EIC Electroweak Workshop: Summary · 2010. 6. 8. · 8 June 2010 EIC Electroweak Workshop: Summary Physics Topics Studies of the Electroweak Interaction •Charged Lepton Flavor Violation

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,

and speakers at the Workshop

June 8, 20102010 JLab Users Group Meeting

Jefferson Laboratory

https://eic.jlab.org/wiki/index.php/Electroweak_Working_Group



8 June 2010 EIC Electroweak Workshop: Summary

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


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


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


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


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

Anselmino, Efremov & Leader, Phys. Rep. 261 (1995)

i ≡ γ, γZ,Z

A‖ =f(y)gγ

1

F γ1

APV =GF Q2

2√

2πα

[gA

F γZ1

F γ1

+ gVf(y)

2F γZ

3

F γ1

]


Lepton Flip PV Asymmetry

7

€

a(x) =

C1iQi fi(x)i∑

Qi2 f i(x)

i∑

€

b(x) =

C2iQi fi(x)i∑

Qi2 f i(x)

i∑

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)


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



10



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

Sonny Mantry, M.J. Ramsey-Musolf, G.F. Sacco arXiv:1004.3307

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


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:


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


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)

TopicsfromEWWorkingGroup

Electroweak studies• WNC couplings • Charged Lepton Flavor Violation τ -> e

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!


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


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


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


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


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


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.


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


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


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


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

sea quarks

standardmodel

higher twist

chargesymmetryviolation


EIC DIS Kinematics

31

Documents

EIC Electroweak Workshop: Summary · 2010. 6. 8. · 8 June 2010 EIC Electroweak Workshop: Summary Physics Topics Studies of the Electroweak Interaction •Charged Lepton Flavor Violation