Physics at an Upgraded Fermilab Proton Driver

Steve Geer UEC Dec 11, 2004

1. Introduction & Process2. Main Motivation: Neutrino Oscillations3. Neutrino Scattering4. Muons5. Kaons, pions, neutrons, …..6. Summary

Fermilab

Introduction 2

Following the recommendations of the Fermilab Long Range Planning Committee, the Fermilab Director has requested:

“Preparation of documentation sufficient to establish mission need for the Proton Driver as defined by the Department of Energy CD-0 process.”

“Development and documentation of the physics case. I would like this to include both support for a forefront neutrino program at Fermilab in the decade 2010 and beyond, and identification of other opportunities that could potentially be enabled with a Proton driver facility.”

Proton Driver Physics StudyWorking Groups and Conveners

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WG1: Neutrino OscillationsD. Harris (FNAL), S. Brice (FNAL), W. Winter (Princeton)

WG2: Neutrino InteractionsJ. Morfin (FNAL), R. Ransome (Rutgers), R. Tayloe (Indiana)

WG3: MuonsR. Ray (FNAL), R. Roberts (BU)

WG4: Kaons and PionsH. Nguyen (FNAL), T. Yamanaka (Osaka U.)

WG5: AntiprotonsD. Christian (FNAL), M. Mandelkern (UCI)

WG6: Tevatron ColliderH. Cheung (FNAL), Penny Kasper (FNAL), P. Ratoff (Lancaster U.)

WG7 NeutronsT. Bowles (LANL), G. Greene (ORNL)

Proton Driver Scientific Advisory Committee4

Peter Meyers (Chair) PrincetonEd Blucher ChicagoGerhard Buchalla MunichJohn Dainton UKYves Declais CERNLance Dixon SLACUmberto Dosselli INFNDon Geesaman ANLGeoff Greene ORNLTaka Kondo KEKMarvin Marshak MinnesotaBill Molzon UCIHitoshi Murayama UC BerkleyJames Siegrist LBNLAnthony Thomas JLabTaku Yamanaka Osaka

1. Give the emerging physics case a critical review

2. Help us to reach out to a broad community as we develop aconstituency excited by the Proton Driver Physics Program

Workshop, Documentation & Review 5

Fermilab Proton Driver Physics Workshop, 6-9th October, 2004133 participants. Lots of enthusiasm for a Proton Driver physicsprogram: http://www-td.fnal.gov/projects/PD/Physics.html

The working group conveners have prepared draft reports presenting the case for the Proton Driver Meyers Committee last week.

We have scheduled a Proton Driver Scientific Advisory Committee meeting on Dec. 16th to review the emerging physics case … a representative from the UEC at this review would be welcome.

The working group documents plus the output from the review will be used to begin to prepare the CD0 documentation … which I hope will be ready for a 2nd review end January.

Colloquium to present the emerging physics case: Jan 26th

A New Fermilab Proton Driver would offer Flexibility for the Future Physics Program in General, & the Neutrino Program in Particular

6

~ 700m Active Length

2 MW 8 GeV Linac

X-RAY FEL LAB

Slow-Pulse Spallation Source& Neutrino Target

Neutrino“Super- Beams”

MainInjector@2 MW

8 GeV

NUMI

Anti-Proton

SY-120Fixed-Target

Off- Axis

To Homestake120 GeVand 8 Gev

Neutrinos are Everywhere 7

Neutrinos outnumber ordinary matter particles in the Universe (electrons, protons, neutrons) by a factor of ten billion.

Depending on their masses they may account for a fraction (few % ?) of the “dark matter”

Neutrinos are important for stellar dynamics: ~7109 cm-2s-1 stream through the Earth from the sun. Neutrinos also govern Supernovae dynamics, and hence heavy element production.

If there is CP Violation in the neutrino sector, then neutrino physics might ultimately be responsible for Baryogenesis.

To understand the nature of the Universe in which we live we must understand the properties of the neutrino.

Neutrino Oscillations are Exciting 8

The Standard Model needs modification accommodate neutrino mass terms, which require either the existence of right-handed neutrinos Dirac mass terms, or a violation of lepton number conservation Majorana mass terms. The physics of neutrino masses & mixings is physics beyond the Standard Model

We know that neutrino masses & mass splittings are tiny compared to the masses of the other fundamental fermions. This suggests radically new physics, which perhaps originates at the GUT or Planck Scale, or indicates the existence of new spatial dimensions, or …..

We don’t know the neutrino mass spectrum & have only partial know-ledge of the mixing matrix for the 3 known eigenstates.

Neutrinos have nonzero masses and mixings !

Its exciting because:

Neutrino Measurements Drive Theoretical Ideas 9

Although we don’t have complete knowledge of the neutrino mixing matrix, we do know it is qualitatively very different from the quark mixing matrix. This necessarily constrains theoretical ideas about the underlying relationship between quarks and leptons.

Over the last few years knowledge of neutrino oscillation parametershas eliminated a previous generation of GUT models, leading to a newset of models designed to accommodate the data.

Further oscillation measurements will necessarily reject the majorityof the new models, and hopefully lead to new ideas about physics beyond the Standard Model

Neutrino Oscillation Measurements Drive Theoretical Ideas. This is expected to continue to be the case throughout the Proton Driver era.

A Long-Baseline Fermilab Proton Driver Programwould make Critical Contributions to the Global Program

10

The long-term path will depend on the unknown parameter 13, & who builds what and when. However, the first step with a Proton Driver does not depend critically on these uncertainties, and in allscenarios it appears the Proton Driver has a critical role to play.

sin2213

Fra

ctio

n of

-s

pace

CP Violation (3)MassHierarchy(95% CL)

11The 8 GeV Beam offers an interesting (unique) possibility

The off axis beamsAre “NuMI” beams.

Doug Michael, Chris Smith Mark Messier

The Neutrino Oscillation Case for a Fermilab Proton Driver seems to be Strong

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The physics is exciting, World Class, multi-phase, with the potential for further discoveries

The Proton Driver program would make critical contributions to theGlobal program in all 13 scenarios, & (within reason) independent of exactly what else is built and when.

We can already design the first round of Proton Driver long-baseline experiment(s)

Fermilab can build upon its existing significant investment in hosting the US accelerator based neutrino program … it makes sense for Fermilab to host the Proton Driver program.

Neutrino Scattering 13

In the pre-Proton Driver era we expect high precision neutrino measurements of CC & NC (quasi)elastic scattering, and CC & NC producion of pions and strange particles off nuclear targets. However: (i) The antineutrino event rate is down by a factor of 3-5 (depending on energy) compared to the neutrino rate … due to the cross-sections and the +/ - production ratio, and (ii) The H2 & D2 target rates are down by an order of magnitude compared to nuclear target rates.

We will need the Proton Driver to make high-precision measurements with antineutrino beams on nuclear targets, and with both neutrino and antineutrino beams on nucleon targets (H2,D2).

Neutrino Scattering Motivation 14

High precision neutrino and antineutrino measurements with nuclear & nucleon targets are needed for the oscillation physics program to reduce systematics from cross-section uncertainties.

CC QE Scattering Nucleon structure & binding of the nucleons within the nucleusNC Elastic Scattering Spin structure of the nucleon & the strange quark contributionResonant & coherent production of pions Resonant structure of the nucleon & non-perturbative QCD testsStrange Particle Production Understand backgrounds for proton decay searchesNeutrino-Electron Elastic Scattering Neutrino magnetic moment

Neutrino scattering measurements are of interest in their own right:

Interest of Nuclear Physicists15

Neutrino scattering experiments at a Proton Driver would enable progress in:

Hence there is a broad program of nuclear physics measurements that provide important input for astrophysics & nuclear physics calculations, and complements the electron scattering program at JLab.

Weak Form FactorsPDFs (d/u at high x)Generalized PDFsStrange quark contentQuark-Hadron Duality tests (structure functions in the resonant region)

Interface between Particle & Nuclear Physics:One Example – The Weak Form Factor

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For many years it was assumed that charge and magnetic distributions within the nucleon are exponential. However JLab measurements show a different form for Electric Form Factor … the charge distribution is broader than the magnetic one.

In the language of particle physics, the Perturbative QCD prediction is that Q2F1/F2 is constant. Instead it appear that QF1/F2 approaches constant. Although the underlying reason is not understood, it appears to be something to do with angular momentum between the quarks.

To make further progress we would like to know the Weak Form Factor … which can be determined from neutrino-nucleon elastic (or QE) scattering at a Proton Driver.

Old data (triangles) wrongbecause of large radiativecorrections

8 GeV Neutrino Scattering Program 17

The 8 GeV beam would play a critical role, enabling low energy (~1GeV) neutrino interactions to be measured with a narrow band beam, no high-energy (background generating) tail, and a 64-fold increase in intensity (wrt MiniBooNE).

Important measurements to reduce systematic uncertainties on neutrino oscillation results.

First precision measurements of low energy antineutrino scattering on nuclear targets, and neutrino & antineutrino scattering on nucleon targets.

Neutrino-electron scattering measurements provide way to improve sensitivity to neutrino magnetic moment sensitive to new physics.

Statistics will still limit the precision of many measurements, motivating the full 2MW beam power at 8 GeV.

MI Neutrino Scattering Program 18

The 120 GeV beam would enable lower cross-section processes to be explored, and precision measurements of the DIS regime.

The primary interest will be in high-precision measurements with antineutrino beams on nuclear targets, and with both neutrino and antineutrino beams on nucleon targets (H2,D2).

The antineutrino beam needs to be a sign-selected beam to reduceneutrino contamination.

Muon Physics – An Ideal Source 19

Low energy precision muon experiments require high intensity beams & an appropriate bunch structure. Different experiments require different bunch structures, hence flexibility is desirable.

A 0.5-2 MW Proton Source at 8 GeV together with the Fermilab Recycler (used for rebunching) could be an ideal (& unique) front end for a cutting edge World class long-term muon program.

Recycler ring would be loaded with one Linac pulse (1.51014 protons) every 100 ms, and the protons chopped into 588 bunches, 3ns bunch width

MARS simulations yield0.2 muons/p …momentaO(100 MeV/c), occupyinglarge transverse phase space

31021 muons per year (107 secs)

Muon Physics: g-2 20

Sensitive to muon substructure, anomalous gauge couplings, leptoquarks, supersymmetry, …).

The present BNL g-2 result shows a 2.7 effect ???

Minimal SUSY models predict, for some regions of parameter space, large contributions to a – arising from loops with a chargino and muon sneutrino and loops with a neutralino and smuon.

If SUSY is discovered at the LHC and sparticle masses measured, a new round of muon g-2 measurements would yield information about tan and SUSY mixing.

If new physics is not seen at the LHC, a new round of g-2 measurementswould provide one of the few ways of probing higher mass scales.

Muon Physics: EDM21

Electric Dipole Moments violate P & T invariance & hence CP (if CPT conserved). Non-zero EDMs would provide unambiguous evidence for new physics.

There are regions of SUSY parameter space that predict large EDMs. Present EDM limits provide SUSY limits.

If SUSY is discovered at the LHC, measurements of the muon EDM,together with a, will provide information about the new CP-violating phases difficult to obtain any other way.

Muon Physics – LFV Decays 22

e, e conversion, eee, …

Observation of flavor mixing in the neutral lepton sector provides additional generalmotivation for searching for flavor mixing in the charged lepton sector.

Note that in SUSY Seesaw models LFV depends on SUSY breaking, and can be sizable. If SUSY is observed at the LHC, LFV searches/measurements can provide information about SUSY breaking.

LFV decays probe off diagonal elements of the slepton mixing matrix, and are Therefore complementary to g-2 and EDM measurements:

~~~~

~~~~

VV

VV

e

eee

Figure 1. In SUSY models, g-2 and Electric Dipole Moments (left) probe the diagonal elements of the slepton mixing matrix while Lepton Flavor Violating decays, such as e(right) probe the off-diagonal elements.

Muon Physics - Sensitivity 23

Muon Source Requirements to Needed Make Progress

The estimated number of low energy muons that could be provided with a new

Proton Driver (31021 per year ) is very large … but its utilization will probablybe very inefficient (large phase space).

Most experiments require energies p < 29 MeV/c, good extinctionfactors, small p/p.

To make progress we need to try to design a cost-effective muon source, the matching tothe candidate exper-iments evaluate cost & performance.

Cost may be the make or break issue.

Kaons and Pions 24

Interface between particle & nuclear physics meson & baryon spectroscopy & Lattice Gauge Theory tests. Would complement the JLab program. Would use 8 GeV proton beam + Recycler as a stretcher. Baryon spectroscopy requires a 2.5 GeV/c /K tagged secondary beam.

Decays: e2 & 2 decays most precise probe of e- universality in the weak interaction. Theoretical predictions 40 more precise than experiment. Also +

e+0 potentially offers improved Vud measurement.

Present generation of rare kaon decay experiments are already rate limited. Future experiments at the Proton Driver would need to benefit from a large duty cycle (refit Tevatron Ring with permanent magnet dipoles ?) and the improvements in instrumentation expected in the next few years. If this can be accomplished the Proton Driver would offer the possibility of advances in kaon decay sensitivity.

Pions

Kaons

Neutrons 25

Proton Driver would be comparable in its neutron capabilities withan upgraded SNS. There are some physics topics that will not be covered by the SNS program, and could be unique to the Proton Driver: (i) Production of ultra-cold neutrons neutron EDM and lifetime, (ii) neutron induced “upsets” in semiconductors, (iii) n-nbar oscillations (improve sensitivity by 100)

AntiprotonsThe antiproton source could be used with the Proton Driver for a continuation of the low energy antiproton program: (i) Bottom-onium formation (?), (ii) CP Violation in hyperon decays – order of magnitude improvement in sensitivity over HyperCP, (iii) Light hadron spectroscopy (?)

Tentative Conclusions26

The neutrino oscillation physics case seems to be strong and robust (does not depend on unknown parameters or, within reason, what else is built).

A World Class neutrino scattering program would be a natural part of the package.

A World Class muon physics program using the 8 GeV beam might be a great supporting program … but we need to design a source & its interface to experiments to know if it is likely to be affordable and pin down performance.

Interesting (World Class) programs using secondary hadron beams would also be possible … not all the documentation is available yet to fully assess this.

2 MW in the MI is motivated by the oscillation physics program.

2 MW at 8 GeV is motivated by neutrino oscillation & scattering programs, and possibly also by the muon program.

Low Energy Neutrino Event Rates 27

FNAL 2 MW SNS 1.4 MW at 8 GeV at 1.3 GeV

P/yr 1.6 1022 6.7 1022

DAR (/p) 1.5 0.13DAR (/yr) 2.3 1022 0.92 1022

e Events/yr 8900 REC 3500 REC

Events/yr 1500 REC 600 REC

Events/yr 3200 REC 1200 REC

Bri

ce, G

eer,

Pau

l & T

aylo

e

Event rates for a MiniBooNE-like detector at L = 60 m(scaled from G. Van Dalen nucl-ex/0309014)

Neutrino production from Decays At Rest

1. MiniBooNE-type beam: 25KW ~2MW

2. Decays at Rest: