Past, Present and the Future of Precision sin 2 q W Measurements

Past, Present and the Future of Precision sin2W Measurements

Jae Yu (for NuTeV Collaboration)University of Texas at Arlington

NuFact’03, June 9, 2003Columbia University, New York

• Introduction• Past measurements• Current Improvement• Measurement at a Neutrino Factory• Conclusions

June 9, 2003 J. Yu: Past, Present and Future of Precision sin2W Measurements, NuFact’03

2

NuTeV CollaborationT. Adams4, A. Alton4, S. Avvakumov7, L.de Babaro5, P. de Babaro7,

R.H. Bernstein3, A. Bodek7, T. Bolton4, S. Boyd8, J. Brau6, D. Buchholz5, H. Budd7, L. Bugel3, J. Conrad2, R.B. Drucker6, B.T.Fleming3, J.A.Formaggio2, R. Frey6, J. Goldman4, M.

Goncharov4, D.A. Harris3, R.A. Johnson1, J.H.Kim2, S.Kutsoliotas9, M.J. Lamm3, W. Marsh3, D. Mason6, J.

McDornald8, K.S.McFarland7, C. McNulty2, Voica Radescu8, W.K. Sakumoto7, H. Schellman5, M.H. Shaevitz2, P.

Spentzouris3, E.G.Stern2, M. Vakili1, A. Vaitaitis2, U.K. Yang7, J. Yu3*, G.P. Zeller2, and E.D. Zimmerman2#

1. University of Cincinnati, Cincinnati, OH45221, USA2. Columbia University, New York, NY 10027 3. Fermi National Accelerator Laboratory, Batavia, IL 60510 4. Kansas State University, Manhattan, KS 66506 5. Northwestern University, Evanston, IL 60208 6. University of Oregon, Eugene, OR 97403 7. University of Rochester, Rochester, NY 14627 8. University of Pittsburgh, Pittsburgh, PA 15260 9. Bucknell University, Lewisburg, PA 17837*: Current affiliation at the University of Texas at Arlington#: Current affiliation at the University of Colorado, Boulder


3

sin2W and -N scattering• In the electroweak sector of the Standard Model, it is not known a priori what

the mixture of electrically neutral electomagnetic and weak mediator is This fractional mixture is given by the mixing angle

• Within the on-shell renormalization scheme, sin2W is:

• Provides independent measurement of MW & information to pin down MHiggs

• Comparable size of uncertainty to direct measurements• Measures light quark couplings Sensitive to other types (anomalous) of

couplings • In other words, sensitive to physics beyond SM New vector bosons,

compositeness,-oscillations, etc

2

22 1sin

Z

WShellOn

w MM


4

How did we measure?

• Cross section ratios between NC and CC proportional to sin2W

• Llewellyn Smith Formula:

)(CC

)(CC

W4

W22

)(CC

)(NC)(

σσ1θsin

95θsin

21ρ

σσR

WEMweak QIcoupling 2)3( sin)3(weakIcoupling

Some corrections are needed to extract sin2W from measured ratios (radiative corrections, heavy quark effects, isovector target corrections, HT, RL)


5

Previous Experiment

• Very small cross section Heavy neutrino target e are the killers (CC events look the same as NC events)

• Conventional neutrino beam from /k decays • Focus all signs of /k for neutrinos and antineutrinos• Both , in the beam (NC events are mixed)


6

Charged Current Events

Neutral Current Events

How Do We Separate Events?

x-view

y-view

x-view

y-viewNothing is coming in!!!

Nothing is coming in!!!

Nothing is going out!!!

Event Length


7

Event LengthDefine an Experimental Length variable Distinguishes CC from NC experimentally in statistical manner

Compare experimentally measured ratio

to theoretical prediction of R

Candidates CC

Candidates NC

Cut

Cut

Long

ShortExp N

NLLLL

NNR


8

Past Experimental Results

• Significant correlated error from CC production of charm quark (mc) modeled by slow rescaling, in addition to e error

2ShellOnW

Z

WShellOnW

2

0.16GeV/c80.14M

0.00310.2277MM

1θsin


9

The NuTeV Experiment• Suggestion by Paschos-Wolfenstein by separating andbeams:

Reduce charm CC production error by subtracting sea quark contributionsOnly valence u, d, and s contribute while sea quark contributions cancel outMassive quark production through Cabbio suppressed dv quarks only

• Smarter beamline – Separate and beam– Removes all neutral secondaries to eliminate e content

r1RRθsin

21ρ

σσσσR W

22

CCCC

NCNC


10

Events and EHad After Event SelectionEvents passing cuts: 1.62M 350k (<E>~100GeV)


11

NuTeV Event Length Distributions

250k101k

1167k457k

R=Nshort/NLongNlongNshortMode

t)0.0007(sta0.3916t)0.0016(sta0.4050

Energy Dependent Length cut implemented to improve statistics and reduce systematic uncertainties.

Good Data-MC agreement in the cut region


12

Event Contamination and Backgrounds

•SHORT CC’s (20% 10%) exit and rangeout•SHORT e CC’s (5%) eNeX•Cosmic Rays (0.9%)

•LONG NC’s (0.7%)hadron shower punch-through effects

•Hard Brem(0.2%)Deep events


13

Sources of experimental uncertainties kept small, through modeling using and TB data

Other Systematic Effects

Effect Size(sin2W) ToolsZvert 0.001/inch +- events

Xvert & Yvert 0.001 MC

Counter Noise 0.00035 TB ’s

Counter Efficiency 0.0002 events

Counter active area 0.0025/inch CC, TB

Hadron shower length 0.0015/cntr TB ’s and k’s

Energy scale 0.001/1% TB

Muon Energy Deposit 0.004 CC


14

MC to Relate Rexp to Rand sin2W

• Parton Distribution Model (<Q2> ~ 25 GeV2 for , 16 GeV2 for )– Correct for details of PDF model Used CCFR data for PDF– Model cross over from short CC events

• Neutrino Fluxes ,e,,e in the two running modes e CC events always look short

• Shower length modeling– Correct for short events that look long

• Detector response vs energy, position, and time– Continuous testbeam running minimizes systematics


15

sin2W Fit to Rexp and R

exp

• Thanks to the separate beam Measure R’s separately• Use MC to simultaneously fit and to sin2W and mc, and sin2W

and

• R Sensitive to sin2W while R isn’t, so Ris used to extract sin2W and R to control systematics

• Single parameter fit, using SM values for EW parameters (=1)

input as GeV/c 0.141.38c

m w/ (syst) 0.06(stat) 0.091.32cm2

(syst) 0.0009(stat) 0.00130.2277θsin W2

expRexpR

•Two parameter fit for sin2W and yields

0.0410.9979ρ0.00310.2265θsin

0

W2

)(CC

)(CC

W4

W22

)(CC

)(NC)(

σσ1θsin

95θsin

21ρ

σσR

Syst. Error dominated since we cannot take advantage of sea quark cancellation


16

NuTeV sin2W Uncertainties

150GeVMln0.00032

50GeV175GeVM0.00022θδsin

H

2

22tshell)(On

W2

1-Loop Electroweak Radiative Corrections based on Bardin, Dokuchaeva JINR-E2-86-2 60 (1986)

0.00005Non-isoscalar target

0.00014Higher Twist

0.08MW (GeV/c2)

0.00162Total Uncertainty0.00064Total Physics Model Systmatics

0.00011RadiativeCorrection

0.00022

0.00032RL

0.00047CC Charm production, sea quarks

0.00063Total Experimental Systematics0.00027 (23)Length (Other effects)

0.00030Event Vertex

0.00039e flux

0.00135Statistical

sin2WSource of Uncertainty Dominant uncertainty

/


17

Past vs Present Uncertainty Comparisons

Technique worked!

Beamline worked!

Dominant error


18Confidence level in upper Mhiggs limit weakens slightly.

The Present (NuTeV) sin2W

2ShellOnW

2Z

2WshellOn

W2

ShellOnW

2

GeV/c 0.0880.14M

MM1θsin

(syst) 0.0009(stat) 0.00130.2277θsin

Comparable precision but value smaller than other measurements


19

• Performed the fit to quark couplings (and gL and gR)– For isoscalar target, the N couplings are

– From two parameter fit to and

Model Independent Analysis

W42

02R

2R

2R

W4

W22

02L

2L

2L

θsin95ρdug

θsin95θsin

21ρdug

expR

0.00110.0308g0.00140.3001g

2R

2L

(SM: 0.3042 -2.6deviation)

(SM: 0.0301 Agreement)

Difficult to explain the disagreement with SM by:Parton Distribution Function or LO vs NLO or Electroweak Radiative Correction: large MHiggs

expR


20

• R- technique is sensitive to q vsq differences and NLO effect– Difference in valence quark and anti-quark momentum fraction

• Isospin symmetry assumption might not be entirely correct– Expect violation about 1% NuTeV reduces this effect by using the ratio

of and cross sections Reducing dependence by a factor of 3• s vss quark asymmetry

– s ands needs to be the same but the momentum could differ if +30% asymmetry

• NuTeV LO di- measurement shows s=s -s ~-0.0027 • NuTeV NLO analysis show no-asymmetry (D. Mason, et al., ICHEP02

proceedings)• NLO and PDF effects

– PDF, mc, Higher Twist effect, etc, are small changes• Heavy vs light target PDF effect (Kovalenko et al., hep-ph/0207158)

– Using PDF from light target on Iron target could make up the difference NuTeV result uses PDF extracted from CCFR (the same target)

What is the discrepancy due to (Old Physics)?


21

• Heavy non-SM vector boson exchange: Z’, LQ, etc– LL coupling enhanced than LR needed for NuTeV

• Propagator and coupling corrections– Small compared to the effect

• MSSM : Loop corrections wrong sign and small for the effect• Gauge boson interactions

– Allow generic couplings Extra Z’ bosons???• LEP and SLAC results says < 10-3

• Many other attempts in progress but so far nothing seems to explain the NuTeV results – Lepto-quarks– Contact interactions with LL coupling (NuTeV wants mZ’~1.2TeV, CDF/D0: mZ’>700GeV)– Almost sequential Z’ with opposite coupling to

What other explanations (New Physics)?

Langacker et al, Rev. Mod. Phys. 64 87; Cho et al., Nucl. Phys. B531, 65; Zppenfeld and Cheung, hep-ph/9810277; Davidson et al., hep-ph/0112302


22

• To address concerns within the community– Don’t expect to see large effects

• LO x-sec model describe CC x-sec data well• Gambino, et al., (hep-ph/0112302) shown little NLO PDF effect to R- level shifts to R- small (Davidson, hep-ph/0112302 & Kulagin, hep-ph/0301045)

• To calculate O(s) pQCD corrections to the differential X-sec for DIS

• NuTeV (Zeller & McFarland) is collaborating with Theorists– FNAL Theory group: K. Ellis, B. Dobrescu, W. Gigele– DESY: Seven-Olaf Moch– others

• Approach based on Altarellu, Ellis & Martinelli, NP B143, 521 (1978)– X-sec’s written in terms of xF1, F2, xF3

– pQCD corrections affect 2xF1-F2=FL & xF3-F2

– FL effect taken into account via RL

– Need s correction of xF3-F2, because s2 is small (Zijlstra, PLB297, 377, 1992)

• Calculations and Implementation of the correction in progress

NLO Upgrade of sin2W Analysis


23

• Neutrinos come from decays– Good understanding of the beam content and flux

• Better collimated than conventional beam• Large neutrino flux (105~106 higher than the current)But…• Always two neutrinos simultaneously in the given beam

( e+ or e)– Traditional heavy target detector will not work

• Will screw up NC counting due to e CC events– Need light target detectors Can afford to do this

• Might need new techniques for NC to CC ratio– Can’t distinguish e vs induced NC events

sin2W Measurement at a NuFact


24

A Light Target sin2W Detector at a NuFacte and from muon decays are in the beam at all times Must use light target (D2) detectors

1m

P-ID & Momentum Hadronic Energy -ID and Momentum


25

Expectation at a NuFact

3.20x10-4 9.00x10-5RL

2.20x10-4 1.50x10-4

0.080.025MW (GeV/c2)

1.62x10-35.15x10-4Total Uncertainty

6.40x10-44.6x10-4Total Physics Model Systmatics

1.10x10-4 1.10x10-4Radiative Correction

5.00x10-5 0 (D2 target)Non-isoscalar target correction

1.40x10-4 1.40x10-4Higher Twist

4.70x10-4 2.40x10-4CC Charm production, sea quarks

6.30x10-49.00x10-5Total Experimental Systematics

1.80x10-4 9.00x10-5Energy Measurements

3.0x10-4 3.0x10-6Event Vertex

3.9x10-40e flux

1.35x10-32.13x10-4Statistical

sin2WSource of Uncertainty

/

Using a 1m thick D2 target, one can obtain about 20M CC events per yearWith the help of good p-id, the stat doubles Length related uncertainties become irrelevant


26

Experimental Issues • Must be able to reverse beam polarity and measure current well• Detector must be light weight• Must be able to distinguish primary e, and

– Need to control overall p-ID efficiency to be better than 10-3

• High electron detection efficiency• Good EM and Hadronic shower ID• Good charged particle momentum measurement• Good vertex measurement w/ triggering capability at the targetTheoretical Issues• Better measured charm CC x-sec• Need to understand radiative correction better• Better understanding of higher twist effects

Experimental and Theoretical Issues


27

Conclusions• NuTeV has improved sin2W

– NuTeV result deviates from SM prediction by about +3(PRL 88, 091802, 2002)

– Interpretations of this result implicates lower left-hand coupling (-2.6but good agreement in right-hand coupling with SM

• NuTeV discrepancy has generated a lot of interest in the community• Still could be a large statistical fluctuation (5 has happened before) • No single one can explain the discrepancy

• NuTeV working on NLO analysis of sin2W

• A Neutrino factory can provide a dramatic improvement in sin2W• Large neutrino flux (both e and )

• Significant improvement in uncertainties (MW<25MeV)• Light target detector with p-id would be necessary• Theoretical improvement will help further improving the measurement

2ShellOnW

shellOnw

2

0.08GeV/c80.14M

(syst) 0.0009(stat) 0.00130.2277θsin

Documents

Past, Present and the Future of Precision sin 2 q W Measurements