Majorana - DM Summary of Issues

Transcription

1 Majorana - DM Smmary of Isses Brown University, Department of Physics see information at Gaitskell v8

2 Projected Sensitivity Basic BG Model Assmptions 5 mdr flat, 1 kev threshold <1 kg-year for sig-to-noise method / 2500 kg-yr for Ann. Mod

3 Dark Matter Halo Models Halo Models - Data Comparison DAMA is creating certain amont of confsion concerning comparison of data from varios experiments Effectively they varying halo model to redce apparent s associated with positive signal making it look more difficlt to test We shold plot qantity related to s x f (rather than only s) to avoid some of halo model x-comparison isse Also qote annal mod signal as fraction of continm sed - This is the relevant behavior from a given halo model (rather than details of halo model) Scale for NaI, not Ge

4 Low Thresholds Vital Very Typical WIMP Signal Graph shows integrated event rates for E>Er for Xe (green), Ge (red) and S (ble) Large nclei enhanced by nclear coherence, however, in reality <<A 2 Ú E r dn de Ge QUENCHING FACTOR 25-30% so 1 kevee is 4 kevr Threshold of 4 kevee (14 kevr) is still within factor 2 of zero threshold rate Example cross-section shown is at bottom of Std Halo DAMA allowed region

5 Dark Matter Direct Detection: History & Ftre Homestake (87) 90% CL Limit on Cross section for 60 GeV WIMP (scalar copling) Gaitskell (astroph ) Oroville (88) [m=20 GeV] ~1 event kg -1 day -1 Different Colors Indicate Different Technologies H-M (94) Edelweiss (98) Ge UKDMC (96) H berg-moscow (98), IGEX (00) [m=100 GeV] DAMA (98) DAMA (00) NaI CDMS SUF (99) DAMA (96) Edelweiss (01) Cryodet CDMS SUF (02) Edelweiss (02) Liq Xe DRIFT II 1 kg CS 2 (T) Gas CS 2 ZEPLIN I Xe (02) (T) Target NOW Signal Majorana Phase 1 (T) GENIUS TF (T) 10 kg Ge Diode ~1 event kg -1 yr -1 CDMS Sodan (T) 7 kg Ge+Si Cryodet DRIFT III 100 kg CS ZEPLIN II+III 10 kg Xe (T) 2 (T) GENIUS (T) 100 kg Ge Diode LHC XENON / ZEPLIN 1t Xe ~1 event 100 kg -1 yr -1 CryoArray (T) tonne Cryodet [m = xx GeV - if significantly better limit obtained at different mass] Not meant to be a complete list - see rjg

6 Dark Matter - Majorana - Isses Segmentation Expect significant redction in low energy Compton continm Need to Monte Carlo how configrations affect low energy b/g SEGA will also allow s to stdy this 1 kev threshold more realistic in segments Althogh 1 kevee not vital, <4 kevee OK PSA Not realistic in tre region of interest <20 kevee? (a,n) Netrons 40 cm poly will give ~0.001 mdr netrons (based on CDMSII simlation, not yet confirmed by experiment bt it won t be far off) We cold se a significantly thinner poly shield Pnch Throgh Netrons 0.1 mdr at 2000 mwe with 40 cm poly Mons in Shielding Pb will be dominant sorce of netrons for 2000 mwe 0.5 mdr at 2000 mwe CDMS II Shield (otside) 40 cm poly 18 cm Doe Rn Pb 5 cm Ancient Pb 10 cm Poly (inside) Monte Carlo, not yet verified by Exp.

7 Backgrond Projections Event Rate [mdr] Expose [ 1000 kg-day] Raw Events [conts] Reject [%] Post rejection [conts] Sbtract 90% CL [conts] Sys'tic 90% CL [conts] GAMMA CDMS I * % CDMS II , % Heidelberg-M * n/a CryoArray , % BETAS CDMS I * % CDMS II , % 75 CDMS 14 II Shield 4 CryoArray , % 75 14(otside) 4 NEUTRONS 40 cm poly CDMS I*(Shield) % 1 18 cm - Doe Rn -Pb CDMS CDMS II I*(Rock) (a,n) (mlti) n/a 5 cm 4 Ancient Pb - CDMS II (Sh) Mons % Veto cm Poly - CDMS II (Rk) Mons (mlti) n/a 6 (inside) 1 CryoArray (Sh) , % 8 Monte - Carlo, not - CryoArray (Rk) (mlti) n/a yet 21 verified by Exp. 8 dr = 1 event kev -1 kg -1 day -1 Energy Range kev

8 IGEX-DM: Low energy backgrond TAUP 2003 IGEX Talk S. Cebrián 1.0 conts/kev/kg/day BACKGROUND LEVELS 4-10 kev: 0.22 c/kev/kg/day kev: 0.10 c/kev/kg/day kev: 0.04 c/kev/kg/day Previos spectrm (236 kg-days) Since smmer 2001, netron shielding improved (40 cm) (194 kg-days) Frther increased netron shielding (80 cm) (82 kg-days) Energy (kev) A thorogh stdy has been carried ot to Gaitskell - More than 40 cm poly has no effect at this level (each investigate 10 cm makes the origin ~10x of redction the remaining backgrond: (a,n) netrons, so even 40 cm was overkill c.f. CDMS reslts) radioactivity? netrons? References: - A. Morales et al, Phys. Lett. B 532 (2002) A. Morales et al, Phys. Lett. B 489 (2000) cosmogenics? tritim? Dark S. Cebrián, Matter - Majorana Canfranc - 10 Undergrond Sept 2003 Laboratory, Zaragoza University TAUP 2003, Seattle

9 Annal Modlation Annal Modlation - Specific Instrmentation Isse Need carefl consideration of how to establish low energy bin 0.1% Compton Calibrations Direct plsing of channels at many different levels Note that we may have both event modlation above and below recoil spectrm pivot point

10 60-90 days at Sea Level & 1 year cool Most possibles contribte << 5 mdr 68Ge Prodction atoms/kg/day (t 1/2 ~ 270 days) Tritim Cosmogenic Activation Ga K(L) x-ray lines 10.4(1.2) kev will contribte peaks 50(5) mdr-kev given 90 days at SL Not removed by crystal growth So K energy region will need to be bracketed Also se time correlation with chain events ~5 x effective redction - need to model atoms/kg/day (clock starts after crystal growth) Max in decay 3 kevee is cts/kevee/day/300 3 H atoms This is implies <~2 days above grond reqired, transport nder shielding IGEX data seems consistent with prodction rates qotes above This is clearly a major constraint on prodction/transport protocols 2nbb as Backgrond Raw <0.1 mdr below 60 kev 2% Dead layer will not create significant process to convert high energy events (10 decays/kg/day) into low energy range (say 0-20 kev where we wold need >0.1 /kg/day to be a problem) Shold Monte Carlo - bt not worried

11 IGEX-DM: Low energy backgrond TAUP 2003 IGEX Talk S. Cebrián Tritim Best Fit 2.58 c/kg/day Exposed for ~120 days above grond Data taken in Canfranc dring days after a decay period of 1632 days A flat contribtion of 40 mdr sbtracted Tritim [Hess] 1.85 c/kg/day Tritim [Lal] 1.48 c/kg/day Tritim [Cosmo] 0.92 c/kg/day A sbstantial part (bt not all) of the remaining backgrond may be de to 3 H Gaitskell - I think they have nderestimated above grond exposre calc slightly However, looks like activation estimates consistent with the data Dark S. Cebrián, Matter - Majorana Canfranc - 10 Undergrond Sept 2003 Laboratory, Zaragoza University TAUP 2003, Seattle

12 IGEX-DM: Reslts TAUP 2003 IGEX Talk S. Cebrián Exclsion plots sbstracting the tritim contribtion from the IGEX spectrm Gaitskell - Redction below Red line not sefl for DM discovery big ncertainty in the tritim estimate Dark S. Cebrián, Matter - Majorana Canfranc - 10 Undergrond Sept 2003 Laboratory, Zaragoza University TAUP 2003, Seattle

13 Monte Carlos Monte Carlos What low energy component arises from or estimates of high energy lines? Internal vs External Internal gives Highest Peak vs Continm NOTE: We simply want to see what low energy continm might be possible. I do not advocate Sbtraction Will not be well received by commnity, and personally, I don t think it adds any sensitivity for discovery of DM. Doesn t help in annal modlation either. Segmentation We need to stdy optimm config for DM, and how this compared to DBD optimization

14 Screening How do we modify screening strategy for low energy region? Are there possible mechanisms for low energy emitters to get to active srfaces of detectors? Rn-plating / 210Pb, 3H, 14C

15 GENIUS (Reminder) Backgrond Model at Low Energies 5 mdr Tritim Not Inclded 18.6 kevee is ~60 kev in recoil

16 TAUP 2003 IGEX Talk S. Cebrián PROSPECTS of Dark Matter Searches with Ge Backgrond of c/kev/kg/day is reasonably expected. Anticoincidence between crystals Lower components/detector mass ratio Frther radioprity of components (from lessons learned in IGEX) Qantitative stdy (simlations) of the GEDEON backgrond is now in progress. conts/kev/kg/day Energy (kev) Dark S. Cebrián, Matter - Majorana Canfranc - 10 Undergrond Sept 2003 Laboratory, Zaragoza University TAUP 2003, Seattle

17 Conclsions 5 mdr Seems reasonable/achievable goal Tritim protocol is most significant concern - can we do <2 days SL in phase I of experiment? Undergrond prodction becomes mandatory later Are we ptting orselves at a disadvantage for DM by being conservative at this stage Bt how realistic is it to talk of 0.5 mdr? At this stage it wold seem fancifl - need more details fro, SEGA/MEGA To make a lower target rate credible we wold need to describe low energy screening infrastrctre that will be sed to get down there

18 GENIUS (Reminder) Backgrond Model at Low Energies