8 June 2010 EIC Electroweak Workshop: Summary 1 EIC Electroweak Workshop: Summary Krishna Kumar University of Massachusetts, Amherst Acknowledgement: A. Deshpande, W. Marciano, K. Paschke, M.J. Ramsey-Musolf, P. Souder, and speakers at the Workshop June 8, 2010 2010 JLab Users Group Meeting Jefferson Laboratory https://eic.jlab.org/wiki/index.php/Electroweak_Working_Group
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8 June 2010 EIC Electroweak Workshop: Summary 1
EIC Electroweak Workshop: Summary
Krishna KumarUniversity of Massachusetts, Amherst
Acknowledgement:A. Deshpande, W. Marciano, K. Paschke, M.J. Ramsey-Musolf, P. Souder,
Physics TopicsStudies of the Electroweak Interaction•Charged Lepton Flavor Violation τ -> e •Weak Neutral Current couplings
Studies using the Electroweak Interaction•high-x structure functions - higher twist, charge symmetry violation, d/u of the proton•PV EMC effect in nuclei, F3γZ
•new spin structure functions
EIC Electroweak Physics is a largely unexplored subfield
Detailed studies of experimental feasibility have yet to be done!
Workshop featured reports of significant theoretical progress
2
8 June 2010 EIC Electroweak Workshop: Summary
Workshop Program
3
First day: •primary physics topics•EIC Options Overview•inclusive physics in general
Concluded with a discussionof experimental capabilities
K. Paschke, Co-convenerD. Armstrong, local organization
Held at the College of William and Mary
8 June 2010 EIC Electroweak Workshop: Summary 4
Specific choices of kinematics and target nuclei probes different physics:• In mid 70s, goal was to show sin2θW was the same as in neutrino scattering• Early 90s: target couplings carry novel information about hadronic structure• Now: precision measurements with carefully chosen kinematics can probe physics at the multi-TeV scale
(gAegV
T +β gV
egAT)
Parity-Violating AsymmetriesWeak Neutral Current (WNC) Interactions at Q2 << MZ
2
Polarized lepton-nucleon collisions- flip ONE polarization (average over the other)- flip both SIMULTANEOUSLY
€
10−4 ⋅Q2
€
APV ~ 10−5 ⋅Q2 to gV and gA are function of sin2θW
To date, only lepton helicity-flip asymmetries using unpolarized fixed targets
Talks by M. Ramsey-Musolf, W. Marciano
8 June 2010 EIC Electroweak Workshop: Summary
TeV-Scale e-q Interactions
Many new physics models give rise to non-zero Λ’s at the TeV scale: Heavy Z’s, compositeness, extra dimensions…
One goal of neutral current measurements at low energy AND colliders: Access Λ > 10 TeV for as many f1f2 and L,R combinations as possible
€
Lf1 f2=
4πΛ ij2 ηij
i, j= L ,R∑ f 1iγµ f1i f 2 jγ
µ f2 j
Consider
€
f1 f 1→ f2 f 2
€
f1 f2 → f1 f2orΛ’s for all f1f2 combinations and L,R combinations
Eichten, Lane and Peskin, PRL50 (1983)
A
V
V
A
€
δ(C1q )∝ (+ηRLeq +ηRR
eq −ηLLeq −ηLR
eq )
€
δ(C2q )∝ (−ηRLeq +ηRR
eq −ηLLeq +ηLR
eq )PV elastic e-p scattering, APV
PV deep inelastic scattering
8 June 2010 EIC Electroweak Workshop: Summary
Electroweak Structure Functions
6
QPM Interpretation
e-
N X
e-
Z γ*
Vogelsang and Weber, Nucl. Phys. B 362 (1991)
Ji, Nucl. Phys. B 402 (1993)
Anselmino, Gambino and Kalinoski, hep-ph/9401264v2
QED Double-spin Asymmetrypolarized electron, unpolarized hadron gV, gA are the electron vector-
and axial-vector couplings
€
APV =GFQ
2
2παa(x) + f (y)b(x)[ ]
Q2 >> 1 GeV2 , W2 >> 4 GeV2
APV in Electron-Nucleon DIS:
For 2H, assuming charge symmetry, structure functions largely cancel in the ratio:
€
a(x) =310
(2C1u −C1d )[ ] +L
€
b(x) =310
(2C2u −C2d )uv (x) + dv (x)u(x) + d(x)
+L
For 1H, the leading term (vector-quark) is maximally sensitive to d(x)/u(x)
0.001 0.01 0.1 1 10 100 1000
! [GeV]
0.225
0.230
0.235
0.240
0.245
0.250
sin
2!
W
^(!"
APV(Cs)
Qweak [JLab]
Moller [SLAC]
"-DIS
ALR
(had) [SLC]
AFB
(b) [LEP]
AFB
(lep) [Tevatron]
screening
antiscreening
Moller [JLab]
PV-DIS [JLab]
SM
current
future
Czarnecki and Marciano (2000)Erler and Ramsey-Musolf (2004)
8 June 2010 EIC Electroweak Workshop: Summary
From JLab to EIC
8
SOLID SOLIDQweak
At end of JLab program (Qweak, MOLLER, SOLID): Interest in couplings and inthe weak mixing angle will depend on LHC results
•At high Q2:•“huge” asymmetries•large y range
•At low Q2:•Very forward angle•small y; can map out higher twist in detail
Collider kinematics:
Operator Product Expansion
Figure 1: Comparison of quark-quark correlations and quark-gluon correla-tions
Figure 2: Diagrams corresponding to DGLAP evolution. The exception isdiagram (d), which is a quark-gluon operator.
10
Figure 1: Comparison of quark-quark correlations and quark-gluon correla-tions
Figure 2: Diagrams corresponding to DGLAP evolution. The exception isdiagram (d), which is a quark-gluon operator.
10
Figure 1: Comparison of quark-quark correlations and quark-gluon correla-tions
Figure 2: Diagrams corresponding to DGLAP evolution. The exception isdiagram (d), which is a quark-gluon operator.
10
Twist-2
Quark-quark correlation(Twist-4)
Quark-gluon correlation (Twist-2 + Twist-4)
3
neutral current (WNC), and interference of the vector EM current and axial vector WNC;
and Y1,3 are functions of Bjorken x, the kinematic variable y [see Eq.(10) below] and the
ratios Rγ and RγZ of longitudinal and transverse cross sections for purely EM and WNC-
EM vector current interference cross sections [see Eq. (14) below]. In the SM, at leading
twist and in the absence of CSV effects, the Y1 term in Eq.(2) is independent of y and
depends only on geA and the vector current coupling of the Z-boson to quarks [3]. Since
geV = −1 + 4 sin2 θW ∼ −0.1, the Y1-term dominates the asymmetry, making its scrutiny
particularly important for the interpretation of the Jefferson Lab PVDIS program.
Considerable theoretical effort has been devoted to disentangling the various contribu-
tions to the asymmetry. The effect of twist-four contributions to the asymmetry was first
considered in papers by Bjorken and Wolfenstein [17, 18] more than thirty years ago, where
it was shown to arise from a single, non-local four-quark operator in the limit of good isospin,
negligible sea-quark and CSV effects, and up to corrections in αs(Q2). Quantitative esti-
mates of twist-four effects were first obtained in [19] where the contribution of the spin-two
operators was estimated using the MIT Bag Model. This analysis was extended in [20] to
include corrections to the F3 structure function(see Eq. (13) below). More recently, twist-
four effects to the asymmetry were estimated by the authors of Ref. [21], who considered
the possibility that Rγ #= RγZ at twist-four (see Eq. (14) below). These authors argued that
such a difference could introduce hadronic uncertainties that might impede the extraction
of CSV effects from ARL.
In this paper, we draw on the observations of [17, 18] that the twist-four contribution to
the Y1 term in ARL for deuterium, given in Eq. (2), arises from a single four-quark operator
involving up- and down-quark fields
Oµνud(x) =
1
2[u(x)γµu(x)d(0)γνd(0) + (u ↔ d)] (3)
to revisit the analysis of Ref. [21]. Noting that the contribution of Oµνud(x) to the electroweak
structure functions satisfies the Callan-Gross relation at leading order in the strong coupling,
we find that
RγZ = Rγ and Y1 = 1, (4)
at twist-four up to perturbative corrections. Consequently, all twist-four effects entering the
dominant term in the asymmetry reside in the ratio F γZ1 /F γ
1 .
Using the power law dependence in Q2 of the twist-four effects to the Y1-term it may be
possible, with the precision and the wide kinematic range of the PVDIS program at JLab,
to disentangle twist-four effects from CSV effects depending on their relative overall sizes.
To provide theoretical guidance for such a program, we utilize the MIT Bag Model[22] to
estimate the size and variation of the twist-four contribution with Bjorken-x and Q2 as
shown in Fig. 1. These estimates extend the earlier work of Ref. [20] by allowing for the
x-dependences of the twist-two and twist-four contributions to F γ(γZ)1 to differ. We find that
CSV vs Higher Twist
• Negligible higher twist effects can allow for a cleaner extraction of CSV or new physics effects.
22
0.3 0.4 0.5 0.6 0.7 0.8
!0.03
!0.02
!0.01
0.00
0.01
0.02
0.03
R1(CSV )
R1(HT )
R1(CSV )
x
κ = −0.8
κ = 0.65
FIG. 2: The relative magnitudes of R1(HT ) and R1(CSV ) as a function of the Bjorken-x variablefor a representative value of Q2 = 6 GeV2. using δu−δd = 2κf(x) where f(x) = x−1/2(1−x)4(x−0.0909) for κ = −0.8. The top curve and bottom curves give R1(CSV ) for the choices κ = −0.8and κ = 0.65 respectively in Eqs.(77) and (78). The middle curve is the MIT Bag Model estimatefor R1(HT ).
VI. CONCLUSIONS
Parity-violating electron scattering has become a powerful tool for probing both novel
aspects of hadronic and nuclear structure as well as possible indirect signatures of physics
beyond the Standard Model. Its efficacy depends on both significant experimental advances
in controlling systematic uncertainties and attaining high statistics as well as on substantial
developments in the theoretical interpretation of the parity-violating asymmetries. PVDIS
represents a prime example of this synergy between experiment and theory. The first mea-
surements of the deep inelastic asymmetry for a deuterium target relied on the simplest
parton-level description of hadrons, yet the result with a 17% experimental uncertainty (for
the two highest energy points) was sufficient to single out the Standard Model descrip-
tion of the weak neutral current interaction from other alternatives. Today, one anticipates
lower-energy measurements at Jefferson Lab with experimental errors below one percent for
individual kinematic points, making for O(0.5%) combined uncertainties on quantities of
interest. The challenge for theory is to provide a framework for interpreting such precise
results.
In this study, we have attempted to do so for the leading term in the deuterium asymme-
try. In principle, it can be kinematically separated from the subleading term (suppressed by
recently in Ref. [43], though the analysis applied to the asymmetry as a whole and not the Y1 term alone.
After taking into considerations constraints from other electroweak precision observables and direct search
limits, corrections of up to 1.5% on the asymmetry are currently allowed in supersymmetric models.
Bag model estimate of higher twist
20
by the Bag Model picture, which correlates the up- and down-quarks largely through the
confinement radius and the Pauli exclusion principle. On the other hand, the absence of
large power corrections would imply that the Y1 term can be interpreted primarily in terms
of the underlying electroweak interactions and/or possible CSV in the parton distributions.
We comment on the implications for probes of CSV and new physics in the following section.
V. CHARGE SYMMETRY VIOLATION AND NEW PHYSICS
To the extent that R1(HT) is either tiny as suggested by the MIT Bag Model estimates
or large enough to be extracted utilizing the 1/Q2-dependence, one may hope to use the
deuterium asymmetry as a probe of CSV and/or new physics. In terms of the former, it has
recently been suggested that HT contributions to the Y1 term in the deuterium asymmetry
may be too large and too theoretically uncertain to utilize this term as a probe of CSV [21].
These suggestions were based on the possibility that Rγ and RγZ could differ substantially,
a possibility we have shown cannot apply at twist four. We now compare the MIT Bag
Model estimate of R1(HT) to the CSV correction, R1(CSV). To that end, we follow the
parameterization of CSV effects utilized in Ref. [21]:
up = u+δu
2
dp = d+δd
2(75)
un = d− δd
2
dn = u− δu
2.
(76)
In terms of the δu and δd one has
R1(CSV) =
[1
2
(2C1u + C1d
2C1u − C1d
)− 3
10
](δu− δd
u+ d
). (77)
The δu and δd have been constrained by structure function data utilizing the ansatz
δu− δd = 2κf(x)
f(x) = x−1/2(1− x)4(x− 0.0909) , (78)
with κ lying in the range −0.8 ≤ κ ≤ +0.65. Detailed phenomenological and theoretical
analyses of CSV effects can be found in Refs.[21, 40, 41]. In Fig. 2, we show the relative
magnitudes of R1(HT) and R1(CSV) for a representative value of Q2 = 6 GeV2 and κ
given by the extremes of the allowed range. We observe that the Bag Model higher twist
correction is considerably smaller than the possible range for CSV effects. To the extent that
20
by the Bag Model picture, which correlates the up- and down-quarks largely through the
confinement radius and the Pauli exclusion principle. On the other hand, the absence of
large power corrections would imply that the Y1 term can be interpreted primarily in terms
of the underlying electroweak interactions and/or possible CSV in the parton distributions.
We comment on the implications for probes of CSV and new physics in the following section.
V. CHARGE SYMMETRY VIOLATION AND NEW PHYSICS
To the extent that R1(HT) is either tiny as suggested by the MIT Bag Model estimates
or large enough to be extracted utilizing the 1/Q2-dependence, one may hope to use the
deuterium asymmetry as a probe of CSV and/or new physics. In terms of the former, it has
recently been suggested that HT contributions to the Y1 term in the deuterium asymmetry
may be too large and too theoretically uncertain to utilize this term as a probe of CSV [21].
These suggestions were based on the possibility that Rγ and RγZ could differ substantially,
a possibility we have shown cannot apply at twist four. We now compare the MIT Bag
Model estimate of R1(HT) to the CSV correction, R1(CSV). To that end, we follow the
parameterization of CSV effects utilized in Ref. [21]:
up = u+δu
2
dp = d+δd
2(75)
un = d− δd
2
dn = u− δu
2.
(76)
In terms of the δu and δd one has
R1(CSV) =
[1
2
(2C1u + C1d
2C1u − C1d
)− 3
10
](δu− δd
u+ d
). (77)
The δu and δd have been constrained by structure function data utilizing the ansatz
δu− δd = 2κf(x)
f(x) = x−1/2(1− x)4(x− 0.0909) , (78)
with κ lying in the range −0.8 ≤ κ ≤ +0.65. Detailed phenomenological and theoretical
analyses of CSV effects can be found in Refs.[21, 40, 41]. In Fig. 2, we show the relative
magnitudes of R1(HT) and R1(CSV) for a representative value of Q2 = 6 GeV2 and κ
given by the extremes of the allowed range. We observe that the Bag Model higher twist
correction is considerably smaller than the possible range for CSV effects. To the extent that
,
HigherTwistContribu1onstoPV‐DIS
•small y, good (low) Q2 range; search for higher twist
Collider kinematics:
• Twist-4 effects in vector term of 2H APV come only from quark-quark correlations
• A single 4-quark twist-4 matrix element contributes to the vector WNC term
• The relation RγZ = Rγ holds true at twist-4 up to perturbative corrections
€
APV =GFQ
2
2παa(x) + f (y)b(x)[ ]
only quark-quark correlations given by a single matrix element
QuarkKinema1csHigh-x resolution requires measurement of hadronic flow
Constant FJB contours
Chapterr 6
Kinematicc reconstruction
6.11 Reconstruction methods
AA DIS event can be characterised by four independent measurable quantities: the energy E[
andd the polar angle 9e of the scattered positron, and the variables Sh{— E^ — PZ:h) and Pr,h-
Heree Eh is the energy of the hadronic final state and Pz^ and Pxth are the longitudinal and
transversee momentum, respectively. From the latter two an angle 7/, and an energy F^ can be
definedd which correspond to the polar angle and the energy of the scattered quark in the naive
quarkk model (see figure 6.1):
PPT,hT,h ~ (
Eh ~
pz,h)
2 ,„ .>
ffThTh + (hh - yz,hy
P£P£hh + {Eh-Pzh)2
Sincee a DIS event is completely determined by only two independent variables x and Q2
theree is some freedom to choose any two quantities out of the set of four to reconstruct the
Figuree 6.1: schematic picture of a DIS event showing the definition of the measurable quantities
E'E'ee,, 0e, Fh and 7^. In this plot a positron with energy Ee comes from the left and a quark inside
thethe proton with energy Eq from the right.
67 7
Jacquet-Blondel reconstructionelectron
kinematics
K. Paschke
8 June 2010 EIC Electroweak Workshop: Summary
Precision EW Tests
• Measure DIFFERENCE of y-dependent and y-independent terms in APV for 2H– electron beam polarization systematic suppressed by a factor of 10
– 2% measurement of 2C2u-C2d would be comparable to best 2 collider measurements and MOLLER at JLab
• Measure the RR-LL combination– Enhanced total effective polarization
– Suppression of polarization systematic error
– Both 1H and 2H become largely independent of structure functions!
– Can thus go well beyond the best fixed target measurements
• Luminosity requirement likely to approach 1000 fb-1...– need to incorporate Z-exchange for highest Q2
11
Incremental improvements can be made on DIS EW couplings over the 12 GeV JLab program at higher Q2 but can one make ultraprecise weak mixing angle measurements?
(W. Marciano)
Outlookforhigh‐xstructurefunc1ons
It is hard to beat fixed-target luminosity• SOLID aims for many bins at measuring APV at 0.5%. At an EIC, this
would seem to require 1035 cm-2 at very high s.• Not yet carefully checked... requires study for conclusion• Potentially may provide the best independent constraint on C2q’s• Significance and importance will depend on JLab 12 GeV and LHC
results
• collider gives Q2 range with small y : measure 4-quark twist-4 operator• first-ever empirical bound on single HT quark-quark operator?
• additional topics in high-x p.d.f.’s: CSV (eD), d/u (ep), and sea quarks• combined analysis with charged current interactions
Definite conclusions must await detailed studies of detector capabilities and kinematic reach of various EIC options
Parity Violating DIS: Lead
28 /37
Q2 = 5 GeV2
Z/N = 82/126 (Lead)
0.8
0.9
1
1.1
a 2(x
A)
0 0.2 0.4 0.6 0.8 1
xA
a2
anaive2
9
5− 4 sin2 θW Q2 = 5 GeV2
Z/N = 82/126 (Lead)
−0.1
0
0.1
0.2
0.3
a 3(x
A)
0 0.2 0.4 0.6 0.8 1
xA
a3
anaive3
9
5
(
1 − 4 sin2 θW
)
! For a N " Z target:
a2(x) =9
5− 4 sin2 θW −
12
25
u+A(x) − d+
A(x)
u+A(x) + d+
A(x)
a3(x) =9
5
(
1 − 4 sin2 θW)
{
u−
A + d−Au+
A + d+A
−13
[
125
u−
A+d−Au+
A+d+A
u+A−d+
A
u+A+d+
A
− u−
A−d−Au+
A+d+A
]
}
! After naive isoscalarity corrections medium effects still very large
! Large x dependence of a2(x) " evidence for medium modification
5%
NuclearStructureFunc1ons
More generally, F2(γZ) and F3(γZ) for nuclear DIS interesting and new
• proposes that a neutron or proton excess in nuclei leads to an isovector-vector mean field dominated by ρ exchange
• shifts quark distributions: “apparent” CSV violation• Isovector EMC effect: explain 1/2 of NuTeV anomaly• Would be a smoking gun demonstration of medium modification
• requires polarized e- with A (available for “free”?)• inclusive rates for eA at low x, with y separation• need theoretical input on relevance of nuclear F3γZ
Cloet, Bentz, Thomas, arXiv 0901.3559
Target‐FlipPVAsymmetry
ATPV =GF Q2
2√
2πα
[gV
gγZ5
F γ1
+ gAf(y)gγZ1
F γ1
]unpolarized electron, polarized hadron
★Enough y range to separate vector and axial-vector pieces★1H, 2H and 3He measurements★Precise measurements to x ~ 0.01 at low s and x ~ 0.001 at high s
2∆u− + ∆d− + ∆s−
4u+ + d+ + s+
∆u+ + ∆d+ + ∆s+
4u+ + d+ + s+
3∆u− + 3∆d− + 2∆s−
u+ + d+ + s+
∆u+ + ∆d+ + ∆s+
u+ + d+ + s+
1H2H
y-independent y-dependent
– EW amplitudes measure a different linear combination of quark polarizations, allowing a direct determination of ∆s: no SU(3)f or other theory uncertainties
– initial indications: very competitive with semi-inclusive, and phase 1 designs can already produce measurements with significant impact
A New Opportunity at the EIC
Low‐xSpinStructureFunc1ons
Start with focus on spin-dependent PDFs, ∆s extraction
• In the long term, there are 15 different combinations that can be measured (EM, γZ, W, with 1H, 2H, 3He)
• W production needs to be fully explored:– two structure functions g1 and g5
– 1H + 2H with e- equivalent to 1H with e- & e+ ?• New sum rules, new dynamics in Q2 evolution:
– first moments of g1(x) and g5(x) provide new information on singlet and non-singlet pieces of spin structure functions
– New “Bjorken Sum Rules” with different QCD corrections– test SU(3)f and SU(2)f in the polarized quark sea (Vogelsang)– comprehensive analysis of twist-3 matrix elements (Bluemlein)
New frontier in precision QCD tests in inclusive DIS:
8 June 2010 EIC Electroweak Workshop: Summary
Charged Lepton Flavor Violation• The discovery of neutrino mass and mixing
– lepton number violation theoretically favored
– potentially enhanced charge lepton flavor violation within reach of proposed experiments
• help decipher the mechanism of neutrinoless double beta decay• R-parity violating Supersymmetry
• Experimental LFV searches undergoing revival– Ongoing at existing facilities (PSI, B-Factories), and also
being looked at seriously for the future (J-PARC, Fermilab)
– The Mu2e project at Fermilab was given the highest near- term priority in the recent P5 report for US HEP
• Thus, it is interesting to see if EIC has a role to play in this subfield
16
Theoretical motivation w.r.t. EIC initiated by M. Ramsey-Musolf
€
e−
€
e−
€
νM
€
W −
€
W −
€
u
€
u
€
d
€
d
€
e−
€
e−
€
χ 0
€
˜ e −
€
u
€
u
€
d
€
d
€
˜ e −
MEG
Mu2e
10 3
10 4
10 -2 10 -1 1 10 10 2
κ
Λ (T
eV)
B(µ→ eγ)>10-13
B(µ→ eγ)>10-14
B(µ→ e conv in 48Ti)>10-16
B(µ→ e conv in 48Ti)>10-18
EXCLUDED
.
.
Project X Mu2e
8 June 2010 EIC Electroweak Workshop: Summary
Decay vs Scattering
17
“Contact Terms”
?
?
?
Supersymmetry and Heavy Neutrinos
Contributes to µ→eγ
Exchange of a new, massive particle
Does not produce µ→eγ
Λκ
LCLFV =mµ
(κ + 1)Λ2µRσµνeLFµν +
κ
(1 + κ)Λ2µLγµeL(uLγµuL + dLγµdL)
“Loops”
SINDRUM
André de Gouvêa, Project X Workshop
Golden Book
hig
her m
ass
scal
e
MEGA
Λ (TeV)
κ
€
τ
€
e
€
γ €
τ
€
e
€
A Z,N( )
€
X
Similarly Exp: Bτ->eγ ~ 1.1 x 10-7
10 to 100 fb-1 DIS dataset at EIC energies competitive
(Theory input from M.J. Ramsey-Musolf)
e.g. leptoquarks
ProjectedLeptoquarklimits
Matt Gonderinger, M Ramsey-Musolf
!
!"#$% !
"# !$%&'()*&$()+ ! (*,!-%)./0%1!2343 ! !"#
τ → eγspecific LQ
HERA limit
LQ - quark couplings
(ΛM
)2
(ΛM
)2
HERA
!!CLFV: EIC, HERA & Rare Decays
Gonderinger, R-M in process
HERA & EIC
Rare Decays
!!eqq eff op General Classification
RL
z = ("2 / M2 ) / ("2 / M2 )HERA
! ! !""#$
!!!!!e #
~30x improvement for (21)@ luminosity of 10 fb-1 :
EIC @ 10 fb-1 can decrease many existing limits by a factor of 2 to almost 2 orders of magnitude
• EICDetectorWorkshop,June2010
Iden1fyingTauLeptonse− + p→ τ− + X
1
• If mixed in with hadron remnants, the tau would be boosted• If forward in the incident electron direction, the tau would be
isolated• Potential for clean identification with high efficiency:
– look for single pion, three pions in a narrow cone, single muon: should be able to devise several good triggers
– tau vertex displaced 200 to 3000 microns: would greatly help background rejection and maintain high efficiency if vertex detector is included in EIC
Topology: neutral current DIS event; except that the electron replaced by tau lepton
e− + p→ µ+ + X e− + p→ τ+ + XMust also investigate the sensitivity and motivation for
Lepton Number Violation
• Monte Carlo study to design cuts,efficiency and background rejection
• vertex tracker will likely be required
• work starting on this study at Stoney Brook (A. Deshpande et al)
hard to beat fixed target, but further studies neededextensive MC study requiredbut potentially also phase 1
Most promising topics: electroweak interaction to study QCD
• high-x structure functions - higher twist, charge symmetry violation, d/u of the proton
• PV EMC effect in nuclei, F3γZ
• ∆s, other novel structure functions prospects for a phase 1 machine
Sufficient theoretical guidance to launch these topics - present bottleneck is getting the experimentalist time for rate studies and other calculations
main outcome of workshop
Totally new topics: deliverable might be delayed!
8 June 2010 EIC Electroweak Workshop: Summary
Summary• Lepton-Quark Weak Neutral Current Couplings
– EIC with highest luminosities may allow precision beyond planned facilities, both for BSM physics and nucleon stucture
• interest level might be magnified depending on LHC results and results of the JLab program
• theoretically very clean; e.g. higher twist effects can be cleanly isolated• detailed look at experimental systematics needed!
– An optimized (smaller) data set with polarized 1H, 2H and 3He• new parity-violating structure functions• separation of quark helicity distributions from x = 0.005 to 0.5• Possibly critical for disentangling new physics in W asymmetries
– e-A with polarized electrons (available “for free”)?• novel probe of EMC effect?
• Charged lepton flavor and number violation searches
– electron to tau conversion might be a unique window of opportunity21
8 June 2010 EIC Electroweak Workshop: Summary
Outlook• Physics topics defined
– Anything inclusive can be in this working group!
– Ultra-precise weak mixing angle
– higher twist effects
– novel nucleon spin structure functions
– novel nuclear structure functions
– lepton flavor/number violation
• Begin quantitative studies– pros and cons of 4 machine options
– luminosity vs COM energy
– produce physics plots, especially for phase I options
• Mesh into EIC’s overall efforts– Impact on detector design
– Seattle workshop and white paper towards LRP22
Plenty of opportunitiesfor postdocs & junior faculty to get involved in defining unexplored aspects of EIC physics: there is potential for topics to be quite important and exciting
8 June 2010 EIC Electroweak Workshop: Summary 23
CSV with PVDISParton-level charge symmetry assumed in deriving 2H APV
Charge Symmetry Violation
• u,d quark mass difference• electromagnetic effects
• Important implications for high energy collider pdfs
• Could explain significant portion of the NuTeV anomaly
•At collider kinematics, x dependence can be explored with little uncertainty from F3 and axial-hadronic current
SOLID Sensitivity
8 June 2010 EIC Electroweak Workshop: Summary 24
PVDIS on the Proton: d/u at High x
Deuteron analysis has largenuclear corrections (Yellow)
APV for the proton has no such corrections
The challenge is to get statistical and systematic errors ~ 2%
3-month run
SOLID sensitivity
Once again, collider kinematics will reduce axial hadronic uncertainties
8 June 2010 EIC Electroweak Workshop: Summary
EW Couplings in Nuclei• They propose that a neutron or proton excess in nuclei leads
to an isovector-vector mean field dominated by ρ exchange• shifts quark distributions: “apparent” CSV violation
• Isovector EMC effect: explain 1/2 of NuTeV anomaly
25
Cloet, Bentz, Thomas, arXiv 0901.3559
8 June 2010 EIC Electroweak Workshop: Summary
EIC DIS Kinematics
26
K. Paschke
•Electroweak tests must be done at high x: 0.3 - 0.8•Spin structure function measurements can be done at x: 0.001-0.1•In either case, jet direction and total hadron energy must be measuredThese issues and the constraints they pose on the accessible kinematic range for precision measurements are being investigated.
8 June 2010 EIC Electroweak Workshop: Summary 27
PVDIS: From JLab to EICEIC
•Much high Q2: no higher twist issues•“Huge” Asymmetries•Large range in y
•y-dependence separates V & A•High precision @ x ~ 0.01 to 0.001•1H, 2H and 3He measurements•At highest luminosities: new precision QCD tests in inclusive DIS
•Q2 evolution•new “Callan-Gross” relations•new “Bjorken” sum rules
•11 x 60: 50 going to 500 •4 x 250: 2 going to 20•11 x 250: 100 going to 1000•20 x 325: 5 going to 50
Machine configurations: GeV & fb-1
Back of the envelope:s x luminosity is roughly constant
Physics Topics•Beyond the Standard Model•Nucleon Helicity Structure•Novel Aspect of EMC Effect•Lepton flavor & number violation
8 June 2010 EIC Electroweak Workshop: Summary 28
Published Measurements
16 TeV17 TeV
0.8 TeV 1.0 TeV (Zχ)
0.01•GF
95% C.L.
Running of sin2θW established to 6σ
T
6σ•Czarnecki and Marciano •Erler and Ramsey-Musolf•Sirlin et. al.•Zykonov
Limits on “New” Physics
8 June 2010 EIC Electroweak Workshop: Summary 29
A Design for Precision PV DIS Physics at JLab
• High Luminosity on LH2 & LD2
• Better than 1% errors for small bins• x-range 0.25-0.75• W2 > 4 GeV2
• Q2 range a factor of 2 for each x– (Except x~0.75)
• Moderate running times
• Solenoid (from BaBar, CDF or CLEOII ) contains low energy backgrounds (Moller, pions, etc) trajectories measured after baffles • Fast tracking, particle ID, calorimetry, and pipeline electronics• Precision polarimetry (0.4%)
SoLiD Spectrometer at JLab
Proposal received conditional approval in January 2009
8 June 2010 EIC Electroweak Workshop: Summary
Proposed SoLiD Dataset
30
4 months at 11 GeV
2 months at 6.6 GeV
Error bar σA/A (%)shown at center of binsin Q2, x
Strategy: sub-1% precision over broad kinematic range for sensitive Standard Model test and detailed study of hadronic structure contributions