The new g2m experiment Brendan Casey Fermilab University

The new (g-2)m experiment Brendan Casey, Fermilab University of DØ, 9/23/10 Im am hm SM Re A proposal to measure the muon anomolous magnetic moment to ± 0. 14 ppm precision B. Casey, UD 0 9/23/10 1

What is g-2? • Gyromagnetic ratio, g = spin / angular momentum – Should be the Bohr magneton for elementary particles • g factor = difference between g and the Bohr magneton • g=2 from relativisitic quantum mechanics due to extra degrees of freedom of the electron • g-2 ≠ 0 from radiative corrections in quantum field theory • From Bohr to Schwinger, the magnetic moment played a central role in developing theories of elementary particle physics B. Casey, UD 0 9/23/10 2

g-2 today 5 Kinoshita et al 4 • (g-2)e measured to 0. 28 ppt 6 3 – Gabrielse PRL 100, 120801 (2008) – Most precise determination of a. QED 8 7 2 9 10 1 • (g-2)m measured to 0. 54 ppm – BNL E 821 PRD 73, 072003 (2006) – ( mm / me )2 enhancement to massive loops QED QCD EW g W m e g g m m W n m m m p – About a 3 s difference from the predicted value – Evidence that we don’t understand the muon magnetic moment B. Casey, UD 0 9/23/10 3

(g-2)m and new physics g • (g-2)m now sensitive to electroweak corrections – Easiest to classify things in terms of weak scale mass and couplings • Three classifications of new physics: W m W n m – Weak scale couplings and weak scale masses • Ruled out by LEP / Tevatron … – Enhanced couplings and several hundred Ge. V scale masses (tanb, N(extra dimensions) …) • Accessible at Tevatron and favored by current (g-2)m – Weak scale couplings and several hundred Ge. V scale masses • Accessible at LHC and goal of new (g-2)m experiment B. Casey, UD 0 9/23/10 4

(g-2)m and the Tevatron g g W m ~± c W n m m n~ ~± c m (g-2)m SUSY Snowmass points and slopes B. Casey, UD 0 9/23/10 5

(g-2)m and the New Standard Model • Hopefully we will soon see things that allow us to begin putting together a New Standard Model. • (g-2)m will play a major part in this in three ways – Precision – Universality – Lepton flavor violation B. Casey, UD 0 9/23/10 6

Precision • (g-2)m will be one of the most precise ways to measure fundamental parameters of the New Standard Model Fermilab-prop-0989 (g-2)m LHC at 100 fb-1, 14 Te. V, SPS 1 a, tan b = 10 B. Casey, UD 0 9/23/10 7

Universality • Will need to predict and see consistent effects in all sectors to demonstrate we really understand the New Standard Model tan b B→ tn – (g-2)m, Kaon + B meson mixing and decay, Z pole. Tevatron and/or LHC… Example from the current Standard Model B. Casey, UD 0 m(H+) Possible example from the New Standard Model 9/23/10 8

Lepton Flavor Violation Isidori ar. Xiv: 0710: 5377 • With Mu 2 e + (g-2)m results, can disentangle new physics scale from size of LFV m – Drives muon and tau LFV programs – Results sensitive to new physics scale and size of LFV – Expect effects in both Mu 2 e and (g-2)m e • Te. V scale LFV expected in most models m m B. Casey, UD 0 9/23/10 9

The experiment • Produce polarized muons and inject them into a storage ring with vertical B field • B field is mapped using NMR probes • Muon spin precesses around the B field • Positrons decay along spin direction so precession frequency is measured by counting positrons B. Casey, UD 0 9/23/10 10

Muon production 8 Ge. V protons from Booster Select ~3 Ge. V p+ K pp K p Select 3. 1 Ge. V m+ m target Momentum Spin • Use existing target, lens, beamlines from pbar source Pbar complex • 900 m decay line – 10 x longer than at BNL – 10 x less background target ring B. Casey, UD 0 • @ Fermilab, can produce 20 x BNL statistics in ~1 year – Higher booster rep rate keeps muons per fill at about the same level 9/23/10 11

Storage ring continuous circular superconducting coils and pole pieces, r~7. 1 m passive and active shimming for ~ 1 year to give uniform field Field measured using fixed probes around the ring plus an NMR trolley that ran through the ring average field seen by muons uniform at the ppm level B. Casey, UD 0 9/23/10 12

Helicopters! B. Casey, UD 0 9/23/10 13

Positron counting single muon bunch injected into ring, stored for 700 ms lower momentum positrons swept inward by B field and detected in 24 calorimeter stations entire fill digitized. Offline algorithms extract positron signals (particularly pileup) B. Casey, UD 0 9/23/10 14

T 1005 • Dominant systematic from BNL was pileup • Upgrade by segmenting calorimeters – Possibly readout with Si. PMs • Have performed beam tests and results look good B. Casey, UD 0 9/23/10 15

Frequency measurement spin leads momentum due to precession, positron trajectory follows spin E 821 total data set: positrons versus time Michel spectrum Asymmetry due to momentum cut Figure of merit NA 2 N A <A>=0. 4 positron momentum fraction Cut at 1. 8 Ge. V B. Casey, UD 0 9/23/10 16

Tracking • Tracking is needed to measure muon distribution and measure beam oscillations – E 821: 1 scallop replaced by tracking system • Did the job but several disadvantages – Upgrade: place straws inside the vacuum B. Casey, UD 0 9/23/10 17

Tracking R&D • Tracking system currently a collaboration of Fermilab and PNPI – But still room for others Top view of the vacuum chamber Positron trajectory Calo Tracking volume B. Casey, UD 0 9/23/10 18

CKM test stand Cosmic telescope Tasha Laura Mandy Beam window straws outside DAQ + HV Vacuum chamber w/straws inside B. Casey, UD 0 Bjoern’s favorite part of the test stand 9/23/10 19

Expectations Fermilab-prop-0989 0. 46 ppm→ 0. 1 ppm stat error + = 140 ppb experimental error B. Casey, UD 0 9/23/10 20

Predicted value: LO QCD e g g m p m e • Theoretically clean, experimentally hard • Problem: hadrons Ba. Bar KLOE – Absolute cross section well below % level • Solution: – Get ~10 experiments to measure the same cross section B. Casey, UD 0 9/23/10 21

Predicted value: tau data QCD p+ e g g m p m e p - p+ t W n p 0 • Can also use tau data to estimate LO QCD – Experimentally cleaner, theoretically dirtier mainly due to isospin breaking • Hasn’t agreed well with e+e- in the past but now have pretty good agreement with more data and better understanding B. Casey, UD 0 9/23/10 22

Predicted value: h. Lb. L • Non perturbative but higher order • Expected to be dominant error soon • New program at KLOE to measure dominant contributions to this diagram with 2 photon physics at very low Q 2 • With this new data, (g-2)m theory error will be almost entirely driven by independent experiments B. Casey, UD 0 9/23/10 23

Putting it all together As of last week: Goal for next round: B. Casey, UD 0 9/23/10 24

Other measurements: Muon CPV • Differences between matter and antimatter interactions allowed a small amount of matter to escape annihilation in the early universe – (4 -6)x 10 -11 baryon to photon ratio • Observed CP violation in neutral meson mixing and decay only partially explains this – From CKM: < 6 x 10 -27 baryons/photon • Huet, Sather PRD 51 379 (1995) • New effects needed. A small permanent electric dipole moment (EDM) of elementary particles is a good candidate. – Violates P and T s d B. Casey, UD 0 9/23/10 25

EDMs and the Tevatron • The large anomalous CPV in Bs mixing reported at the Tevatron + minimal flavor violation predicts EDMs are “around the corner!” – Gino Isidori, ICHEP 2010 plenary talk Large Bs CPV shrinks available parameter space 10 -25 • Need lepton and quark EDM searches to distinguish new weak interaction from a small QQCD • Need different leptons to determine if the new phase is universal 10 -30 Bs CPV Titanium neutron Mercury Buras, Isidori, Paradisi ar. Xiv: 1007. 5291 Muon may be the only competitive place we can study EDMs outside the first generation B. Casey, UD 0 9/23/10 26

Muon EDM expectations Im dm < 3 x 10 -22 e-cm am hm • EDM can be seen as the imaginary part of the anomalous magnetic moment Re SM 3 x 10 -9 • Current (g-2)m measurement constrains the muon EDM • We can reach this with a dedicated experiment at Project X • We propose here an intermediate step, parasitic to the new (g -2)m measurement, to reach 10 -21 e-cm B. Casey, UD 0 9/23/10 27

Experimental setup • Relativistic muon in magnetic field sees a motional electric field pointing into the ring in the muon rest frame. • Muon EDM will tilt the precession plane • Results in an up-down asymmetry in the positron decay angle, 90° out of phase • Was measured using a straw tracking system in front of one calo station for the BNL (g-2)m experiment B. Casey, UD 0 9/23/10 28

Proposed update • Previous measurement based on ~10 million reconstructed positron tracks • Tracking detectors in front of all calorimeter stations could reconstruct ~1011 tracks in the new experiment – Factor 100 improvement in statistics • Baseline is straw systems in the vacuum optimized for EDM measurement in front of all calorimeter stations rbit Muon o Positr on tra jector y Tracking volume B. Casey, UD 0 9/23/10 29

Tracking design considerations Convoluted with Michelle Spectrum • Effective maximum asymmetry – Optimize design for positron momentum near 1. 5 Ge. V • Inherent angular spread in decay angle – Sets upstream material budget: keep multiple scattering below this. • Occupancy throughout the fill – Sets how early we can take data B. Casey, UD 0 ~11 mrad RMS inherent decay angle in positron decay 9/23/10 30

Tracking design Progress • Calculating/simulating – Fermilab Geant 4 and beam simulation experts helping to get ring simulation running at FNAL • Building a team – Fermilab, PNPI, … – Leveraging shared infrastructure with Mu 2 e at Fermilab – Leveraging infrastructure, human resources used for ATLAS straws at PNPI – Casey applying for Office of Science Early Career Grant to design and partially construct the system • Resurrected a straws-in-vacuum cosmic test stand designing prototypes – Very attractive to post docs analyzing Tevatron data but also looking for hardware experience Resolution degradation due to quads ~10 % at 1. 55 Ge. V Positron p (Ge. V) High School physics teacher Terry Barchfeld Fermilab DØ/g-2 postdoc Mandy Rominsky B. Casey, UD 0 9/23/10 31

EDM conclusions • Best current knowledge indicates EDMs will be seen in experiments this decade • To understand what we see requires a measurement of the muon EDM • We know how to improve by 2 orders of magnitude by adding tracking stations to the new (g-2)m experiment • This naturally progresses into a dedicated muon EDM experiment at Project X B. Casey, UD 0 9/23/10 32

Status • P 5 very supportive of physics but could not fit it into given program scenarios for ~60 M • Reevaluation of civil construction needs greatly reduced the cost • Reduced cost proposal (~20 M) submitted to Fermilab PAC March 2009 – Very enthusiastic about physics motivation, asked for a cost review • Internal costing exercise added a lot of extra contingency – Fermilab management provided needed engineering to reduce contingency • PAC reviewed cost at November 12 -14 meeting – Said the experiment is ready to be aproved, check with the DOE to make sure it can be funded. • Updated proposal just submitted directly to the DOE HEP for peer review. – One of the top candidates for money made available by the LHC upgrade delay • Expect ~4 years between approval and data taking B. Casey, UD 0 9/23/10 33

Schedule B. Casey, UD 0 9/23/10 34

Future: The charged Lepton program An observation of charged lepton flavor violation expected in the next decade implies existence of a new mixing matrix. Expect same as quarks, neutrinos: multi-decade program to determine 4 parameters of the matrix Cold traps, intense muon sources, super B factories, t/charm factories, lepton colliders, Hadron colliders… m→eg, m. N→e. N t→eg, eee t→mg, mmm (g-2)e, (g-2)m, (g-2)t CP violation: lepton EDM measurements B. Casey, UD 0 9/23/10 35

Conclusions • The Fermilab accelerator complex presents us with a golden opportunity to do some outstanding muon physics. • (g-2)m could be the first in a long line of these experiments • For roughly a 10% increase in cost, (g-2)m doubles the physics output of Fermilab’s planned muon program B. Casey, UD 0 9/23/10 36