# Presentation: 312946

## Physics at an Upgraded Fermilab Proton Driver

- Steve Geer                                                           Colloquium                  Jan 26th, 2005

- Introduction
- Main Motivation: Neutrino Oscillations
- Neutrino Scattering
- Muons
- Kaons, pions, neutrons, antiprotons .....
- Summary

## Introduction

- 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 StudyWorking Groups and Conveners

- WG1:  Neutrino Oscillations
- 	D. Harris (FNAL), S. Brice (FNAL), W. Winter (Princeton)
- WG2:  Neutrino Interactions
- 	J. Morfin (FNAL), R. Ransome (Rutgers), R. Tayloe (Indiana)
- WG3:  Muons
- 	R. Ray (FNAL), R. Roberts (BU)
- WG4:  Kaons and Pions
- 	H. Nguyen (FNAL), T. Yamanaka (Osaka U.)
- WG5:  Antiprotons
- 	D. Christian (FNAL), M. Mandelkern (UCI)
- WG6:  Tevatron Collider
- 	H. Cheung (FNAL), Penny Kasper (FNAL), P. Ratoff (Lancaster U.)
- WG7  Neutrons
- 	T. Bowles (LANL), G. Greene (ORNL)

## Neutrinos are Everywhere

- 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  few %  of the unknown “dark matter”  in the UniverseNeutrinos are important for stellar dynamics:  ~71010 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.

## We Don’t Know Everything About Neutrinos

*What are the masses of the neutrinos?*
*What is the pattern of mixing among the different types of neutrinos?*
*Are neutrinos their own antiparticles?*
*Do neutrinos violate the symmetry CP?*
*Are there “sterile” neutrinos? *
*Do neutrinos have unexpected or exotic properties?*
*What can neutrinos tell us about the models of  new physics beyond the Standard Model?*

- From the US APS Multi-Divisional Study on the Physics of Neutrinos

## Neutrino Oscillations are Exciting

- 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

- Neutrinos have nonzero masses and mixings !

- This is exciting because:

- We don’t know the neutrino mass spectrum  but we do 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 .....

## Neutrino Measurements Drive Theoretical Ideas

- 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.

## Neutrino Mixing

- Within the framework of 3-flavor mixing, the 3 known flavor eigenstates (e, , ) are related to 3 neutrino mass eigenstates (1, 2, 3) :

- We know that UMNS  is very different from the CKM Matrix

## Neutrino Mixing Matrix

- In analogy with the CKM matrix, UMNS can be  parameterized using 3 mixing angles (12 , 23 , 13 ) and one complex phase () :

- We do not know the values of 13 or the CP phase .  If 13 and  are
- non-zero, there will be CP Violation in the neutrino sector.

## Neutrino Mass Spectrum

- The oscillations are driven by the mass splittings:   m2ij    m2i - m2j

## Measured Parameters

- For the moment, set aside the LSND result. From the solar-, atmospheric-, and reactor-neutrino data we already know a lot about the mixing matrix and mass splittings:

- ...  but note that we have only an upper limit on 13, and know nothing about   We need to search for   e oscillations !

- Solar Neutrinos

- Atmos. Neutrinos

-   e not seen

## We want to determine ...

- 13,   and the mass hierarchy
-   ....   BUT ....

## Determining all of the Parameters will be Challenging

- _Determining all of the Parameters will be Challenging_

- In Vacuum:

- In Matter   (For anti-, A  -A,  AND the sign of A depends on the sign of m322 )

## ... but what about LSND & MiniBooNE ?

- IF MiniBooNE confirms the neutrino oscillation interpretation of the LSND data life gets much more complicated (and very exciting)

## Why Do We Need High Intensity Proton Beams

- We want to study rare processes. The upper limit on the all important e oscillation amplitude is ~5% !

- NEED MW-CLASS MULTI-GeV  PROTON SOURCES

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

- In all scenarios it appears the Proton Driver has a critical role to play.

-      sin2213

- Fraction of -space

- CP Violation (3)

- Mass
- Hierarchy
- (95% CL)

- 0.1

- 0.1

- 0.01

- 0.01

- 0.001

- 0.001

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

- _The 8 GeV Beam offers an interesting (unique) possibility_

- The off axis beams
- Are “NuMI” beams.

- Doug Michael, Chris Smith Mark Messier

## Neutrino Scattering Motivation

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

## Neutrino Scattering: Need for Higher Intensity

- 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).

## Interest of Nuclear Physicists

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

- Hence there is a program of nuclear physics measurements which complements the electron scattering program at JLab and  _provides important input for astrophysics & nuclear physics calculations_.

- 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

- For many years it was assumed that charge & magnetic distributions within the nucleon are exponential. However JLab measurements   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 appears that QF1/F2 approaches constant.  The underlying reason is not understood, but 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

- 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

- 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.

## Low Energy Probes of  High Mass Scales

- Mass Limit

- Many of these experiments are rate limited. Progress requires new beams and progress with detectors and/or readout

- Normalized Rate < 6.1  10 -13

## Muon Physics

- Lepton Flavor Violation (LFV) has been established in the neutrino sector,
- suggesting new LFV processes at high mass scales. This physics might resultin observable effects in the muon sector (?)
- In addition, precision muon experiments are sensitive to new physics at the TeV scale ... complementary to the LHC experiments. Examples:  muon (g-2), Electric Dipole Moment, and LFV muon decays.

## Muon Physics – An Ideal Source

- 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 a rebuncher (the Recycler ?) could provide an _ideal (& unique) front end_ for a cutting edge World class long-term muon program.
- Recycler ring would be loaded with one Linac pulse (1.51014 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

-  31021 muons per year (107 secs)

- Kevin Paul et al

## Muon Physics - Sensitivity

- The estimated number of low energy muons that  could be provided with a new Proton Driver (31021 per year ) is very large ... but its utilization will probablybe very inefficient (large phase space).

- Most experiments require p < 29 MeV/c, good extinction
- factors, 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.

## Muon Physics:   a = (g-2)/2

- 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 Tevatron or 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, new g-2 measurements would provide one of the few practical ways of probing higher mass scales.

## Muon Physics:   EDM

- Electric Dipole Moments violate P & T invariance  & hence CP (if CPT conserved). Non-zero EDMs would indicate a new source of CP violation beyond the Standard Model.
- There are regions of SUSY parameter space that predict large EDMs. If SUSY is discovered at the Tevatron or LHC, measurements of the muon EDM, together with a, will provide information about the new CP-violating phases difficult to obtain any other way.
- Present EDM limits (d < 3.7  10-19 e-cm).  An experiment has been proposed at JPARC to obtain a sensitivity of 10-24 e-cm. To go further will need better beam structure with many short pulses, each separated by >500s. Depending on the fate of the JPARC proposal a Fermilab Proton Driver experiment might be designed to have a sensitivity anywhere in the range 10-24 - 10-26 e-cm

## Muon Physics – LFV Decays

- _Muon Physics – LFV Decays_

-   e,   e conversion,   eee, ...

- In SUSY Seesaw models LFV depends on SUSY breaking, & can be sizable. If SUSY observed at the LHC, LFV searches/measurements  information about SUSY breaking.

- _Example_:      e

- Present limit:  BR < 1.2  10-11. The MEG experiment at PSI expected to improvesensitivity to ~ 10-14  by end of decade ... the MEG sensitivity will complement LHC measurements. _Further progress depends requires an improved muon source __& better detector technology giving better background rejection (i.e. resolutions) __& enabling higher rates._

## Example:    e        (Fritz DeJongh).

- Example:    e        (Fritz DeJongh).

- Use BTeV silicon pixel detectors for tracking  sensitivity comparable to MEG, limited by scattering in relatively thick pixels.
- Imagine pixel thickness reduced by 10. With idealized detector geometry it has been shown that BR sensitivities O(10-15 – 10-16) are plausible.

## Pions

- Interface between particle & nuclear physics:  Meson & baryon spectroscopy & Lattice Gauge Theory tests. Would complement the JLab program. Baryon spectroscopy requires a 2.5 GeV/c /K tagged secondary beam.

- Use 8 GeV proton beam + Recycler (?)  as a stretcher.

- e2 & 2 decays   precise probe of e- universality in the weak interaction. Theoretical predictions 40  more precise than experiment.
- +  e+0 potentially offers improved Vud measurement.

## Kaons

- _Present generation of rare kaon decay experiments are already rate limited_. Future experiments at the Proton Driver would need to benefit from a DC beam with a large duty cycle (refit Tevatron Ring with permanent magnet dipoles ?) & 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.

## Neutrons

- 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)

- _Antiprotons_

- The 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 (?)

## SUMMARY:  The Neutrino Physics Case for a Fermilab Proton Driver seems to be Strong

- Neutrino Oscillation physics is exciting   World Class multi-phase program with the potential for big 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.
- Neutrino scattering physics broadens the program   many thesis topics
- Fermilab can build upon its existing significant investment in hosting the US accelerator based neutrino program.

## SUMMARY:  The Proton Driver could support a diverse physics program

- Physics of LFV  Probing the GUT scale:   Neutrino Oscillations, precision muon experiments.
- Physics at the TeV-scale (complementary to the LHC program): Precision muon and kaon experiments, neutron experiments (?)
- Interface between particle and nuclear physics (complementary to Jlab program):
- Neutrino scattering, hadron spectroscopy ....
- Other possibilities:
- Neutrons, antiprotons, ...

## Invitation

- Much has been done, but there is much more to do.