may 20, 2006 dis parity at 12 gev p. a. souder dis-parity 12 gev how to reach high x: prospects with...

May 20, 2006 DIS Parity at 12 GeV P. A. Souder

DIS-Parity 12 GeV

How to reach high x:

Prospects with a High-Lumonosity

Solenoidal Spectrometer

P. A. SouderSyracuse University

Thanks to Bosted, Brodsky, Chudakov,Kumar, Londergan, Meziani, Michaels,

Reimer, Ramsey-Musolf,Paschke, Pitt, Zheng


OUTLINE

• DIS-Parity and the Standard Model

• Discovering new hadronic physics

• Requirements for a new spectrometer

• Solution: Solenoidal Spectrometer


•The couplings gT depend on electroweak physics as well as on the weak vector and axial-vector hadronic current •For DIS-Parity, 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

(gAegV

T + gV

egAT)

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

2

Longitudinally Polarized Electron Scattering off Unpolarized Fixed Targets


New Physics Reach: Qweak and Møller

Kurylov, Ramsey-Musolf, Su

To be relevant, new SMtests must have smallenough errors to show

up on plots like this


3%10%

-10%

Add DIS-Parity: ±

DIS-Parity requires a factor of 5-10 improvementIn δA/A to be competitive with Qweak, Møller

No 1-4sin2θW suppression of APV

1.0%


Hadronic Structure for Parity Violating Electron DIS

fi(x) are quark distribution functions

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

a(x) 3

10(2C1u C1d )

b(x) 3

10(2C2u C2d )

uv (x) dv (x)

u(x) d(x)

APV GFQ2

2a(x) f (y)b(x)

a(x) C1iQi f i(x)

i

Qi

2 f i(x)i

e-

N X

e-

Z* *

y 1 E / E

b(x) C2iQi f i(x)

i

Qi

2 f i(x)i

x xBjorken

Especially for x>0.5 or so

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


Quark Distribution Functions vs x

JLab can explore theValance region

0.5<x<0.8

What can possiblygo wrong?


Why should we believe DISparitywhen no one Believes NuTeV?


PW Ratio depends on the following assumptions: • Isoscalar target (N=Z)• include only light (u, d) quarks• neglect heavy quark masses• assume isospin symmetry for PDFs • no nuclear effects (parton shadowing, EMC, ….)• no higher twist effects• radiative corrections OK? (γ-W boxes?)• no contributions outside Standard Model

Assumptions for the Paschos-Wolfenstein Ratio

Nobody believesthat this is the

problem

JLab 12 GeVissues


Use PV To Study hadronic structure?

• PV might have the smallest errors:<1%– PV: Systematics are Pe and <Q2>

– Cross sections: Systematics are target length, solid angle, etc.


Search for CSV in PV DIS

Sensitivity will be further enhanced if u+d falls off more rapidly than u-d 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:

•u-d mass difference•electromagnetic effects

•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

up (x) dn (x)?

d p (x) un (x)?

For APV in electron-2H DIS: du

du

A

A

PV

PV

3.0

u(x) up (x) dn (x)

d(x) d p (x) un (x)


Phenomenological Parton CSV PDFs

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

Choose restricted form for parton CSV:

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

MRST ADEL

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

90% conf limit (κ)


Higher Twist Coefficients in parity conserving (Di) and nonconserving (Ci)

Scattering

F2(x,Q2) F2(x)(1 D(x) /Q2)

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

(Does not Evolve)

Evolves accordingTo DGLAP equations

Higher Twist iswhat is left over

Higher Twist is anyQ2-dependent deviationFrom the SM prediction


Going from LO to NNNLO Greatly Reduces

the Extracted Higher Twist Coefficients

x D(x) D(x) Q2min D/Q2

min(%) D/Q2min(%)

LO NNNLO LO NNNLO

0.1-0.2 -.007 0.001 0.5 -14 2

0.2-0.3 -.11 0.003 1.0 -11 0.0

0.3-0.4 -.06 -0.001 1.7 -3.5 -0.5

0.4-0.5 .22 0.11 2.6 8 4

0.5-0.6 .85 0.39 3.8 22 10

0.6-0.7 2.6 1.4 5.8 45 24

0.7-0.8 7.3 4.4 9.4 78 47

F2(x,Q2)=F2(x)(1+D(x)/Q2) Q2=(W2-M2)/(1/x-1) Q2min=Q2(W=2)

If D(x)~C(x), Parity might show higher twist At high x without needing QCD evolution.


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.


Probing Higher Twist with PV

Sacco, R-M preliminary

APV Q2

y

Looking beyond the parton descriptionPV Deep Ineslastic eD (J Lab 12 GeV)

~0.4%

E=11 GeV =12.50

Different PDF fits


APV in DIS on 1H

APV GFQ2

2a(x) f (y)b(x)

a(x) u(x) 0.91d(x)

u(x) 0.25d(x)

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

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

a(x) 3

2

2C1uu(x) C1d (d(x) s(x))

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

b(x) 3

2

2C2uuv (x) C2d dv (x)

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

+ small corrections


Uncertainties in d/u at High x, and the Errors we Would Like to Achieve with

PV Measurements

Deuteron analysis has nuclearcorrections

APV for theproton has no such

corrections

Must simultaneously constrain higher twist effects

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


Complete PV DIS Program (Including 12 GeV)

• Hydrogen and Deuterium targets• Better than 2% errors

– It is unlikely that any effects are larger than 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: search for TeV physics •With larger solid angle apparatus: higher twist, CSV, d/u…


Scorecard

x y Q2 p d

Higher twist Yes No Yes X

Isospin Yes? No No X

d/u Yes No No X

New Physics No Yes No X


Apparatus Needed for PVDIS


Reaching Large x at 11 GeV

22

/

4

8.06.0

4

4020

GeVW

y

GeVE

50% azimuthal coverage assumed

6 GeV

Need Largeθ for largex and Q2

HMS and SHMSare fine for

small θ

(and large y)

W<2


•2 to 3.5 GeV scattered electrons•20 to 40 degrees•Factor of 2 in Q2 range at moderate x•High statistics at x=0.7, with W>2

Range of W and Q2


Cut on 0.6<y<0.8

• Large range in Q2 for HT study• High x (>0.7) accessible with W2>4• Large acceptance allows feasible runtime requests• /e ratio is not extreme, but cannot integrate

Details on Kinematics and π/e Ratio


Large Angle Large Acceptance: Concept

•CW 90 µA at 11 GeV•40-60 cm liquid H2 and D2 targets•Luminosity > 1038/cm2/s

JLab Upgrade

•Need high rates at high x

•For the first time: sufficient rates to make precision PV DIS measurements

•solid angle > 200 msr•Resolution<2%•Count at 100 kHz• online pion rejection of 102

Need magnet to block γ’s andlow energy π’s


Solenoid vs Toroid

Solenoid takes advantageof the small beam spotrequires less bending

Problem: shield detectorfrom line of sight photons

B points out of page


Geometry for a Solenoidal Spectrometer


Shielding the detector with

baffles

Large acceptance inThe θ direction

Shield in the ø direction


Use Many Slits for Large ø Acceptance

Curvature matchestrajectories of

Scattered particles

There are 20segments


Plan View of the Spectrometer

CDF orBaBar

Solenoid?


Detector Packages

• Pb Glass TA Counter (material exists?)

• Gas Cerenkov (Easy for <4 GeV electrons)

• Tracking: GEM detectors


The COMPASS GEM Detector

Size: 31×31 cm2

Rate: 25 kH/mm2


COMPASS GEM Time and Spatial Resolution


Resolution of Spectrometer

θ P 2 GeV 3 GeV 5 GeV

20o 1.5% 2.4%

30o 0.7% 1.0% 1.4%

40o 0.8%


Rates as a function of kinematic bin


Example: d/u of Proton

d/u

Bjorkenx

Compare MAD Spectr. to Solenoid Spectr.

off shell

on shell

Curves fromMelnithouk

and Thomas

What Physics is Allowed by New Device?

MAD 120 daysSolenoid 40 days


EMC effect in Parity Violation ?

Cross section data from J. Gomez et.al. PRD 49 (1994) 4348

This study mightbe done with

8.5 GeV beam,50 μa beam


Other Users of the Spectrometer

1. A1n

2. Charm from H3. DVCS4. Two γ

A1n

x0 1

0

A1n→1 as x→1??

(Show that resultis independent of

W, Q2)


Summary and Outlook• Parity-Violating DIS can probe exciting new physics at high x• One can start now (at 6 GeV)

– Do 2 low Q2 points (P-05-007, X. Zheng contact)• Q2 ~ 1.1 and 1.9 GeV2

• Either bound or set the scale of higher twist effects– Take data for W<2 (P-05-005, P. Bosted contact)

• Duality• Could help extend range at 11 GeV to higher x

• A short run to probe TeV physics in PV DIS off 2H: Hall A or C• The bulk of the program requires a dedicated spectrometer/detector• CSV can be probed at high x• Higher twist can be controlled or exploited• Additional physics topics could be addressed by dedicated spectrometer

– Transverse (beam-normal) asymmetries in DIS – Polarized targets: g2 and g3 structure functions


Conclusion

• A lot of interesting physics happens at JLab with an 11 GeV beam.

• Why not build a solenoidal spectrometer to observe it??? (With good precision)

may 20, 2006 dis parity at 12 gev p. a. souder dis-parity 12 gev how to reach high x: prospects with...

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