Research in

Nuclear and Particle Physics

 

The Program --

This experimental research program seeks to learn more about the fundamental properties of nuclei and elementary particles. These are the smallest entities in our universe. All known matter on earth and in the wider universe is made of these particles. The best known desription of this matter is known by the name "The Standard Model" of fundamental particle physics. But this model is known not to be the "final answer"; there are too many numbers and conservation laws in the model for which there is no fundamental theoretical explanation. Therefore, each of our experiments tests the limits of the Standard Model to learn where and how it is inadequate, incomplete, or even wrong. Other theories are waiting to step forward as more comprehensive models: string theory and supersymmetry are two of the most promising among these theories.

Our experiments are carried out at particle accelerator facilities such as -

and at a nuclear reactor facility located at -

It is here at these premier laboratories that these particles and nuclei are studied using modern, state of the art equipment and facilities, and from which the data are then analyzed and results reported in published form.

In each of these experiments, the Valparaiso University research group collaborates with physicists from other universities and national laboratories located in the US and in foreign countries. The size of these collaborations ranges from the neutron EDM experiment with ~10 physicsts, to the TWIST experiment with 25 physicists, to the STAR experiment on which there are over 550 physicists. At Valparaiso University, the data are analyzed, simulation studies are done, equipment is prepared and constructed, and faculty and students work together to uncover new insights into the structure of matter on the smallest of scales.

 

The Valparaiso University Research Group --

There are five professonals who are working on these experiments:

Prof. Donald D. Koetke, Principal Investigator and Group Leader

Prof. Robert W. Manweiler

Prof. T. D. Shirvel Stanislaus

Dr. David P. Grosnick, Visiting Professor and Research Associate

Dr. Jason Webb, (VU '95) Postdoctoral Research Fellow

Mr. Paul Nord, (VU '91) Techincal Specialist

 

The Students --

Each year since 1983, one or more students work with this group full time during the summer and part time during the academic year carrying out various aspects of the experimental work and analysis. This work may be done at Valparaiso University and/or at the above named accelerator or reactor sites.

  • Summer, 1998: Two students, junior Adam Gibson and sophomore Jon Thoms spent approximately two weeks at the Alternating Gradient Synchrotron at the Brookhaven National Laboratory during the time the experiment was running and collecting data. During the remainder of the summer, they worked on code development and physics analysis on the UNIX workstations at Valparaiso University.
  • Summer, 1999: Jon Thoms spent the entire summer studying neuton simulations in the Crystal Ball detector. Jon was selected by the American Physical Society to present his summer research at the Division of Nuclear Physics meeting in Santa Fe, NM in October 1998 and in Monterey, CA in October 1999.
  • Summer, 2000: Daniel Allen and Christopher Hoffmann worked here and at TRIUMF (photos) in Vancouver, BC on preparations for the TWIST (E614) experiment at TRIUMF, and Steve Wolf and Robert Greene worked on aspects of the analysis of data from the Crystal Ball experiment.
  • Summer, 2001, Steve Wolf and Tyler Parkison worked on the analysis of data from the Crystal Ball experiment.
  • Summer, 2002. Ross Corliss and Sarah Schlobohm conitinued work on the analysis of data from the Crystal Ball experiment. Ross Corliss (photo) and Sarah Schlobohm (photo) were selected by the American Physical Society to present their summer research at the Division of Nuclear Physics meeting at Michigan State University in October 2002.
  • Summer, 2003: Brian Bucher worked on analysis of the Crystal Ball data while Ross Corliss, Tim Rogers, and Sarah Schlobohm worked on the STAR experiment at VU (photos) and at Brookhaven National Laboratory (photos).
  • Summer, 2004: Ross Corliss and Josh Vredevoogd worked on the STAR experiment and Jason Summerlott worked on the Crystal Ball experiment. Each of them (photos) were selected by the American Physical Society to present their summer research at the Division of Nuclear Physics meeting in Chicago in October 2004.
  • Summer, 2005: Josh Vredevoogd and Ted Hopkins worked on the STAR experiment to significantly advance the study of electron/hadron separation from signals in the Endcap Electromagnetic Calorimeter on STAR. Jason Summerlott worked on the Crystal Ball experiment.
  • Summer, 2006: Josh Vredevoogd and Noah Schroeder and Daniel Trubey all worked on analysis problems for the STAR experiment. All three spent a week at RHIC to work in the STAR control room on data collection.
  • Summer, 2007: Josh Vredevoogd worked briefly to pass on his expertise to Ansel Hillmer, Daniel Trubey, and Melissa Bitters. Josh went on to graduate school at Michigan State University while Ansel, Daniel, and Melissa each pursued their own research topic in STAR for summer 2007 and spent a week at RHIC to work in the STAR control room.
  • Summer, 2008: Megan Kania, Nathan Kellams, and Tim Olson worked on the STAR experiment both at Brookhaven National Laboratory for two weeks doing hardware/electronics upgrades (photos), and at VU for the rest of the summer working on a project to understand the characteristics of the "underlying event" caused by interactions between quarks and gluons that are not the quarks and gluons responsible for the reaction of interest. These interactions constitute a background from which the interesting physics must be sorted out.
  • A summary of VU student summer research for the past several years is posted.

 

The Funding --

The funding for this research comes from the U. S. Department of Energy Grant #DE-FG02-88ER-40416.

 

The Experiments --

The STAR-spin Experiment (RHIC-STAR) - ongoing

The TWIST Experiment (TRIUMF 614) - all data have been collected

The Crystal Ball Experiment (BNL 913) - writing the final papers

The Neutron EDM/MDM Experiment (NIST) - in the early stages

The NuSea Experiment (FNAL 866) - completed

The MEGA Experiment (LAMPF 969) - completed

 

Recent Publications --

2008

“Precision measurement of the muon decay parameters rho and delta”, The TWIST Collaboration, R. P. MacDonald, et al., Physical. Review D 78, 032010 (2008).

“Measurement of Upsilon Production for p + p and p + d Interactions at 800 GeV/c”, The NuSea Collaboration, L. Y. Zhu, et al., Physical Review Letters 100, 062301 (2008).

“Measurement of the K-p --> sigmao pio reaction between 514 and 750 MeV/c”, The Crystal Ball Collaboration, R. Manweiler, et al., Physical Review C 77, 015205 (2008).

A complete list of STAR publications for 2008 on which we were co-authors can be found here.

2007

A complete list of STAR publications for 2007 on which we were co-authors can be found here.

2006

“Mesurement of Pmu Xi in polarized muon decay”, The TWIST Collaboration, B. Jamieson, et al., Physical Review D74, 072007 (2006).

“Longitudinal Double-Spin Asymmetry and Cross Section for Inclusive Jet Production in Polarized Proton Collisions at sqrt(s) = 200 GeV”, The STAR Collaboration, Phys. Rev. Lett. 97 (2006) 252001

A complete list of STAR publications for 2006 on which we were co-authors can be found here.

2005

“Measurement of the muon decay parameter delta, The TWIST Collaboration, A. Gaponenko et al., Physical Review D71, 071101(R) (2005)

“Measurement of the Michel parameter rho in muon decay”, The TWIST Collaboration, J.R. Musser et al., Physical Review Letters 94, 101805 (2005)

“Precision planar drift chambers and cradle for the TWIST muon decay spectrometer”, The TWIST Collaboration, R.S. Henderson et al., Accepted to Nuclear Instruments and Methods, February 2005.

“Test of charge conjugation invariance”, The Crystal Ball Collaboration, B.M.K. Nefkens et al., Phys.Rev.Lett. 94, 041601, (2005)

A complete list of STAR publications for 2005 on which we were co-authors can be found here.

2004

“Y scaling in quasifree pion-single-charge exchange”, R.J. Peterson et al., Phys.Rev. C69, 064612, (2004)

“Measurement of inverse pion photoproduction at energies spanning the n(1440) resonance”, The Crystal Ball Collaboration, A. Shafi et al., Phys.Rev.C70, 035204, (2004 )

“Reaction K-p --> pio pio lambda from pk- = 514-mev/c to 750-mev/c”, S. Prakhov et al., Phys.Rev. C69, 042202, (2004)

“Measurement of pi- p --> pio pio n from threshold to p(pi-) 750-MEV/C”, The Crystal Ball Collaboration, S. Prakhov et al., Phys.Rev. C69, 045202, (2004)

“Differential cross-section of the charge exchange reaction pi- p --> pio n in the momentum range from 148-mev/c to 323-mev/c”, The Crystal Ball Collaboration, M.E. Sadler et al., Phys.Rev. C69, 055206, (2004)

“Does the sigma(1580)3/2- resonance exist?”, The Crystal Ball Collaboration, J. Olmsted et al., Phys.Lett. B588 29-34 (2004)

“Cross-sections and transverse single spin asymmetries in forward neutral pion production from proton collisions at s = 200-GeV”, The STAR Collaboration, J. Adams et al., Phys.Rev.Lett. 92, 171801, (2004)

“Does the sigma(1580)3/2- resonance exist?”, The Crystal Ball Collaboration, J. Olmsted et al., Phys.Lett. B588 29-34 (2004)

A complete list of STAR publications for 2004 on which we were co-authors can be found here.

Publications before 2004 can be found here --



STAR

The Solenoid Tracker at RHIC

The STAR detector is really a collection of numerous detectors that are integrated into one whole, very large detector system. There is cylindrical symmetry around the path of the colliding beams shown by the red line. The size of the detector system can be gauged by the size of the stairs and the railings; it is roughly the height of a three-story residential building.

This is a picture of the tracks of the many particles produced when two gold nuelei collide at ~100 GeV of kinetic energy each. The Time Projection Chamber (TPC) records the information needed to trace out the trajectories of these charged particles. This picture looks into the STAR detector system along the axis of the colliding beams.

The STAR experiment is a large collaborative experiment involving over 550 physicists and engineers from 51 institutions. located in 12 different countries. The STAR experiment took first beam at RHIC in 2000. Valparaiso University was accepted into full collaborative membership in July 2002. The experiment is being done at the Brookhaven National Laboratory (BNL) using the Relativistic Heavy Ion Collider (RHIC) accelerator. There are now two major experiments at RHIC, PHENIX and STAR with STAR being the largest. (Two smaller experiments have concluded their experimental programs.) The STAR detector is very large to allow physicists to trap and analyze the many particles that are emitted in the collisions of in the collisions of heavy ions (e.g., gold, copper, lead, etc.) with substantial kinetic energies.You can view an interesting www slide-show describing the central detector in STAR (the Time Projection Chamber) and the associated physics. (Its a very good piece.)

There are two main physics programs within STAR.

  • Relativistic heavy ion physics is of international and interdisciplinary interest to nuclear physics, particle physics, astrophysics, condensed matter physics and cosmology. The primary goal of this field of research is to re-create in the laboratory a novel state of matter, the quark-gluon plasma (QGP), which is predicted by the standard model of particle physics (Quantum Chromodynamics) to have existed ten millionths of a second after the Big Bang (origin of the Universe) and may exist in the cores of very dense stars. In fact, along with the other three major detectors in the RHIC ring, there has been tantilizing evidence that features of the sought-after quark-gluon plasma may have been observed. [There is an interesting Scientific American article on the QGP, and a summary article is published "Experimental and Theoretical Challenges in the Search for the Quark Gluon Plasma: The STAR Collaboration's Critical Assessment of the Evidence from RHIC Collisions", Nucl. Phys. A 757 (2005) 102 .]
  • The physics of polarized proton collisions is the second main focus for STAR. RHIC is the first accelerator to be able to collide two beams of polarized protons. In particular, this research program will attempt to understand the origin of the intrinsic spin angular momentum of the proton. Remarkably, even though the proton is a conplex object composed of quarks and gluons, every proton has exactly the same "spin". A naive notion would suggest that the proton spin was formed by the sum of the spins of the quarks in the proton. However, .recent deep inelastic scattering experiments have shown that the combined spins of all of the quarks and antiquarks in the proton can account for only ~30% of the proton spin. The remaining contributions to the proton spin is then assumed to come from the gluons (the carriers of the strong nuclear force) and the angular momentum that comes from the rotational motion of the quarks and gluon within the proton. The RHIC STAR-spin physics program will be the first time that the contributions of the gluons to the proton spin will be measured directly.

More about the physics of STAR can be found at the STAR www site.

RHIC runs approximately 25-30 weeks per year during which time the STAR experiment collects data for the two physics programs noted above. Because the heavy ion program collides heavy nuclei such as gold and the spin physics program collides polarized protons, data for these two cannot be taken simultaneously. In recent years, the run-time each year was divided between the two physics programs. 2006 was the first year entirely dedicated to polarized proton collisions and the run in 2007 was dedicated to heavy ion collisions. In 2008, we expect that half of the running period will be devoted to polarized protons. The analyhsis of the 2006 data is in process at the various collaborating institutions working on this physics program.

The protron spin-physics studies make use of the tracking in the TPC detector and the silicon detectors near to the interaction vertex, but they depend on the data obtained from the electromagnetic calorimeters (EMC) positioned outside the TPC. The EMC are especially useful for detecting and measuring the energy of photons and electrons that are, in turn, important to studying the gluon contributions to the proton spin. One calorimeter, in the form of a barrel, surrounds the outer cylinder of the TPC. The other EMC is positioned at one end of the cylinder outside the TPC. The first is called the "Barrel EMC - BEMC" and the second is known as the "Endcap EMC - EEMC". The EEMC was added to the STAR detector system in 2004 and Valparaiso University students, faculty and staff worked on fabricating and installing a substantial number of the EEMC components. You can see photographs of VU research students working at VU and at RHIC/STAR on the EEMC. A complete online description of the EEMC and the physics to be done with it is availalble. A remarkable compendium of articles describing RHIC, and the four detector systems at RHIC, STAR, PHENIX, BRAHMS and PHOBOS can be found in Nuclear Instruments and Methods in Physics Research A 499, March 2003, Nos. 2-3. (You can also view photographs of the construction of the STAR detector.)

The Present Status --

The STAR detector is an evolving system with new components being proposed and added as the experiment matures.. This year, 2008, is the eighth year of physics data-taking and a rather large number of STAR publications are already in print. The 2006 polarized proton data offer a promising data sample for studying the gluon contribution to the proton spin and analysis is in process. At Valparaiso University we are focused on detecting gamma-ray photons in the EEMC that signal the production of πo from a quark-gluon or gluon-gluon interaction from the colliding polarized protons. The asymmetry in the direction the πo particles are produced can give some measure of the gluon polarization (helicity) in the proton and this, in turn, can be compared to predicted values for this asymmetry as a function of πo momentum. The present run has been dramatically curtailed due to lack of federal funding for the Department of Energy, Office of Science in the FY08 federal budget!

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TWIST

The TRIUMF Weak Interaction Symmetry Test

 

(The TWIST high resolution magnetic spectrometer.)

The muon decays essentially all of the time to an electron and two neutrinos (μ -> e νμ νe). The fundamental reaction which describes this decay is characteristic of the weak nuclear force. According to this theory, the elementary reactions in this decay are only of two types called vector (V) and axial-vector (A) and these occur in only one combination, (V-A). This combination is a "signature" of the fundamental nature of decays that are brought about by the weak nuclear force, sometimes called "weak decays". Weak decays proceed slowly on the scale of nuclear processes; the mean lifetime for the muon decays is 2.2 x 10-6 s. We also know that this weak-interaction decay is mediated by a heavy particle known as the "W" particle which comes in two charges states (+ and -). The W-particle, predicted by the electroweak theory that has become part of the Standard Model of particle physics, has been detected in copious numbers at high energy accelerators (LEP at CERN in Switzerland, and Fermilab in Illinois, west of Chicago). The mass of this particle has been measured to be 80.4 GeV/c2, or approximately 85 times more massive than the proton.

Another feature of these weak interactions is that they involve only particles that are "left-handed" particles, i.e., ones whose spin is preferentially oriented opposite to the particle vector momentum, p. No evidence has been seen for particles that have a right-handed weak interaction. (Anti-particles are right-handed having exactly the opposite properties of their companion particle.) This means that the W-particle mediates only left-handed intereactions (WL). If a right-handed weak interacation were to exist for particlea, it would need a W-particle that would mediate the interactions between right-handed particles (WR). Right-handed particles and a WR are explicitly excluded from the Standard Model of particle physics.

However, it is widely accepted that this model is not the ultimate fundamental theory. Consequently, it is imperative to test the model predictions to determine to what precision it is correct. By doing a very precise study of the characteristics of the decay of muons, one can test the predictions of the Standard Model and various extensions to the Standard Model. In particular, we can test whether there are any other contributions to the weak interaction decay besides (V-A) and whether there is any contribution from left-handed interactions.

The Valparaiso University group is part of an international collaboration that is doing experiment (E614) known as TWIST, that is being done at the Tri-Universities Meson Facility TRIUMF in Vancouver, BC, Canada. This experiment is a highly precise and extremely accurate test of the Standard Model predictions for muon decay. The experiment is funded by the Canadian National Science and Engineering Research Council. The U.S. Department of Energy also provides support for TWIST for faculty and student work on this experiment and for ~$450,000 for electronics hardware. The analysis of the massive amounts of data collected and data simulated using Monte Carlo programs is accomplished using the very large western Canadian computing grid (Westgrid) centered at the University of British Columbia in Vancouver, BC. To learn more about the TWIST experiment you can go to the TWIST public www site.

The Valparaiso University group has been responsible for the determining the precise location of drift chamber planes in the particle spectrometer and for assisting with the data collection. The Valparaiso University group has developed an event display for this experiment which allows the physicists to study individual muon decays in detail in the detector elements. An example event is shown below with the muon entering from the left (seen in green), coming to rest in the central target where it decays to a positron that is seen leaving and traveling downstream (to the right and shown in yellow). (The neutrinos are not detected in this detector.) The small red tick marks at the bottom of this display give evidence of the relative time of the passage of the particles through the drift chambers; time increases downward on the display. The display shown here is viewed with one set of drift chamber wires in the plane of the picture and the other perpendicular to the picture (and therefore not seen). The z-axis (along the axis of the spectrometer and parallel to the solenoidal magnetic field) is shown from left to right in the picture. The three-dimensional helical orbits are seen as sinusoidal paths when projected onto this plane. The data are the "hits" in the drift chambers shown as rectanagles. The smooth track is the result of the fit of a helix to these points and drawn here to illustrate the path of the particles.

The Present Status --

Based on data collected in 2002, 2003, and 2004 at the TRIUMF accelerator, two physics papers have been published in the Physical Review Letters and one paper was published in the Physical Review D. These papers report the measurement of three of the four (Michel) parameters use to describe normal muon decay μ -> e νμ νe known as ρ, δ,andPμξwhere Pμ is the muon polarization. These measurements have increased the precision and accuracy with which these parameters are known to uncertainties ~10-3 which is 2.5 to 3 times better than previously known. This now allows us to draw meaningful insights into what underlying processes may be at work to cause this familiary decay. These three measurements are all consistent with the Standard Model predictions but the decreased uncertainties allow us to set more stringent constraints on theories beyond the Standard Model and on the possible existence of right-handed particles in nature. This concluded phase one of the experiment during which time we learned much about the sources of systematic errors that limited our accuracy in these measurements. In phase two, we are using data taken in 2005, 2006 and 2007 to achieve an accuracy of ~2-4 x 10-4 on ρ, and δ, in keeping with the goals of the experiment. The accuracy of the Pμξ result is expected to be ~10-3 or less. This will then conclude the TWIST experiment. It is worth noting that the measurements of these muon decay parameters are carried out using a blind analysis.

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The Crystal Ball Experiment

The Crystal Ball is the name of a detector developed and used for many years at the Stanford Linear Accelerator Complex (SLAC). The detector consists of 672 individual NaI(Tl) photon detector crystals, structually held together to form a spherical enclosure around an interaction target located at its center. This experiment, known as the Crystal Ball experiment, is designed to study all neutral particle final states resulting from (π- p) and (K- p) intereactions in a liquid hydrogen target located at the center of the Crystal Ball spectrometer.

In 1996 the Crystal Ball was moved from SLAC to the Alternating Gradient Synchrotron (AGS) at the Brookhaven National Laboratory (BNL) where it was positioned in the C-6 beam line to study π- and K- interactions with protons in a hydrogen target. In particular, the significant feature of the detector is its ability to detect neutral particles, most importantly photons, which result from the decay of short-lived neutral particles produced in the initial (π- p) and (K- p) intereactions. A scintillator veto barrel around the target allows us to veto charged particles from the reaction and thereby study fully neutral final states. It is in this physics regime that the Crystal Ball affords a unique contribution to hadron spectroscop, i.e., the study of the particle states produced from these strong nuclear interactions. The initial approved experiments at BNL were E913 and E914.

The Present Status --

In 1997, the Crystall Ball was fully commissioned. Initial tests and calibrations were done with radioactive sources as we awaited beam from the accelerator. In April, 1997 we did a 2 week engineering run to test the detector, the data acquisition system, the associated electronics, and the beam transport to the target. All of the goals of this engineering run were realized and data from the run were analyzed especially at Valparaiso University where detailed energy calibration analyses were done. In late May 1997 we took data for another 2 weeks.

The 1998 run began in July 1998 and extended into October 1998. There were four weeks of (K- p) data, some (pi- p) data to conclude the data collection begun in 1997, and some ancillary measurements with nuclear targets and a variety of tests. Beam was delivered to the experiment on 13 July 1998. The pion beam was used to test the detector and the beam line elements and to take data which could be used for a precision energy calibration of the crystal ball. By 16 July 1998 a K- beam tune was established and (K- p) interactions were observed. This crystal-by-crystal energy calibration was done by the Valparaiso University group. The following is a chronological list of some of the progress on the analysis of these data.

  • An extensive study of neutron interactions in the Crystal Ball was done at Valparaiso University. In all of the (π- p) and (K- p) intereactions which result in neutral final states, a neutron will be present and may often interact in the NaI crystals. We believe it will be helpful to apply pattern recognition algorighms to discriminate between photon interactions and neutron interactions in order to help determine the specific interaction which took place in the target. The preliminary results of these analyses were presented at the 1998 meeting of the Division of Nuclear Physics of the American Physical Society in Whistler, BC.
  • We have done a more careful calibration analysis which sharped the resolution of the neutral final states observed in these data.
  • The first physics results were presented at the Division of Nuclear Physics (DNP) of the American Physical Society in Monterey, CA in October 1999. The Valparaiso University group presented three papers on our K-p analyses and the study of neutron interactions in the Crystal Ball detector.Overall, the collaboration presented 13 papers on our analysis of these data.
  • The first physics paper has been published [S. Prakhov et. al., PRL 84, 4802 (2000)] in May, 2000. Other papers have been published and are listed above.
  • A paper describing measurements of the energy dependent efficiencies for the detection of neutrons in the Crystal Ball has been published in Nuclear Instruments and Methods A 462, 463-473 (May, 2001).. The lead authors on the paper are Prof. Stanislaus and Prof. Koetke.
  • A Crystal Ball Collaboration meeting (August 2000) was held at Valparaiso University. Approximately 30 participants from various collaborating US universities and collaborators from Germany, Russia, and Canada were also in attendance. The meeting gave testimony to the rich collection of physics analysis which is underway in both (p- p) and (K- p) intereactions.
  • The Valparaiso University group is focusing its analysis efforts on the study of two reactions: K- p -> Σ γ and K- p -> Σ π0. Students have been especially helpful in doing this complicated analysis and studies of systematics. The results for the K- p -> Σ π0 reaction are now published in Physical Review C.

A list of publications by the Crystal Ball Collaboration is available.

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The Neutron EDM/MDM (NIST)

According to fundamental symmertries, all elementary particles are prevented from having a permanent electric dipole moment (EDM). (A magnetic dipole moment is surely allowed and it is observed for a proton and neutron.) If one were to find the existence of an electric dipole moment, it would imply a violation of a fundamental symmetry as we understand it and the adavent of "new physics". The search for such an electric dipole moment has focused on the neutron because the neutron has a net zero charge. (The net electric charge on the proton would make the search for an extremely small electric dipole moment essentially impossible.) For many years, physicists have conducted searches for a neutron EDM with null results. The present limit on the value of a neutron EDM is extraordinarily small. Nonetheless, experiments are being mounted now to push that limit to even smaller values. Most such experiments are very elaborate and very expensive and involve the use of "ultracold neutrons" that move with very slow velocities and can then be contained in "trap" or "bottle".

A small group of physicists from Argonne National Laboratory (ANL), Fermilab (FNAL), the Indiana University (Bloomington, IN), NIST, and Valparaiso University are pursuing a novel and cost-effective method for such a measurement. It involves "trapping" neutrons at room temperatures for sufficiently long periods of time to observe the effects of an EDM if one were present. The "trapping" is done in a single-crystal of silicon whereby Bragg scattering (reflections) are used to contain the neutron. During these reflections, the neutron penetrates the surface of the silicon and encounters the electic field produced by the silicon atoms in the crystal. These fields are many orders of magnitude larger than could be produced in the laboratory in other EDM experiiments and, because the net effect of an EDM interaction is proportional to the E-field strength, this experiiment may be even more sensitive to a neutron EDM than those involving ultracold neutrons. But, some careful experimental magnetic field settings are required to "manage" the neutron spin as it progresses through the silicon crystal.

An EDM experiment with this apparatus must first be preceded by several "proof-of-principle" experiments that are designed to demonstrate that there is a hope of doing an EDM experiment with this method. One such experiment has been completed and the results published. In this experiment, we measured the probability for the neutrons to reflect from the silicon surfaces. If this were not very high (close to 1.00), there would be little hope of doing an EDM experiment where the neutrons must endure ~10,000 such reflections. The second experiment that we are now preparing to do at NIST involves a measurement of the neutron magnetic dipole moment (MDM) interaction in a perfect silicon crystal.. Because

  • the value of the magnetic dipole moment is known to exist and its value has been measured, and,
  • because it is much, much larger than the present limit on the EDM, and,
  • because it involes much the same technique for an EDM measurement,

if we cannot do the MDM experiment, we will have no hope of doing the EDM experiment. In this sense a successful MDM experiment is a "proof-of-principle" experiment.

These experiments rely on using a single crystal of silicon into which onr or more slots have been machined and subsequently etched to provide a very smooth surface. The neutrons travel in a zigzag path within the slots in the crystal by bouncing back and forth due to Bragg scattering off the crystal planes in the walls of the slot. An early version of the crystal that was used for the reflectivity measurement had 17 slots machined. While this was suitable for the reflectivity measurement where we were only counting the number of neutrons that emerged from the slot, it would not work for the MDM or EDM experiment where the phase of the neutron spin must be the same for all neutrons emerging from all slots - and this was not feasible to guarantee with the multi-slot crystal. Therefore, a much simpler crystal design will be used for the MDM and EDM measurements. (The actual crystal to be used for the EDM measurement will need to have much longer slots.) In preparation for the MDM measurement, a solenoidal magnet was designed and manufactured at FNAL and transported to VU where it has been mapped by student Ross Corliss.

Recently, it was decided that a wider slot (1 cm) would be more effective for the MDM measurement because variations of the neutron penetration depth into the walls would constitute a smaller fraction of the neutron flight path between the crystal walls. This crystal with the wider slot needed to be longer (12.5 cm) to obtain enough interactions with the wall on its transit down the slot. Because the longer crystal would no longer fit inside the bore of the solenoid magnet, a new magnet was designed, at VU that would provide a very uniform field over a volume that would contain all of the crystal and two flipper coils placed just outside the crystal. The nonuniformities are expected to be ~10-4.

The Present Status --

The reflectivity was measured to be R = 0.999 976±0.000 075. The MDM experiment is in the process of being set up at NIST where a dedicated beamline in the NCNR guide hall has been established. The new magnet designed at Valparaiso University will be fabricated in early 2008. The necessary power supplies will be computer controlled with programs written by Mr. Paul Nord. The rest of the appartus is being assembled and we are expecting to commission the experiment in 2008.

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NuSea

 

NuSea Spectrometer GIF Image
(Click on the image for an expanded view of the spectrometer)

This experiment was designed to study the distribution of the sea anti-quarks inside nucleons and nuclei. In particular, the principal focus of this experiment was to study the distribution of the anti-up quarks and the anti-down quarks in nucleons by using the Drell-Yan effect whereby quark-anti-quark interactions result in the production a pair of opposite sign muons, mediated by a virtual photon. The data for this experiment have been collected at Fermilab which is located approximately 2 hours from Valparaiso, during the 12 month period August 1996 to August 1997. The spectrometer has been used in this beamline for several previous experiments. The calorimeter and the ring imaging Cherenkov counter were not needed for this experiment. Upgrades were made to the scintillator hodoscope counter planes and some of the drift chambers used for precise tracking. The data are in the process of being analyzed.

The Valparaiso group, along with colleagues at Texas A & M University, has designed and implementated an entirely new fast trigger system. The new trigger system was a major advance that permitted rapid trigger decisions and ease of trigger configuration and implementation in software. An article describing the trigger system has been published in Nuclear Instruments and Methods (see above list).

The Present Status --

We began data collection when the Fermilab Tevatron began to deliver beam to the fixed target experiments in August 1996 and concluded the run in August 1997. Data to study the sea anti-quark distributions in the nucleons were collected at various settings of the spectrometer magnets which correspond to various effective mass ranges for the outgoing muon pairs. The results were compared with predictions of various quantum chromodynamic models (QCD) such as the those developed by the CTEQ group.

In addition to the Drell-Yan studies taken with protons incident on liquid hydrogen and liquid deuterium targets, we have also taken data with protons striking several nuclear targets including Be, Cu, and W to examine the degree to which the nuclear environment might affect the sea-quark distributions in nucleons.

These data have also provided us with copious numbers of J/psi and psi' events and large numbers of upsilon events and the higher mass upsilon states. Analysis of these data has largely been completed and the results published.

One Valparaiso University graduate (Jason Webb VU '96) has completed his Ph.D.in fall, 2002, at New Mexico State University by measuring differential cross sections for Drell-Yan production at various kinematic values - a difficult task. (Congratulations, Jason!)

You can obtain --

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M E G A

The muon decays essentially all of the time to an electron and two neutrinos. One feature of this decay mode is that it conserves the number of leptons (electrons, muons, and taus) separately, i.e., separately, the numbers of electrons, muons, and taus (all leptons) in the universe appears to be a constant and no reaction has been observed that can alter these numbers. For the muon decay, this means that the reaction has always been observed to decay with an electron-type neutrino (or anti-neutrino) and a muon-type neutrio (or anti-neutrino) in the decay products. The fact that all observed decays of the muon to date are ones which conserve lepton family number is now articulated as an ad hoc conservation law in the Standard Model of elementary particle physics. However, there is no known fundamental reason why this should occur in this restricted way.

Absent some fundamental reason which would absolutely forbid a decay in which the number of electrons (muons, or taus) is not conserved in the decay, one asks whether a decay which would not obey this conservation principle could actually happen and be observed.

The MEGA experiment was done at the Los Alamos National Laboratory Meson Physics Facility (LAMPF) accelerator. The experiment was a high precision search for the yet un-observed decay mode for the muon, μ-> e + γ. The experiment set out to either discover this decay mode, or to set a new world limit for the precision with which we can say it has not been seen.

The experiment was begun in 1986, and in ensuing years, a major effort in detector development was made. Data were finally taken in 1993, 1994, and 1995 and the analysis completed in 1999. The Valparaiso University group of faculty, staff and students made significant contributions to the successful completion of this experiment and these are noted for reference. The physics results have been published in Physical Review Letters and a comprehensive paper on the experiment has been submitted to Physical Review D (2001). 

The MEGA detector is a high precision spectrometer designed to detect the photon and the electron from the decay of a muon stopped in the target at the center of the apparatus.

The photon spectrometer detects the photon from this decay by pair conversion and precise tracking and with tracking in drift chambers, determines the photon energy, momentum, and conversion point. The electrons are detected in a uniquely designed set of high precision multi-wire proportional chambers used for tracking in the electron spectrometer. All of the detector is housed inside a 1.5 T solenoidal magnetic field.

The Present Status --

The MEGA experiment completed its data-taking phase and and the analysis of these data to search for evidence of the μ-> e + γ was carried out during the succeeding three years. The experiment acquired data from 1993-95. Roughly 1.5 x 1014 muons were stopped in the apparatus in about 1.1 x 107 seconds. There were 454 million events on tape. The statistical weight of the samples is roughly 1:2:3 for the years 1993:1994:1995.

In late 1998 we finished the very difficult analysis of these data and in 1999 we published the results. At times, our collaboration had 29 high powered UNIX workstations simultaneously analyzing data to complete the entire data analysis. In addition, a substantial amount of Monte Carlo simulation was needed to determine the efficiencies and detector acceptances for the μ-> e + γ signal, should one be present. We found no evidence for a μ-> e + γ signal to a 90% confidence limit of 1 event in 1.2 x 10-11, or a factor of five better than the prior best measurement. This result was published in Physical Review Letters in 1999. A comperhensive publication describing the entire experiment was published in Physical Review D in 2002. Over the 13 years that the Valparaiso University group was active on this experiment, we made many important contibutions to the experiment, both in hardware and software. One Valparaiso University graduate (Keith Stantz VU '88) received his Ph.D. from Indiana University based on work done on the MEGA experiment. (Congratulations, Keith!)

With the publication of the Physical Review D paper the collaboration has concluded its work.

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