the 12 gev solenoid pvdis proposal - institute for nuclear ... · nov 8 2008 int electroweak...

Nov 8 2008 INT Electroweak

The 12 GeV Solenoid PVDIS ProposalP. Souder


Deep Inelastic Scattering

iii fff ±≡±

fi(x) are quark distribution functions

For an isoscalar target like 2H, structure functions largely cancel in the ratio:

a(x) =310(2C1u − C1d ) 1+

2s+

u+ + d+

b(x) =

310(2C2u − C2d )

uv + dvu+ + d+

+L

APV =GFQ2

2παa(x) + Y (y)b(x)[ ]

a(x) =C1i Qi fi

+(x)i

∑Qi

2 fi+(x)

i∑

e-

N X

e-

Z* γ* y ≡1− ′ E /E

b(x) =C2i Qi fi

− (x)i

∑Qi2 fi

+ (x)i

∑

x ≡ xBjorken

Especially for x>0.5 or so

At high x, APV becomes independent of x, W, with well

defined SM prediction for Q2 and y

Axial quark coupling C2qSensitive to new physics at the TeV scale


PVDIS and SUSY

20 15 10 5 0 5 10 2

1.5

1

0.5

0

0.5

1

(QWe )

SUSY/(Q

We )

SM (%)

(A

d) SU

SY/ (

Ad) S

M

(%

)

(a)

15 10 5 0 5 10 15 2

1.5

1

0.5

0

0.5

1

(QWp )

SUSY/(Q

Wp )

SM (%)

(A

d) SU

SY/ (

Ad) S

M

(%

)

(b)

PVDIS requires <1% precisionIn δA/A to be competitive with Qweak, Møller

No (1-4sin2θW) suppression of APV

RPV Susy is typical of most models


Lessons from INT

• Leptoquark phenomenology is complex.• Calculation of limits has not been done for

DIS.• There seems to be no reason to think that

some new physics would affect the C2’s and not the C1’s.

• Can anything useful be said about extra dimensions or compositeness?


Plots with samescale would be

useful for comparingdifferent

experiments


Design I for PVDIS Physics

• 20o - 35o, E’~ 1.5 - 5 GeV• δp/p ~ 2% some regions 10’s of kHz/mm2

• Pion rejection with Cerenkov + segmented calorimeter.• Asymmetric yoke, detectors in magnetic field


Double Toroidal Spectrometer

ČE-cal

Tracking Chambers

Design II (very preliminary)

CustomToroids

Features:1.SimplerDetectors2. Betteracceptance


Broad Kinematic AcceptanceQQ22 QQ22

xx xx

11 GeV11 GeV 8.8 GeV8.8 GeV

JLabJLab 11GeV can provide new probe of nucleon structure and unique mea11GeV can provide new probe of nucleon structure and unique measure sure of Weak axialof Weak axial--vector quark couplingsvector quark couplings

xx

QQ22 • 11 GeV Solenoid• 8.8 GeV Solenoid• 11 GeV HMS / SHMSIs this data good

enough to measureApv

Bj to 0.5%?


Hadronic Structure for PVDIS

APV =GFQ2

2παa(x) + f (y)b(x)[ ]

∑∑

+

+

=

iii

iiii

xfQ

xfQCxa

)(

)()( 2

1

e-

N X

e-

Z* γ*

∑∑

+

−

=

iii

iiii

xfQ

xfQCxb

)(

)()( 2

2

x ≡ xBjorken

y ≡1− ′ E /E

iii fff ±≡±

fi(x) are quark distribution functionsFor an isoscalar target like 2H, structure functions largely cancel in the ratio:

[ ]

+

+−= ++

+

dusCCxa du21)2(

103)( 11 L+

+

+−= ++

−−

dudu

CCxb du )2(103)( 22

(2C2u-C2d)/(2C1u-C1d)=0.136Especially for x>0.5 or so

APV becomes independent of x, Q2, W, and depends only on y


Search for CSV in PV DISδu(x) = up (x) − dn (x)δd(x) = d p (x) − un (x)

•u-d mass difference•electromagnetic effects

up (x) = dn (x)?d p (x) = un (x)?

•Direct observation of parton-level CSV would be very exciting!•Important implications for high energy collider pdfs•Could explain significant portion of the NuTeV anomaly

dudu

AA

PV

PV

+−

=δδδ 28.0For APV in electron-2H DIS:

Sensitivity will be further enhanced if u+d falls off more rapidly than δu-δd as x → 1

•measure or constrain higher twist effects at x ~ 0.5-0.6•precision measurement of APV at x → 0.8 to search for CSV

Strategy:


CSV and PV-DISRCSV =

δ APV x( )APV x( )

= 0.28δu x( )− δd x( )

u x( )+ d x( )For PV-DIS from 2H:

Sensitivity will be enhanced if u+d falls off more rapidly than δu - δd as x → 1

%

δAD

AD

from Londergan, using MRST fit

Effects at high-x are predicted to be very large


Problem:

• x-independent CSV is indistinguishable from Standard Model violation.

• What error should we add? 2%?


Higher Twist Coefficients in parity conserving (Di) and nonconserving

(Ci) Scattering

)/)(1(),(),( 222

22 QxDQxFQxF DGLAP +=

Evolves accordingTo DGLAP equations

Higher Twist iswhat is left over

APV (x,Q2) = APV (x)(1+ C(x) /Q2)

Higher Twist is anyQ2-dependent deviationFrom the SM prediction

(Does not Evolve)


Blumlein andBotcher


Ptroblem:

• Can we assume that HT is larger at higher x?

• If so, we can really neglect HT at x-values that are best for the Standard Model test.

• At INT, the answer seems to be a resounding NO!


Interpretation of Higher Twist

≠

• APV sensitive to diquarks: ratio of weak to electromagnetic charge depends on amount of coherence

• Do diquarks have twice the x of single quarks?• If Spin 0 diquarks dominate, likely only 1/Q4 effects• On the other hand, some higher twist effects may cancel in ratio, so APV may have

little dependence on Q2.

Observing a clean higher twist operatorhas recently become very interesting.


What is going on at high x?

• Real higher twist• Slow convergence of NnLO analysis• Limited Q2 range

Consensus: real higher twist(DIS008)


Complete PV DIS Program (Including 12 GeV)

• Hydrogen and Deuterium targets• Better than 2% errors for each point

– It is unlikely that any effects are larger than 5-10%• x-range 0.25-0.75• W2 well over 4 GeV2

• Q2 range a factor of 2 for each x point– (Except x~0.75)

• Moderate running times

•With HMS/SHMS: integrates all of this physics •With larger solid angle apparatus: higher twist, CSV, d/u…


Scorecard

XNoYesNoNew Physics

XNoNoYesd/u

XNoNoYes?Isospin

XYesNoYesHigher twist

dpQ2yx

Problem: Cannot change Q2 and y independently


Theory Error Budget to Interpret ±1% Data

b(x)/a(x)~13%0.3<f(y)<0.8

a(x)Theory dirt must be <0.5%

Observe hadronic physics effects>3%Background for electroweak studies

`Theory dirt’includes unknownand uninteresting

effects

b(x)Theory dirt must be <3%

Set new limits on the small C2’s


Phenomenology and R

T

LRRFFσσγγ =→+= )1(21

γγσ21

2

)2

1(22 FE

xyMyy

xyFdxdyd

EM

−−+∝

])2

1(22[22 21

2ZZ

A

V

Z

FE

xyMyy

xyFgGdxdyd γγ

γ πασ

−−+−∝

])2([22 3

2Z

V

A

Z

FyxgGdxdyd γ

γ πασ

−−∝

EM

AZxbyf

σσγ=)()(

EM

VZxa

σσγ=)(

EM

AZ

VZPV

BAσ

σσ γγ +=


Most QCD cancels in a(x)

ασσγ Gxa

EM

VZ ≈=)(

Assumptions:1: CVC (Charge Symmetry)2: Quarks contribute incoherently (Higher Twist)Goal of program is to test these assumptions.

R=σL/σT cancels (in DIS limit)

Charge Symmetry1: Strange quarks (absent at large x)2: up≠dn (Our main interest)


Higher Twist without the QPMBjorken,

PRD 18, 3239 (78)

∫∫

⋅

⋅+∝

4

4

|)0()(|

|)0()()0()(|

deDjxjDl

xdeDjxJJxjDlA

xiq

xiq

νµµν

νµνµµν

Wolfenstein,NPB146, 477 (78)

( ) ( )dduuSdduuV µµµµµµ γγγγ +=⇔−= xdeDVxVDlVV xiq 4|)0()(|∫ ⋅= νµµν

SSVV

SSCCVVCCA

dudu

31

)(31)( 1111

+

++−= Zero in QPM

xdeddxuxuDlSVSVSSVV xiq 4)0()0()()(|))(( ⋅∫∝+−=− νµµν γγ

δ3.01−∝ASSVVSSVV

+−

=δ


Hobbs and Melnitchouk

2

22 1

νQr +=

Question: Is RγZ-Rγ~αQCD+O(1/Q2)?


R is ~20%;→10% in f(y)→1% in f(y)b(x)

Large xbins

Data on R vs x


Problem

• RγZ introduces new parameters.• RγZ introduces new higher twist terms.• We can only vary Q2 in a way correlated

with Y• Can HT of RγZ be related to F1 HT?• Can RγZ be computed perturbatively?


Axial hadronic current2 Methods:

1: Use data only:a: σγZ

A≈F3ν and use neutrino data

b: σγ from electromagnetic data2: Use QPM and make corrections:

a: Sea quarks are absent at high xb: R from electromagnetic datac: Ignore higher twist

EM

AZxbyf

σσγ=)()(

Should be goodto ~3%, which

is ample

Is higher twista big problemat the highest

a values?)1(22)1(1)(

2)()(

2

2

22 Ryyyyf

CCxbyf

du ++−−−

≡≈−


Conclusions

• APV to ~0.5% is useful.• CSV is potential source of unertainty.• Issues with RγZ are another important

source.• By the way: aren’t these issues also

serious for some other JLab experiments in DIS?


Compare ν F3 to global parton fitson a linear scale

15%

40%

Note verticalscale

0.45 0.55

0.65 0.75

3

3

QPMxFxFδ

Useful at x~0.5Problems at x~0.7


Parton Distribution FunctionsSea quarks that contributeto a(x) and s quarks thatcontribute to a(x) vanish

rapidly for x>0.5

CAUTION:PDF’s use as input

40 years of precise dataplus ‘reasonable’ guesses.One must distinguish whichfeatures are data and which

features are guesses.


How do we know that antiquarksare negligible at large x?

spx L

F2

≡ 21 xxxF −=

sxxM 212 =µµ

Drell-Yan production of muon pairs

p p

µ+

µ-

θσ 2cos1+∝Ωd

d

When xF=0, x1=x2=x, and M=x2s.Hence x for both the quark and

anti-quark are known.The cross section drops rapidly with x

The small quantityis directly observed.No subtractions are

needed, as is thecase for F3 data.

Clean data exist with x~0.6 and Mµµ2>10 Smith et al.,

PRL 46, 1607(81)


Electron-Quark Phenomenology

C2i ≡ 2gVe gA

i

V

AC1i ≡ 2gA

e gVi

A

V

C1u and C1d will be determined to high precision by Qweak, Cs

C2u and C2d are small and poorly known: one combination can be accessed in PV DIS

New physics such as compositeness, leptoquarks:Deviations to C2u and C2d might be fractionally large


PV AsymmetriesWeak Neutral Current (WNC) Interactions at Q2 << MZ

2

Longitudinally Polarized Electron Scattering off Unpolarized Fixed Targets

(gAegV

T +β gVegA

T)

•The couplings gT depend on electroweak physics as well as on the weak vector and axial-vector hadronic current •For PVDIS, both new physics at high energy scales as well as interesting features of hadronic structure come into play•A program with a broad kinematic range can untangle the physics


Electron-Quark Phenomenology

C2i ≡ 2gVe gA

i

V

AC1i ≡ 2gA

e gVi

A

V

C1u and C1d will be determined to high precision by Qweak, Cs

C2u and C2d are small and poorly known: one combination can be accessed in PV DIS

New physics such as compositeness, leptoquarks:Deviations to C2u and C2d might be fractionally large


Phenomenological Parton CSV PDFs

Best fit: κ = -0.2, large uncertainty ! Best fit remarkably similar to model CSV predictions

MRST ADEL

Bag model

MRST Phenomenological PDFs include CSV for 1st time:Martin, Roberts, Stirling, Thorne (03):

Choose restricted form for parton CSV: 90% conf limit (κ)

[f(x): 0 integral; matches to valence at small, large x]


APV in DIS on 1HAPV =

GFQ2

2παa(x) + f (y)b(x)[ ]

b(x) =322C2uuv (x) − C2d dv (x)4u(x) + d(x) + s(x)

a(x) =322C1uu(x) − C1d (d(x) + s(x))

4u(x) + d(x) + s(x)

a(x) =u(x) + 0.91d(x)u(x) + 0.25d(x)

+ small corrections

•Allows d/u measurement on a single proton!•Vector quark current! (electron is axial-vector)

•Determine that higher twist is under control•Determine standard model agreement at low x•Obtain high precision at high x


Uncertainty in d/u at High x; and Needed Errors in PV Measurement

Must simultaneously constrain higher twist effects

The challenge is to get statistical and systematic errors ~ 2%

Deuteron analysis has nuclearcorrections

APV for theproton has no such

corrections. (BONUSuses proton tagging.)


Neutrino data on xF3 from NuTeV, CCFR, CDHSW

Nice data set!

But it is shown on a log plot.

What does it looklike on a linear scale?

the 12 gev solenoid pvdis proposal - institute for nuclear ... · nov 8 2008 int electroweak...

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