentedbythepointswiththeerrorbars
representing the statistical uncertainty. The blue (dark) histogram represents the non-τ background MC, the green (medium dark) histogram
representstheτbackgroundsexcludingtheτ− →h−h−h+ντcross-feedwhicharerepresentedbytheyellow(light)histogram. Fortheunfolded
massplots,thedataisrepresentedbythepointswiththeinnererrorbars(green)representingthestatisticaluncertaintyandtheoutererrorbars
(yellow)representingthestatisticalandsystematicuncertaintiesaddedinquadrature.Theintegraloftheunfoldeddistributionhasbeennormalized
to1.TheblackdashedlineisthegeneratorlevelMCdistributionusedintheBABARsimulation.ThereddottedlineistheCLEOtuneforTauola
2.8[6].
2222)V/c)V/c)V/c)V/c (a) BABAR 2222)V/c)V/c)V/c)V/c (b) BABAR 22222)V/c)V/c)V/c)V/c)V/c (c) BBAABBAARR 2222)V/c)V/c)V/c)V/c (d) BABAR
MeMeMeMe preliminary MeMeMeMe 6666000000000000 preliminary MeMeMeMeMe pprreelliimmiinnaarryy MeMeMeMe preliminary
nts/(10nts/(10nts/(10nts/(10 2222000000000000 nts/(10nts/(10nts/(10nts/(10 nts/(10nts/(10nts/(10nts/(10nts/(10 22222000000000000000 nts/(10nts/(10nts/(10nts/(10 2222000000000000
EveEveEveEve EveEveEveEve 4444000000000000 EveEveEveEveEve EveEveEveEve
1111000000000000 11111000000000000000 1111000000000000
2222000000000000
0000 0000 00000 0000
1111 1111....2222 1111....4444 1111....6666 0000....8888 1111 1111....2222 1111....4444 1111....6666 00000.....55555 11111 1111 1111....5555
MMMM((((KKKK----ππππ----ππππ++++)))) ((((GGGGeeeeVVVV////cccc2222)))) MMMM((((KKKK----ππππ++++)))) ((((GGGGeeeeVVVV////cccc2222)))) MMMMM(((((πππππ-----πππππ+++++))))) (((((GGGGGeeeeeVVVVV/////ccccc22222))))) MMMM((((KKKK----ππππ----)))) ((((GGGGeeeeVVVV////cccc2222))))
2)MeV/c 00..0045 (e) BprAeliBmiAnaRry 2)MeV/c 0.15 (f) BprAeliBmiAnaRry 2)MeV/c 0.03 (g) BprAeliBmiAnaRry 2)MeV/c 0.04 (h) BprAeliBmiAnaRry
+)]/N)/(10 0.03 +)]/N)/(10 0.1 +)]/N)/(10 0.02 -)]/N)/(10 00..0023
-pp-([dN/dM(K 00..0021 -p([dN/dM(K 0.05 pp-([dN/dM( 0.01 -p([dN/dM(K 0.01
0 0 0 0
1 1.2 1.4 1.6 0.8 1 1.2 0.5 1 0.8 1 1.2 1.4
M(K-p-p+) (GeV/c2) M(K-p+) (GeV/c2) M(p-p+) (GeV/c2) M(K-p-) (GeV/c2)
Figure2: Thereconstructedandunfoldedinvariantmassspectrafortheτ−→K−π−π+ντchannels.Thereconstructedinvariantmassdistributions
for(a) M(K−π−π+), (b) M(K−π+), (c) M(π−π+)and(d) M(K−π−)arepresentedinthefirstrow. Inthesecondrow, the(e) M(K−π−π+), (f)
M(K−π+),(g)M(π−π+)and(h)M(K−π−)unfoldedinvariantmassspectraareshown. Forthereconstructedmassplots,thedataisrepresented
bythepointswiththeerrorbarsrepresentingthestatisticaluncertainty. Theblue(dark)histogramrepresentsthenon-τbackgroundMC,the
green(mediumdark)histogramrepresentstheτbackgroundsexcludingtheτ− → h−h−h+ντ cross-feedwhicharerepresentedbytheyellow
(light)histogram. Fortheunfoldedmassplots,thedataisrepresentedbythepointswiththeinnererrorbars(green)representingthestatistical
uncertaintyandtheoutererrorbars(yellow)representingthestatisticalandsystematicuncertaintiesaddedinquadrature. Theintegralofthe
unfoldeddistributionhasbeennormalizedto1.TheblackdashedlineisthegeneratorlevelMCdistributionusedintheBABARsimulation.Thered
dottedlineistheCLEOtuneforTauola2.8[6].
/NuclearPhysicsBProceedingsSupplement00(2013)1–2 4
2222)V/c)V/c)V/c)V/c 1111000000000000 (a) BABAR 2222)V/c)V/c)V/c)V/c 1111000000000000 (b) BABAR 22222)V/c)V/c)V/c)V/c)V/c 33333000000000000000 (c) BBAABBAARR 2222)V/c)V/c)V/c)V/c 888800000000 (d) BABAR
MeMeMeMe preliminary MeMeMeMe preliminary MeMeMeMeMe pprreelliimmiinnaarryy MeMeMeMe preliminary
nts/(10nts/(10nts/(10nts/(10 nts/(10nts/(10nts/(10nts/(10 nts/(10nts/(10nts/(10nts/(10nts/(10 22222000000000000000 nts/(10nts/(10nts/(10nts/(10 666600000000
EveEveEveEve 555500000000 EveEveEveEve 555500000000 EveEveEveEveEve EveEveEveEve 444400000000
11111000000000000000
222200000000
0000 0000 00000 0000
1111....2222 1111....4444 1111....6666 1111 1111....2222 1111....4444 00000.....88888 11111 11111.....22222 1111 1111....5555
MMMM((((KKKK----ππππ----KKKK++++)))) ((((GGGGeeeeVVVV////cccc2222)))) MMMM((((KKKK----KKKK++++)))) ((((GGGGeeeeVVVV////cccc2222)))) MMMMM(((((πππππ-----KKKKK+++++))))) (((((GGGGGeeeeeVVVVV/////ccccc22222))))) MMMM((((KKKK----ππππ----)))) ((((GGGGeeeeVVVV////cccc2222))))
2)V/c 0.06 (e) BABAR 2)V/c (f) BABAR 2)V/c 0.15 (g) BABAR 2)V/c 0.04 (h) BABAR
Me preliminary Me preliminary Me preliminary Me preliminary
N)/(10 0.04 N)/(10 0.04 N)/(10 0.1 N)/(10 0.03
-+p-)]/K([dN/dM(K 0.02 -+)]/K([dN/dM(K 0.02 +p-)]/K([dN/dM( 0.05 -p-)]/([dN/dM(K 00..0021
0 0 0 0
1.2 1.4 1.6 1 1.2 1.4 0.8 1 1.2 0.8 1
M(K-p-K+) (GeV/c2) M(K-K+) (GeV/c2) M(p-K+) (GeV/c2) M(K-p-) (GeV/c2)
Figure3: Thereconstructedandunfoldedinvariantmassspectrafortheτ−→K−π−K+ντchannels.Thereconstructedinvariantmassdistributions
for(a) M(K−π−K+),(b) M(K−K+),(c) M(π−K+)and(d) M(K−π−)arepresentedinthefirstrow. Inthesecondrow,the(e) M(K−π−K+),(f)
M(K−K+),(g)M(π−K+)and(h)M(K−π−)unfoldedinvariantmassspectraareshown. Forthereconstructedmassplots,thedataisrepresented
bythepointswiththeerrorbarsrepresentingthestatisticaluncertainty. Theblue(dark)histogramrepresentsthenon-τbackgroundMC,the
green(mediumdark)histogramrepresentstheτbackgroundsexcludingtheτ− → h−h−h+ντ cross-feedwhicharerepresentedbytheyellow
(light)histogram. Fortheunfoldedmassplots,thedataisrepresentedbythepointswiththeinnererrorbars(green)representingthestatistical
uncertaintyandtheoutererrorbars(yellow)representingthestatisticalandsystematicuncertaintiesaddedinquadrature. Theintegralofthe
unfoldeddistributionhasbeennormalizedto1.TheblackdashedlineisthegeneratorlevelMCdistributionusedintheBABARsimulation.Thered
dottedlineistheCLEOtuneforTauola2.8[6].
2222)V/c)V/c)V/c)V/c (a) BABAR 22222)V/c)V/c)V/c)V/c)V/c 111115555500000 (b) BBAABBAARR 2222)V/c)V/c)V/c)V/c 33330000 (c) BABAR
MeMeMeMe preliminary MeMeMeMeMe pprreelliimmiinnaarryy MeMeMeMe preliminary
Events/(10Events/(10Events/(10Events/(10 22220000 Entries/(10Entries/(10Entries/(10Entries/(10Entries/(10 111110000000000 Events/(10Events/(10Events/(10Events/(10 22220000
11110000 5555500000 11110000
0000 00000 0000
1111....5555 1111....6666 1111....7777 11111 11111.....11111 11111.....22222 11111.....33333 1111 1111....1111 1111....2222
MMMM((((KKKK----KKKK----KKKK++++)))) ((((GGGGeeeeVVVV////cccc2222)))) MMMMM(((((KKKKK-----KKKKK+++++))))) (((((GGGGGeeeeeVVVVV/////ccccc22222))))) MMMM((((KKKK----KKKK----)))) ((((GGGGeeeeVVVV////cccc2222))))
2)V/c (d) BABAR 2)V/c 0.4 (e) BABAR 2)V/c 0.2 (f) BABAR
N)/(10Me 0.1 preliminary N)/(10Me 0.3 preliminary N)/(10Me 0.15 preliminary
+)]/K +)]/K 0.2 -)]/K 0.1
-K -K -K
-K 0.05 M( M(
dN/dM( ([dN/d 0.1 ([dN/d 0.05
([
0 0 0
1.5 1.6 1.7 1 1.1 1.2 1.3 1 1.1 1.2
M(K-K-K+) (GeV/c2) M(K-K+) (GeV/c2) M(K-K-) (GeV/c2)
Figure4: Thereconstructedandunfoldedinvariantmassspectrafortheτ−→K−K−K+ντchannels.Thereconstructedinvariantmassdistributions
for(a)M(K−K−K+),(b)M(K−K+)and(c)M(K−K−)arepresentedinthefirstrow. Inthesecondrow,the(d)M(K−K−K+),(e)M(K−K+)and
(f) M(K−K−)unfoldedinvariantmassspectraareshown. Forthereconstructedmassplots,thedataisrepresentedbythepointswiththeerror
barsrepresentingthestatisticaluncertainty. Theblue(dark)histogramrepresentsthenon-τbackgroundMC,thegreen(mediumdark)histogram
representstheτbackgroundsexcludingtheτ− →h−h−h+ντcross-feedwhicharerepresentedbytheyellow(light)histogram. Fortheunfolded
massplots,thedataisrepresentedbythepointswiththeinnererrorbars(green)representingthestatisticaluncertaintyandtheoutererrorbars
(yellow)representingthestatisticalandsystematicuncertaintiesaddedinquadrature.Theintegraloftheunfoldeddistributionhasbeennormalized
to1. TheblackdashedlineisthegeneratorlevelMCdistributionusedintheBABARsimulationwhichassumesthatτ− → K−K−K+ντ decays
entirelythroughτ−→φK−ντ.