universityofvirginiapibeta.phys.virginia.edu/docs/talks/bonn_2003/bonn2003_slides.pdf · recent...
TRANSCRIPT
Pion beta decay,Vud and π → `νγ
Emil Frlez
for the PIBETA Collaboration
University of Virginia
4th International Workshop on
CHIRAL DYNAMICS 2003
Theory and Experiment
Bonn, GERMANY
8–13 September, 2003
�
�
The PIBETA Collaboration:
M. Bychkov, E. Frlez, W. Li, R.C. Minehart, D. Pocanic,L.C. Smith, W.A. Stephens, B.A. Vandevender,
Y. Wang, K.O.H. Ziock
University of Virginia, Charlottesville, VA 22904, USA
W. Bertl, J. Crawford, Ch. Bronnimann, M. Daum,R. Horisberger, S. Ritt, R. Schnyder, H.-P. Wirtz
Paul Scherrer Institut, CH-5232 Villigen, Switzerland
T. Kozlowski
Institute for Nuclear Studies, PL-05-400 Swierk, Poland
B. G. Ritchie
Arizona State University, Tempe, AZ 85287, USA
V.V. Karpukhin, N.V. Khomutov, A.S. Korenchenko,S.M. Korenchenko, N.P. Kravchuk, N.A. Kuchinsky
Joint Institute for Nuclear Research, Dubna, Russia
D. Mzhavia, Z. Tsamalaidze
Instit. for High Energy Physics, Tbilisi St. Univ., Georgia
I. Supek
Rudjer Boskovic Institute, Zagreb, Croatia
�
�
The PIBETA Experiment: MOTIVATION
Provide precision tests of Standard Model and
QCD predictions:
• π+ → π0e+νe – main goal
◦ SM tests from CKM unitarity
• π+ → e+νeγ(ee)
◦ FA/FV , π polarizability (χPT prediction)
◦ tensor coupling besides V − A
• µ+ → e+νeνµγ(ee)
◦ departures from V − A in Lweak
• π+ → e+νe – 2nd phase
◦ e-µ universality
◦ pseudoscalar coupling besides V − A
◦ massive neutrino, Majoran, ...
Pion Beta (πβ) Decay: Theory
Quark-Lepton Universality
The basic weak-int. V -A form (e.g., µ decay):
〈e|lα|νe〉 → ueγα(1 − γ5)uν
is preserved in hadronic weak decays
〈p|hα|n〉 → upγα(GV − GAγ5)un with Gi ' 1 .
Departure from GV = 1 (plain CVC) comes from
weak quark mixing (Cabibbo 1963):
GV = Gµ cos θC(= GµVud) cos θC ' 0.97
which with 3 q generations is generalized in the
Cabibbo-Kobayashi-Masakawa matrix (1973):
Vud Vus Vub
Vcd Vcs Vcb
Vtd Vts Vtb
CKM unitarity cond.: |Vud|2 + |Vus|
2 + |Vub|2 ?
= 1,
provides a means of testing the limits of the SM.
Status of CKM Unitarity
|Vus| ' 0.2196 ± 0.0026 from Ke3 decays.
|Vub| ' 0.0036 ± 0.0007 from B decays.
(a) Superallowed Fermi nuclear β decays
1990 Hardy reconciled discrepancies between Ormand
& Brown and Towner et al. ft values:
|Vud|2 + |Vus|
2 + |Vub|2 = 0.9962 ± 0.0016,
or 1 − 2.4σ.
(b) Neutron β decay
3∑
i=1
|Vui|2 = 1.0096 ± 0.0044, or 1 + 2.3σ,
[after Erozolimskiı et al. (1990)]
3∑
i=1
|Vui|2 = 0.9917 ± 0.0028, or 1 − 3.0σ.
[Abele et al, PRL, May 2002]
(c) Pion β decay – this work
Pion Beta Decay:
π± → π0e±ν BR ' 1 × 10−8
Pure vector transition: 0− → 0−
Theoretical decay rate at tree level:
1
τ0=
G2F |Vud|
2
30π3
(
1 −∆
2M+
)3
∆5f(ε, ∆)
= 0.40692 (22)|Vud|2 (s−1) .
With radiative and loop corrections we get:
1
τ=
1
τ0(1 + δ) ,
so that the branching ratio is
BR(πβ) =τ+
τ0(1 + δ)
= 1.0593 (6) × 10−8(1 + δ)|Vud|2 .
Recent calculations of pion beta decay
radiative corrections
(1) In the light-front quark model
W. Jaus, Phys. Rev. D 63 (2001) 053009.
• total RC for pion beta decay:
δ = (3.230 ± 0.002) × 10−2 .
(2) In chiral perturbation theory
V. Cirigliano, M. Knecht, H. Neufeld and
H. Pichl, hep-ph/0209226
• χPT with e-m terms up to Oe2p2
• theoretical uncertainty of 5 × 10−4 in
extracting |Vud| from BR(
πe3(γ)
)
.
Pion Beta (πβ) Decay: Experimental Method
PIBETA Experiment:
◦ stopped π+ beam◦ segmented active tgt.◦ 240-elem. CsI(p) calo.◦ central tracking◦ digitized PMT readout◦ cosmic µ antihouse◦ stable temp./humidity
AT
MWPC1
MWPC2
PV
AD
AC1
AC2BC
CsIpure
π+beam
10 cm
PIBETA Detector Assembly (1998)
Experimental Method: Summary
• Detect π+ decays at rest (during a delayed
180 ns gate).
gate
π stop
beam veto
π
-30 0 150 ns
• Use π+ → e+ν prescaled for normalization.
• Accept every πβ trigger – unbiased (γγ
coincidences above Michel endpoint)
1
τπβ
=1
τπ+
·BReνfpresc
BRπ0→γγ
·Aeν
Aπβ
·Nπβ
Neν
Aπβ , Aeν are acceptances for the decay modes,
respectively.
Online “πβ” Energy Spectrum:
True πβ events buried deep under overwhelming
background!
πβ Signal-to-Background Ratio
πβ Timing and Angular Distributions
πβ: Normalization to π → eν Yield
����������� ��� � ������� ��������� � ����� �!#"%$ &'$�(*),+.-/+.0213$54 6�0�78($�+.- 9:(*;�"�)<7>=
PRELIMINARY? 9 @ A�BDC�EGF�H C%BDC�CJI H C%BDC�C�K LMA*CONQP
R ;S7T1U7>BWV R ;S4%;S7>BWV
X Y[Z 13$�)\1]0�(^([7:1J) B`_badcUe�fTgih'jlk%gnm oqpsr t u�=
? 9 @ A�vDCGw]x:H C%vDC�E�yzL A*C NQP
{ X &|$�(*}�+ Y 78+,~G0 _badm`���O�*�s�U� u�=
? 9 � A�vDC�E�F�� A�vDCJI�A�L A*C NQP R y�C�� �#B���BWV
_�o>���s�Ut�� o>���s� r#��o��G�O� j8�G�T��gG���>��gn�l�s� �TgDu
&'¡£¢ w]C�CGw�= ¤�¥U¦§� C%vDy�KJEJI R F�V&|6 ?©¨�ª¬« $�(®),+.- = ¤�¥U¦§� C%vDy�KJE�K R I�C�VqB
����� � ���� �� ��� �����������������������!
"�#%$'&�( )+*,"-&."!/10�2435276.8."-24$:9 ;=<?>4>�$'&@# A�&."!/BDCFE BDCFE
$HG�#I$J>I&."!/6�3K):& /K3K*L$M#I35NO$ P?QRP?S'T P?QRP?S'TUWV B�X Y Z\[.E P?QR]+] ^ P?_5S\`UWV B�XbacY dedfE P?QRP+]:g P?QRP+]:g
35&@#I$J>I&."!/h BiXkj,E4l h BmZ\[.E P?QRn o P?_R]prq Bsdut ZvE P?QRP+] P?QRP+]w #x8�>�$'2�8�)+/5( o P?_5S o P?_5S
2y#z"�#I352y#I35;'"!/{9 P?Q}| ^ P?_R]#I)!#z"!/{9 ^ P?_R~ � P?_��
Radiative Pion Decay (π → eνγ): Theory
Anything beside V–A in RPD?
� � ����� � ��� � � � ����������������� "! # $ % & ' (*) �+�-,./0�1�32 )4 5 4 687 9 4 :<; 9 4 =
4 = 5 > ?A@CB D E�FHGI JLK�MON P = QR SAT KUN VCW > XZYZ[ R NZ\]_^a`cb S Ned f ]1g_]ih 5 jI�k ^a`cb S N
lmonqpsr9 P�t u v`I�w ` u S v x V W 9 X [ v y z { 9 V W > X [ v y z |~}9 P t u `w ` x V W 9 X [ y {���e� 9 V W > X [ y |���e� }9 P = u v`w ` u S � � 9 P = u v`w ` u S v � v
�o�� � X 5 P t f P��
REVIEW OF PARTICLE PROPERTIES
Particle Data Group
π± → l±νγ AND K± → l±νγ
FORM FACTORS
Written by H. S. Pruys (Zurich University)
“The electroweak decays of the pseudoscalar
mesons are investigated to learn something about
the unknown hadronic structure of these mesons,
assuming a standard V −A structure of the weak
leptonic current. The experiments are quite dif-
ficult, and it is not meaningful to analyse the
results using parameters for both the hadronic
structure (decay constants, form factors) and
the leptonic weak current (e.g., to add pseu-
doscalar or tensor couplings to the V − A cou-
pling).”
LAMPF: L. E. Piilonen et al.,
Phys. Rev. Lett. 57, 1402-1405 (1986)
π → eνγ Signal
LAMPF: L. E. Piilonen et al.,
Phys. Rev. Lett. 57, 1402-1405 (1986)
π → eνγ Analysis
π → eνγ Signal-to-Background Ratios
π → eνγ Invariant Masses
π → eνγ Timing Distributions
π → eνγ Axial-to-Vector Form Factor Ratio
π+ → e+νeγ Exp vs Theoretical Branching Ratios:
Glimpse at Pion Weak Form Factors
Fit Fixed Fitted χ2
Parameters Parameters
FV = 0.0170(80)PGP FA = 0.0116(16) None 2751
FT = 0
SM/ FV = 0.0259(5) FA = 0.0123(4) 275.0CVC FT = 0 γ = 0.475(18)
CVC FV = 0.0259(5) FA = 0.0141(5) 1.0FT = −0.0022(4)
π+ → e+νeγ Exp vs The Branching Ratios:
���������
� ����� ����� ������� ����� � ����� �����
��� � �!� "#�%$ ��� �&�&�%$ ')(*&+�,.-0/�1 ��2 ')(*&+�,43�/�1 ��2 ')(*5+�,.-6/�1 ��2 7�89�#:<;!=6>?=�@����A��>?B ;�=0>?=0@C���&��>?B DE')(F ,.-0/�1 ��2 DG')(F ,.-6/�1 ��2 DG')(F ,43�/�1 ��2
H 36I ;�JLKGM�NPO /RQ /#36S HUT I 9���V� WYX�O[Z Q /�\ HUT I�]�3�/#^`_ W<XaO 30Q Z0b H c I!]�3�/R^ed W<X�O -RQ T - H 36S0I�]�3�/#^ed cRf S : S;�JLKGMhgiO /#Q /#3�3 fVH 3 f I WYj�O 30Q f S�S H 3%I�]�3�/#^`_ W<j�O 36Q \ b - H 3%I!]�3�/R^ed W<jiO.Z Q f S Z H 36I!]�3�/R^edM ( O /
H \�Ilk 2 k M�NPO /RQ /�\�- b H -�I MhgiO /RQ /#3%\ Z H c I WYX�O \�Q T S H S0I�]�3�/ ^`_ W<XaO 30Q \ Z H c I!]�3�/ ^ed W<X�O c Q / TVH 3%\�I�]�3�/ ^ed cRf : bM ( O / WYj�O \RQ S�3 T#H 3%I�]�3�/#^`_ W<j�O 36Q cRf0TVH 3%I!]�3�/R^ed W<jiO.Z Q b c S H 36I!]�3�/R^ed
H Z I M ( O / M N O /RQ /V3 b H \�I W X O \�Q T - H S0I�]�3�/ ^`_ W X O 30Q \ Z H c I!]�3�/ ^ed W X O c Q /�S H 3%\�I�]�3�/ ^ed Z - : SM g O /RQ /#3 b H \�I W j O \RQ S6\#3 H 3%I�]�3�/ ^`_ W j O 36Q c Z \ H 3%I!]�3�/ ^ed W j O.Z Q b�Z f#H 36I!]�3�/ ^ed
H c Ilk 2 k M N O /RQ /�\�- b H -�I M g O /RQ /#3 c 3 H -�I W X O \�Q S0- H S0I�]�3�/ ^`_ W X O 30Q Z 3 H c I!]�3�/ ^ed W X O[Z Q T0fVH 3�3%I�]�3�/ ^ed / : 36SM ( O4m /#Q /�/�\�\ Hnc I W j O \RQ S Z 3 H 3%I�]�3�/ ^`_ W j O 36Q Z / fVH 3%I!]�3�/ ^ed W j O.Z Q T b \ H 36I!]�3�/ ^ed
o
π+ → e+νeγ: λ Distribution
PIBETA EXPERIMENT:
PROGRESS SUMMARY
• π+ → π0e+ν Branching Ratio
• Current PIBETA Statistical Uncertainty
0.4%, Systematic Uncertainty 0.7%
• Extracted Branching Ratio in Agreement
with CVC Hypothesis and Radiative
Corrections
• π+ → e+νγ Decay
• Extracted Axial-to-Vector Form Factor
Ratio in Agreement with Chiral
Prediction, γEXP = 0.475± 0.018 vs
γCHIRAL = 0.463 (B. R. Holstein 1986)
• Limit on Phenomenological Tensor Term
FT ≤ 3 · 10−3 at 95% CL