A new experiment to measure the hadronic contribution to g-2....From T. Blum et. al., “The Muon...
Transcript of A new experiment to measure the hadronic contribution to g-2....From T. Blum et. al., “The Muon...
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A new experiment to measure the hadronic contribution to g-2
Luca TrentadueUniversità di Parma
and INFN Milano-Bicocca
on behalf of the proponents of the project
June 27th 2018
1
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C. M. Carloni Calame, M. Passera, L. Trentadue. and G. Venanzoni,”A new approach to evaluate the leading hadronic corrections to the muon g-2”, Phys. Lett. B 746 (2015) 325
G. Abbiendi, C.M. Carloni Calame, U. Marconi, C. Matteuzzi, G. Montagna, O. Nicrosini M. Passera, F. Piccinini, R. Tenchini, L.Trentadue and G. Venanzoni,“Measuring the leading hadronic contribution to the muon g-2 via mu-e scattering”, Eur. Phys. J. C77 (2017) 3, 139. arXiv:1609.08987 [hep-ex].
work based on:
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is a new experiment to measure the Hadronic Leading Order ( HLO) contribution to the muon g-2 by using
elastic scattering
3 L. Trentadue - QCD@Work 27 June 2018 Univ. Parma and INFN Milano Bicocca
µ+ e ! µ+ e
Outlook:- Physics Motivations- Tools to perform the measurement- The first testbeam (CERN)- Future plans and developments
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This talk is about how to measure the Vacuum ( the hadronic contribution to )
Vacuum, since a long time ( 2500 years ), constitutes an always present issue in Physics or, better, in Natural Sciences
PhilosophyParmenides, Democritos, Leucippos,…..Torricelli, von
Guericke, Casimir, Schwinger, ….. to mention only a few until nowadays
In Quantum Field Theory, in the perturbative phase, Vacuum is naturally represented by the vacuum polarization contribution
Historical Aside
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e2 ! e2 (q2 ) = e2
1+ ("(q2 )#"(0))!(q2 ) = !(0)
1#$!; $! = #%e "(q2 )#"(0)( )
Vacuum Polarization makes αem runningassuming a well defined “effective” value at any
scalevacuum polarization and the “effective charge” are
defined by:
α
Δα takes contributions from leptonic and hadronic and gauge bosons elementary states
Among these the non-perturbative Δαhad
Δα = Δαleptonic + Δαgb + Δαhad + Δα top
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The physics motivations
6
aSMµ = 116591783(35)⇥ 10�11
F. Jegerlehner, MITP Workshop, 19-23 February 2018 Mainz
aexpµ = 116592089(63)⇥ 10�11
G.W. Bennet et al., Phys. Rev. D73(2006_072003
aµ =g � 2
2The muon g-2 has been measured with high precision
The Standard Model prediction gives:
�aµ(exp� SM) = 306± 72
Systematics of the measurement ?Systematics of the theoretical prediction ?
New Physics ?
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from M. Passera
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The muon g-2 - The Hadronic contribution
from M. Passera
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.From T. Blum et. al., “The Muon g-2 Theory Value: Present and Future” arXiv:1311.2198 [hep-ph]
Comparison between the SM predictions and the experimental determinations
Theory parametrizations DHMZ ( M.Davier et al. ) , HLMNT ( K. Hagiwara et al. )SMXX is the average of the two previous values
BNL-E821 04 average is the current experimental value of aμ
New (g-2) exp. is the same central value with a fourfold improved precision of future g-2 experiments at Fermilab and J-PARC.
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will this possibly change in the next few years ?The present experimental error as from the BNL E821 is
�aExpµ ' 6.3 · 10�10[0.54 ppm]
The new experiments in preparation at Fermilab and J-PARCare aiming to a precision of *
(*assuming the same central value as today’s one)
�aExp�FL/J�PARCµ ' 1.6 · 10�10[0.14 ppm]
a fo
urfo
ld g
ain
The question is how to cope with such an improvement from the theoretical side
The physics motivations
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discrepancy between the experimental value of the muon anomalous magnetic moment and the Standard Model prediction
aµ =g � 2
2
Within the framework of low-energy high precision measurementsthe long-standing (~ )
�aµ(Exp� SM) ' 28± 8 · 10�10
The accuracy of the SM prediction 5 · 10�10
is limited by strong interactions effects
The present error on the leading order hadronic contribution to muon g � 2
It constitutes the main uncertainty of the SM predictions
�aHLOµ ' 4 · 10�10
The physics motivations
�
4�
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The physics motivations
The largest contribution to the theoretical uncertainty comes from the term which can be measured experimentally
In order to understand the discrepancy between the experimental measurement and the Standard Model prediction it is needed to reduce the theoretical uncertainty to have a more precise determination
�↵had
12
More theoretical work is necessary: Radiative corrections, Lattice evaluations, etc…
The Standard Dispersive Approachto the evaluation of the HLO contribution to the muon anomalous magnetic moment goes
back to the ‘60
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The Standard Dispersive Approach
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from F. Jegerlehner talk in Frascati March 23, 2016
aHLOµ = (
↵mµ
3⇡)2
Z 1
4m2⇡
dsK(s)Rhad(s)
s2
Optical Theorem
K(s) =
Z 1
0dx
x2(1� x)
x2 + (1� x) sm2
µ
aHLOµ = (
↵
⇡2)
Z 1
0
ds
sK(s) Im⇧had(s+ i✏)
Rhad(s) =�(e+e� ! hadrons)
�(e+e� ! µ+µ�)
Im ⇧had(s) ! �hadtot (s)
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from F. Jegerlehner talk in Frascati March 23, 2016
�aµ (��aµ)2
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Measurement of the running of αemA direct measurement of αem(s/t) in space/
time-like regions can show the running of αem(s/t)
It can provide a test of “duality” (far away from resonances)
It has been done in past by few experiments at e+e- colliders by comparing a “well-known” QED process with some reference (obtained from data or MC)
!(q2 )!(q0
2 )!
"#
$
%&
2
~Nsignal (q
2 )Nnorm (q0
2 )
Nsignal can be any QED process, muon pairs, etc…Nnorm can be Bhabha process, pure QED as γγ pair production, a well as theory, or any other reference process.
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We propose an alternative approach
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aHLOµ = (
↵
⇡)
Z 0
�1
dt
�t(1� �
1 + �)2⇧had(t) = �(
↵
⇡)
Z 0
�1
dt
�t(1� �
1 + �)2�↵had(t(x))
t(x) = �x2m2
µ
1� x� =
r1�
4m2µ
t↵(t) =
↵(0)
1��↵(t)
�↵had(t) is the hadronic contribution to the running of ↵
t = �|q|2 �↵had(t) = �↵(t)��↵lep(t)
This may be obtained by using Bhabha scattering
aHLOµ =
↵
⇡
Z 1
0dx (1� x)⇧had(t(x)) =
↵
⇡
Z 1
0dx (1� x) �↵had(t(x))
The alternative approach of using a space-like formula for the vacuum polarization
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�↵lep(t)
�↵had(t)
�↵i(t(x))
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xpeak = 0.914 tpeak = �0.108 GeV 2is given by the total area under the curve
↵had
The smooth integrand function
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The space-like kinematics allows a direct comparison with the lattice
evaluations
[22] C. Aubin, T. Blum, Phys. Rev. D 75 (2007) 114502; P. Boyle et al., Phys. Rev. D 85 (2012) 074504; X. Feng et al.,Phys. Rev. Lett. 107 (2011) 081802; M. Della Morte et al. ,J. High Energy Phys. 1203 (2012) 055. [23] T. Blum et al., PoS LATTICE 2012 (2012) 022.
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aµ=(g-2)/2
aµHLO = !
!"
(1! x)0
1
" #had (!x2
1! xmµ2 )dx
t =x2mµ
2
x !10 " !t < +#
x = t2mµ
2 (1! 1!4mµ
2
t); 0 " x <1;
t = !ssin2(!2)
!!had (t) = "#had (t) for t < 0
aµHLO = !
!"
(1! x)0
1
" #!had (!x2
1! xmµ2 )dx
To summarize
with the “t” kernel
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A.Arbuzov, D.Haidt, C.Matteuzzi,M.Paganoni, L.T. Eur. Phys. J. C 34 (2004) 267
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AN EXAMPLE OF A SPACE-LIKE APPROACH
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A. Arbuzov, D. Haidt, C. Matteuzzi, M. Paganoni and L.T., Eur. Phys. J. C 34 (2004) 267
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each one of them known with an accuracy of at least 0.1% 1st factor
The Born cross section contains all the soft and
virtual corrections
Bhabha is a pure QED processQuarks enter only in loops
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2nd factor Vacuum polarization effectsgives the running of alpha
3rd factor
with all the real and virtual effects not incorporated in the running of alpha
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↵(0) is the Sommerfeld fine structure constant
measured with a precision of
O(10�9)
from loop contributions to the photon propagator�↵(q2)
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A couple of years later….
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!
"#had(5) (MZ
2 ) = $#MZ
2
3%Re ds
4m%2
&
' R(s)s(s$MZ
2 $ i()
time-like
Running of αem
space-like
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A new possibilityvia
scatteringµe ! µe
32
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µe ! µe
s ' 0.16 GeV 2 � 0.14 t 0 GeV 2 0 x 0.93
• High intensity muon beam available in the CERN North Area E =150 GeV • pure t-channel process d�
dt=
d�0
dt|↵(t)↵(0)
|2
Same process can be used for signal and normalization
1.3⇥ 107µ/s
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Muon and electron scattering angles are correlatedThis very important constraint may be used to select elastic events, reject
background from radiative events and minimize systematics
Electron scattering angle (mrad)0 10 20 30 40 50
Muo
n sc
atte
ring
angl
e (m
rad)
0
1
2
3
4
5 Muon beam momentum = 150 GeV
= 0.1 GeV
e
x = 0.1, E = 0.5 GeV
e
x = 0.2, E = 1.4 GeV
e
x = 0.3, E = 2.9 GeV
e
x = 0.4, E = 5.5 GeV
e
x = 0.5, E = 9.8 GeV
e
x = 0.6, E
= 17.8 GeV
e
x = 0.7, E
= 35.0 GeV
e
x = 0.8, E
= 88.5 GeVex = 0.9, E
= 130.7 GeVex = 0.928, E
x = 0.932 = 139.5 GeVe E
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U. Marconi at the CSN1 May 2017
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i) Initial muons have to be tagged with their direction and momentumii) 60 Be (C) layers interfaced with Si planes spaced by 1m air gap modularly spacediii) The use of a low Z material in order to reduce multiple scattering and background
iv) A final EM calorimeter to discriminate e/mu at small angles ( 2-3 mrad )
The Detector
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Statistics
Systematics
Theory
µ beam 1.3⇥ 107µ/s for 2⇥ 107s/yr
2⇥ 1012 events/yr statistical precision 0.3% in 2 yrs running
many effects have to be under control:efficiencies (uniformity, acceptance, tracking, trigger, PID) alignment of the Si planes, uncertainties in vertex location, incoming muon momentum, effect of multiple scattering (different in “control” and “signal” regions) ……………………(many others, can be studied with data themselves).
Electroweak radiative corrections ( including subleading logaritmic and mass contributions) have to be under control at the NNLO accuracy
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This idea has been proposed in 2016 at the “Physics Beyond Collider Workshop” at CERN• The idea has been presented in 2016 to the “Physics Beyond Collider Study Group”
• C. Matteuzzi and G. Venanzoni are members of the board as the experiment representatives.
• Physics Beyond Collider Study Group will select in fall 2018 experiments aiming to:
• Enrich and diversify the CERN scientific program: Exploit the unique opportunities offered by CERN’s accelerator complex and scientific infrastructure Complement the laboratory’s collider programme (LHC, HL-LHC and possible future colliders). The scientific findings will be collected in a report to be delivered by the end of 2018.
This document will also serve as input to the next update of the European Strategy for Particle Physics.
Also proposed to the INFN NSCI in 2017 and 2018
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from U. Marconi
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Prepared for submission to JHEP
Master integrals for the NNLO virtual corrections to
µe scattering in QED: the non-planar graphs
Stefano Di Vita,aStefano Laporta,
b,cPierpaolo Mastrolia,
b,cAmedeo Primo,
dUlrich
Schuberte
aINFN, Sezione di Milano, Via Celoria 16, 20133 Milano, ItalybDipartimento di Fisica ed Astronomia, Universita di Padova, Via Marzolo 8, 35131 Padova, ItalycINFN, Sezione di Padova, Via Marzolo 8, 35131 Padova, ItalydDepartment of Physics, University of Zurich, CH-8057 Zurich, SwitzerlandeHigh Energy Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA
E-mail: [email protected], [email protected],
[email protected], [email protected],
Abstract: We evaluate the master integrals for the two-loop non-planar box-diagrams
contributing to the elastic scattering of muons and electrons at next-to-next-to-leading
order in QED.We adopt the method of di↵erential equations and the Magnus exponential to
determine a canonical set of integrals, finally expressed as a Taylor series around four space-
time dimensions, with coe�cients written as combination of generalised polylogarithms.
The electron is treated as massless, while we retain full dependence on the muon mass.
The considered integrals are also relevant for crossing-related processes, such as di-muon
production at e+e� colliders, as well as for the QCD corrections to top-pair production
at hadron colliders. In particular our results, together with the planar master integrals
recentely computed, represent the complete set of functions needed for the evaluation
of the two-loop virtual next-to-next-to-leading order QED corrections to eµ ! eµ and
e+e�! µ
+µ�.
Just a few days ago !
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TEST Beams 2017/2018 at CERN
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from U. Marconi
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from U. Marconi
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from U. Marconi
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from U. Marconi
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from U. Marconi
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from U. Marconi
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from U. Marconi
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Setup located in the North Areabehind COMPASS detector
52from U. Marconi
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Tentative timeline of the project
• Studies with Geant4 ( underway )
• Detector geometry, number of planes, thickness, calorimeter for pid,…
• Test beam 2018 ( muons ) 2019 ( electrons )
• Assemble the detector -> 2020
• Start to collect data 2021
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• We propose to measure muon electron scattering by using the muon beam in the CERN North Area ( 150 GeV ) to extract the space-like quark vacuum polarization
• This measurement will allow to obtain the leading hadronic contribution to the g-2 in a new independent way and will constitute a crosscheck with previous time-like determinations and with the lattice results
• The goal is to determine the origin of the presently observed discrepancy between experiments and Standard Model predictions of the g-2 and the origin if within SM or if it could be attributed to BSM physics
Conclusions
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The End